# REW & MiniDSP. Have I got this right?



## Pieface (Sep 4, 2013)

Greetings Forumers  I hope this is in the right place...

I am in the process of setting up a 2.2 system with music as the primary focus but with the ability to watch some movies too when the fancy takes me. I have no experience with room measurement and treatment so be gentle with me 

I have become convinced that room measurement and proceeding to treat/EQ from there will be a pretty bang for buck way to maximise what I can get out of my hardware with a reasonable level of simplicity with the current integration between the REW and MiniDSP products. The REW and UMIK-1/MiniDSP seems like a pretty good way to get started without an undue outlay but I have a couple of questions I would like help with to make sure I get the correct package to achieve my aim.

Firstly, is the UMIK-1 through the miniDSP site adequate or is an independently calibrated UMIK-1 essential to get worthwhile accuracy?

My current thinking is to insert the mini-DSP between my preamp and power amplifer acting as an active cross over to send the appropriate frequencies to the active subs and the higher frequencies to my main speakers while also running whatever EQ filters REW determines. I believe for my unbalanced system the correct miniDSP to get is the 2x4 unbalanced and to get the 2.1 advanced software plug in. I should be able to try my subs in both stereo and mono format with this set up ie daisy chain the subs for mono or run them each directly from the miniDSP for stereo. Is my understanding correct at this point?

Assuming I have the nuts and bolts correct...

I can use the UMIK and REW to experiment with speaker placement and main listening position to try and achieve the best response prior to running any EQ. Once I have my head around these measurements I should be able to determine what issues I have with room response and a rough idea of what kind of passive treatment measures are required/would be beneficial - I understand this is likely to be a bit of a learning curve and that my passive treatments are unlikely to have a great impact on any issues at the bass frequencies - at least with the sized passive treatments that are likely to get past the wife.

Once I have reached the point where no more passive treatments are to be installed I can proceed to looking at DSP for sub EQ via the filters that REW generates to try and reach a target curve that pays respect to the capabilities of the hardware and the limitations of the room.

Am I understanding the process correctly and choosing the correct equipment for the task? Please correct me if I'm off base.

Depending on how well I've got the concept I'll have some more specific questions about REW.

Cheers!


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

I’ve heard lots of complaints about limited headroom with the unbalanced version, so you might want to get the balanced version instead.

Room treatments merely dampen room reflections and make the room more “dead.” That can improve imaging and give other benefits, but its effects on frequency response will be minimal, if anything.

Regards, 
Wayne


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## JohnM (Apr 11, 2006)

Dampening the reflections helps even out the response as well, since the peaks and dips are the combined result of the direct sound and the various reflections.


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## charlieblue (Aug 17, 2013)

The 2.1 advanced plugin looks right for your case (movies & stereo).

Just a thought, Paul Spencer says miniDSP not good for stereo, because not enough digital delay available. This obviously depends on the distance between each main speaker and its respective sub (edit: with respect to distance from listening position, but you got that in the first place, I guess  ), though. 
Still OK for home theater : )

PS you do not require timing measurements, right ? USB mics won't help much there...


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## charlieblue (Aug 17, 2013)

Pieface said:


> My current thinking is to insert the mini-DSP between my preamp and power amplifer acting as an active cross over to send the appropriate frequencies to the active subs and the higher frequencies to my main speakers while also running whatever EQ filters REW determines.


That's how I'm using the mini-DSP. Did go for balanced version, just like Wayne suggests. Then again, I do not require extra delay: speakers and subs are on an arc, less than 5'/1,5m away from LP. Might bring the subs even closer too: been reading interesting stuff on HTS about flanking subs at less than 3'/1m from LP... supposedly leads to perceptual immunity from room modes, plus gives much much more headroom.. all good stuff there, got to try that out!

One more thing though, re-reading your post: active subs probably use digital amplifiers. Those may add another small delay (_EDIT: up to_ 1-2msec _if supporting DSP. Principal applies to all different amplifiers, though_) to the signal. That should be accounted for = added to the delay of the power amplifier for main speakers, assuming that is an ordinary/old school analogue (fractions of usec to few tenths of usec delay) design.

And that's where being able to measure distances (acoustical rather than physical) comes to play...:devil: in the details !

