MSP 34x7G
PRELIMINARY DATA SHEET
2.3. Preprocessing for SCART
2.5. Audio Baseband Processing
The SCART input need only be adjusted in level by
means of the SCART prescale register.
2.5.1. Automatic Volume Correction (AVC)
Different sound sources (e.g. terrestrial channels, SAT
channels, or SCART) fairly often do not have the same
volume level. Advertisements during movies usually
have a higher volume level than the movie itself. This
results in annoying volume changes. The AVC solves
this problem by equalizing the volume level.
2.4. Source Selection and Output Channel Matrix
The Source Selector makes it possible to distribute all
source signals (one of the demodulator source chan-
nels or SCART) to the desired output channels (loud-
speaker, etc.). All input and output signals can be pro-
cessed simultaneously. Each source channel is
identified by a unique source address.
To prevent clipping, the AVC’s gain decreases quickly
in dynamic boost conditions. To suppress oscillation
effects, the gain increases rather slowly for low level
inputs. The decay time is programmable by means of
the AVC register (see page 27).
For each output channel, the sound mode can be set
to sound A, sound B, stereo, or mono by means of the
output channel matrix.
For input signals ranging from −24 dBr to 0 dBr, the
AVC maintains a fixed output level of −18 dBr. Fig. 2–4
shows the AVC output level versus its input level. For
prescale and volume registers set to 0 dB, a level of
0 dBr corresponds to full scale input/output. This is
If Automatic Sound Select is on, the output channel
matrix can stay fixed to stereo (transparent) for demod-
ulated signals.
– SCART input/output 0 dBr = 2.0 Vrms
– Loudspeaker output 0 dBr = 1.4 Vrms
output level
[dBr]
−18
−24
input level
[dBr]
−30
−24
−18
−12
−6
0
Fig. 2–4: Simplified AVC characteristics
2.5.2. Quasi-Peak Detector
The quasi-peak readout register can be used to read
out the quasi-peak level of any input source. The fea-
ture is based on following filter time constants:
attack time: 1.3 ms
decay time: 37 ms
12
Micronas
MICRONAS [ MICRONAS ]
