# Help with ART USB Dual Pre issue



## fotto (Jan 17, 2010)

I recently upgraded from a UCA202 to the ART Dual Pre and Dayton calibrated mic. After about 1.5 hours of fussing with it last night, I was finally able to get a good calibration done. I wasn't getting anything out of the ART until I figured out that I needed to adjust the output pot on the back and not the gain. So, with both L and R gains at 0, I simply adjusted that rear output control and was able to achieve the following:



















Thought I was good to go until I connected up to my AVR Aux input, and was getting next to no signal volume at all through the AVR to either the sub or speaker level checks in preferences tab. With the UCA202 I had my master volume at 70.5 on the AVR to achieve 75dB when calibrating through my RS SPL meter. I cannot think of any reason this ART set-up should be any different based on the level checks etc, except possibly one....

The outputs of the ART are TRS "Inputs can be either XLR balanced or 1/4-inch TRS. Each of the 1/4-inch TRS outputs is buffered low impedance balanced.". I bought a simple *mono* 1/4 *TS* to RCA plug from monoprice (p/n 7148) and am thinking that might be the issue. I saw in another post under soundcard section that another user used a "1/4" *TRS* female to dual RCA (HOSA YPR-257)" as output connector to get the RCA to RCA for the AVR connection (along with a male to male TRS cable).

Could this be the reason (mono vs. stereo/TS vs. TRS) I'm not getting enough signal strength to the AVR, or should I be looking at other things? I'm out of ideas at this point.


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## EarlK (Jan 1, 2010)

> Sounds to me like you should simply stick with what you know ( which in cabling terms, is , male RCA to male RCA )

> So with that in mind; Get a 3.5mm (1/8" stereo ) male ( adapter ) to 2 female RCA . Like this ;









> Plug the adapter into the headphone output on the back of the unit . Seen here ;










> Then use your regular RCA cables ( male to male ) from the adapter to your AVR .

> If this doesn't work it means you don't yet know how to operate your soundcard & have more studying to do from the following resource ;
>  *USB Dual Pre User Manual* 

:sn:

BTW ; keep that "Mix" control set to "Computer" or ( hard right ) :T


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## fotto (Jan 17, 2010)

Thanks Earl, will give that a go. Hopefully can pick up that connector at the local RS.
I do have the mix control turned all the way to "computer". 

Is it safe to say that I could/should have both gain controls to 0, and just use the rear level to get me to where I currently am in terms of the in/out -12dB matching that I showed in the second pic?


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## EarlK (Jan 1, 2010)

> Some of each .

> You need to adjust input gains ( on any preamp ) up & down from the zero mark to avoid overloading the circuit or feeding too low a signal into REW . 
> I would start with the input gains set to 14 or 18 ( just make sure the red "Clip" light indicator doesn't light up ) .









> You need to adjust output levels ( on that soundcard ) with the same criteria kept in mind . Set the AVR to say 40% of it's input gain and then see if you can easily drive REW up to 70 or 80 db ( measured with your RS SLM ) . If you need to make up some output gain / use the area REW or the AVR which has the most left to give ( headroom ) .

> The same holds true with the level controls within REW .

> Knobs are there to be turned / so don't be afraid to do that .

:sn:


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## EarlK (Jan 1, 2010)

BTW, I think you should change your input to "right" and then run another soundcard calibration .

If you don't get signal, it's because you haven't yet setup Win7 ( or Vista ) to record in 2-channel mode .










<> :sn:


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## aackthpt (Jan 24, 2011)

Interesting. According to the MobilePre manual the output jacks are unbalanced vs. the balanced on this ART unit.

I did find this possibly pertinent information on the wiki entry for TRS:


> In some TRS inserts, the concept is extended by using specially designed TRS jacks that will accept a mono jack plug partly inserted "to the first click" and will then connect the tip to the signal path without breaking it. Most standard TRS jacks can also be used in this way with varying success, but neither the switch contact nor the tip contact can be relied upon unless the internal contacts have been designed with extra strength for holding the plug tip in place. Even with stronger contacts, an accidental mechanical movement of the inserted plug can interrupt signal within the circuit. For maximum reliability, any usage involving "first click" or "half-click" positions will instead rewire the plug to short Tip and Ring together and then insert this modified plug all the way into the jack.