Best,

Charlie


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## Pieface (Sep 4, 2013)

Thanks for the information Shacksters


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## Pieface (Sep 4, 2013)

Slow and steady wins the race they say...

Something finally arrived in the mail! Now to find time to run some measurements :s


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## fabricetaboga (Sep 15, 2014)

je pense installer des panneaux acoustiques dans ma salle, mais je voudrais avant faire une analyse avec rew, vous pouvez me dire comment ça marche ?


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## Pieface (Sep 4, 2013)

Well I managed to have a quick play with the UMIK-1 yesterday...very cool for the PnP experience but of course I now have a bunch of questions (and some ugly looking graphs :rofl2: )

My main question is how loud am I supposed to run the measurement sweeps? The only place I could readily see a procedure was on the miniDSP site so I followed the instruction to use the REW generator to get the system playing at 75dB with the level set @ -12dBFS and then to run the measurement sweeps at -12dBFS from there.

Heres the full range measurement, 1/6 smoothing for the Left and Right Mains laying with the subs. Red trace is the left main for reference. Mains and subs are crossed at 80Hz in the AVR. Now my immediate reaction is that the subs are way too hot in relation to the mains but I am worried that with the bulk of the measurement on the mains only sitting 10-15dB off the rooms noise floor the measurements might not be good? Can anyone point me in the right direction with this? I also had the mic pointing to the ceiling when taking the measurements. Should I have had it pointed at the "centre channel area" with the standard miniDSP calibration file?

Any assistance appreciated.


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## HifiZine (Feb 7, 2013)

Hi, mic orientation only makes a significant difference at high frequencies.

I'm not sure why I can't see your graph now, but I'd be inclined to measure and EQ the speakers and subs independently. You may find that repositioning will help. It can never hurt to do some additional measurements around the listening position to understand how the response varies. With the individual responses done, turn your attention to bass management.

HTH


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## HifiZine (Feb 7, 2013)

Um, sorry, I should clarify the comment about moving subs/speakers  I'd want to know if moving the speakers will even out the 120-240 region, and if moving the sub can be used to reduce the 25-40 Hz peak. (EQ works better with a better starting point)


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## Blacklightning (Nov 22, 2011)

Pieface said:


> Well I managed to have a quick play with the UMIK-1 yesterday...very cool for the PnP experience but of course I now have a bunch of questions (and some ugly looking graphs :rofl2: )
> 
> Mains and subs are crossed at 80Hz in the AVR. Now my immediate reaction is that the subs are way too hot in relation to the mains but I am worried that with the bulk of the measurement on the mains only sitting 10-15dB off the rooms noise floor the measurements might not be good? Can anyone point me in the right direction with this?
> Any assistance appreciated.


I would turn the Sub off and do another sweep full range. Then work on main speaker placement.


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

Pieface said:


> I also had the mic pointing to the ceiling when taking the measurements.


 MiniDSP only provides a 0-degree file for the UMIK, so measure with the mic pointed at one of the speakers, and turn off the other. Upright measurements should only be used with a 90-degree calibration file, and even then they can get questionable results depending on the room. With some rooms 0-degree vs. 90-degree measurements with the right calibration file gets identical readings, but with others there can be a significant difference between the two. Bottom line, 0-degree measurements with the proper calibration file will always be the most reliable.

However, as HifiZine noted, this will only make a difference in the upper frequencies, above ~ 2kHz. Below that point the mic is omnidirectional.

The reason your upper frequencies in your graph are so low is that you performed the “Check Levels” routine using a subwoofer signal, and you are running your sub really hot. If you want to get the mains part of the graph “out of the dirt” then select “ Use main speakers” when you check levels.

Regards, 
Wayne


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## Pieface (Sep 4, 2013)

Thanks Hifizine and Wayne

I am going to take some new measurements on the weekend. I have worked out/been gently nudged that my subwoofers are (way) too high and that has made for awkward measurements.

In my eagerness to get measuring I forgot that the best first step would have to been to use my UMIK to properly set my speaker output levels rather than proceed with what I had achieved with my iphone app originally - I really didn't allow anywhere enough for the roll off of the phone mic + excitement of new toys that go boom I guess :duh:

I will orient the mic correctly this time around also! Thanks for the advice, I am feeling more confident about trying again already


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## Pieface (Sep 4, 2013)

Hi Again 

I managed to take some more measurements, learned a bit more and looking forwards to trying again, although the early arrival of a baby has put paid to this for a while 

Firstly I reset my speaker levels with the UMIK1 as below. Big improvement straight off the bat for dialogue!

