1. APRIL 2021

Generate spectrograms with arecord, sox and ffmpeg/avconv


Create a spectrogram (image)

The following command creates a WAV file using Alsa (Device 2.0). In this case, Sox is additionally piped, which is completely unnecessary here, however, Sox could still add various filters to the resulting test.wav change:

arecord -D hw:2,0 -r 32000 -f S16_LE -c 1 -t wav | sox -t wav -c 1 -L -b 16 -r 32000 - test.wav

Using the file test.wav that has just been created, a spectrogram is now generated:

sox test.wav -n spectrogram -o image.png

The file image.png then looks something like this (in this case a simple whistle)


Similar can also be created using avconv:

avconv -i test.avi -lavfi showspectrumpic=s=hd480:legend=0,format=yuv420p out.png


Create a spectrogram (Video)

The following instruction creates a spectrogram from a video test.avi. This is saved as a video under the name out.avi.

avconv -i test.avi -filter_complex "[0:a]showspectrum=s=854x480:mode=combined:slide=scroll:saturation=0.2:scale=log,format=yuv420p[v]" -map "[v]" -map 0:a -b:v 700k -b:a 360k out.mp4


Instead of avconv, ffmpeg could also have been used. The Debian version does not currently support all parameters here.


A spectrogram of a video can also be created with mplayer or with the mplayer/sox combination.

First a WAV file is created using MPlayer:

mplayer test.mp4 -ao pcm:file=/dev/stdout -vo null > test.wav

This is followed by the creation of the spectrogram:

sox test.wav -n spectrogram -o test.png

The graphics created in this way can be compared directly. With some (apparently identical) WAV files this can be difficult.

For this reason, the display of a spectrogram diff is recommended.

First a WAV diff is created:

sox -m -v 1 source1.wav -v -1 source2.wav diff.wav

Then the spectrogram diff is created:

sox diff.wav -n spectrogram -o diff.png

Document-ID: blog/cda1c13f-a4ba-4063-9648-f0895b6ceef0

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