I want to change the frequency of an audio file. Meaning: the whole file should sound (say) one octave higher or lower. How to do it? Using
ffmpeg or other command line open source tool would be preferable.
ffmpeg -i <input> -af asetrate=44100*0.5,aresample=44100 <output>
Here, 0.5 is the pitch factor. Or see the other answer for more details.
If you need a GUI, use Audacity, it's a free, open source, cross platform audio editing tool.
Features: Change the pitch without altering the tempo, or vice-versa.
As an alternative, try sox. Something like that:
sox <infile> <outfile> pitch <shift>
where gives the pitch shift as positive or negative ‘cents’ (i.e. 100ths of a semitone). There are 12 semitones to an octave, so that would mean ±
1200 as a parameter.
Find input audio rate beforehand thus:
ffmpeg -i input.mp4
Assuming input audio rate 44,100 Hz, this command will do the job:
ffmpeg -i input.mp4 -af asetrate=44100*3/4,atempo=4/3 output.mp4
The factor of 3/4 will change most female and “skinny” (chipmunk) voices into male and “fat” voices. Use 4/3 for the opposite:
ffmpeg -i input.mp4 -af atempo=3/4,asetrate=44100*4/3 output.mp4
Notice reversed filter order to prevent signal degradation. Whenever possible, lossless operation should come before lossy operation. I’m not 100% sure whether I’m not making some mistake here from misunderstanding FFmpeg filters.
asetrate should have a variable named
ir for input audio rate, in analogy to
ih in some video filters, but I couldn’t find any mention of it in the documentation.
For factors greater than 2 (such as 4/1 or 1/4), you must use multiple
atempo filters (1/4 = 1/2 * 1/2 or 4/1 = 2/1 * 2/1):
ffmpeg -i input.mp4 -af asetrate=44100*4,atempo=1/2,atempo=1/2 output.mp4
I don’t know how to obtain “skinny” male voice and “fat” female voice.
-af, you can write