# Newbie Questions on REW



## Kix_N_Grins (Feb 14, 2015)

Hello,

I'm a newbie at REW and room equalization. I'm still reading various material and haven't really tried REW yet. I have a couple of questions based on what I've read so far. From what I gather, the emphasis on room equalization is on the Subwoofers and Fronts. I have a 7.1 system, and I'm wondering why it isn't important to equalize the center channel, surrounds and rears? Did I misread something?

Also, when using REW, do you run the Subs and Fronts separately? If so, does it matter whether you do the Subs first or the Fronts first? On the Fronts, do you run Left and Right separately or together?

I'm using two sets of speakers for my Fronts because I didn't like my Mains upper response (so one set of speakers are my Front "Mains" and the other my Front "Assists". So, coming out of my AV Processor's Front output, I'm using a "Y" cable to two separate equalizers and amps. For the Mains, I'm using a SAE 2800 equalizer (parametric) and a Carver TFM-35 amp. For the Assists, I'm using a Numark 2600 equalizer (1 octave graphic) and a Carver TFM-15CB amp. Again, I have about the same questions as above: Do I adjust the sets separately using REW, or do I treat the pair of speakers (per side) as a single Front speaker? I hope this question makes sense...

Thanks in advance,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Typically if only the subwoofers are being equalized, it’s best to first generate graphs running the subs only. Then another with the main speakers added, typically only the front pair, to see if there are any problems in the region of the crossover frequency.

People do indeed equalize the main speakers. Most people these days have receivers that have auto-EQ functions, but there are old-school “die hards” that run outboard equalizers and equalize them manually - i.e., based on their interpretation of REW graphs.

For EQing the main channels, typically you want to measure them independently one at a time. 

As far as what to do about your dual speaker set up, if the deficiencies you’re hearing from your main speakers are coming directly from the speakers themselves and not room acoustics, I would think your SAE equalizer would be able to take care of it. Maybe with REW measurements you could see exactly where they are deficient and set filters to adjust the issues much more precisely than you have been by ear, and then you could retire the “assist” speakers

Regards, 
Wayne


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## Kix_N_Grins (Feb 14, 2015)

Awesome information. I'm up to chapter 20, reading the REW EQ Wizard help files (out of 40) and this fills in most of the gaps I wasn't understanding. As far as a sub equalizer goes, I'm going to take your advice given on my "Assist" speakers above and wait until I take my first REW measurements before adding/removing anything.

I'm still curious about the center, side, and rear speakers on a 7.1 system. Maybe I just haven't read far enough yet. Why haven't I read anything about equalizing them into room acoustics and why wouldn't someone want to equalize them? I read your papers on "House Curves" and wonder how the center, side, and rear channels factor into that as well.

Thanks for helping me understand,
Kix


Btw: I guess I'm in the "old die-hard" camp. Aside from my center channel speaker and its equalizer, everything I have audio-wise is vintage 1978-1989. But, I'm an old dog that can still learn new tricks...


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## Wayne A. Pflughaupt (Apr 13, 2006)

Personally I think equalization of the center and surrounds is important as well (assuming it is needed), and I’ve done it with mine. The main reason people don’t use outboard equalization for these channels is that it gets expensive real quick. You can’t add equalizers to a common AVR as there is no provision for connection. So, it requires the addition (and cost) of outboard amplifiers, as well as the equalizers themselves. And while you can get away with a cheap equalizer for subwoofers, equalizers for the main channels need to be high quality, ultra-quiet units –read “not cheap.” All told, you can easily rack up a $1000+ premium to obtain outboard equalization for all channels, even if you go with used equipment.

But just because you don’t see outboard EQs in someone’s equipment list that doesn’t mean they aren’t using any. Most receivers these days have built-in equalization, and pretty powerful and effective ones at that. Most AVRs these days have fairly effective auto EQ systems, and some have equalizers with manual adjustments on top of that. I have a Yamaha RX-V2500 in my bedroom system that’s several years old, and it came with a pretty effective parametric EQ for the main channels. It only had 1/3-octave resolution, but it was capable enough to get what my speakers needed. My center channel would be virtually unlistenable without it. If they ever move up to 1/6-octave resolution, I’ll be giving serious thought to ditching my outboard EQs on my main system.

Regards,
Wayne


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the reply Wayne.

Well, I got started setting up REW and thought that I would get a little farther along than I have before needing advice. I got the soundcard calibrated. It's not what I expected, with the IR slightly curving up above 600Hz. It looks a little like the example of someone forgetting to turn off the C-weighting, but not on both ends. I'm using a pretty cheap PC from Walmart that I bought for my kids and stuck in the livingroom. So my first thought and question is, is my soundcard good enough?

Here's what it looks like:








So, next up was the "Check Levels". I disconnected the RCA cable feeding soundcard output into its input, turned back on C-weighting, and plugged the output into a Y RCA connector feeding my AVP. I had turned off all EQ's and amps, so was only using AVP and two sub-woofers. I immediately began hearing a "noticeable" hum from the SW's without even starting the test. I unplugged the SW's, turned on the EQ's and amps to the mains, sides, etc and was still hearing the hum (just a little crisper). Next I turned all external EQ's and amps off again, and hooked the PC directly to the sub-woofer and no hum at all.

The hum sounds like 60Hz to me. I measured my room's ambient SPL and measured 53dB with everything turned off (except furnace, it's Iowa...). Measured again with my PC connected to the AVP and two SW's and measured 66dB. So, the hum is about 13dB.

So, I have two questions. First, does my soundcard & cal look like it's okay? Second, any ideas why I'm getting this humming noise (ground-loop?). and where I might start looking to correct it? System sounds fairly good when it's not connected to the PC soundcard...

Thanks in advance,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Soundcard calibration looks good. The hum is probably coming from the computer. Some of them have poor-quality power supplies, especially lower-end desk-top models.

Regards,
Wayne


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## JohnM (Apr 11, 2006)

Lots of advice and suggestions in this thread on fixing hum caused by ground loops.


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the replies, Wayne and John.

Took the better part of the night to read through 315 posts in the link above, but it was worth it (I hope). Since I don't have any pro equipment yet, the unbalanced/balanced cable converter probably isn't going help me. I still got some good ideas reading though, and it gave me a plan of attack....

I did a little more testing tonight. I think I may have 2-3 sources that are producing the hum. The biggest source is my cable connection to my TV. Second biggest, is when I connect my PC to the AVP. Last, even with no cable or PC connected, I have a very faint hum.

The right way to fix the problem seems to be to figure out why the grounds are different for these sources. Unfortunately, it's -12F outside and I'm 54 years old. So, the right way will need to wait until Spring. So, I'm going to have to do it the Kix way for a bit (patch) until Spring arrives.

I know this isn't the right thread for this type of discussion, so I'll just leave the subject right here. Still hope to make my first measurements yet this week or weekend...

I just wanted to reply and say "Thanks again for the guidance".

Regards,
Kix


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## Kix_N_Grins (Feb 14, 2015)

Okay, I must be doing something wrong. I recalibrated my soundcard, no problem. Now I'm trying perform the Check Levels procedure and either I've set something wrong in REW, or I'm not getting a signal out of my SPL Meter and into my Line In on the soundcard.

I'm using a Galaxy CM140. I've adjusted the volume on my AVP so that the SPL meter reads 75dB. I'm using an mono 1/8" connector to the CM140 and a single RCA plug on the other end. On the Line In on the soundcard, I'm using a stereo "Y" connector with two RCA jacks on one end and 1/8" connector to the soundcard. I'm using the "red" RCA connector on both line in/out (white RCA connector is unused).

