Normalising audio with the CLI
Recently I’ve been learning Pure Data, a visual
programming language for creating music. One of the things I consistently screw
up is correct signal control around volume. As a result, there are some
videos/patches I post of my Pure Data findings that have inconsistent volume
from patch to patch.
To hack around this (the correct way is to use Pure Data properly), I use a
ffmpeg, read on!
The easiest way to normalise audio is with SoX,
it just works™.
Let’s say you have a quiet audio file with a tolerable signal-to-noise ratio,
you can do the following:
sox --norm my_file.wav my_normalised_file.wav
And that’s it, you’ll now have a normalised wav file.
Changing file formats
What you might find is that a file format you want to normalise isn’t
supported by SoX. For example, SoX doesn’t work with mp3’s out of the box so
you need to transfer your file to a format that SoX does work with.
ffmpeg is another life changing program that you should learn about. Changing
file formats is as simple as:
ffmpeg -i my_file.mp3 my_file.wav
And now you have a wav file.
There are also dedicated tools for audio normalisation that I came across such
as ffmpeg-normalize but I find
sox ubiquitous enough to not need another third party solution.