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Audio Diff Maker Help!
Tenson
post Dec 28 2012, 01:47
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Hi all, I'm new here. smile.gif

I wanted to find how much my pre-amp added to the signal, so I thought I would try to record with my M-Audio Fast Track Ultra output linked directly to the input, and then do the same with the pre-amp in the chain and subtract one from the other, leaving only the difference the pre-amp adds. I was using Adobe Audition to do that and it never nulled better than -55dB.

I then found Audio DiffMaker so gave that a go. http://www.libinst.com/Audio%20DiffMaker.htm

To test if it is working correctly I took two recordings, one directly after the other, of the soundcard output linked to input and tried to subtract them with DiffMaker. No matter what settings I use, I can't get it to null better than -78dB!

Is this normal? It seems very wrong but I can't find the problem, the soundcard seems to be working right.

I uploaded the two files:
http://www.audiosmile.com/forum/soundfiles/Direct.wav
http://www.audiosmile.com/forum/soundfiles/Direct%202.wav



Thanks!
Simon

This post has been edited by Tenson: Dec 28 2012, 01:51
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pdq
post Dec 28 2012, 02:51
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Unless the two files are exactly aligned sample to sample you will not get perfect cancellation. You can improve this by upsampling to a very high sample rate and then aligning the files, but it still will not be perfect.
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Tenson
post Dec 28 2012, 03:18
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Oh, I think I've sorted it! smile.gif I spent most of the evening fussing with this, and about 30min after posting on here I figured it out, lol.

The problem was that my recordings all started with a few seconds of silence. So when DiffMaker tried to align the files, it was of course trying to align random noise in the first part of the files. Having cut the silence off the begining of each file, the auto align settings in DiffMaker work a treat.

Here is the result for now, made with recordings of a 1KHz tone. The Red trace is the null between two recordings from my M-Audio soundcard. The null should be as good as it gets since both recordings were made one after the other with no changes to the set-up. The Blue trace is with my Cyrus 'Pre' preamp in the chain and set close to unity gain as possible.

Tomorrow I will try the same with real music rather than a sine-wave.

I can really recommend Audio Difference Maker as it not only auto aligns the files to far better than 1 sample, but also has correction for clock drift too, which I have always found made nulls of recordings made using ADCs impossible.



Below are the settings I used in Audio Diff Maker.

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AndyH-ha
post Dec 28 2012, 03:48
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You might want to look at RightMark Audio Analyzer
http://audio.rightmark.org/index_new.shtml
which is designed to make such measurements easier.
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Arnold B. Kruege...
post Dec 28 2012, 15:01
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QUOTE (Tenson @ Dec 27 2012, 19:47) *
Hi all, I'm new here. smile.gif

I wanted to find how much my pre-amp added to the signal, so I thought I would try to record with my M-Audio Fast Track Ultra output linked directly to the input, and then do the same with the pre-amp in the chain and subtract one from the other, leaving only the difference the pre-amp adds. I was using Adobe Audition to do that and it never nulled better than -55dB.


Wrong tool for the job at hand.

Please check out RMAA - the Audio Rightmark Testing program (freeware).
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