I'd think it would be similar to buy a TS cable, remove the TS from one end and put a TRS in its place. I can't speak to any level issues that might be encountered though.

So does the "level" control near the headphone jack also control the monitor output levels on this unit? On the MobilePre I'm almost certain the knob near the headphone jack is only for the headphone level and does not control the output levels at all. If it does control the line out levels, it must work similarly to the Tascam US-122mkII which is clearly marked for the knob to control the level of both.


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## fotto (Jan 17, 2010)

aackthpt said:


> Interesting. According to the MobilePre manual the output jacks are unbalanced vs. the balanced on this ART unit.
> 
> I did find this possibly pertinent information on the wiki entry for TRS:
> 
> ...


Good to know that, although I believe I tried a "partial insertion" of the jack but will try again. The manual appears to indicate that the headphone and output of the line level are both controlled by the level knob.
Specific note on that here; http://www.artproaudio.com/downloads/manuals/omusbdualpreps.pdf (page 6 "Monitor Level")
I assumed the same as you and had the level control at minimum which was the cause of my original issues getting any signal for calibration with loopback. I was just turning the gain control up and the signal was crazy/intermittent. When I turned gain down to 0 and adjusted the output level all was well.



EarlK said:


> BTW, I think you should change your input to "right" and then run another soundcard calibration .
> 
> If you don't get signal, it's because you haven't yet setup Win7 ( or Vista ) to record in 2-channel mode .
> 
> <> :sn:


I have 2 channel mode selected, and can get same reading from either left or right input in terms of -12dB signal. I also did the Windows 7 mic calibration that ART lists on their FAQ. Also, I "turned the knobs" in various mixtures (input gain vs output level) and that also didn't affect things.


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## mtbdudex (Jan 2, 2008)

Ahh, someone gets to be the guinea pig with this, good luck Floyd figuring it all out so others can learn from you.


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## fotto (Jan 17, 2010)

mtbdudex said:


> Ahh, someone gets to be the guinea pig with this, good luck Floyd figuring it all out so others can learn from you.


OK "guinea boy" checking back in here ....made some progress last night but not totally flushed out yet. Will report back later after additional testing, but one question I'd like to get answered which will hopefully save me some iterations:

When doing a card calibration, would preferred setting for input gain (with R channel looped back) be 0, and just use the monitor level control to get the REW in/out signals to match at the -12dB sweep level? I'm thinking this would be better than doing a card calibration with X amount of gain included in the loop. Or, are you (Earl) suggesting to apply around 14dB of input gain during calibration, and using less output level during calibration?

Sorry if that's a a basic question, but my Daddy never taught me nothing about pre amps.


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## EarlK (Jan 1, 2010)

> I generally set & leave my soundcards' output controls in one general place ( static ) . Usually around 2 pm ( fwiw to anyone else without this soundcard ) .

> That position gives good drive level to my stereo systems inputs ( so that is why it's left there ) .

> Within my soundcards virtual output mixer , I strive to keep the output level as close to peaking at zero db , as I can get them without clipping the outputs .

> With that in mind ( strong, optimized output levels ) / when I do a soundcard calibration ( on this M-Audio FT, Ultra ) I have no problem getting input levels to register at the minus 12db point . These input levels are adjusted up or down with the inputs' gain controls of my soundcard .

> When I do a soundcard calibration, I only do it for the channel that will be used by the measurement microphone .

:sn:

PS : Hope something in the above is useful to you . :T


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## fotto (Jan 17, 2010)

I think I'm feeling you Earl.....what I think I'm hearing, and my opinion is that the pre amp's monitor level out is mutually exclusive of the input gain. If the REW sweep signal is at -12dB (and remains constant throughout the sweep), it seems to make sense to me that the pre amp monitor out signal strength (as presented to the AVR) is wholly dependent on the actual level control setting for that monitor out (or assigning a different REW sweep level). And, input gain ONLY adds gain to the level of what the mic is reading, and is and reflected in REW's line in bar graph level.

