What is the best way to remove the echo from an audio file?

Question

I want to run an audio file through something like skype's echo cancellation feature. iChat and other VoIPs have this feature too, but I can't find any software that I can import or open my file into.

Solution 1

basic approach:

determine the delay. determine the amplitude offset.

invert the signal. apply the delay. adjust the amplitude. play back both audio files.

any multitrack audio app is capable of this (e.g. audacity, protools, or logic).

for more complex signals, you will need to be more smart about your filtering, and ideally you would suppress the signals before they interfere (in a Skype scenario).

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Sounds cool, and makes a lot of sense theoretically, but I still don't really know how I should go about doing it. I am fairly experienced with Logic, but I don't know how to determine the delay. Should i just make a copy of the file, invert it and move it around until it sounds good?

Just line up the transients of the 2 signals visually to determine the delay. Then you have to zoom way in and determine the delay to the sample to achieve the best cancellation. If it's not close, it won't cancel but add.

What do you mean by amplitude offset, is that the volume difference between the original and the echo noise?

Exactly. Apart from very unusual cases, the echo is going to be a different (typically lower) amplitude than the source, and you need to know this difference to cancel it best (this offset is applied to the inverted signal, btw). If the amplitude is wrong, then you will introduce the inverted signal (audibly) or, in the odd event the echo is louder than the source, reduce only part of the echo.

Once the transients are aligned (to the sample) and the signal's inverted, then determine the difference in volume -- if it's too high or too low, it won't cancel as much as it could.

Again, that's a basic approach. You can do a lot to improve it, depending on the signals and processors you have. In most cases, this approach will result in suppression, not elimination.

Solution 2

In order to remove echo, you need TWO files: mic & reference. The mic is the signal that contains the echo. The reference is the signal that contains the original audio that generated the echo.

After you have both these files You can start building the logic of echo removal. Start with the wiki page on the subject.