Will post again soon with some other graphs


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## Pieface (Sep 4, 2013)

Next step was dropping the mains from their current high in the sky location to get the tweeters a lot closer to ear level. I got a big surprise at how much more treble energy got to the mic. I guess it really is directional!

Unfortunately I only have the first location with the subs running so I hope it's clear. The green trace is the new position with no subs. Still need to try some moving around but starting to get a feel for how to run the REW for this part of things anyway. Still lots to learn re waterfalls and the impulse side of things...


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## Blacklightning (Nov 22, 2011)

Nice, each graph is looking better and better. The time that you put in now will go really far. It may take weeks but in the end, you will enjoy your system... until you add or upgrade something. Then it starts all over again.

Plus I find that it is foolish to upgrade until you have maximized your current setup.


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## AustinJerry (Apr 2, 2010)

Wayne A. Pflughaupt said:


> MiniDSP only provides a 0-degree file for the UMIK, so measure with the mic pointed at one of the speakers, and turn off the other. Upright measurements should only be used with a 90-degree calibration file, and even then they can get questionable results depending on the room. With some rooms 0-degree vs. 90-degree measurements with the right calibration file gets identical readings, but with others there can be a significant difference between the two. Bottom line, 0-degree measurements with the proper calibration file will always be the most reliable.
> 
> However, as HifiZine noted, this will only make a difference in the upper frequencies, above ~ 2kHz. Below that point the mic is omnidirectional.
> 
> ...


What is the difference if someone purchases a USB mic from someplace other than Cross Spectrum Labs, and downloads the calibration file from the vendor website? Both Dayton Audio and Mini-DSP allow a customer who has purchased a microphone to log into the support website, enter the mic's serial number, and download a calibration file. Is this calibration file better, inferior, or the same as the custom calibration files from CSL?

I ran the test for my UMIK-1 (although I also have a UMM-6, and could run the test for that mic as well, if anyone is interested). Here are the results:









I used the CSL 0-degree cal file (Blue), the 90-degree file (Red), the non-CSL cal file downloaded from the web page (Green), and no calibration file (Black). For all three measurements, the mic was pointed towards the ceiling (90-degree orientation), which is the normal orientation for REW measurements (here is where my opinion is different from Wayne's).

The most pronounced differences are in the higher frequencies above ~10kHz. For lower frequencies, the differences among the calibration files are small enough that there should be no concern. Hopefully this test will help you understand the effect of the different calibration files on your measurements.


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

AustinJerry said:


> What is the difference if someone purchases a USB mic from someplace other than Cross Spectrum Labs, and downloads the calibration file from the vendor website? Both Dayton Audio and Mini-DSP allow a customer who has purchased a microphone to log into the support website, enter the mic's serial number, and download a calibration file. *Is this calibration file better, inferior, or the same as the custom calibration files from CSL?*


Based on the four comparison graphs posted here, I’d say CSL is better (the fourth is on Page 2).




> I used the CSL 0-degree cal file (Blue), the 90-degree file (Red), the non-CSL cal file downloaded from the web page (Green), and no calibration file (Black). For all three measurements, the mic was pointed towards the ceiling (90-degree orientation), which is the normal orientation for REW measurements (_*here is where my opinion is different from Wayne's*_).


Not to mention Herb Singleton, JohnM, gazoink (audio professional), measurement mic manufacturer B&K (see free field picture on P.14 and Figures 10 and 13 on P.7, Measurement equipment manufacturers Gold Line (See item #6 under heading “General Procedures for Equalization”), AudioControl (scroll down to see picture) and Behringer (see page 15). 




> The most pronounced differences are in the higher frequencies above ~10kHz.


The accuracy of 90-degree measurements are very much room dependent. Didn’t seem to matter much in your case, but this fellow wasn’t as fortunate. 