REW takes input over USB from the mic input, and transmits output sweep signal over USB to the pre amps output right? There should be no "mixing" of those two signals within REW where the input would affect the output or vice versa.


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## EarlK (Jan 1, 2010)

> I think I'm feeling you Earl.....what I think I'm hearing, and my opinion is that the pre amp's monitor level out is mutually exclusive of the input gain. If the REW sweep signal is at -12dB (and remains constant throughout the sweep), it seems to make sense to me that the pre amp monitor out signal strength (as presented to the AVR) is wholly dependent on the actual level control setting for that monitor out (or assigning a different REW sweep level). And, input gain ONLY adds gain to the level of what the mic is reading, and is and reflected in REW's line in bar graph level.


Yes, your assessment of the differences between input & output signal paths, is correct ( for REW purposes, they are & must remain, mutually exclusive ) .

There must not be any mixing of input signal back into output signal ( controlled via the mix knob ) .

:sn:


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## aackthpt (Jan 24, 2011)

Did you ever get it to work right, Floyd?


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## fotto (Jan 17, 2010)

I was able to accomplish some sweeps but wouldn't call it "working right" by any stretch. I have one more thing I'm trying tomorrow (have to pick up another cable today, and have had daughter home all day so couldn't play) and will roll up some commentary tomorrow.
Thanks for checking in.


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## fotto (Jan 17, 2010)

OK, after WAY too much time spent on this, here’s my "layman’s" review of the ART USB Dual Pre. 

I have come to the conclusion that the main downfall of the ART is that it does not provide a true “line level” output to the AVR, which results in having to max out it’s output, and turn up AVR MV higher than needed. I HAVE been able to do some sweeps with it, but adding in both speakers or a sub and speaker after setting it up initially to measure just one results in having to back off settings due to clipping, readjust SPL etc. There isn’t enough headroom unless you start with the input pretty low like in the -20dB+ range.

What was vexing me on this compared to the UCA202 (which was simple math compared to the ART) was that when I set up the UCA202, I had perfectly matched out/in levels at -12dB (level check with loopback) with AVR MV setting at 71 and SPL reading of 75dB. While setting up the ART, I had a TRS to XLR cable providing the R channel loopback for card calibration and subsequent level check. I only had to turn the out/monitor level from 7:00 “0 position” to about 8:00 to achieve -12dB in/out during level check. Subsequently, connecting that to the AVR and doing level check resulted in almost no perceivable SPL through the speakers. Just didn’t make sense.

So, I got out my multimeter and starting measuring. The UCA outputs approximately *430mv* AC during level check at -12dB, which aligns with definition of a “line level” signal. The ART outputs a whopping *5mv* at same -12dB. Furthermore, with the output/monitor level fully maxed out, it only was able to output 250mv. Needless to say, even with that output level maxed, in order to achieve 75dB SPL via the AVR, one would need to bump AVR MV quite a bit.

Additionally, having the left channel looped back to itself while measuring with “loopback as timing ref” resulted in that channel input maxing out and clipping. Seems this is similar to what diffserv is seeing with his M-audio set-up.

I do have one follow-up question...say that I have the unit doing level check with output level maxed and AVR MV turned up to achieve 75dB as measured by my RS meter. My previous attempt with that scenario required me to turn the mic gain to around +28db in order for the REW input to get to -12dB. Sweeps there resulted in very low headroom of about 2dB and as I mentioned, adding in another speaker or sub then made the input signal clip. So, if I lower the mic gain to somewhere lower so I don't clip, won't I lose accurate SPL reading in the resulting frequency response graph? Any approach to solve that disparity?

