How to create spectrograms for audio files using sox

Using spectrograms is one of the most accurate procedures in order to identify the quality of audio files. Let’s say that you were given an music album with 16/44.1 flacs and you want to check wether the files included are “redbooks” or not.

One of the best tools I’ve found for this purpose is sox.

To install it under Archlinux, just give the following:

 pacman -S libsoxr

In order to create a spectrogram for a specific flac file, you need to give the following command:

sox blabla.flac -n spectrogram -o blabla.png

Now, lets see a quicker procedure in order to create a set of spectrograms for the whole album with the help of a simple bash script:

#!/bin/bash
mkdir -p spectrograms
for file in *.flac;do
    outfile="${file%.*}.png"
    sox "$file" -n spectrogram -o "$outfile"
    mv "$outfile" spectrograms/
done
mogrify -strip -quality 80% -sampling-factor 4:4:4 -format jpg spectrograms/*.png
rm /spectrograms/*.png

This script must be run within the album directory. It creates a directory named spectrograms where it stores the .png files. Then, mogrify converts the png to
much smaller .jpg images and finally the un-needed png files get deleted.

Now we have a directory that includes all spectrograms for our files. Their size is really small and we can keep the spectros for all our music library.

Below you can see a sample of the final image, showing the spectrogram of a redbook (16/44.1) flac: