Apply a Lowpass Filter to an mp3 Audio File

A lowpass filter can be applied using the command line tool sox. It tool can be installed like this on Ubuntu:

sudo aptitude install pacpl sox

Convert the audiofile to wave first (using Perl Audio Converter as sox has no mp3 support compiled in on Ubuntu systems):

pacpl --to wav basstest.mp3

Now apply the lowpass filter using sox:

sox basstest.wav basstest_low-freq.wav lowpass 100

if you want to see the filter you just applied, then use the plot option:

sudo aptitude install octave3.2
sox  --plot octave basstest.wav basstest_low-freq.wav lowpass 100 > lowpass.plt
octave lowpass.plt

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