I haven't totally abandoned this unit yet, but it's getting close :rant:


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## JohnM (Apr 11, 2006)

fotto said:


> The UCA outputs approximately *430mv* AC during level check at -12dB, which aligns with definition of a “line level” signal. The ART outputs a whopping *5mv* at same -12dB.


Very odd, almost seems like there is another volume control somewhere in the output path that is at a low setting.



> I do have one follow-up question...say that I have the unit doing level check with output level maxed and AVR MV turned up to achieve 75dB as measured by my RS meter. My previous attempt with that scenario required me to turn the mic gain to around +28db in order for the REW input to get to -12dB. Sweeps there resulted in very low headroom of about 2dB and as I mentioned, adding in another speaker or sub then made the input signal clip. So, if I lower the mic gain to somewhere lower so I don't clip, won't I lose accurate SPL reading in the resulting frequency response graph? Any approach to solve that disparity?


Sweep measurements are pretty tolerant to signal levels, backing off the mic gain should not degrade accuracy but make sure you redo the SPL meter calibration at the mic gain setting you end up using so the REW plots are drawn at the correct level on the graphs.


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## fotto (Jan 17, 2010)

Thanks for replying John. One other interesting thing with the voltages....if you do sound card cal using a 1/4 TRS (stereo) jack to XLR cable for loopback adjusting for -12dB level match, and then use a TR (mono) 1/4 to TR 1/4 cable, you will now see that the input is at -17dB. I found the reason for this is that the TRS to XLR has 5mv from each of the + and - pins to ground, and 10mv between + and - pins. The sound card must be summing those signals for 10mv in stereo connection while only using 5mv while in mono which is reflected in the delta in dB.

One other question that I thought of....when setting level matching in preferences, I previously described turning up the output level on the ART to max, and then AVR to get the 75dB signal at the mic position. Would it be better to use less level out and more AVR MV, or just stay with max level out?

I may give ART a call today to see what they have to say about their output level, although this seems consistent amongst others using this SC (at least one other). Looking at many of the other units which appear to work with REW, most (if not all) of them have a "line level" output. The ART Dual does not promote their outputs as such, only as "buffered low impedance balanced".


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## EarlK (Jan 1, 2010)

> There should be no difference in listening levels if/when you play tunes ( iTunes etc. ) through either the UCA202 or the ART DualPre , into your AVR/Stereo . So;

> Forget your input settings for the time being / your current failure is in establishing reasonable output levels with that ART USB-Pre card , therefore use the UCAs' rca output ( driven by a "Test Level" signal from REW at minus 12 ) to establish a 75db level from your AVR ( as measured with your RS SLM at 3ft from the speaker ) .

> Make sure the UCA is driving "full volume" from both the WAVE & Master Out sections within REW & from your OS(s)' audio control panel . 
> Swap in the ART unit ( refraining from adjusting the AVRs' gain level ), now adjust the ARTs' output knob to achieve the same 75db reading ( on the SLM ) as the UCA ( make sure all of REWs output level adjustments matchup between the 2 cards ) .

> If successfull, mark it ( the output level on the ART ) and leave it ( refrain from adjusting this knob in the future unless you absolutely can't get full drive level / ie; you should first adjust other level controls , before touching this master output knob ) .

> With a test mic plugged into the ART ( placed 3 ft from the speaker ) adjust the input gain on the ART to read minus 12 ( within REW ) . 

> That should be all you need to do for live testing ( apart from adusting the AVR when you move the test mic to a different position further away / as well as a SPL/SLM calibration ) .

> To calibrate the ART soundcard , start by calibrating line out to line in ( using a TRS to TRS cable ) before "graduating" to doing a Line out to Mic in calibration ( using a TRS to XLR cable ) . 
> Make sure the Phantom Power is "off" when doing this sort of calibration . 
> The Output Sections ( of most electronics ) really don't "appreciate" 48V forced into them . 

:sn:

PS :


fotto said:


> The sound card must be summing those signals for 10mv in stereo connection while only using 5mv while in mono which is reflected in the delta in dB.


