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Let's say I have two recordings (or more) of the same event. Maybe one has been recorded slightly slower or faster (different "pitch") than the other one and has been started several seconds after or before the other one.

Let's also say, for simplicity's sake, that there are no gaps in the recordings.

I can synchronize the recordings manually in a software such as Audacity by importing the different recordings as tracks and shifting/stretching them, but is there any way to do that process automatically?

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Not sure it's clear what you mean by "recorded slightly slower or faster (different 'pitch')"? Regardless, you will have to find very specific software (most likely a very specific plugin), because the most "automatic" such a process can get still requires several parameters to be defined. For example, how is a "match" determined? Even the "same event" (a gunshot, even a metronome blip!) will have different signatures. Similar waveform? Similar frequency spectrum? Both (a mix)? To what tolerance? From a theoretical standpoint I think you'll have trouble finding an out-of-the-box solution. – user2754 Aug 10 '12 at 19:17
There's no silver bullet, I think. If you have video, you may set anchor points at sharp movements, and align tracks by those points. However, if the recording suffers jitter, and jitter is non-deterministic (random), it makes synchronization more difficult. – bytebuster Aug 11 '12 at 13:14
By "slightly slower or faster", I was thinking of a situation where two analog tape recorders were used to record the same sound/event from two different places and the tapes were not running exactly at the same speed. – Olivier Bruchez Aug 12 '12 at 13:42
Here are two examples of recordings that I might want to align/synchronize automatically: - several audience/soundboard recordings of the same concert (goal: make a "matrix recording" of the concert) - several versions of the same album (let's say one original, one remastered, one remixed, etc.) (goal: put version 1 on left channel and version 2 on right channel to compare the two versions; some remixed versions of old albums have elements that are added/missing from a version to another) – Olivier Bruchez Aug 12 '12 at 13:43

There is a plugin called vocalign that will do this. It is designed mainly for aligning vocal overdub and replacment dialog but it should work for what you are doing. You can use it as a VST in audacity. It isn't cheap but, if my memory serves me correct, it has a fully functioning demo.

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You can try Ableton live and its wrapping feature.

To glue them together you can also use a bit of reverb and maybe some little compression.

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