#153 New feature: using a profile for highpass/lowpass filter

Elio Blanca

It would be very useful to be able to specify a profile for applying a highpass/lowpass filter.This way one could filter/keep sounds below/above a specified frequency, while varying this threshold according to a particular audio file. Actually sox can filter sounds above/below a given frequency but this frequency is used for the whole file. What I mean is a way to filter sounds for the first N seconds, then filter different sounds in the following M seconds and so on.
A time-based text file would contain times and frequencies, and so it could appear:

0:00:00,000 -> 0:05:00,000

0:06:00,000 -> 0:09:00,000

(I'm sure you already know these timings, isn't it?)
Well, this file would mean a request for a constant threshold at 14 KHz from the beginning of the audio for 300 seconds and a different constant threshold at 10 KHz from minute 6 to minute 9. Between them, the profile would be a linear gradient from 14 KHz to 10 KHz. Of course, if I apply a highpass filter this means keeping all the frequencies above this profile, else, if I apply a lowpass filter, this would mean discard these high frequencies (and keeping the lower ones).
What do you think, guys?


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