> The correct connector terminology to use is "Balanced" & "UnBalanced" ( not stereo or mono ) . 
> Yes, the "plus & minus" legs of a balanced connector do get "summed" , thus accounting for the greater "drive-level" available from a balanced output ( versus , an unbalanced, "single-ended" output ) . 

> Your "timing reference" loopback should be made with a TRS to TRS cable ( not a TRS to XLR adapter cable ) .


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## fotto (Jan 17, 2010)

Earl, 
Just did your experiment, results follow. All PC settings were correct with speakers/microphone setting at 100%.

UCA202
Using level check with UCA looped back, achieved -12dB matching from out to in.
Using speaker level check in REW preferences, to achieve RS SPL of 75dB, my AVR MV was at 61.5.
Additional inifo...with RS SPL meter output connected to UCA input, level check in pref tab showed -12dB out and -28.5dB in

ART
Swapped ART in per instructions with TRS to TRS loopback on right channel. Did level check and the ART required minimal level adjustment to achieve -12 to -12 out/in. The knob was turned from about 7:00 to between 8:00 and 9:00 position.
Next, fed TR to RCA signal to AVR (keeping MV at 61.5). RS SPL reading turned out to be 71dB with ART level knob at it's max position. 

So, I am considering this experiment failed unless I'm missing something. In order to get 75dB SPL level at the RS meter, with the ART card output level at maximum, the AVR MV needed to be turned up to 65.5.

In my opinion, these results correlate closely to what I showed previously. Any other ideas or comments?

Edit: One more observation...with ART set up with max out level and AVR at 65 to achieve 75dB, and with mic gain at 23 to achieve 75dB for mic calibration, I selected loopback under preferences with TRS to TRS connection on ART left channel. Taking a measurement immediately drove left channel level to full red/clipping. So, that doesn't work either.


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## EarlK (Jan 1, 2010)

> So, I am considering this experiment failed unless I'm missing something. In order to get 75dB SPL level at the RS meter, with the ART card output level at maximum, the AVR MV needed to be turned up to 65.5.


What is your definition of failure here ? ( I really don't get where you are coming from ) .

> Having to turn-up your AVR ( by 4 db ) to match output levels between 2 different soundcards isn't unusual . 

> BTW; you may be able to get a few more db output from the ART card by making a custom output cable that doesn't "short out to ground" the minus side of that balanced output . 
> Connect "T" ( TRS ) tip to RCA tip , connect "R" (TRS) ring to RCA ground, connect "S" ( TRS ) shield at the TRS end, but don't connect it ( the shield ) at the RCA end . 

:sn:


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## EarlK (Jan 1, 2010)

> Edit: One more observation...with ART set up with max out level and AVR at 65 to achieve 75dB, and with mic gain at 23 to achieve 75dB for mic calibration, I selected loopback under preferences with TRS to TRS connection on ART left channel. Taking a measurement immediately drove left channel level to full red/clipping. So, that doesn't work either.


> Don't follow ( avoiding clipping is the job of the input gain knobs ) . 
> Obviously, they ( L & R chnl ) can have different settings ( & most likely require different settings since one is being used on an acoustic pickup while the other "loopback" chnl is pure, straight electronic signal ) .

> Assuming your normal test channel is the Right Input / can't you simply turn down the gain knob ( of the left channel input ) so both inputs read minus 12 db ? 
> Or does this left channel gain knob not work what-so-ever ( ie; is by-passed ) when the left TRS input is used ?

:sn:


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## fotto (Jan 17, 2010)

Yes, maybe "failure" wasn't the best term for me to use, but I have been concerned about having to use max settings and all of the possible issues (extra noise due to gains etc) that can be introduced. Was really expecting this to be more plug and play vs. the plug and pray I have been going through. Maybe chalk it up to inexperience, but not getting the output levels I expect to get doesn't make me feel very good about it. I've got at least 8+ man hours into this and just getting fussy and want to move on...was really hoping to be measuring during this week instead of what I've been doing. I do appreciate the help you are offering.

