stretching files

I searched the forums and did not see this. I recorded a live show on 2 decks not sync'd. is there a simple way to stretch a source roughly ..090 seconds or shrink it. I usually do 4 tracks on the same deck so it has not been a problem. any help appreciated. thanks

simple answer is: 'probably not'

as with everything else audio how easy or successful sync'ng material that were not 'clock' locked while recording depends on specific hardware and specific content. 

the difficulty tends to be not merely 'offset' but 'drift'

Offset can be compensated for relatively easily but even identifying a total amount of 'drift' typically does not allow one to stretch (though shortening tends to be slightly more successful, i.e. modifying the longer of the two files) merely by that amount.  Success for even scaling the drift to ably from beginning to end tends to depend on how small the selection on which the stretch is.  The smaller the selection the more successful the effect.

Ability for audiences to discriminate temporal differences in material recorded on different decks is partially dependent on the material itself. Tempo & duration of defining 'beat' will influence individual discrimination.  Different individuals will have different thresholds for rhythmic discrimination.  Generally, for an 'average' listener, offset perception threshold seems to be in the 6-20ms range.  in moderately paced (for some this would be lethargic to point of boredom)  pop music a quarter note might occupy a 160ms window.  Even small amount of drift can be discernible. 

Which means trying to match material not sync'd during recording process tends to be involve a lot of content/project specific manual work.  How successful even this tedious work is depends on material and sophistication of intended audience.

good luck

I assume you have recorded by 4 different microphones and want to get a stereo mixdown. A basic question is whether they represent well separated sources such as 4 voices. In this case you may get a result at best rated as satisfactoy by proceeding such as oretez has described. But as soon as you have sound sources with similar intensity on more than a single microphone, you need a sample true sync to get a stable stereo image. Otherwise you risk even to get "rotation" on your image and a badly disturbed frequency reproduction. In practice, the second case is a NOGO for sure.

I've certainly done this before but I can't remember if I used Audition or Reaper. Reaper certainly makes it easy as you just right click on whatever you want to change, go to item properties and then choose the speed you want it to play at. I seem to remember that I had to permanently change the speed in Audition by using pitch shift from the edit view.

James.

Reaper still is not an 'editor'.  So you make running changes in an audio w/o altering the underlying file.  You can then render the mix down to a new file if desired.

You can actually, perhaps, do the same thing in multitrack view in AA and depending on content and preferred work flow either destructive or non destructive editing can be as efficient.

Certainly in the 'bad old days' sync'ng audio that was not only offset in time but drifted through out the length of the file placed a high CPU demand during non destructive editing.  Additionally destructive editing algorithms for this type of thing tended to be at least slightly more accurate (see acidized beat matching for example).

I have not worked with current version of Reaper for this type of thing but certainly depending on the scope of the drift Reaper, based on how they handle clip creation during non destructive editing might well be an efficient way to do this type of thing.  Typically I tended only to use the older versions of Reaper for this type of beat matching (so to speak) if content had a lot of short segments with clear 'breaks'.  Which of course a lot of pop music has.

but the initial point that if issue includes drift as well as offset then resolving it requires a lot of manual massaging remains intact no matter what software you use