harmonic algorithm for extending compressed bandwidth of audio file I just found this site and feel at home :) 

I've been playin around with python and some compression ideas and was wondering if there's anything like what I am trying to figure out...

I've noticed that mp4's uploaded to instagram go from ~0 to 13100Hz and on Youtube from ~0 to ~14000Hz... which is OK, but what if there was an algorithm to extend or at least soften this highcut, by taking the amplitudes of the frequencies within the respective bandwidths and applying a harmonic function, (possibly with averaging/weights), to add in implied values to the currently non-existant values (i.e. the and additional bandwidth from 14,000 to 20,000Hz would be harmonically synthesized and still have realistic values.) It could be a plug-in or something.

Anyways, I'm going to check out the board some, and hope to hear some smart replies! thanks!
there is also this answer in this comp.dsp thread.


high-pass filter your input signal (keep the unmolested input around for later).  the cutoff frequency should be adjustable.  i would think a 2nd-order HPF with a Q approx= 0.707 (Butterworth) would be good enough.
square that HPF output,
add (maybe with an adjustable gain coefficient) that squared HPF back to the original input and output that audio sample.


see if that brightens up your day.