The problem lies in the fact that the Tascam never quite plays at the same exact speed twice, and the speed of the motor varies slightly as it runs. Over time, the tracks will get out of shape as small variances in the speed of the tape motor get exaggerated.
There are a couple ways to transfer music from a cassette 4-track to a PC:
The best way is to get a soundcard with 4 inputs and, assuming the Tascam has a separate output for every track, record all four tracks at once. You'll have perfect synch. This is the best way to do it.
If you don't have 4 inputs or are trying to use this technique to get lots more than 4 tracks into the PC, you are going to have to correct the lag in your audio editor. This is a royal pain the !@#$ and you'll pretty shortly either give up in frustration or get really good at editing. I have only done this a few times and it was a nightmare, and some kinds of music just don't work with it, so I don't recommend it. If you try it and end up pulling out your hair, don't bill me for the Rogaine.
First, almost any soundcard can record in stereo, so record tracks two at a time. At least that way each pair of tracks is synched perfectly. Get all four tracks lined up at the start. Assuming your audio editor has a time stretch function, this is where the fun begins. Play back the tracks on the PC and start listening for the discrepency between the two sets of tracks. When you hear it, wind back a little ways and pick a section of audio on one of the pairs of tracks, preferably a spot where no instruments are playing, and use the time stretch function to either stretch the section out or shrink it--just a little bit--to correct for the lag relative to the other track. You don't want to change the pitch--just the time. You'll just have to play with it until the discrepency is compensated for but the section you've changed sounds okay, too. You will probably have to experiment around to find a section of audio you can stretch and an amount by which you can stretch it. Once you've got it back again, you'll have to play the song again and look for the next spot where things seem to get out of synch.
Good Luck,
OB
