Har-Bal Users Forum BBS

I have read quite a bit about what clock source to use when recording. The answer I get is always use the internal source of your sound card, which makes sense especially when the AD Converter is built in to the card. My question here is if I'm using an outboard A/D Converter,should I use its own clock as well, or should it be synced to the Sound card where the recording takes place. Regards Skip B

It depends on whether your card supports clock syncing to an external clock and which clock has less jitter. The presence of clock jitter results in inter-modulation products and noise (albeit at a pretty low level). If you have two or more stages of conversion from digital to analog and then analog to digital, if the clocks aren't synchronous and the reconstruction and anti-aliasing filters don't eliminate all the aliased audio products above sampling frequency then the resampling process will modulate those aliasing products into the audible band. If the clocks are synchronous that aliasing doesn't happen, just the initial aliasing that occurs on first sampling the signal.

My advice on it is to sync the clocks if at all possible and if not don't fret about it. The levels of aliasing products rejection in current generation ADC and DAC technology is high enough for you to be struggling to hear any problems arising from re-sampling. From my point of view, the issue of clock jitter has been hyped up way out of proportion by hi-fi gurus. Truth is, if you tried to measure its affect you'd be struggling. When CD's were first introduced mag reviews attempted to measure wow and flutter (which is essentially what bad clock jitter will do) and always came up with "immeasurable". The thing I find amusing about all this is that clock jitter is almost regarded as infinitely bad yet a "little wow and flutter" was not.

Cheers,


Paavo.