This is what I'm seeing in REW after pressing Check Level button:

(Please check the following reply for the screen-shot. It didn't like my first attempt, and I can't see the attach button in edit mode)

I'm expecting to see something in the graphic panel under "In", but there isn't anything (-99dB FS). I'm unable to adjust Input Volume or Output Volume and both are set to 0 (which makes sense why I'm seeing -99db FS in the graphic area. If I uncheck the two "Control Input/Output Volumes", it still doesn't allow me to adjust them. Although they are no longer grayed and are enabled, they "try" to adjust, but automatically go back to 0.

Any thoughts on what I might be doing wrong? I used my DMM to make sure the cable is good from SPL meter 1/8" plug to the plug on the soundcard "Y" connector and it's good. I guess I could reconnect my speakers to the soundcard out and validate "something" is coming out of the CM140.... It's a new meter that I got a couple weeks ago. But it seems strange that I can't adjust REW's Input Volume, as that seems like what the purpose of this step is, make the dB reading in REW match the SPL meter.

Thanks in advance,
Kix


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## Kix_N_Grins (Feb 14, 2015)




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## Wayne A. Pflughaupt (Apr 13, 2006)

Probably need to find out about your computer’s line input. If it’s stereo, the RCA to mono 1/8” cable you’re using isn’t going to work.

Regards,
Wayne


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## JohnM (Apr 11, 2006)

Pretty odd to have the levels set to zero. If you uncheck REW's control can you adjust the levels using the Windows recording and playback volume controls?


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## Kix_N_Grins (Feb 14, 2015)

JohnM said:


> Pretty odd to have the levels set to zero. If you uncheck REW's control can you adjust the levels using the Windows recording and playback volume controls?


Thanks John and Wayne,

Wayne was spot on. After calibrating the sound card, I didn't like the way the RCA to 3.5MM adapter fit into my soundcard. The adapters were thick and the line in/out connectors were close together, so the two adapters were somewhat forced in. So, I bought some adapter cables to replace them. Long story short, I was basically using a mono cable into the line-in instead of just into the right channel.

Waiting for different cables to come in....

Kix


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## Kix_N_Grins (Feb 14, 2015)

Got the new adapters for the soundcard, which fixed my issue of not having an input signal from the SPL meter. Also got an isolator for my TV's cable line, which fixed the majority of my ground-loop problems (at least until Spring and I can fix the root-cause of the problem). There's still some faint humming going on....

Just for kicks and grins until cables come in for my Sub EQ, I played around with REW and took my first measurements of my subs without EQ. Not quite sure what I'm seeing, but I either wouldn't expect that dip at 85Hz on SPL then bounce back up to continue it's decline, or I would expect it to dip beginning at 80 and just keep falling from there. I have the cross-overs on the subs set to 80Hz. I'd also expect it to remain flat at 80db until it got to 80Hz, instead of starting to decline at 45Hz. Any thoughts?

I also have no clue what the phase is telling me, aside from being close to 180. Does that mean something's 180 out of phase?









I'm also curious about Gain Structure... I probably ought to post these questions on Wayne's thread about Gain Structure, but if it's not applicable in my case, I don't want to pollute his thread. Is that something that needs to be done "before" taking measurements in REW? After reading the articles, is it even applicable to my set-up? I'm using a consumer AVP and consumer amps, but a pro EQ. I believe the EQ has a +4 dBu/-10 dBv switch on it. Should the output of the AVP be tested, just to determine the max I want to turn up it's volume?

I appreciate any advice,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Kix_N_Grins said:


> Just for kicks and grins until cables come in for my Sub EQ, I played around with REW and took my first measurements of my subs without EQ. Not quite sure what I'm seeing, but I either wouldn't expect that dip at 85Hz on SPL then bounce back up to continue it's decline, or I would expect it to dip beginning at 80 and just keep falling from there. I have the cross-overs on the subs set to 80Hz.


Part of the problem is the way you have the graph scaled vertically – see the post linked below. With proper scaling you’d see a steeper decline. It’s an easy adjustment you can make in REW, no need to re-measure.

Getting Graphs Ready to Post




> I'd also expect it to remain flat at 80db until it got to 80Hz, instead of starting to decline at 45Hz. Any thoughts?


You expected virtually ruler-flat response all the way up to the crossover frequency? Have you studied the graphs from any other threads? 




> I also have no clue what the phase is telling me, aside from being close to 180. Does that mean something's 180 out of phase?


You can ignore the phase trace. Better yet, just turn it off for future graphs uploaded, it just muddies up the graphs. :T




> I'm also curious about Gain Structure...
> Is that something that needs to be done "before" taking measurements in REW? After reading the articles, is it even applicable to my set-up? I'm using a consumer AVP and consumer amps, but a pro EQ. I believe the EQ has a +4 dBu/-10 dBv switch on it. Should the output of the AVP be tested, just to determine the max I want to turn up it's volume?


There is no gain structure issue in your situation. As stated in Part 9 of the gain structure article, “If you have a pro audio equalizer or other processor, just connect it between the AVR and amp (either consumer or professional) and you’re done. The processor has no level-adjustment requirements (as thoroughly documented in Parts 4 and 5).”

As far as the switches on the equalizer, you can start with them in the -10 dBV setting. If the EQ has level meters and you see them hitting red, then you can switch to the +4 dBu setting. Or, you could just start with +4 and be done with it. :T

Regards,
Wayne


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## Kix_N_Grins (Feb 14, 2015)

Wayne A. Pflughaupt said:


> You expected virtually ruler-flat response all the way up to the crossover frequency? Have you studied the graphs from any other threads?


Well, of course I expected it to be flat all the up to 80Hz.  Like everything else, I start with high expectations and lower them if needed, versus the opposite. LOL I try to read every new post on this forum, but haven't had a chance to read much further back than a couple weeks from when I joined. I'll see if I can't find some other sub-only SPL's for comparison.

BTW. Thanks for the reply Wayne. I really do appreciate it.

I changed the vertical scaling and dropped the phase as suggested, and you're right, the drop became steeper (and looks worse to these newbie eyes). Here's the results:









Also, the Mic/Meter seems strange. A 5dB drop from 100Hz to 30Hz seems like a lot, so does another 2.5dB drop 30Hz to 20Hz. Is that normal?

I'm not going to do anything yet, but I'm SO tempted to raise the cross-overs on my subs so they don't drop at 45Hz like they are, or at least that low.

Even though I don't need to deal with Gain Structure, does it make sense to find out where my AVP begins clipping, just to avoid hitting it or going above it? It seems like it should matter, since I'd want to avoid sending a clipped signal to the EQ, then Amps (regardless if commercial or pro). Or, am I still missing a point in your articles?

Please, if anyone else has an opinion, chime in. 

Thanks,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Kix_N_Grins said:


> Also, the Mic/Meter seems strange. A 5dB drop from 100Hz to 30Hz seems like a lot, so does another 2.5dB drop 30Hz to 20Hz. Is that normal?


It is for a SPL meter mic. Most budget meters don’t have an option for flat (i.e. Z-weighted) response, only for A or C weighting. C-weighting is flatter than A, but nevertheless rolls out below 100 Hz. So naturally the calibration file is compensating for that.




> I'm not going to do anything yet, but I'm SO tempted to raise the cross-overs on my subs so they don't drop at 45Hz like they are, or at least that low.


Can’t hurt to try, but I doubt it’ll make a difference. If it does it will mean your crossover is grossly inaccurate.




> Even though I don't need to deal with Gain Structure, does it make sense to find out where my AVP begins clipping, just to avoid hitting it or going above it? It seems like it should matter, since I'd want to avoid sending a clipped signal to the EQ, then Amps (regardless if commercial or pro).


Not really necessary, but it might be useful to determine at what volume setting on your pre-amp that distortion sets it. I expect you will find it to be much higher than you’d ever use.

Regards,
Wayne


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## Kix_N_Grins (Feb 14, 2015)

Well, you were right about a couple things Wayne. First, playing with the crossovers on the Subs or via AVP didn't really make much difference in freq response. I also tried moving the subs closer to the wall, moving further away from the wall, and rotating them slightly inward and outward with not much change.

Also, from what I can tell, I was never able to hear where my AVP begins clipping. I tried several times and couldn't hear any overtones with the 1KHz signal as I ramped up to full volume. Output voltages from the AVP at max volume was:

FR 2.069vac
FL 2.049
SR 1.914
SL 1.979
Ctr 2.002
Sub7.61
RR 2.014
RL 2.079

I was a little surprised the Sub was so much higher than everything else. But it makes me wonder if that's contributing to an issue that I'll describe below in the charts. I used a Carver TFM15CB amp. Not pro, but has input gain controls.

So, back to measuring with REW... I definitely must have something funky going on with my room. From the LP, I'm still dropping out at 45Hz. However if I place the Mic about 12 inches in front of the sub, it improves dramatically. I have all speakers in my AVP set to small, with XO's set 80Hz.

This first graph is overlaying my subs from the LP and also 1 foot in front of one of the subs. LP is green trace. It's definitely showing some change above 50Hz when mic is 1 ft away from the sub..

Edit: Refer to graph, second from the bottom of this post. The title is wrong!!! It says Front Mains - LP and 1Foot, it's really Subs - LP and 1Foot. Sorry, but I haven't figured out how to edit an attachment.

View attachment 86818


Okay. So, here are my Fronts using the same "Use subwoofers to set levels" level as in my Subs chart:

Edit: Refer to graph, at the bottom of this post.
View attachment 86826


Now for 15-22KHz.... Besides the "spike at 60Hz ground-loop problem" that is evident, why is the SPL so low when measuring my Fronts compared to my Subs between 20-45Hz? I mean, between the Subs and Fronts charts, it's like it falls off the edge of the earth above 45Hz. Is it the ground-loop issue at 60HZ? Surely, it can't be that my AVP Sub out is 7.4vac and so much higher than all others (my levels are ~75db either way)???

















I'm limited as to where I can place two subs. One, I can swap positions of the Fronts and Subs. Currently on the front wall, Subs are between Fronts and Center. Two, I can place the left sub in the rear left corner of the room, and the right sub I can slide up to about half of the right wall. I plan to play around with this, this weekend. If this isn't the correct forum, please feel free to move.

Any thoughts as to my next approaches or what seems to be going on with with what I'm seeing in REW?


Regards,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hey Kix,



> So, back to measuring with REW... I definitely must have something funky going on with my room. From the LP, I'm still dropping out at 45Hz.


You’re not really dropping out below 45 Hz. You just have a peak in that area, and response naturally has to fall on either side of a peak. You actually have good extension out to about 21-22 Hz, which is pretty respectable actually...




> However if I place the Mic about 12 inches in front of the sub, it improves dramatically.


Well sure, to a large extent you’ve minimized the effect of the room with close mic placement.




> This first graph is overlaying my subs from the LP and also 1 foot in front of one of the subs. LP is green trace. It's definitely showing some change above 50Hz when mic is 1 ft away from the sub.


As above. :T




> Edit: Refer to graph, second from the bottom of this post. The title is wrong!!! It says Front Mains - LP and 1Foot, it's really Subs - LP and 1Foot. Sorry, but I haven't figured out how to edit an attachment.


You can’t - you have to go back to REW and re-save your graph (i.e. no need to re-measure). Before you do that you can change the title.




> Now for 15-22KHz.... Besides the "spike at 60Hz ground-loop problem" that is evident, why is the SPL so low when measuring my Fronts compared to my Subs between 20-45Hz?


You have to re-do REW’s SPL calibration routine before switching from subs to mains measurements, and vice-versa. With a given signal, subs will always measure a higher SPL than the main channels, especially if you’re measuring only one speaker.




> I'm limited as to where I can place two subs. One, I can swap positions of the Fronts and Subs. Currently on the front wall, Subs are between Fronts and Center. Two, I can place the left sub in the rear left corner of the room, and the right sub I can slide up to about half of the right wall. I plan to play around with this, this weekend. If this isn't the correct forum, please feel free to move.


You have a nasty drop between 45-85 Hz that’s so severe it can’t be fixed with EQ. Try any other locations you have available. The closer to a corner the better, and full in-corner is usually best. Not necessarily perfect, but response that can easily be cleaned up with equalization is good enough. And remember, you don’t have to separate the subs. If you only have one location that gives best results, they can be stacked. Not pretty, admittedly...

Regards,
Wayne


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the input, Wayne. You're a tremendous help (along with so many others here).

As soon as my living room is "freed up" tonight (read, wife goes to bed), I'll focus a little more on my Mains & the SPL Cal and see if I can't raise the signal level some. Might make some measurements of each Main separately too. Saturday, I can wire up a YDP2006 to the Subs and try to find a better location for them. My XLR to RCA adapters came in today. 

Kix


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## bolaworldstudios (Mar 12, 2015)

few questions


1. why does my interface while calibrating - shows graphically out/in/ref in and on youtube videos is out/left/right

2. after i finished calibrating, save the soundcard calibration and checked the levels, just before starting the measuring it asks me to do a db SPL calibrating to..after i do it it says my SPL is really low...once i proceeded without SPL measuring and it went but my frequency response chart was on the top of the graph...how should i adjust it to be in the middle of the graph, i cant zoom out.

and so on, and so on..im followed GIK youtube tutorial but it wont work smootlhy as in the video..defaullt presets are not good maybe or? i just want to measure my room and go on with my life...this is frustrating
i have an scarlet 2i2 and behringer mic and i am an schooled audio guy so left and right, peaks, healthy gains, routing and so on is not a problem i guess....i dont know what im doing wrong.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum!

Are you using a Mac and / or ASIO? I believe the Youtube video is using Windows w/o ASIO. If you are your screen interfaces will look different. 

Regards, 
Wayne


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## bolaworldstudios (Mar 12, 2015)

im using mac, what about the rest of the problems,why do i have low spl? if i measure it.. and if i proceed it is over the top and my frequency chart is on the top of the graph


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## JohnM (Apr 11, 2006)

The video was made with an older version of REW, that is why it looks a little different.

To get the SPL figures reading correctly the SPL meter needs to be calibrated, that tells REW how to translate the signal levels from the mic into an SPL reading. It is described in the Calibrating the SPL Reading section of the REW help http://www.roomeqwizard.com/wizardhelpv5.1/help_en-GB/html/inputcal.html#top


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## bolaworldstudios (Mar 12, 2015)

ok.. i read that..but is nowhere written what to do if a problem occurs....for example now my spl showed 171 db..after matching it to the external spl it showed maximum of 203 db.. i dont get it?? is this normal for a small room? another thing..do i have to do the soundcard calibration again..save it, and then import it, ist it connected,does it have to be always imported what ever you do in the program according to the same room? actually i dont have a clue what am i doing because it is not self explanatory..can you please guide me through the process, because i lost already 2 days, searching on the forums and youtube..i could already calculate all the room modes on the paper and acoustically insulate my room.


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## Lumen (May 17, 2014)

First of all, Kix_N_Grins, sorry for the psuedo-hijack but you may be interested in this info as well... :R



bolaworldstudios said:


> ok.. i read that..but is nowhere written what to do if a problem occurs.... actually i dont have a clue what am i doing because it is not self explanatory..can you please guide me through the process, because i lost already 2 days, searching on the forums and youtube..


