Playback noise when overdubbing!

[polkat]

Recently I had to reinstall Audacity. The computer is a PC with Windows XP Home and SP3. The sound card is a Sound Blaster Live 24 bit. I use a hardwired mic into a preamp and then to the line-in on the card. I record at 44100 at 16 bits. Before the reinstall, this combo worked perfectly.

But now after reinstalling, I'll lay down a first track and it plays back just fine, both in Audacity and other players. But if I go to add a 2nd track, I can hear the first track occasionally breaking up, and sometimes skipping. If I delete the track I tried to add, and then play the first track, it again plays just fine. If I try keeping the added track and playing back both, the first track is fine, but the added track looses sync at the place where the first track broke up. Hope that makes sense.

It is not a latency problem. I've tested for that several times with the click tracl method, and gotten it perfect. And as I said above, before the reinstall, it all worked perfectly. Have I got something wrong in Preferences?

[steve]

Recently I had to reinstall Audacity.

Why was that?

I don't think it's a set-up problem with Audacity. It sounds more like a data bottleneck somewhere.
Try defragmenting the hard drive, rebooting then turning off all non-essential programs /processes and see if that makes any difference.
Have you installed any new security products recently?

Also have a look here: http://wiki.audacityteam.org/wiki/Troub ... ings#Skips

[polkat]

have to wipe the disk after a nasty virus, then reinstall everything. I've been through everything to make sure all hardware/software is running correctly. I'm fairly computer savy, but this one has got me. No, nothing new installed and I have tried all you mentioned. I too now think it's some kind of bottleneck.

But i have imported finished songs with 5 or more tracks and they all play fine. It's just when I try to add a track......

[steve]

It's just when I try to add a track......

So it's when the sound card is operating in "duplex" mode (playing and recording at the same time)?

Which version of the Sound Blaster Live 24 bit is it? PCI or USB?

[polkat]

Right, it''s just when both recording and playing. It's a PCI internal card. Like I said, it worked just fine in duplex mode before the virus, will play back at least 5 tracks in Audacity just fine, and still works fine in any other program.

I don't think it's the card, but rather some other bottleneck, however the sound card is at IRQ #18 (under ACPI control) and I've read that when ACPI is in control, IRQ's above #15 can cause problems even if the card is the only thing sharing that IRQ number. Perhaps I should ditch the CPI control.............?

[steve]

Have you checked that DMA access is enabled for your hard drive?

If you switch to 16-bit default sample format 44100 Hz default sample rate (Edit menu > Preferences > Quality), does it make any difference (better or worse)?

[polkat]

As stated in the original post, it IS set to 44100 at 16 bits. I always set my drives to DMA. This sounds more like something running in the background is effecting the sound card, although I can't find anything running except basic windows? As asked above, I'm wondering if some kind of IRQ problem is taking place?

[steve]

It's possible that it's an IRQ problem, though why should that occur now when it didn't before?

I'd probably look in the Task Manager to see what processes are running and check which can be shut down.
Have you had a look to see how much CPU usage and how much disk activity is occurring while you record?