Epic time shift fail

[Dsurian]

'Ello forumers.

So, my greatest interest in the Aud. would be recording my own voice over current songs to (IMHO) improve them. So i would import an mp3, then apply the playback of the track, start recording and i sing over it; never have had a problem with this multi-track recording process until now - My most recent attempt has had a very strange consequence; when i finish recording, i pause to observe the track, and then hit stop to then hit play and have a listen at my work. Only problem is when i hit 'stop', the second track that i had just recorded moves. Now it sounds just like this little prob, but its not...the beginning of the song is still perfectly lined up and the ending ends up being more than .5 sec.'s off...so using the Timeshift tool to flush up the end will just screw up the beginning. So, its obviously been stretched automatically...my question being, if its easy enough, how do i un-stretch it *or* can i/how do i disable this automatic insanity?

And as far as why this problem started, the only reason i can think of is that i got a new headset. Old headset had a not so great mic but a built in sound card. This uses the sound off the mobo (which is still great) and has a better mic...either/or, still dont know why its happening.

[steve]

So, its obviously been stretched automatically...

Yes, but not by Audacity. It has been "stretched" by your audio hardware.

The problem is that each sample that is played or recorded is timed by the audio hardware. When sampling at 44.1kHz, the sound card will send samples to Audacity 44100 times per second. When Audacity plays, Audacity simply throws the data to the sound cards, and the sound card outputs it at a rate of 44100 samples per second.

All fine and dandy so far, but what if the recording hardware is running a little faster or a little slower than the playback hardware - well, you've just found out. If you record one track while listening to another and the recording and playback hardware are running at slightly different speeds, the two tracks will gradually drift apart.

Yo may be able to correct it by using the "Change Speed" effect, though it will be tricky to get it to line up exactly. If you use the change speed effect on short sections you may be able to drag them close enough, but the underlying problem is the new hardware.

[Dsurian]

Right...so, buy a sound card. In the meantime, i still dont get how it pans out normally when recording...like i said, i can pause the recording and it'll stay in place - it'll stretch after i hit 'stop'...so is there anyway to fix it in its original position?

[steve]

I think that the shifting that you see is the normal "latency correction" as described in the link that you posted. Latency correction moves the entire track by the same amount, so it will not help resolve an issue where the tracks are drifting out of sync.

It may be worth seeing if there are any updated drivers for your hardware, and also trying Audacity 1.3.8, Updated drivers can sometimes (but not often) help with synchronisation issues, and Audacity 1.3 can use alternative methods (such as direct X) to communicate with the audio hardware which may improve things.

In Audacity 1.3 you can override the latency correction settings and set it to any amount that you want. Setting latency correction to zero will mean that the track does not move when you press stop (but the track you have just recorded will sound a bit behind the other track(s) because of latency (which has now not been corrected).

This type of synchronisation issue is most common when a different audio device is being used for playback to the device that is being used to record. If the same sound card is being used for both then the synchronisation is usually better. Very cheap and on-board sound cards quite often have this problem.