Hello bolaworldstudios, and welcome. There's no magic pill. It's all sweat and tears (okay, maybe just a few tears). So you'll just have to grin and bear it like the rest of us!  Seriously now, I was also struggling with finding a "bird's eye view" of the process. The REW Online Help is indispensable for understanding and operating REW. Another great guide came to my attention through member "ntran" in Post #8 of this thread. I've attached it here for convenience: *
View attachment REW 101 - A Step By Step Guide.zip
*

The guide seems to be a companion to the REW Online Help version, and includes detailed measurement strategy. I must have missed it somewhere in my advanced searches on this site. *Does that sound like a good idea to you, Wayne--can we add a link to the supplemental guide attached above on our REW Information Index page?*. It was authored on another site, AVS Forum, so I'm not sure about the rules. For that matter, I hope I'm not breaking any by attaching it. My sincerest apologies if I broke any rules or stepped on any toes, or opened a can of political worms, or--well, you get the idea. 

:hide:


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## Kix_N_Grins (Feb 14, 2015)

No problem, BlueRockinLou. It is a newbie question on REW, and fits the title of this thread. :bigsmile: I've been trying to keep all my REW questions on one thread just as an easy way to find things that I've asked and learned as I get started. Some of my trials and tribulations are covered in more detail on more appropriate HTS forums...

Just to re-enforce what you said in your reply above, my first post on this thread and to this forum was on Feb 25, and I'm "still" working on getting started after 5-6 weeks. It DOES take a lot of time and effort to learn REW. And for myself, also hardware, room acoustics, acronyms, forum etiquette, etc.

I also found ntran's post #8 very useful (refer to your link above). I spent the better part of the evening last night reading it and also the links within it, and found it a BIG help. I particularly liked the link within about "Bass Integration", and found it all very helpful in seeing the bigger picture.


Regards,
Kix


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## Lumen (May 17, 2014)

Kix_N_Grins said:


> No problem, BlueRockinLou. It is a newbie question on REW, and fits the title of this thread. :bigsmile: I've been trying to keep all my REW questions on one thread just as an easy way to find things that I've asked and learned as I get started. Some of my trials and tribulations are covered in more detail on more appropriate HTS forums...
> 
> Just to re-enforce what you said in your reply above, my first post on this thread and to this forum was on Feb 25, and I'm "still" working on getting started after 5-6 weeks. It DOES take a lot of time and effort to learn REW. And for myself, also hardware, room acoustics, acronyms, forum etiquette, etc.
> 
> ...


Thanks for the leeway, Kix! Speaking of rules... one of the big ones is not to post material that causes members to have discussions on other websites. It's okay to refer to material there, just _please_ remember to post questions or start discussions on HomeTheaterShack.com

Just keep at it. The rewards are great, as are the members here. No ridiculing or flaming or gouging or kicking or screaming or other unwelcome stuff. Good luck and have fun--that's what this hobby is all about--so don't forget to watch a movie or take in some tunes! 
:wave:


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## Lumen (May 17, 2014)

I just figured out why that document hasn't been officially referenced on this site... it was written by members of AVSforum.com, and includes specific instructions which meet their requirements (example: submitting graphs). Like "ntran" and you and I found out, some of it is very useful in a general sense.

Are there any moderators following this? If possible, could we please reference portions of the document or write our own versions? There doesn't seem to be an overview of REW measurement _strategy_ on our forums (please see pages 86-88 of the document attached to Post #26 above).


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## AudiocRaver (Jun 6, 2012)

The link has been created on our REW Information Index page.


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## JohnM (Apr 11, 2006)

bolaworldstudios said:


> now my spl showed 171 db..after matching it to the external spl it showed maximum of 203 db.. i dont get it?? is this normal for a small room?


Only if the room is underneath a NASA rocket launch pad . What was the reading on your external SPL meter? That is the same figure you need to type into the box in the REW calibration window, so if your external meter read 78 you type in 78.


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## Lumen (May 17, 2014)

AudiocRaver said:


> The link has been created on our REW Information Index page.


:thankyou:


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## willis7469 (Jan 31, 2014)

JohnM said:


> Only if the room is underneath a NASA rocket launch pad . What was the reading on your external SPL meter? That is the same figure you need to type into the box in the REW calibration window, so if your external meter read 78 you type in 78.


 wow! Rofl!!!!!


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## Robbiesd (Mar 27, 2015)

Hi All,
I'm new to this also, thinking I'd like to learn to use REW. The computer I'd use is the ultra small size Dell Optiplex 960 without a soundcard (onboard sound), WIN 7 PRO, no HDMI out, just VGA and DVI. I have a Radio Shack SPL meter. From what I've read so far I see I shouldn't use the Mic input the computer has so that I shouldn't connect the SPL meter to the Mic input. So I'm seeking suggestions on what to buy. I was thinking about a Behringer EMC8000 mic with an XLR to USB cable. Or should I find an external sound card and use the SPL meter? Or? Or is this computer without HDMI the wrong machine to use? As I said, I'm new and confused as to what I should buy to get setup. 
Thanks for your suggestions.
Robbie


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## JohnM (Apr 11, 2006)

The rear mic input on the Optiplex is a combined mic/line input, you can connect the REW SPL meter to that and get going without buying anything else besides a simple adaptor, details are in the Cabling and Connection Basics thread.


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## Robbiesd (Mar 27, 2015)

Thanks John, I didn't recall that but just looked at the manual and it's true...so I can connect the Radio Shack SPL there but not the ECM8000.


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## Robbiesd (Mar 27, 2015)

John,
I jumped the gun with my question last night as I've now found the REW forums and FAQ's, etc. I also may have jumped the gun in ordering a Behringer ECM8000. With my Optiplex should I just re-sell it and buy a USB mic like the UMIK-1 and forget about a Xenyx502 and SB Live external card? Sure would be less mess.
Thanks,
Robbie


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## JohnM (Apr 11, 2006)

For most acoustic measurement a UMIK-1 works perfectly. The only thing it can't offer is measurements with a timing reference, which might be used if trying to align measurements of different drive units in a speaker, or compare arrival times from different speakers in different measurements. They aren't things most users need to do.


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## Kix_N_Grins (Feb 14, 2015)

It's been awhile since my last posting. Had to upgrade some AV hardware. I did something since my last post, to change the Windows 7 PC I'm using for REW, and for the life of me, I can't figure out how to restore things back to when REW was working for me last. I'm hoping someone can help....

My initial problem was, I can't turn the volume on my AVP up more than 3-5 db from min without getting some serious feedback. So, I thought I'd start from square one with a Soundcard Cal. I'm using two 1/8" mini-headphone to individual left/right RCA connectors (plugged into Line In and Speaker output on soundcard), and using a single RCA to RCA connector to patch the red RCA connectors coming from the soundcard.

The next 2 screens show my prelim setup in REW:















This next one is what I get as I run the cal. Note that the Ref In portion of the display never gets much higher than what is shown:








This last screen-shot is my measurement that was taken:








Regards,
Kix


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## Wayne A. Pflughaupt (Apr 13, 2006)

Feedback is an indication that the sound card’s monitor needs to be turned off (i.e. set for “Computer”).

Regards, 
Wayne


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## JohnM (Apr 11, 2006)

Also make sure that "Listen to this device" is *not* selected on the Listen tab of the Windows Recording Devices properties for the input you are using.


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the replies, Wayne and John.

I did find that "Listen to this device" is WAS selected on the Listen tab of the Windows Recording Devices, so I unchecked it. It changed things for calibrating my soundcard, but something's still not right.

