For the benefit of those who haven't been following audio advances
recently (not you guys). Today, most sound cards have two seperate
units: a controller and a codec.

The codec contains all the analog-to-digital and digital-to-analog
converters. The codec also contains a mixer.

The controller's job is twofold: first, to transfer data between host
memory and the codec and, second, to expose the codec's registers to
the host. In modern sound cards, this means interfacing with the PCI
bus.  In addition, the host controllers on some cards do FM synthesis,
3-D processing (a la Aureal 3D or SB Live!), or sample rate
conversion, though this is not required.

Lennart Augustsson <lennart@augustsson.net> writes:

> Do these new codecs only operate for certain sample rates?

AC-97, an Intel standard for codecs and their interface, only requires
that codecs operate at 48khz. The codecs rely on the AC-97 controller
(like the Ensoniq 1371) or host to do the sample rate
conversion. However, AC-97 codec CAN support sample rate conversion
and there is a standard interface for this.

The PC2001 specification (from Intel/Microsoft) states that the
hardware does not need to support sample rate conversion
since Windows 98/2000 has WDM drivers to do it in software. See
http://www.pcdesguide.com/

Intel is already generating such hardware. The 810 chipset has an
integrated AC-97 controller on the 82801AA/AB chip. The controller
does not do sample rate conversion. (BTW, the interface is
beatifully simple - it even memory maps the codec registers!).

Going forward, then, software sample rate conversion is a must.

-Costa