Regarding the clipping of the left channel during loopback... this is independent of left gain setting (and right as well). I did another test just to make sure with BOTH L and R gains at 0 and the left channel went to clipping/full scale almost immediately after sweep started. Not sure if there's any way to fix that or not. John commented here where diffserv has an M-Audio and is experiencing similar (post 14): http://www.hometheatershack.com/for...-input-levels-soundcard-cal-2.html#post483716

I also took a number of sweeps with left gain to zero and right at zero, right at 14dB and I believe with right at 20dB gains. Even with the clipping on left input, all of the sweeps looked the same and ETC's as well. Maybe it's just something to ignore? My purpose for using it is for accurate TOF measurement for ETC and hunting down reflections...nothing more. As long as it's not interfering with the right channel measurement data, I guess I don't care whether it clips or not. 

I think your idea on the custom cable has a lot of merit. I did another test using check levels in pref tab where I first did TRS to TRS loopback and adjusted ART output level at -12. Then I replaced with TR to TR loopback cable and that reading was -18dB...a full 6 dB difference. So, it appears that using a standard TR to RCA connector at the output does not live up to full output potential and one should be able to benefit using your custom cable idea. Would you suggest using a TRS and cable for the majority of the length and then terminate the far end to an RCA (keep cable shielding going as far as possibly) vs. opposite of terminating nearer the TRS connector and running RCA/cable over distance? Seems like the former would be better.


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## EarlK (Jan 1, 2010)

> Would you suggest using a TRS and cable for the majority of the length and then terminate the far end to an RCA (keep cable shielding going as far as possibly) vs. ,,,,


> Yes !

:sn:


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## EarlK (Jan 1, 2010)

> Regarding the clipping of the left channel during loopback... this is independent of left gain setting (and right as well). I did another test just to make sure with BOTH L and R gains at 0 and the left channel went to clipping/full scale almost immediately after sweep started. Not sure if there's any way to fix that or not.


> I don't understand your resistance to turning knobs .

> Doesn't your AVR still have a lot of headroom to accomplish a "rebalance" ( of output level to acoustic input level ) ?

> If so , simply turn down the Master output knob of the ART unit by the appropriate amount of db to avoid clipping the left chnl "timing" loopback . 
> Maybe its' 6 db or more / you tell me after you discover the number .

> Then once you've turned the master output down by whatever amount / you must now turn up your AVR by the same amount to recover these db(s) & to get back to seeing 75 acoustic db ( measured on the SLM at the test position ) for your right input channel ( to have a reasonable hope of reading minus 12 db ) .


:sn:

PS ; You can also toss away a few db ( overloading ) your left input channel if you feed it with an un-balanced signal ( ie ; TS to TS ) .


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## fotto (Jan 17, 2010)

I'm sorry but I don't understand the relationship on the rebalancing you are describing having bearing on the left channel clipping issue. If I lower the ART master out, and increase AVR proportionally to achieve 75dB, will I not need to have similar gain on the right mic input as I had previously? If the soundcard is clipping left channel during loopback with BOTH L and R gains at *0*, how will rebalancing output and AVR MV affect that?

I am in the mid 70's on MV currently with output of ART maxed, so yes it appears I should have headroom to turn that up and output down, but again I just don't understand the gain connection.

I've turned a lot of knobs so far and am not afraid to turn them further.


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## EarlK (Jan 1, 2010)

fotto said:


> I'm sorry but I don't understand the relationship on the rebalancing you are describing having bearing on the left channel clipping issue.


> Educate yourself as to what signals get affected when you adjust the ARTs Master Output level ( up & down ).

> Start by turning it completely off and then running a sweep ( with the left channel loopback still in place ) .
> Obviously, you shouldn't hear anything through your speakers .
> Also, you shouldn't see any input coming into your left timing channel . If you see any input on that left channel , then you have a problem of some sort ( hardware or software based ) . 
> That's the primary rebalancing relationship that you need to grasp ( the ARTs output is directly driving signal into the input of the left channel ) .



