I get terrible crackles when I overdub audio over virtual instrument performances.

Powerbook 1.5 ghz g4 15" 512mb/ Tiger/ Firewire 410 (latest driver)
Cubase SX1/ Sampletank 2

What Disk and audio buffer settings etc should I be using?

I'm on 12 disk buffers, 128kb disk buffer size and 512 samples audio buffer. I tried 8 disk buffers 1st and it seemed better but then it resumed the crackles. There's loads of system memory left. Not even got any effects or EQs running.

Sampletank runs fine normally & Audio records fine normally, even with sampletank running idle in the background. It's when you overdub audio over a midi piece that sampletank is playing, that the thing crackles.

Is it a matter of buffers?

Have you set up the CPU to max operations, disable NAP? If not, do so.

Are you running the files from your internal hard drive? If so, run for a firewire drive NOW!

Next possibilities are the 410 or Cubase, but it's better to let people in the know having a go at it. I'm not omniscient

Hya,
Thanks for the input. Can you tell me how I set the CPU for max operations? and what is NAP?

I eventually found that having much smaller disk buffers actually had it perform without a problem.

I don't know if you have any ideas on this? Will I run into other problems? and what are the ball-park figures I should set everything to?

The best solution for SX is a dual G5, i gave up on it with my powerbook and went to Logic.
Try larger buffers, freezing tracks.

CPU to max is available in the energy saving preferences, note it's better to run of mains then

NAP is an energy saving mode where parts of the CPU are not working at all Here for some info on this…

You can disable NAP by installing utilities for developers, especially one called Processor which is an Apple developer prefpanel, available on the ADC website and maybe (didn't check) on the developer part of the install disck(s).

On the buffers, depending on the set up, the 128-512 is the normal zone for most softwares.