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Old 6th May 2007, 12:03 AM   #1
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Default About fft and distortions analysis using a sound card

Hello

Even wen we use a very low distortion sine wave oscillator the biggest problem wen using a fft or distortion analysis software using the sound card are the sound card distortion itself. Is there a way to do a first calibration with the sine wave oscillator alone and keep in memory the sound card + oscillator distortion spectrum and substract that distortion spectrum for the amplifier analysis, wen you do a spectrum and distortion analysis you will mostly have only the amplifier distortion showed in the analysis, so even if it's not a perfect method it would do a better job.

BTW, I have an Ensoniq Audio Pci sound card and use the auxilliary input. I know there is much better sound card but they cost to much.


Thank

Gaetan (Canada
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Old 6th May 2007, 03:30 AM   #2
dangus is offline dangus  Canada
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Try RightMark... it does noise and distortion tests. SB Audigy 2 cards are pretty cheap now.
http://audio.rightmark.org/downloads/rmaa6.exe

There's a paper that shows how to configure and test an Audigy 2 with RightMark, and the performance numbers are impressive: http://audio.rightmark.org/downloads...r-rmaa-5.3.zip
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Old 6th May 2007, 07:09 AM   #3
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Hi,

Distortion of the oscillator and the soundcard for FFT is multiplicative rather than additive. That means that these distortions cannot be subtracted from the total result. These distortions set your measurement limits. So use equipment with has low distortion by itself.

The Rightmark tool is pretty good, simple to use and free. I personally prefer ARTA which is more advanced and can do long FFT’s and averaging that reduces the noise floor. However it is relatively easy to use for this kind of software. The demo version is full functional and not time limited, only you cannot save to files. But you can copy the images from the screen.

Cheers
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Old 6th May 2007, 11:56 AM   #4
SY is offline SY  United States
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The thing about the Audigy cards is the awful drivers. I used a 2Zs for a couple years and got very good results from it, but each time out was an adventure and a wrestling match trying to get things to work properly. I changed out cards and drivers to an M-Audio Audiophile192 and have not had any problems whatsoever. Raw performance is slightly better, usability is hugely better.
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Old 6th May 2007, 02:44 PM   #5
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Hi SY,

Have looked at the M-Audio Audiophile192. But is appears that it doesn’t do sample rates below 44.1 KHz. Is that correct?

Cheers

Btw. Here is the distortion of the M-Audio Audiophle 2496 at 24 bits:
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File Type: png distortion_24bit.png (15.6 KB, 421 views)
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Old 6th May 2007, 03:35 PM   #6
SY is offline SY  United States
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25Hz spectrum of an input transformer taken at 11kHz sample rate.
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File Type: gif ampex input xfrmr 2vp 25hz.gif (12.8 KB, 414 views)
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Old 6th May 2007, 05:15 PM   #7
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Thanks SY,

The datasheet ( http://www.m-audio.com/products/en_u...192-focus.html ) only mentions 44.1 kHz and higher. Anyway it sells at almost 2 times the price as the 2496 at the moment.



<Edit>

Just downloaded the manual which makes it more clearer.
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Old 7th May 2007, 04:50 PM   #8
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I did found an interesting web page about distortion maseurment.

http://www.daqarta.com/dw_0d0e.htm

Gaetan
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Old 7th May 2007, 05:27 PM   #9
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Here's a way for very low distortion measurement, but the
adjustment to compensate for phase shift in the amplifier seem quite difficult ???

http://www.angelfire.com/ab3/mjramp/golopid6.html

Anybody did try that way of low distortion measurement ?


Gaetan
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Old 8th May 2007, 02:07 AM   #10
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Quote:
Originally posted by SY
The thing about the Audigy cards is the awful drivers. I used a 2Zs for a couple years and got very good results from it, but each time out was an adventure and a wrestling match trying to get things to work properly. I changed out cards and drivers to an M-Audio Audiophile192 and have not had any problems whatsoever. Raw performance is slightly better, usability is hugely better.

That's good to know - I was trying to decide which card I wanted to use. Have you heard anything about their Revolution 7.1 PCI card? It would seem to be a dandy output for an active PC crossover.
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