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Technical Reference Guide
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
5-29
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.
Figure 5-13.
AD1881 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.
Left
Audio
Compaq
Premier
Sound
Components
Rec
Gain
Right
Audio
Sample
Rate
Gen.
Audio
Format
AC97
Link
I/F
SD IN
SD Out
S
e
l
e
c
t
o
r
Mic In
Line In (L)
Line In (R)
CD In (L)
CD In (R)
Σ
/Mixer
Audio
Controller
Rec
Gain
PB
Gain
PB
Gain
SW
3D Proc.
3D Proc.
(L)
(L)
(R)
(R)
(L)
(R)
S
E
L
Rec
Data (L)
ADC
Rec
Data (R)
DAC
DAC
PB
Data (L)
PB
Data (R)
ADC