USB Audio for Test

Hi All,

So, I've been searching the forums on and off for about a week, not finding a good answer, I finally bit the bullet and decided to post.

I'm sure this has been covered in the past, but most of the threads are a few years old with many having hundreds of pages of posts. So, here it goes...

Currently shopping for a USB audio card for testing Amps, and eventually loudspeakers. I'd like to find at least 24bit at 192Khz on several channels in and out full duplex. Bias for a mic would be nice, as would support for both differential and single ended inputs. This should be in the $100 to $250 range (Maybe more, if the spec's warrant it!). ASIO, etc sort of a must. A huge plus would be sub 1Hz low end, or better yet DC coupled (even with modifications necessary to do so.) Not all of these are a must, just a wish list.

I've tentatively identified these as possibilities:
Scarlett 2i2 3rd Gen
scarlett-4i4
QA401 Audio Analyzer


Anyway, can you all recommend a few candidates? Basically trying to get the most bang in terms of noise floor, sample rate, and resolution for the $$ here. Especially looking for cards that you all have used, and trust, for this sort of stuff.

Thanks!
Dan
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
Those are all good choices. Add the Motu M2 which seems to have really good performance as well.
However, except the QA401 they will all need software (free or $$) and hardware to interface for testing. The QA401 will give you quite the suite of capabilities out of the box. Just more $$$.
 

martyh

Member
Paid Member
2004-02-01 2:58 am
Wisconsin
If you drop the need for the high data rate, Tascam US 1x2 works well. I like the connectivity options and the drivers finally work. As an added bonus the HPA sounds good, indistinguishable from schitt magni 3 (within its power limits) to my ears. IMO 24/96 is plenty of resolution for what you want to do but I am no digital expert.
 

H713

Member
2017-11-24 11:21 pm
Madison WI
Those are all good choices. Add the Motu M2 which seems to have really good performance as well.
However, except the QA401 they will all need software (free or $$) and hardware to interface for testing. The QA401 will give you quite the suite of capabilities out of the box. Just more $$$.

Has anyone tested exactly what the bandwidth of the Motu M2 is?
 
Given you are down below $250, then you can't really expect more than 24/192k unless you luck something second hand.

That also puts you in a typical lower bandwidth range of circa 10-20Hz, but that can be extended to the software lower limit (eg. 2Hz for REW) using a calibration compensation. You may be lucky to find someone who has written up their efforts to lower the bandwidth by swapping out capacitors, but that is a risk you take.

If you haven't spent much time with a test tool like a common USB soundcard module, then I'd recommend just buying something like the latest Scarlett new, or a recent 2nd hand version. Setting it up with suitable probes and connections, and enjoying the journey to find bandwidth and noise and probe impedance limits, and settling on a software tool, and acquiring/comparing real world audio gear results, should settle your perception of whether the tool is limiting your test capabilities in some way. It can be well worthwhile not having the 'best' tool sometimes, as it can force you to appreciate why there is a limit, and ways to circumvent or live with an issue.
 
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H713

Member
2017-11-24 11:21 pm
Madison WI
Given you are down below $250, then you can't really expect more than 24/192k unless you luck something second hand.

That also puts you in a typical lower bandwidth range of circa 10-20Hz, but that can be extended to the software lower limit (eg. 2Hz for REW) using a calibration compensation. You may be lucky to find someone who has written up their efforts to lower the bandwidth by swapping out capacitors, but that is a risk you take.

If you haven't spent much time with a test tool like a common USB soundcard module, then I'd recommend just buying something like the latest Scarlett new, or a recent 2nd hand version. Setting it up with suitable probes and connections, and enjoying the journey to find bandwidth and noise and probe impedance limits, and settling on a software tool, and acquiring/comparing real world audio gear results, should settle your perception of whether the tool is limiting your test capabilities in some way. It can be well worthwhile not having the 'best' tool sometimes, as it can force you to appreciate why there is a limit, and ways to circumvent or live with an issue.

I think the upper bandwidth limit is the bigger issue, really. Unless you want to use it as an oscilloscope (just get an analog scope- I've passed up working scopes for $30 or less), there is minimal reason (in my book at least) to have an analyzer that goes down to DC. The best you'll get with a 192k sound card is about 96kHz upper limit, which is still lower than the 5th harmonic of 20kHz.
 
Hi All,

So, full disclosure, I have a quite extensive electronics lab at home. The day job is designing high speed ADC boards, power supplies, and RF, and digital communications, etc.

I'm looking to add amplifier and speaker testing in the audio band on the cheap(ish). THD, Noise, IMD, etc. Eventually something to test speakers also. There are actually a couple of hardware tests where an audio card with DC coupling would make a nice Data Acq card for other projects (Shock tube testing of transducers, for one).

DC coupling. Yeah, I may be opening a can of worms here (sorry!). I do have my own opinion of what makes a good amplifier, and basically I like to test gain and phase to at least a decade above and below the ends of the audio band (Current lab hardware gets there, but the dynamic range isn't enough for THD/IMD, etc.)

I'll add the other suggestions (MOTU, BEHRINGER, Tascam) to the list as well.

