Gizmosmith

Command Line Audio Editing With Sox

For my ritual spoken word software piece, I recruited a bunch of my friends to say the text of the ritual. Each “stanza” of the ritual has a call and a response, so I broke each recording up into individual clips for each call and response. That gave me about 28 files per person, and over 100 clips total.

The different participants all recorded on different hardware, and at different volume levels. I also wasn’t super-precise about trimming the clips, so each file had silence at the beginning.

This left me with two problems: some participants were much softer than others, and some of the clips lagged each other, which made for bad chorus effects.

To trim the clips, I used sox, a Linux tool for manipulating sounds, with the command:

for file in *.wav; do sox $file $file.wav silence 1 0.1 2%

This results in a file named foo.wav.wav for each foo.wav file in the directory, so I cleaned up with:

rename -f “s/.wav././g” *

Note that this scribbles over the originals, so keep backups. I’m glad I did, because 2% turned out to be a little aggressive, and trimmed off the beginning of clips starting with an “ma-” sound, such as “make us a…”. This is likely because the sound faded in slowly, and so got counted as part of the noise rather than the beginning of a sound.

There is useful documentation for the sox silence filter here.

Turning the volume up on the files was done with:

for file in *.wav; do sox $file $file.wav gain -l 8; done

and another pass of rename, as above. Adjust the “8” up or down to suit your needs. Positive numbers make it louder, negative make it quieter.

If you want to preview a sox effect, just replace “sox” in the command with “play”, and leave off the output file. For example,

play myfile.wav gain -l 8

will play myfile.wav with increased gain, but won’t change the file.