drums from a synth

problems syncing

i have a guitar part recorded and i am attempting to overdub a live drum part with my synth. it’s not going in via midi, just into my tascam 4-track then into the computer. i’m playing the drums myself on the synth and at times it syncs up with the guitar when i play back but at other times it’s a few miliseconds delayed. what could the problem be? it’s quite frustrating knowing that sometimes it’s in sync but other times it’s not.
any help would be appreciated.
thank you!

What soundcard? If it’s a soundblaster or audigy, work at 48kHz. (I assume the tascam is just being used as a mixer or preamp, not as an A/D converter.)

Also, in Preferences -> Options, uncheck both “use system timer for” boxes, and see if that helps.

If you’re using an aftermarket soundcard, be sure you’re using the latest drivers from the manufacturer’s website, not the ones that came in the box.

Finally, dropouts can cause sync problems. By dropouts, I mean cases where the computer doesn’t quite keep up and you hear (in the playback) clicks, pops, zippers, or other anomalies. However, if the track has lots of silence you may not be able to hear them. Try recording some smoother audio and listen carefully for anomalies. (When this happens to me, it usually causes the track to slip ahead in time, not behind, but it’s worth a try if the above doesn’t work.)

StanleyCanuck -I had the same problem you are experiencing, and in my case, it was caused by the drop-outs that LearJeff mentioned. The forum gurus helped me work through the problem, but I could never hear the drop-outs while I was using my ASIO driver. The only way I was able to determine that drop-outs were the problem was by increasing buffer sizes and then checking to see if the synchronization problems dissapeared. Here is the way that I evenually optimized my buffer settings: First I recorded a click track on one track. Then I put a mic in front of one of one of my monitor speakers, and recorded the click track (from the speaker) to another track. Then I would play back the two tracks and listen to how far apart in time the ‘matching’ clicks were. Then I would decrease buffer size, rerecord the second track, and listen to see if synchronization was achieved. When I found the minimum buffer size that worked, I added some back to this buffer size, and my problem was solved. Then new drivers for my audio interface came out, and I was able to decrease buffer size (and latency) a bit more. Finally got it though, thanks to a little help from my forum friends.