> If I lower the ART master out, and increase AVR proportionally to achieve 75dB, will I not need to have similar gain on the right mic input as I had previously?


> If you increase the AVR level proportionally ( back up to 75db ) , the gain knob for the right channel input ( theoretically ) shouldn't need to change from it's previous setting . 



> If the soundcard is clipping left channel during loopback with BOTH L and R gains at 0, how will rebalancing output and AVR MV affect that?


> Please keep in mind the L & R input gains of the ART work independent of each other . 
> Perhaps you don't think that fact is an important point, but you keep lumping them together ( in conversation ) as if they are connected ( or need to be adjusted equally / which is simply wrong ) .
> One adjusts the 2 inputs independent of each others setting,( as seen on the face plate of the ART ) .
> Final position for each is determined by how much input signal one wants/needs to adjust on each REW channel ( ie; to get each up to be around minus 12 db ) .
> Lowering the ARTs output level will lower the input gain of the looped-back left ( timing ) channel .
> Lower it ( ART output level ) until the timing channel no longer clips on a sweep ( with the left channel set to "0" ) .

:sn:


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## fotto (Jan 17, 2010)

Aha...I think a light just came on. What I was failing to grasp in this equation was that the ART output level affects both left and right by the same amount. Having it maxed affects the left loopback signal. Ha, more to come then tomorrow!

On an aside, I have not been under the impression that I have to adjust the L and R gains equally.

Thanks again for the clarification and hopefully this will solve it. I'm surprised you haven't ran out of patience yet. :R


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## fotto (Jan 17, 2010)

I was able to do some additional testing this morning based on Earl's suggestion above. So, started by "rebalancing" the ART output level (lowered) with AVR MV (increased) to get to a point where the left channel was not clipping during loopback. I used a TR to TR loopback connector cable thinking the lower level feedback would work to my advantage vs. a TRS to TRS loopback.

To accomplish above goal, I reduced the ART level out to just about midpoint to get left channel just a touch under clipping level as measured in pref tab "check levels". With that turned down to mid point, I then needed to turn up MV on AVR to 78.5 in order to get 75dB SPL reading at the MLP in my room. The level out and MV were not changed for the remainder of the testing.

The next thing I did was to hook up my MIC to the preamp. Then I went back into pref tab under check levels and adjusted the ART Right input gain to achieve -12dB input level in pref tab. Left there and calibrated SPL, and then took measurements. 

The way I did the readings was to first adjust ART gain setting, noting the R channel input level under pref tabs "check level", calibrate SPL (each time I changed gain), make a sweep using 1 speaker and note headroom, make another sweep after adding in second front speaker, and then noting headroom again. I didn't think about noting headroom and adding in second speaker in first test so don't have that data. Suffice it to say it was VERY close to clipping with one speaker being measured.

Based on the following results in the table below, I am finding it VERY difficult to maintain enough head room to avoid clipping at input levels above -20dB (-18 is right on the borderline).











It seems that the happy median here is with gain at 17 (next to last row).

Is there some other adjustment method that I'm missing? Perhaps having the right input level down around -20dB is totally acceptable (graphs seem to be fine)? I am used to the UCA202 having it's input matched right at -12dB and not having any issues with clipping. Maybe I just need to get over that and move on.


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## aackthpt (Jan 24, 2011)

fotto said:


> Is there some other adjustment method that I'm missing? Perhaps having the right input level down around -20dB is totally acceptable (graphs seem to be fine)? I am used to the UCA202 having it's input matched right at -12dB and not having any issues with clipping. Maybe I just need to get over that and move on.


For "check levels", the REW manual says "As long as the signal RMS level is within the -30 to -12dB range when the speaker/subwoofer cal signal is playing everything should work OK". I always set its level at -18dBFS (maybe this is the number advised in the software? otherwise not sure how I came up with it) and set the reference (left) channel at -12dBFS since it will never have a headroom problem. To my way of thinking, if I understand what you are saying, -20 dBFS on the measuring channel is fine.

