Compaq W4000 manual Audio Codec, PB Data R

Technical Reference Guide

5.8.4 AUDIO CODEC

The audio codec provides pulse code modulation (PCM) coding and decoding of audio information as well as the selection and/or mixing of analog channels. As shown in Figure 5-13, analog audio from a microphone, tape, or CD can be selected and, if to be recorded (saved) onto a disk drive, routed through an analog-to-digital converter (ADC). The resulting left and right PCM record data are muxed into a time-division-multiplexed (TDM) data stream (SD IN signal) that is routed to the audio controller. Playback (PB) audio takes the reverse path from the audio controller to the audio codec as SD OUT data and is decoded and processed by the digital-to- analog converter (DAC). The codec supports simultaneous record and playback of stereo (left and right) audio. The Sample Rate Generator may be set for sampling frequencies up to 48 KHz.

Analog audio may then be routed through 3D stereo enhancement processor or bypassed to the output selector (SEL). The integrated analog mixer provides the computer control-console functionality handling multiple audio inputs.

Mic In	S	Left
	e
Line In (L)		Audio
			Rec

Audio

Format

Rec

Data (L)

	l		Gain
Line In (R)	e
	c	Right
CD In (L)	t	Audio	Rec
CD In (R)	o		Gain
	r

ADC

ADC

Rec Data (R)

SD IN

Σ/Mixer

Sample

Rate

Gen.

AC97

Link

I/F

Audio Controller

		3D Proc.	(L)	SW
	(L)			PB
Analog			(L)
		S		Gain

DAC

PB Data (L)

SD Out

Output	(R)	E		(R)
Circuits		L	3D Proc.		PB
				(R)
					Gain

DAC

PB Data (R)

Figure 5-12.AD1885 Audio Codec Functional Block Diagram

All inputs and outputs are two-channel stereo except for the microphone input, which is inputted as a single-channel but mixed internally onto both left and right channels. The microphone input is the default active input. All block functions are controlled through index-addressed registers of the codec.

Compaq Evo and Workstation Personal Computers5-29

Featuring the Intel Pentium 4 Processor

Second Edition - January 2003