I wasn't able to find where to check that my soundcard's monitor is turned off Wayne, so maybe that's what's still hosed up. 

Below are screenshot's of the playback/recording properties I've checked and have set up:

Playback:
































Recording:
























Sounds - Communications








Volume Mixer:








And here's what my Measurement currently looks like when calibrating the soundcard:








Again, thanks for your help. I just can't see what I'm over-looking... One thing I did notice that doesn't really have to do with the soundcard cal, is that whatever I've done, I think I may have damaged my Galaxy CM140 mic in the process...


Regards,
Kix


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## JohnM (Apr 11, 2006)

That measurement is OK to use. It is slightly noisy at the top end, but bear in mind the scale - the noise is only 0.2 dB or so.


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the reply John.

I guess what threw me off, is that the measurement was sitting right at 0db. And when I compared to my soundcard cal measurement in post #5 above, it was at between 30-35db. I've figured out that in post #5, I had turned off the C weighting and deselected the soundcard file. Now that I'm measuring them both the same way, they are pretty much identical measurements.

That brings me back to my original problem, "massive" feedback when I try to perform the Check Levels and Calibrate SPL Readings steps. I'm still suspecting my Galaxy CM-140 is hosed. 

When I go to Check Levels and slowly increase my AVP volume to 75db on the SPL meter (using Sub signal), I can barely increase the volume. And it sounds like low-frequency feedback, not like the signal that I remember hearing. When I do the Calibrate SPL Readings steps, that portion seemed to work okay, albeit not sounding right. After ending the test, I decided to try increasing my AVP volume from min, and I'm getting the exact same thing with "no" REW signal applied.

So tonight, I tried swapping the Galaxy CM-140 with a Radio Shack digital SPL meter that I have, performed the Check Levels and Calibrate SPL Readings steps, and everything works great. ??? The signal I hear sounds like the 0-200Hz noise I remember, and not the low freq feedback that I got with the Galaxy connected. And, I'm able to turn the AVP volume up to a level I would expect it to be at for 75db.

Something else I noticed... Last week, I made my living room as quiet as I could, and just used the Galaxy as a stand-alone SPL meter. It measured around 42db (in A weighting), but jumped up to around 72db when I switched to C weighting. This week, it seems to be measuring around 60db in C weighting. I know in late March, it was <45db (C weighted) when I made things as quiet as I could using the Galaxy....

I guess what's confounding me the most, is that all of this started in early April when I tried to move one of my subs to a corner of a room (refer to post #20 above). I made multiple changes at the same time. Some changes to placement/wiring by moving the sub, some by installing a Yamaha YDP2006 equalizer for my subs, and I also followed the initial set-up instructions in REW 101 - A Step by Step Guide instead of the REW Help Contents (like I did the first time I set it up). Within 24 hours of doing these, I've been stuck since... I can't believe the odds of my Galaxy CM-140 taking a dump at the exact same time.... But that's what it's looking like to me.

I've swapped the Yamaha YDP2006 with another, I've totally rewired the whole system to make sure I didn't mess up there, I'm stepping through the REW Help Contents step by step.... 

I know there's a lot of smart people on this forum. Am I missing something? Based on what I written in this post, does it also look like by coincidence, my CM-140 hosed up at the same time I made these other changes? Why would swapping the Galaxy with a Radio Shack SPL meter "fix things" ? Is there something I could have done to "break" the Galaxy CM-140 by making the changes I did?

Aside from the frustration of not being able to "see" my sound system and making it better, I guess the positive thing is, it's been sounding really good to me anyway.... :bigsmile:

Any help will be appreciated, :help:
Kix


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## JohnM (Apr 11, 2006)

Post #5 looks like a measurement using the normal Measure button that was taken with a loopback connection. Because it was a measurement REW attempted to assign the SPL calibration value to the result. Loopback calibrations made using the button on the Soundcard preferences don't have any SPL calibration applied because REW "knows" they are loopback measurements and should be nominally 0 dB (which corresponds to unity gain).

What you hear when making a measurement shouldn't have anything to do with what sort of mic or SPL meter you have connected, or whether you have anything connected to the input at all. If you can hear anything at all from your speakers when you speak into or hit the SPL meter you are using then there is some sort of monitoring path active, such as having "listen to this device" ticked for the input. It would be odd though, since the soundcard measurement you posted doesn't show any sign of monitoring being active. 

Sorry to ask the obvious, but your SPL meter is connected to the soundcard input you used when making the soundcard calibration, right?


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## Kix_N_Grins (Feb 14, 2015)

Yes. On both line input and speaker output on the soundcard, I'm using 1/8" (3.5mm) stereo connectors that Y to separate L/R RCA connectors. When performing the soundcard cal, I'm patching the two R RCA's together (both connectors are red). When performing Check Level and Calibrate SPL Readings, I remove the patch cable between the two R RCA's, connect the Galaxy SPL meter to the input RCA using a RCA to 1/8" (3.5mm) mono connector. My AVP is connected to the output RCA connector. In all steps, I'm using the red RCA connectors on the Y adapters.

The only difference when I use the Radio Shack SPL meter instead of the Galaxy, is that the cable I'm using is RCA to RCA to go from meter to R RCA Y adapter to SPL meter. It seems odd that the Radio Shack meter works, but connecting the Galaxy doesn't.

Thanks again for your help,
Kix

PS. Also, just to rule it out, I checked the 1/8" mono to RCA cable I'm using to connect the Galaxy for opens/shorts using a DMM and it's okay.


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## JohnM (Apr 11, 2006)

Pretty strange then, can't see why changing the meter should have any effect on the signal that is produced when measuring.


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the reply John. The only thing I can think of, is the Galaxy somehow is defective.


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## TomFord (Jul 15, 2014)

JohnM said:


> Lots of advice and suggestions in this thread on fixing hum caused by ground loops.



Admin, I believe this subject needs to be pinned. 

Resolution at the bottom. 

When I upgraded my sub I developed a ground loop. Incredibly loud hum, and the loop remained if the LFE was plugged in and the power cord was disconnected. 
After an extensive search it came down to 2 isolators. One by Jensen and the other by Viewsonics. Always cringed when hearing or seeing Jensen and the other was 30$ cheaper, as well as coverage a wider range. For $20 I fixed the issue (link below) and couldn't hear the faintest of hums. Placed it in between the cable that comes from the wall (Comcast) and the DVR. Purchase a 3 foot line of Coaxial on Monoprice or get the Monoprice brand on Amazon and pay the extra 1-2$ it costs. Went ahead and purchased the best quality coaxial from Monoprice with much better shielding than what's to keep as much signal integrity as possible and avoid all the interference I could. 

http://www.amazon.com/Viewsonics-VS...6503485&sr=8-11&keywords=Ground+loop+isolator


Those who live in apartments, I would recommend the isolator to even if you do not hear a hum. The amount of interference is hard to believe. You will most likely see an improvement (slight, but noticeable) in video quality. A bit more clarity on your audio at high volumes wouldn't surprise me at all. 