Regards, 
Wayne


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## AustinJerry (Apr 2, 2010)

Wayne A. Pflughaupt said:


> 90-degree measurements are very much room dependant. Didn’t seem to matter much in your case, but this fellow wasn’t as fortunate.
> 
> Regards,
> Wayne


I agree that 90-degree measurements are room dependent. But when we use REW, are we not usually measuring in the same room and using the measurements to evaluate the effectiveness of a change? So, for example, if I am experimenting with different placements for some new treatments, I am comparing measurement results. The effect the room has on the mic's orientation doesn't change, so as far as the validity of the measurements go, mic orientation doesn't really matter, does it?

Other tools that I use, e.g. Audyssey, always recommend pointing the mic at 90 degrees so that the mic is measuring grazing sound, not direct sound. Why would they be recommending a 90-degree orientation?


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

AustinJerry said:


> I agree that 90° measurements are room dependent.


 I should have expounded on that a bit more. What I meant was that in many (if not most) rooms there will be little difference with frequency response measurements taken at 0° or 90° orientation, as long as the proper calibration file is used for each. But in some cases the two will get drastically different measurements, as can be seen in the link I provided in the last paragraph. So the _reliability_ of 90° frequency response measurements can be questionable, depending on the room. As I mentioned elsewhere in that thread, as long as there is no appreciable difference between the two you’re fine, but if they are significantly different, then the 0-degree measurement is the one to trust.




> But when we use REW, are we not usually measuring in the same room and using the measurements to evaluate the effectiveness of a change? So, for example, if I am experimenting with different placements for some new treatments, I am comparing measurement results. The effect the room has on the mic's orientation doesn't change, so as far as the validity of the measurements go, mic orientation doesn't really matter, does it?


You would be using graphs such as ETC and RT60 etc. and to judge the effectiveness of acoustical treatments, and As Herb mentioned in the link above with his name, 90-degree orientation is fine for acoustics measurements. It's only frequency response measurements that can be questionable.




> Other tools that I use, e.g. Audyssey, always recommend pointing the mic at 90 degrees so that the mic is measuring grazing sound, not direct sound. Why would they be recommending a 90-degree orientation?


As noted in the gazoink link, 90° is typically used when dealing with sound from multiple sources from many directions. Presumably Audyssey and similar systems use it because it’s more convenient for the end user than taking multiple measurements with the mic aimed at each speaker. Not to mention most end users don’t have the auxiliary equipment necessary to accomplish the latter measurement technique (a camera tripod or mic stand).

Nevertheless, there is no shortage of people who have not been pleased with the results from digital room correction (DRC) systems. Assuredly, a certain amount of them are using lower-grade systems, but not all of them. It’s equally assured that in some rooms equalizing from a 90° mic orientation will not bring good results no matter how good the DRC.

Regards, 
Wayne


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## Frank D (Sep 1, 2008)

Great detailed explanation Wayne!


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## tpointon (Mar 18, 2013)

Excuse ma francais svp. Pas beaucoup des gens ici parle francais je pense. Avez vous regardez http://www.hometheatershack.com/forums/home-audio-acoustics/ ?

Je suis un 'newbie' ici et avec REW. Mais je comprends un peu je pense. Je prefere anglais maintenant, s'il vous plait.

I have played with REW. You need Java to run it. As I understand things, REW is well suited to balancing power across frequencies (equalization) and perhaps a bit less suited to analysing and adjusting for time delays. Room treatments are probably more suited to adjusting for time anomalies. REW features for this are waterfall graphs and impulse analysis. I am not very knowledgeable about these.

Bon chance!


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## Pieface (Sep 4, 2013)

Hi there,

A long time between updates. New babies are not conducive to much mucking around with the AV gear.

I just have a quick question for now...

This is where I am at with an 80Hz crossover and no room treatment or DSP correction:










This is both subs loaded into opposite corners on the front wall. Am I realistically going to see much better than this from 2 small, sealed subs? There is obviously some sort of cancellation at 45 and 65Hz but it's basically +/- 5dB 15-90Hz. Is this an acceptable/realistic compromise at this stage?

I somehow managed to overlook getting a sweep with both left and right mains also playing so I will have to revisit that to get a handle on the crossover integration?


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## JohnM (Apr 11, 2006)

Looks pretty decent to me.


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## Pieface (Sep 4, 2013)

Thanks for the input John.

