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5-32 361834-002 Technical Reference Guide
Input/Output Interfaces
5.8.3 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 either routed through an
equalizer or applied directly to 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.
The integrated analog mixer provides the computer control-console functionality handling
multiple audio inputs.
Figure 5-13. AD1981B 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
Analog
Out pu t
Ci rcui ts
Ri ght
Audio
Sample
Rat e
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
Gai n
Rec
Gai n
PB
Gai n
PB
Gai n
(L)
(R)
(L)
(R)
S
E
L
Rec
Data (L)
ADC
Rec
Data (R)
DAC
DAC
PB
Data (L)
PB
Data (R)
ADC
E
Q
E
Q
SPDIF
HP Out L
HP Out R