B. INTEGRAL PARTS AND FUNCTIONALITY
B-4
BeFREE 20 – TECHNICAL OVERVIEW
B.4.
Intercom (Audio Section)
The functional block diagram of the audio section is shown in Figure B.4 below. Left
and Right Speaker are physically/electrically realized as two loudspeakers in parallel to
double the output volume. The Central Speaker, along with associated hardware equalizer,
emphasizes lower frequencies in order to improve naturalness and intelligibility of the
reproduced speech.
Internal signal processing includes analogue-to-digital and digital-to-analogue
conversion (block “USB AUDIO CODEC” which comprises two USB Codec chips),
conditioning (amplification, attenuation, filtering …), sensing and switching. The complete
processing is programmable via ChangeMe software and can be dynamically modified
during the operation in so-called On-Line operating mode (using HID API). USB and
analogue signals can be mixed, resulting in up to six listening (output) audio channels (
3
x
stereo signal) and three parallel
recording (input) channels
(USB
and analogue). The Echo-
Cancellation circuitry is optional (see Chapter D.3 for more details).
Figure B.4 Audio Section (Intercom)
L
R
ANALOGUE
AUDIO
L
R
AMPLIFIER
USB
AUDIO
CODEC
USB AUDIO
L&R
LINE OUT:
LINE IN:
LINE IN:
R
L
L&R
LINE OUT:
R
L
L&R
LINE OUT:
A
B
LINE IN:
∑
∑
M
AMPLIFIER
∑
MICROPHONE
AMPLIFIER