Highly recommend


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## TomFord (Jul 15, 2014)

Can I avoid reading 40 chapters and buy a programmed file? Is there a programmed file that could give me a glimpse of its work? Don't mean to slight REW in any manner, without it I wouldn't of ever found this excellent website. The few times I've started messing with it though it makes me want to nap. I don't take naps 

Know it would make some measure of improvement if I did the mission that REW feels like it would be. Don't feel it would be significant like sound treatment of the room would be. Nor know/understand how it would implement into my audio while watching the DVR or the rare occasion I dust off the PS3's to use


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## Kix_N_Grins (Feb 14, 2015)

Woo-hoo! I think my problems are solved. I have absolutely no idea what actually was causing it, but I know what I did that fixed it. Haven't had a chance yet to try REW, but I can't wait.... In my last post, I mentioned I had reduced everything down to my Galaxy CM-140 possibly being defective. Using it to measure my noise floor, I was getting around 72db. Using my Radio Shack SPL meter, I was around 51db. So, I ordered a new Galaxy which arrived this week. I went to measure my noise floor with it, and to my dismay, it was measuring 73db. I compared to the older Galaxy and it was about the same. Measured with the RS SPL meter and it was 52db. So, now I'm thinking "what the ???". I figured I would take the new Galaxy and the RS SPL to the quietest place I have and compare them there, my un-started car. Using the Galaxy I measured 50db, and using the RS I measured 40db. That clued me in that the issue was something in my living room that was causing the Galaxy to measure much higher than the RS SPL meter, and that something was something I couldn't hear. I figured the Galaxy has a much broader freq response than the RS SPL meter, and the RS just wasn't picking up on it. I have to be honest, but this is also about the time I was thinking that maybe I've lost some of my hearing. I am 55 years old, and I have been to my fair share of rock concerts over the past 40 years... Monday, my 25 y/o son comes over, I made everything as quiet as I could in the living room, and asked if he could hear anything. He could not, except a ticking clock in the kitchen. My Galaxy was measuring 72db, and my RS was measuring 51db. I didn't feel quite so much in doubt about my hearing.... Tonight, I thought I would just start powering everything down in the house while measuring with both the Galaxy and the RS. I took my first measure with everything running for a baseline, and got 52db with the RS and 72db with the Galaxy. After shutting down the central air, I measured 44db on the RS and 72 db on the Galaxy. After shutting down TV, stereo, computer, and ceiling fan, I measured 42db on the RS and 72db on the Galaxy. My last step was going to be shutting off power to the whole house at the electric meter. When I sat the Galaxy down on the sofa cushion next to me, I noticed that it dropped down from 72db to 60db. I went to pick it back up and when my hand got around 6 inches away, it started increasing until I was about an inch away and it was measuring 72db again. I moved my hand farther then closer and verified that the DB increased as my hand got closer. Unbelievable! I went outside and shut the power down at the electrical meter and came back in to measure. I got 38db on the RS and 47db on the Galaxy. My hand had very little effect on the DB reading no matter how close it was to the Galaxy (+- 2 db). Something has definitely changed... I turned the power back on to the house and the reading on the Galaxy was at 48db. Turned on the central air, ceiling fan, stereo, TV, computer and the Galaxy increased to 51db. I don't understand it, but it seems like cycling the power to my house has fixed the problem. Whatever the problem was.... I don't understanding why cycling power fixed things, and I don't understand moving my hand closer to the Galaxy made things worse when I had the problem. Now for the BIG test... Getting my REW to work again. I can't wait for my wife to go to bed.... :bigsmile: Kix


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## Niick (Jan 2, 2015)

That is weird! Now you know why guys who make their living relying on these types of instruments spend the money they do. Are both meters A or C weighted?


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## wtaylorbasil (Nov 27, 2008)

Now that audyssey system has been around for sometime, is REW still King?


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## Kix_N_Grins (Feb 14, 2015)

Gennelle51187 said:


> That is weird! Now you know why guys who make their living relying on these types of instruments spend the money they do. Are both meters A or C weighted?


 Both the RS SPL and the Galaxy CM-140 can be toggled for either A or C weighting. I've been using C weighting on both for everything. I did compare the two using A weighting just for the fun of it. The results were still different, although not as severe of a difference. I'm also using a Jensen optical isolator in my cable going to my TV. I was getting a 60Hz hum. The noise I'm hearing now is very different than when I was having ground-loop issues. My luck did not go much better last night in Checking Levels, although I was able to turn my AVP volume up much higher than before I cycled power to my house. But I'm still getting some severe "noise" when I turn it up. But the noise also sounds different now, like higher in frequency and much sharper. I got frustrated as soon as I heard it, and gave up for the night.


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## Niick (Jan 2, 2015)

Man, I don't know what to tell ya that might be immediately helpful. Sounds like you got your work cut out for ya. Troubleshooting is one of my favorite thing to do at work. I suppose what I would try to do, is eliminate all variables, usually in the process of eliminating variables you'll either find the culprit or at the very least learn something you had been missing before. And I mean ALL variables. Like, in order to do this the way I'm thinking, you'd need at least 2 of EVERYTHING, so ya got 2 meters, do ya have 2 receivers, even an old "throw away" one, 2 TVs, 2 or more different outlets that are wired to 2 or more different branches, probably gonna need some extension cords............... Like, eventually I would think, if you could substitute each component/source of power somehow........it might shed light on the culprit. It would be a pain in the butt, but it sound like it's already frustrating.


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## Kix_N_Grins (Feb 14, 2015)

Thanks for the reply Gennelle.

I don' think substituting equipment is going help, aside from replacing the Galaxy, which I did. There is just something really strange going on, and I don't know where to turn. If there's a better forum to be using at Home Theatre Shack, please let me know. I don't believe the issue is my hardware, I don't think it's the wiring of my hardware, and I don't think it's REW itself.

Tonight, I shut my central air off and walked around the house with Galaxy in hand, it not being connected to anything (being battery powered). I found a spot in my kitchen that measured 95dB. 95dB!!! 75dB is loud to me. It wasn't absolutely quiet, as I could hear my kitchen clock ticking, but it was relatively quiet. No way it was 75dB, much less 95dB.

My last test, I shut the main power off at the electric meter and it seemed to fix the issue. I think tomorrow, I'll try shutting off my breakers to the house one at a time and see if that points to something.

Kix


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## Mariam.1938 (Apr 12, 2015)

Hi all.
REW is a wonderful program.
So far, I have used other programs in the audio-acoustic measurements and now I decided to use REW.
I also have problems for making impulse-gated frequency measurements.
If someone can help me.
Thanks.
Jeanm


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## jtalden (Mar 12, 2009)

Jeanm,
REW 'Help' feature on applying a IR window (gating) has good coverage of the basics. An excerpt from the help screen is shown below. If you had more specific questions we can try to help. It would be best to ask those in a new thread as it is a different topic from the discussion here.


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## phabaudio (Aug 2, 2015)

Hello,

I am a newbie to REW but also to room equalization and more generally to sound measurement. My goal is to improve listening music with my stereo system.
There is no doubt that REW is a fantastic tool but it's not so easy to master it (at least for me)...
My first questions concern the calibration of both the microphone (I am using a UMIK-1 USB mic) and the SPL meter:

The calibration file provided by minidsp includes the sensitivity factor of the microphone. In my case this factor (-.5017dB) is negative and expressed in dB. It looks like it depicts a bias or offset, not a factor. Could someone confirm which is the unit of this number and how it is used by REW ?

From REW online documentation I understand that the step 'SPL Meter Calibrate' need an external SPL meter. I do not have one. Also I am using an USB microphone with sensitivity coded in its calibration file, so I would expect that calibration of the internal SPL meter is not necessary (the volume control of the input path being adjusted at 100 %). Is this step still mandatory (which would imply for me to buy a SPL meter...) ?

For step 'Check Levels' I assume (but perhaps I should not) that the internal SPL meter can be used as is, without calibration (or with default calibration ?), and that it gives acceptable readings. However, I can't get a reading higher than 65 dB, beyond this value the volume of the speakers is too much loud. The distance between the microphone and the speakers is about 3 meters (10 feets). Should I reduce this distance ?
Thanks a lot in advance for any help which might allow me to go to the 'Measure' step, at last !

