change pitch of multiple audio files with Sox

Question

I am intending to take my entire music collection and change the pitch from the original recorded a=440hz to the more natural sounding/feeling a=432hz.

For those of you who are not familiar with this concept, or the "why" for doing this, I highly encourage you to do a google search and see what it's all about. But that is not entirely relevant.

I understand that I could even take Audacity and one-by-one, convert and re-export the files with the new pitch. I have tried this and yes, it does work. However, my collection is quite large and I was excited to find are more fitting command-line option, SOX. Any idea ?

score 6 · Answer 1 · edited Dec 22 '13 at 20:51

6

$ sox your_440Hz_music_file.wav your_432Hz_music_file.wav pitch -31

edited Dec 22 '13 at 20:51

Josh Crozier

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answered Dec 22 '13 at 20:27

Prana

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Consider adding an explanation to this. – Josh Crozier Dec 22 '13 at 20:51
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Wrong. sox's "pitch" filter is in cents, but the poster's numbers are in Hertz. – Camille Goudeseune Apr 02 '14 at 21:52

score 4 · Answer 2 · answered Apr 02 '14 at 21:50

This is asking way more than one question. Break it down into subproblems, for instance:

how to batch-process files (in whatever language you like: perl, bash, .bat, ruby)
how to structure a set of directories to simplify that task
how to change the pitch (with or without changing duration) of a single audio file
how to detect the mean pitch (concert, baroque, or whatever) of a recording of tonal music, by using a wide FFT, so you don't accidentally change something that's already 432 to 424

As you work through these, when you get stuck, ask a question in the form of a "simplest possible example" (SO gives much more advice about how to ask). Often, while formulating such a question, you'll find the answer in the related questions that SO offers you.

score 2 · Answer 3 · answered May 08 '21 at 16:14

sox's pitch filter only accepts 'cents' (100th of a semitone), so you have to calculate the distance between 432Hz and 440Hz in 'cents'. This involves the following logarithmic calculation:

2^x/12 = 432/440
x/12 = log(432/440) / log(2)
   x = log(432/440) / log(2) * 12
   x = -0.3176665363342927165015877324608 semitones
   x = -31.76665363342927165015877324608 'cents'

So this sox command should work:

sox input.wav output.wav pitch -31.76665363342927165015877324608

For those interested; this can also be done with sox's open-source counterpart ffmpeg:

ffmpeg -i input.wav -af "asetrate=44100*432/440,aresample=44100,atempo=440/432" output.wav

Or if ffmpeg is compiled with the Rubberband library:

ffmpeg -i input.wav -af "rubberband=pitch=432/440" output.wav

change pitch of multiple audio files with Sox

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