Bose AV28 Manual page 15

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:
Internal Analog
Audio Sources
(Tuner, DVD 2-Channel
Mixdown)
External Analog
Audio Sources
(TV, VCR, AUX, Tape)
DVD-ROM
Playback
(DVD, CD)
External Digital
Audio Sources
(TV, VCR, AUX, Tape)
Theory of Operation
U201
TEA6422
ANALOG MUX
(Selects the desired
analog input
for each Zone)
ATAPI
U501
PORT
CS8415
S/PDIF MUX
CS98K
(Selects the
DVD
desired
DECODER
S/PDIF input)
15
U303
CS4224
Z1 Codec w/
Volume Control
U403
CS4224
Z2 Codec w/
Volume Control
U306
CS8405
Z1 S/PDIF
XMTR
U1
U406
CS8405
Z2 S/PDIF
XMTR
Zone 1
Record Output
(Fixed)
Zone 1
Speaker Output
(Variable)
Zone 1
Headphone Output
Zone 2
Speaker Output
(Variable)
Zone 1 Digital
S/PDIF Output
Record Digital
S/PDIF Output
Zone 2 Digital
S/PDIF Output