audio capture

[ajmartin]

I did search this board first but could not find a suitable answer, What would be a good DAQ device to use to capture a signal from an audio amplifer for the purpose of measuring distortion and noise. I am building an amp for myself so do not have a manufactures budget.I was thinking of using an HP Frequency generator to input a very clean wave form and then compare this after amplification using Labview built in functions. I have Labview 8.6 SE

Thanks!

Alan

[Online_Courses]

Hi Alan,

We have a product line directed toward sound and vibration measurements which encompasses audio. Specifically I would suggest looking at the USB-9234.  I also recommend contacting the sales representative for your area at (888) 280-7645.  They will be able to find out more information about your application and address any questions or concerns you may have.  Hopefully this helps!

[ChrisR.]

If price is more important than performance, then you might get away with using your computer's built-in audio hardware or an external audio interface.

Chris 

[ajmartin]

Thanks for the thought, but I think the sound card would introduce to much distortion. In fact I hope my amp is going to be cleaan enough that I would actually be measuring the quality of the sound card.

I also thought about using a voltage divider with some high quality resistors. And I JUST started thinking about a very fast high bandwith opamp, configured to attenuate the signal. Still I would be limited to the 10K/Sec sample rate of the USB 6008.

Alan

[ajmartin]

YIKES! 5 grand to measure a home made amp, I am going for a really high quality amp, but Im not planning on selling it, so the price would not be justified. On the other hand I would love to get some practicle LabView experience, my company moved out of town a while back and I declined to go with, So I bought my self a USB 6008 and paid for the LabVew training my self.. Now an out of work CLAD

Alan

[ChrisR.]

Well, if you do a really good job with your amp, then it will be better than anything you can buy to measure it.  What then?

If your amp is inverting, you can sum the input with a divided version of the output and measure that.  If your amp and divider ratio are perfect, there will be no residue, and the distortion of your digitizer won't come into play.  Of course there will be some residual signal, but you should still be able to get a better measurement than you would just digitizing the input and output separately.

This technique seems to be described here: http://www.analogzone.com/tmt_1002.pdf and here http://www.angelfire.com/ab3/mjramp/distortiontest.pdf

Chris 

[ajmartin]

Wow, The second link in your response is great, I have not had time to digest it all yet but scanning it was already very informative. I didn't mean to be snide in my reply to your suggestion to use a sound card, but I have very little respect for sound card input as far as fidelity goes, Im using a sound card input now to record records using a pretty good pono cartrige , the results are not great, I know there are other variables in this , but still........plif

What do you think the best approach is to get the audio signal into LabView (besides the 5K DAQ) I think if I can get the original signal and then the the amplified signal into LabView I can do the work that is mentioned in the link you sent. 

Alan

[ajmartin]

Forgot to mention, I have a USB-6008, maybe I should start with that and sample a 2K signal, just to see how it goes. I'll still need to attenuate the amplified signal some how.

Alan

[ChrisR. · Accepted solution]

I haven't read all through either link.  I just found them with a quick Google search and scanned them quickly.

I didn't see your response as snide at all.  I know all too well how lousy consumer PC audio hardware is.  Nevertheless, I think it could be perfectly appropriate for digitizing an _error_ signal, since the fidelity required is much lower than that required to measure the signals of interest directly.  The method I mentioned has the additional benefit of being insensitive to distortion in the source signal, so you may be able to use PC audio to provide that as well.

Chris 

[ajmartin]

Ok, then, I have lots to keep me busy for a while, not to mention finishing the Amp. Hope to power it up with dummy loads later this week.

Thanks

Alan