"Gary S. Terhune" <none> wrote in message
> I'll ask you, too. What makes onboard sound different than a PCI card in
> this respect?
> Gary S. Terhune
> MS-MVP Shell/User
The noise problem with on board sound is only audible at high
amplification settings, and most noticeable when no other sound
is being generated. On board sound codecs rely on the CPU for
processing and are tightly integrated into the motherboard circuitry,
and subjected to electrical noise, especially on the v+ line. A lot of
the noise is generated by changes in processing load caused by
interrupts. Most interrupt noise is high frequency and random,
and blends into the normal backgroung hiss. A moving mouse
generates a stream of repetitive interrupts in the audible range,
the effects of which can be clearly heard when the volume is set
high. It's the mouse generated noise that is the cause of complaints.
The PCI bus is more electrically isolated from CPU activity. Also,
most quality PCI sound cards do their own on card hardware sound
processing, and have additional filtering on the power connections.