Pierre


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## JohnM (Apr 11, 2006)

phabaudio said:


> The calibration file provided by minidsp includes the sensitivity factor of the microphone. In my case this factor (-.5017dB) is negative and expressed in dB. It looks like it depicts a bias or offset, not a factor. Could someone confirm which is the unit of this number and how it is used by REW ?


The Umik sensitivity figure is the input dB FS value the mic produces when driven by 100 dB with the input volume set to 1.0 (which produces 24 dB gain in the driver)


> From REW online documentation I understand that the step 'SPL Meter Calibrate' need an external SPL meter. I do not have one. Also I am using an USB microphone with sensitivity coded in its calibration file, so I would expect that calibration of the internal SPL meter is not necessary (the volume control of the input path being adjusted at 100 %). Is this step still mandatory (which would imply for me to buy a SPL meter...) ?


No, not if REW recognises that it is using the UMIK (it should detect the UMIK when it is started up with the UMIK connected and ask for the cal file)


> For step 'Check Levels' I assume (but perhaps I should not) that the internal SPL meter can be used as is, without calibration (or with default calibration ?), and that it gives acceptable readings. However, I can't get a reading higher than 65 dB, beyond this value the volume of the speakers is too much loud. The distance between the microphone and the speakers is about 3 meters (10 feets). Should I reduce this distance ?


The SPL meter will only read correctly if the UMIK has been recognised and the cal file has been loaded, in which case the SPL reading will show that it is calibrated (SPL figures will not be red). If the meter says 65 dB but the test signal is loud then it is not reading correctly which suggests it is not calibrated.


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## phabaudio (Aug 2, 2015)

Hello John,

I thank you a lot for providing help.
Before commenting your answer I must precise that I run REW on a linux laptop (Xubuntu 14.04).


> The Umik sensitivity figure is the input dB FS value the mic produces when driven by 100 dB with the input volume set to 1.0 (which produces 24 dB gain in the driver)


Ok. So, I understand that in my case the umik-1 delivers full scale when driven by a 100.5017 dB SPL (2.12 Pa ?) sound pressure, is that right ?
Beside that I could check with alsamixer that at 100% a 24 dB gain is added in the driver. Does it mean that the max measurable sound pressure is 76.5017 dB SPL ? Knowing that is probably not necessary for correct operation of REW, but I am just curious of it.


> No, not if REW recognises that it is using the UMIK (it should detect the UMIK when it is started up with the UMIK connected and ask for the cal file)


Since my previous post I discovered the tutorial "REW 101 Step By Step Setup Guide" by AustinJerry. On page 54 I see that a dialog should pop up at REW start up telling that a UMIK-1 has been detected asking the user to confirm that REW should use it for measurements.
This dialog window does not pop up when REW starts up on my machine. However I can choose the UMIK-1 in the 'Input Device and Input' field on the Soundcard tab of the Preferences window where it appears as U18dB [plughw:1.0].
I tried to uninstall REW (deleting the REW directory) and reinstall it from scratch, but the UMIK-1 is still not automatically detected by REW at start up time. But at the same time if I choose U18dB in the 'Input Device and Input' field, the Mic/meter tab still displays the name of the calibration file ! Is there any place other than the REW directory where configuration data is stored by REW ?


> The SPL meter will only read correctly if the UMIK has been recognised and the cal file has been loaded, in which case the SPL reading will show that it is calibrated (SPL figures will not be red). If the meter says 65 dB but the test signal is loud then it is not reading correctly which suggests it is not calibrated.


In my case the 'Calibrate' button on the SPL Meter window has never been red. Even after having removed the calibration data using the 'Clear Cal' button on Mic/Meter tab.

My impression is that REW does not behave as expected as regards the microphone input. Could this weird behavior be related with the fact I am using OpenJDK (natively installed with Xubuntu) instead of Oracle's JDK ?


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## phabaudio (Aug 2, 2015)

John, I have installed Oracle Java 8:
$ java -version
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) Server VM (build 25.51-b03, mixed mode)​Also I found out that REW stores user prefs in a file named .java/.userPrefs/room eq wizard/prefs.xml.
I uninstalled REW again, deleted the REW and .java directories and then reinstalled REW. At first start up still no autodetect of the UMIK-1 and the button calibrate on the SPL Meter is NOT red (though I have entered no calibration file for the mic yet)...


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## JohnM (Apr 11, 2006)

REW looks for the "UMIK" text in the input name to know whether a UMIK is connected, so without that it will struggle. 

The max input for your mic is 100.5 dB. The sensitivity figure already allows for the 24 dB gain. If you turn down the input volume setting to get 0dB/unity gain (don't know what input volume that corresponds to on Linux, sorry) the max input before clipping would be 124.5 dB.

The digits of the SPL meter are red when it is not calibrated. The calibration is not particularly important unless you need exact SPL readings (it only changes the level of the plot on the SPL axis, not it's shape) so you can "calibrate" the meter by just setting the test signal volume to a comfortable level and telling REW that is 75 dB. To be a bit more scientific you could use a free phone SPL meter app and use that as a reference.


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## Kix_N_Grins (Feb 14, 2015)

I also got a UMIK-1 from Cross Spectrums this weekend. I went to the miniDSP website and downloaded the correct file for my serial number, and pasted the "Sensitivity" line to the cal file from Cross Spectrum.

When I opened the cal file, I noticed that each line of data is preceded by a space. Is this normal? I attached a copy of the cal file. I had to change the file extension from .frd to .txt in order to upload to this site. Also, do I put a space in front of the "Sensitivity" line I pasted in?

Thanks,
Kix

View attachment narrow_band_response_0_degree.txt


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## AudiocRaver (Jun 6, 2012)

Kix_N_Grins said:


> I also got a UMIK-1 from Cross Spectrums this weekend. I went to the miniDSP website and downloaded the correct file for my serial number, and pasted the "Sensitivity" line to the cal file from Cross Spectrum.
> 
> When I opened the cal file, I noticed that each line of data is preceded by a space. Is this normal? I attached a copy of the cal file. I had to change the file extension from .frd to .txt in order to upload to this site. Also, do I put a space in front of the "Sensitivity" line I pasted in?



The space at the beginning of each line is normal, leave it.
Do NOT put a space in front of the "sensitivity" line. It might work, but my file does not have it.


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## 3ll3d00d (Jun 6, 2006)

JohnM said:


> REW looks for the "UMIK" text in the input name to know whether a UMIK is connected, so without that it will struggle.


I guess a Linux user should provide an alias for the device name using an appropriate .asoundrc then - http://alsa.opensrc.org/Asoundrc#The_naming_of_PCM_devices



JohnM said:


> The max input for your mic is 100.5 dB. The sensitivity figure already allows for the 24 dB gain. If you turn down the input volume setting to get 0dB/unity gain (don't know what input volume that corresponds to on Linux, sorry) the max input before clipping would be 124.5 dB.


Fwiw alsamixer should show the gain in dB


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## phabaudio (Aug 2, 2015)

JohnM said:


> REW looks for the "UMIK" text in the input name to know whether a UMIK is connected, so without that it will struggle.


Ok, I see. As Matt told it should be easy to give the appropriate name to the device using an alias.



> The max input for your mic is 100.5 dB. The sensitivity figure already allows for the 24 dB gain. If you turn down the input volume setting to get 0dB/unity gain (don't know what input volume that corresponds to on Linux, sorry) the max input before clipping would be 124.5 dB.


Ok, thanks for the explanation.



> The digits of the SPL meter are red when it is not calibrated.


Sorry, I was looking at the color of the button 'Calibrate', not at the digits. 



