Developer Documentation
PATHHardware Documentation > Original Power Mac G3 Computers Developer Note


Digitizing Sound

The sound circuitry digitizes and records sound as 16-bit samples. The computer can use any one of three sampling rates: 11.025K samples per second, 22.050K samples per second, or 44.100K samples per second. In the case of the Apple DVD-Video and Audio/Video Card sound is always sampled at 44.100kHz and the host performs sample rate conversion for output sample rates not equal to 44.100kHz.

The preferred sound sampling rate for output is specified in the Monitors and Sound control panel when the sound input is not in use. The preferred output sampling rate is overridden by the setting of the input sampling rate, because the input and output sampling rates are physically locked together.

When recording sound from a microphone, applications that are concerned about feedback should disable sound playthrough by calling the Sound Manager APIs.

The Screamer IC on the Apple Audio and Audio/Video card configurations provides separate sound buffers for input and for stereo output so that the computer can record and send digitized sound to the sound outputs simultaneously. The Burgundy IC provides the sound buffers on Power Macintosh G3 configurations with the Apple DVD-Video and Audio/Video Card.


© 1998 Apple Computer, Inc. - Revised 8/13/98