We've had a number of people inquire about computer audio recording cards, and various noises they encounter when using them. What are the causes and solutions?

Putting unshielded (or minimally shielded) audio in close proximity to big power supplies and data lines is a recipe for noise and hum. This is exactly what occurs anytime you put a typical audio card in your computer. The best solution is to keep the analog audio outside of the computer. Many audio systems use external hardware to digitize and route the audio before it goes into the computer. These systems, while costing more, are inherently quieter. If you must bring analog audio inside your computer about the only remaining things you can do is minimize the noise generated by the computer and its systems or shield the audio.

It's pretty hard to shield audio running around on a sound card. I've seen people do some pretty clever things with aluminum foil, but the results are unpredictable and you obviously run the risk of doing damage while rigging it up. Aside from the power supply inducing hum or switching noise into audio cards (for which the only real solutions are moving them away from each other or a cleaner power supply) the other big culprit is disk I/O, especially SCSI. Sometimes just moving a SCSI ribbon cable a few inches away from the card can make a big difference. SCSI termination, cabling, and specific hard drive types can all affect how much extraneous SCSI noise is induced into your audio.

To sum it up, we've had hundreds of technical support calls over the years on this type of thing. As far as I know all of them were solved by dropping the allegedly defective audio card into a different computer in a different environment or by switching the user to a card with an external interface. The good news is that in the grand scheme of things this type of problem isn't very widespread or severe.