> The calibration is not particularly important unless you need exact SPL readings (it only changes the level of the plot on the SPL axis, not it's shape) so you can "calibrate" the meter by just setting the test signal volume to a comfortable level and telling REW that is 75 dB. To be a bit more scientific you could use a free phone SPL meter app and use that as a reference.


Ok, as for now I'll use an approximate calibration done as you suggest.

I have now one big question about the way I should perform the measurements:

Should I measure each channel separately (e.g. left then right) ? In that case should I direct the microphone towards the speaker on test ?
Or is it preferable to measure both channels together ? In that case I assume that the microphone should be directed towards the center between left and right speakers ?


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## phabaudio (Aug 2, 2015)

3ll3d00d said:


> I guess a Linux user should provide an alias for the device name using an appropriate .asoundrc then - http://alsa.opensrc.org/Asoundrc#The_naming_of_PCM_devices


I thank you Matt for your suggestion. So far I never used a .asoundrc file because its syntax (and semantics) looks to me rather obscure. But for the case of merely creating an alias to a sound device I should find easily examples on the web.




> Fwiw alsamixer should show the gain in dB


Right: At 100% it shows a 24 dB gain.
However I am not sure to understand where this gain does come from: Is it a gain added by the USB interface of the microphone, or a gain added by the driver ?
Also I find it strange that the driver reports a 18 dB gain (hence the name U18dB), instead of a 24 dB gain (excerpt from syslog: "usb 3-3: Product: Umik-1 Gain: 18dB")...


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## 3ll3d00d (Jun 6, 2006)

phabaudio said:


> I thank you Matt for your suggestion. So far I never used a .asoundrc file because its syntax (and semantics) looks to me rather obscure. But for the case of merely creating an alias to a sound device I should find easily examples on the web.


there's no doubt that using alsa involves some extremely obscure config files 



phabaudio said:


> Right: At 100% it shows a 24 dB gain.
> However I am not sure to understand where this gain does come from: Is it a gain added by the USB interface of the microphone, or a gain added by the driver ?
> Also I find it strange that the driver reports a 18 dB gain (hence the name U18dB), instead of a 24 dB gain (excerpt from syslog: "usb 3-3: Product: Umik-1 Gain: 18dB")...


you might find this thread useful - http://www.avsforum.com/forum/155-diy-speakers-subs/1797489-massively-clipped-umik-1-a.html - in explaining what the 18dB gain refers to, it's the analogue gain inside the mic itself (the internal preamp basically). If you change these dip switches then you need to adjust the SENS factor accordingly. The 24dB in alsa is applied digitally inside the ALSA stack.


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## phabaudio (Aug 2, 2015)

3ll3d00d said:


> there's no doubt that using alsa involves some extremely obscure config files


I tried the following:
pcm.umik-1 {
type hw
card 4
device 0
}​Audacity sees the microphone with its alias, REW does not :-(
This is possibly because REW gets sound devices info from Java and has no direct access to the info provided by the driver.



> you might find this thread useful - http://www.avsforum.com/forum/155-diy-speakers-subs/1797489-massively-clipped-umik-1-a.html - in explaining what the 18dB gain refers to, it's the analogue gain inside the mic itself (the internal preamp basically). If you change these dip switches then you need to adjust the SENS factor accordingly. The 24dB in alsa is applied digitally inside the ALSA stack.


Very interesting thread. Things are getting a little clearer to me. It might allow me to understand what John meant when he wrote:


JohnM said:


> The max input for your mic is 100.5 dB. The sensitivity figure already allows for the 24 dB gain. If you turn down the input volume setting to get 0dB/unity gain (don't know what input volume that corresponds to on Linux, sorry) the max input before clipping would be 124.5 dB.


I understand he is speaking of the analog gain which in my case is 18dB, not 24dB. So I think that the max input before clipping would be 118.5dB with both analog gain (dip switches inside the mic) and digital gain (inside alsa software) adjusted to 0dB. With factory analog gain (18dB) and digital gain adjusted to 24dB the max input before clipping would be 76.5dB.
But it may be that I still do not completely understand that matter. In your opinion ?


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## 3ll3d00d (Jun 6, 2006)

phabaudio said:


> I tried the following:
> pcm.umik-1 {
> type hw
> card 4
> ...


looks that way -> http://stackoverflow.com/questions/9381940/use-alsa-pcm-outputs-via-the-java-soundsystem

I would think you have 2 options;

1) write a udev rule to rewrite the device name on load (some examples in https://wiki.debian.org/udev or http://alsa.opensrc.org/Udev) 
2) REW gains the ability for the user to define the name of the UMIK device (or it looks for a different name on linux)



phabaudio said:


> Very interesting thread. Things are getting a little clearer to me. It might allow me to understand what John meant when he wrote:
> 
> I understand he is speaking of the analog gain which in my case is 18dB, not 24dB. So I think that the max input before clipping would be 118.5dB with both analog gain (dip switches inside the mic) and digital gain (inside alsa software) adjusted to 0dB. With factory analog gain (18dB) and digital gain adjusted to 24dB the max input before clipping would be 76.5dB.
> But it may be that I still do not completely understand that matter. In your opinion ?


No, the SENS factor and the analogue gain setting are related. If you change the analogue gain then you have to change the SENS factor too so the existing SENS factor already accounts for the 18dB analogue gain and gives you a max SPL of ~100dB. If you reduce the gain in alsamixer to unity from +24dB then you will gain 24dB headroom and will be able to measure a max of 124dB. If you then reduced the analogue gain and adjusted SENS factor accordingly then you could read even higher absolute SPL levels (theoretically ~142dB though whether the mic itself can actually deliver that cleanly is another question).


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## phabaudio (Aug 2, 2015)

Do you mean that the SENS factor takes also in account the 24dB digital gain ?


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## 3ll3d00d (Jun 6, 2006)

phabaudio said:


> Do you mean that the SENS factor takes also in account the 24dB digital gain ?


no, it applies to the analogue gain only. AIUI REW accounts for the digital gain internally.


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## phabaudio (Aug 2, 2015)

What I do not understand is where this 24dB value does come from. How can REW know that the driver add a 24dB gain rather than any other gain value ?
BTW, on the Soundcard tab of the Preferences window the check boxes and fields controlling the input and output volume are disabled (greyed). Output volume has value 0.5 and Input volume has value 0.25. I understand that REW can not read or modify these values. But as the controls are disabled I do not see an other way for setting Input and Output volumes than manually editing the file prefs.xml. Not very handy.


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## JohnM (Apr 11, 2006)

phabaudio said:


> What I do not understand is where this 24dB value does come from. How can REW know that the driver add a 24dB gain rather than any other gain value ?


If the Javasound implementation exposes the input volume setting REW reads that to determine the gain, the relationship between the input volume (which is usually exposed as a 0 .. 1 value) and the dB gain varies with OS, REW knows the mappings for various flavours of Windows and OS X but doesn't know the Linux mappings. On Windows and OS X changing the input volume does not change the SPL reading because REW compensates for the change, on Linux that probably doesn't work.


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## phabaudio (Aug 2, 2015)

JohnM said:


> If the Javasound implementation exposes the input volume setting REW reads that to determine the gain, the relationship between the input volume (which is usually exposed as a 0 .. 1 value) and the dB gain varies with OS, REW knows the mappings for various flavours of Windows and OS X but doesn't know the Linux mappings. On Windows and OS X changing the input volume does not change the SPL reading because REW compensates for the change, on Linux that probably doesn't work.


That would explain why the fields controlling the input and output volumes are disabled on my linux machine.

Sorry John for having bothered you with naive questions. I hope that someone in the future will contribute to REW development so that the linux platform is better supported.


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