Time stretch affecting amplitude

Question

I use CS6. I am digitising some old vinyl and noticed after I had done a few that my record player was running a bit slow (c. 1.8%). No problem, I thought, I'll just use the time and pitch stretch process in Adobe Audition to get it back to normal. Specifically: Effects> Time & Pitch> Stretch & Pitch (process). I have set the Stretch to 98.23% and locked the pitch to the stretch, which should drop the pitch by 0.31 semitones. Unfortunately not that simple. After the stretch, I notice most of the waveform seems to be in Clipping. So I checked using the Amplitude Statistics. The average RMS amplitude before and after are very similar Before:14.16L, 14.47R After: 14.28L 14.55R. However, the number of possibly clipped samples has gone from 5L, 75R (a few more than I would like, but not worth re-recording) to 17921L, 17337R. What is happening? Why does time/pitch stretching affect amplitude at all? How can I stop it?

sealord1 · Answer

OK, I seem to have answered some of my own question. There is another setting in the Stretch process. "Algorithm". The default setting for this is iZotope Radius. The alternative option is Audition.

If I select Audition, the weird amplitude effects I was getting using iZotope Radius disappear and I get what I was expecting - duration and pitch changed, amplitude left alone.

I have no idea why anyone would choose the other result or why it is set as the default option, but at least I now know how to get around the issue I was having.

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