I was having a look at the individual responses of the subs yesterday and comparing them to the combined response:










The Blue Trace is the left corner sub and the purple trace the right. Brown is both subs playing as per the earlier graph. I gain matched the subs so the right sub is obviously getting a fair bit more room gain for whatever reason. 

Now bear with me if I have the concepts not quite right...

The left hand sub is doing an admirable job of filling in the hole in the right subs response bewtween 50-70Hz, which is good. The 45 and 65Hz dips I have do look to be cancellation issues (combined response lower than either individual sub). Should I be playing with the phase control on one of the subs at this point to see if I can improve the dips, without compromising the infill of the large dip in the right hand sub response? is this possible? If so is there a recommended process to go forwards with? The phase control on the plate amp has a pot so there is ALOT of incremental adjustment. Ihave had a bit of a muck around with the EQ filter thing in REW in anticipation of getting my miniDSP. It makes a decent difference knocking down some peaks and making a bit of a difference to the 45Hz dip. It is trying to write 5 or 6 filters though which I have read is not optimal (3 max? ) so it would be good if I can get things better. Here is the predicted response allowing the EQ to try some boost to the filters (3dB max):










Here is the predicted response allowing only cut and a 2dB flatness target:











Here is the prediction for 3dB flatness target where the EQ seems to leave the slightly lower peaks in the lower Hz range alone:











A slightly random question to finish on...

I see guys posting graphs where they are showing output levels much,much higher (>100dB or more) How are they safely doing this type of sweep to check more of a max output than a 75dB target?


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## JohnM (Apr 11, 2006)

Not everyone calibrates their SPL reading, so the graphs don't always reflect true levels. It is possible to test at much higher levels of course, but hearing protection is strongly advised. For subwoofers maximum output is better determined using the CEA-2010 test signal, there's a bit more about that in the signal generator help and some googling will turn up explanatory articles.

To find a good setting for a control like the phase adjustment (or EQ filters) one method is to use REW's pink PN test signal and look at the response on the RTA set up like this:



You can then see the response change live as you make adjustments.


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## Pieface (Sep 4, 2013)

Thanks John. I will try the PN/RTA method you have described. I vaguely remember reading about this in one of the FAQ's. Your program has a of a lot to take in for someone with no experience!! 

I am planning to try and get the subs running as best I can, get the crossover to the mains integrated as best I can and then try to make some sense of what is happening with with my mains. They are taking a beating from modes/SBIR/early reflections in some combination that I will hopefully be able to crack with some better understanding of those concepts, taking measurements and learning to interpret impulse response/ETC information too.


For reference here is the current waterfall plot. I think this is OK for a basic room? The worst ringing sems to be right on the DSP boost in the sub plate amp ~25Hz - I think this is normal/to be expected?


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## JohnM (Apr 11, 2006)

Nothing to be particularly concerned about there as far as ringing is concerned, but it would be nice to reduce that notch between 60 and 70 - tweaking phase might help with that, but it could also be listening position and/or sub positions.


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## Pieface (Sep 4, 2013)

Managed to have a bit of a play.

Here is a baseline measurement and then where I got to fiddling with the phase adjustment

I cured the two dips but traded in a bunch of output 70Hz and up










I mucked around with the delay to the Mains and ended up getting through ok to 100hz where my mains just take a beating irrespective of the subs being on or off








Maybe I'll try a higher crossover next time I get to have a play.

Discovered some other pretty amazing things higher in the frequency range but will save that for another time


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## Pieface (Sep 4, 2013)

Sorry graphs are round the wrong way

fixed!


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## Pieface (Sep 4, 2013)

I updated REW to the latest Beta so i can use the variable smoothing.

I noted on the update notes : USB mic spl 6dB low (verified on UMIK)

What does this mean for all my existing measurements? Are they junk?


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## JohnM (Apr 11, 2006)

No, they just appear slightly lower down on the graph, the shape of the response is not affected at all. You can adjust their position using the offset control if desired.


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## Pieface (Sep 4, 2013)

Thanks John.

I will re calibrate my channel levels next time I have the mic set up and see where things lay. I do recall needing to raise my channel trims by a fair whack when I first used the umik. I had just assumed it was a problem with the iPhone app solution I had initially used.


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