15
Theory of Operation
4.0 Audio Electronics
The AV28 is a 2-Zone audio system, meaning that users can simultaneously listen to one audio
source in one room and a second audio source in another. Therefore, much of the audio path
hardware is split into two sections: Zone 1 hardware and Zone 2 hardware.
Furthermore, the media center outputs each zone’s audio content in two different forms: analog
and digital. The analog outputs are standard left/right, 2Vrms (max) signals similar to those found
on past Bose
®
products. Some of these outputs are variable level, with volume control cells in
series with them. Other analog outputs are fixed level, and remain at the 2Vrms (max) level, re-
gardless of the user’s volume setting. Examples of variable outputs would be the headphone
outputs and the analog left/right signals on the Speaker Output mini-DIN connectors. The only fixed
analog outputs are the Record Out left and right signals. See the diagrams, below.
The digital outputs are serial digital audio data streams in S/PDIF format. These output streams
contain the same audio source material as their analog counterparts in each Zone, but the left/right
information has been digitized and combined into a single datastream. The S/PDIF outputs, how-
ever, may send either 2-channel (PCM) audio, or bursts of compressed multichannel audio (in AC-
3, AAC, MPEG-2, MP-3, or DTS formats). The amplitude information within the S/PDIF streams
never varies with volume level; instead, speakers receiving the streams will perform the volume
control function.
There are both analog and digital options for all AV28 audio inputs, as well. A simplified diagram of
the audio path would therefore be:
U303
CS4224
Z1 Codec w/
Volume Control
Internal Analog
Audio Sources
(Tuner, DVD 2-Channel
Mixdown)
U201
TEA6422
ANALOG M UX
(Selects the desired
analog input
for each Zone)
Zone 1
Speaker Output
(Variable)
Zone 2
Speaker Output
(Variable)
Zone 1
Headphone Output
Zone 1
Record Output
(Fixed)
External Analog
Audio Sources
(TV, VCR, AUX, Tape)
U403
CS4224
Z2 Codec w/
Volume Control
DVD-ROM
Playback
(DVD, CD)
U501
CS8415
S/PDIF MUX
(Selects the
desired
S/PDIF input)
Zone 1 Digital
S/PDIF Output
Zone 2 Digital
S/PDIF Output
External Digital
Audio Sources
(TV, VCR, AUX, Tape)
Record Digital
S/PDIF Output
U1
CS98K
DVD
DECODER
U306
CS8405
Z1 S/PDIF
XMTR
U406
CS8405
Z2 S/PDIF
XMTR
ATAPI
PORT
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