Also, when I test the volume setting on my AVR is significantly higher than my typical listening levels. I usually listen to movies in the range of -20 dB on my AVR, whereas when I test I am typically at -7 to -11 dB to achieve 75-80 dBSPL (I think the docs say to use 75, I usually use 80 though). As long as the levels aren't high enough to wreck a speaker or something, and there is no clipping, all is good.


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## fotto (Jan 17, 2010)

I don't recall seeing that range before, thanks for pointing it out. Always thought that the goal was at -12, but was never sure of ramifications of going lower.

Something else I was wondering about when going through this effort was how does the max dB estimated by SPL calibration process keep increasing with the mic gain and input gain decreasing (seems counter intuitive)? I'm thinking that the max SPL is derived from whatever the calculated headroom is, I.E. how high you can measure before clipping? What makes me question that though is comparing back to the UCA202...I recall that the max SPL was around 108dB or so with that unit with out/in levels matched at -12dB.

Anyway, I took another 30+ measurements today and am feeling good about this set-up finally.

Thanks again Earl for all the support.


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## aackthpt (Jan 24, 2011)

fotto said:


> I don't recall seeing that range before, thanks for pointing it out. Always thought that the goal was at -12, but was never sure of ramifications of going lower.


The only ramification of going lower is that the measurement signal gets into the system noise at some point, and then the signal to noise ratio of your measurement is poor. The signal needs to be a reasonable amount above both the ambient room noise and the electronic noise in the system so that the measurement is meaningful. This is why you set the signal to 75-80 dB SPL and -18 dBFS, the former usually gets you above the room noise without blowing speakers and the latter is a reasonable compromise between measurement headroom and maximizing level above electrical noise. It's pretty much the same reason we don't want any particular stage at extremely high or extremely low gain.



> Something else I was wondering about when going through this effort was how does the max dB estimated by SPL calibration process keep increasing with the mic gain and input gain decreasing (seems counter intuitive)?


I think what it is reporting is the maximum loudness (meaning dB SPL) that can be reached without making the input stage clip. I'm not sure what you mean by "estimated" but it sounds like you aren't quite understanding it. It helps to be very specific between dB SPL (which is the pressure variations in the air) and dBFS which is electrical signal level. It makes sense to me that the maximum dB SPL would be higher with lower input gains - as long as the mic itself (either its element or its preamp) wasn't clipping - because the electrical signal wouldn't be clipping as early. The maximum dB SPL is, I presume, just the dB SPL you told the decibel meter in REW plus the dBFS value. This level is not really that important for casual measuring... as long as REW doesn't report clipping you haven't exceeded it and you needn't worry about it (unless you are using REW for some purpose other than room acoustic measurement).

Gain structure is something about which I had very little clue before I encountered REW and The (HT) Shack.... just another item to learn on this journey! :T


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## randyc1 (Jul 20, 2011)

Was just wondering if your issues have been resolved with the ART Dual Pre ??


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## fotto (Jan 17, 2010)

randyc1 said:


> Was just wondering if your issues have been resolved with the ART Dual Pre ??


Yes, I was able to successfully get many sweeps done with the ART based on settings I posted earlier. I helped another member get his ART setup over the holidays and while going through it with him, found that in his setup he ended up with his monitor master level output turned up to only about 1/2 way with his AVR MV at "normal listening level" (didn't note actual scale) to achieve 75dB as measured from MLP, which would have been more along the lines of what I "expected" to see in my system.

So, it seemed to work a bit different (at lower level/MV setttings) in his scenario. Whether that's tied to his particular set-up and/or variances between his ART and mine is unknown.

Either way, I wouldn't hesitate recommending it at this point.


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## randyc1 (Jul 20, 2011)

I also have the Art dualPre and while i am able to get measurments my amp must be at very high vol ?? 
There is another issue about levels not being correct also ?
Would it be possible to get help, and for me to call you at some point, to ressolve some issues ??

Thanks !


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