[asterisk-users] OT -- echo cancellation of an audio file

Matt Riddell (IT) matt.riddell at sineapps.com
Wed Sep 13 15:30:20 MST 2006

Hash: SHA1

William M Conlon wrote:
> I recorded an internet radio program using iTunes, and somehow got an echo.
> Anyone have any suggestions on how to remove echo from an existing file?
> My wife was on the program, and I promised to record it for her, so I'm
> in the hot seat :).

Er, don't know if this will work well, but:

1) Convert to wav, mono
2) Measure the delay in the echo (find a peak and select to the
repetition of the same peak)
3) Measure the difference in volume between the original peak and the
repeated peak.
4) Create a new file with a silence at the beginning of the length of
the measured delay (in 2), followed by the original sound
5) Lower the volume of the new file by the amount found in 3 (don't
forget the peaks need to stand alone so you get an accurate reading)
6) Invert the phase of the new file
7) Put the new quieter, delayed and inverted copy of the file into the
left channel of a new stereo audio file
8) Put the original into the right
9) Export the file as a new mono file by summing and /2

The result should be reasonably reduced echo.

If this doesn't make sense or you need help with it, mail me, and I'll
have a go here.

- --

Matt Riddell

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