Right now I'm leaning towards the QA401. Software and hardware combo looks pretty nice. The ADC is the AK5397, which according to the datasheet has a High Pass Filter disable pin. Not sure if that's technically accessible, but the option exists. The output is DC coupled, buffered well, with a current limit resistor.

That said, are any of you aware of other USB cards that run the AK5397 ADC? The Low pass filter disable pin has me thinking...

Thanks, and happy new year!
Dan
 
Ordered...

Hi All,

So, As it turns out looking at the specs of some of these cards, we have applications at work where they may be useful. Being relatively low dollar items, I ordered a BEHRINGER UMC202HD and a MOTU M2 2x2 to play with. May order a Focusrite Scarlett 2i2 (3rd Gen) also. I'll be able to drag them home to play with too. So, a win-win.

I'm going to try to capture the output of some of these with a 24bit 400Ksps ADC board here at work. Not saying the THD, IMD of this ADC would be better, as the plan is to test the ADC board with these DAC's. Should be an interesting test to compare all around, tho.

Still looking at the QA401. I really like some of the features it offers for the price. Still in the process of pestering tech support about a few details (and the accountant/wife), but so far all the answers have been favorable.

Thanks again for all the input!

Dan

P.S. Attached is a quick noise floor of the ADC board here. It's quite easy to see the roll off of the anti-alias filter in the linear frequency plot. Overall, not too bad considering it's powered with a couple of switching regulators 0.5 inches away on the same board... ;)
 
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Just ordered a MOTU M2

Very interesting thread - I'm looking forward to what you find when you compare these different units!



So please bear with me, I'm way at the bottom of the learning curve. My personal needs (for now) are pretty basic audio band analysis - I've been getting into restoring vintage audio gear and have reached the point in my mind where doing testing is no longer optional.



Therefore, after reading up for a while on oscillators and audio analyzers, and browsing around for used gear on the Bay, I've concluded that a decent USB audio interface and software-based analysis is the most cost effective way to get started. I plan to use ARTA software, at least to get started.


It's a small leap of faith since there are a very limited number of hands-on reviews, but the new MOTU M2 and M4 look to me to be really good value. I just ordered a MOTU M2 and it should be here on Monday. I passed on the M4 since I don't think I have any great need for the extra pair of channels.


So I'll be watching this thread, wishing you success in doing your mini shootout between a couple of these units. And I will try to replicate your results with the M2.
 
QA401

So, ordered a QA401 for home. Looking over what you get, that complete package is pretty hard to beat for the price. Given time restraints at home, a complete ready to go solution made more sense.

As for the Motu M2 and UMC202HD, just waiting for TRS connectors and some cable.

Hopefully, I'll get to do some comparisons between multiple systems before too long. Will probably drag the QA401 into the mix also...
 
Had a little time to play with the UMC202HD and the Motu M2, and the QA401.

Notes thus far. The Motu M2 has a much lower noise floor than the Behringer. The QA401 is lower yet. (Can't get the Motu and Behringer to send signal in one and out the other with RMAA yet, it just crashes...)

The knobs and buttons on the UMC202HD are nicer. The box is also smaller. However the 48V supply is supplied to both inputs when enabled.

The Motu M2 is bigger. But it does have an LCD screen for level monitoring, which is needed because the gain knob seems to cover a very large range, so can be hard to get set right. The 48V is individually enabled for both inputs (nice), but the buttons seem poor. They're very loose in the case, there's lot of space between them and the switch behind them, so they are loose and can 'rattle around' some. (They're rubber, so don't actually make noise...)

The down side is that the Motu Drivers don't seem to be as stable. RMAA doesn't seem to want to play with the Motu's ASIO drivers. (This is on Win7, so maybe 10 is better???)

Also, spent an evening with the QA401. It just does what I want it to. No knobs to mess with, and it takes up to 20VRMS in directly. The software isn't 100% intuitive (RTFM on my part fixes this!), but it's a very powerful system. In short order I was able to test what I wanted, and ran all of those tests in an evening. It creates nice graphs, and you can add plots to the different graphs.

With the QA401 I was able to get it up and running so fast, I almost took the fun out of it. If you want to find or diagnose a problem, or make improvements to an amp or circuit the QA401 just does it.

I still need to download other software (ARTA, etc.) to test with the MOTU and Behringer, and build voltage dividers to interface to amps... ...if that says anything.

Dan
 

joe

Member
2001-10-23 8:44 pm
Hamburg
I cannot recommend the UMC202HD for measurements.
In a single ended (- pin grounded by TRA adapter) loop-back test it had plenty of 2nd harmonic distortion. Also when I left the neg pin open it was not low distortion. I tried a couple of things but never managed to get good results (THD ~0,3%).

It started to clip at -40dbFS (strange), so even acoustic measurements were difficult, either clipping or low signal level. I tried a couple of things but never managed to get good results.

I am using Linux (with Audionet CARMA and REW) could this be a driver issue? But also read on various places on the web about high distortion. There are some threads here trying to improve it but I want my measurement system working out of the box.

I have already ordered the Tascam US 1x2, hope this will do a better job.I am going to send the Behringer back to the shop.