MSP 44x8G
PRELIMINARY DATA SHEET
2.3. Preprocessing for SCART and
I2S Input Signals
2.5. Audio Baseband Processing
2.5.1. Automatic Volume Correction (AVC)
The SCART and I2S inputs need only be adjusted in
level by means of the SCART and I2S prescale regis-
ters.
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, SCART, or I2S input) to the desired output chan-
nels (Main, Aux, etc.). All input and output signals can
be processed simultaneously. Each source channel is
identified by a unique source address.
In the standard configuration the AVC block is located
in the main channel. Alternatively, the AVC function
can be moved to the mixer path.
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 the AVC
register (see page 29).
For each output channel, the output channel matrix
can be set to sound A, sound B, stereo, or mono.
If Automatic Sound Select is on, the output channel
matrix can stay fixed to stereo (transparent) for demod-
ulated signals.
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
2.4.1. Mixing Unit
– SCART input/output 0 dBr = 2.0 Vrms
– Main and Aux output 0 dBr = 1.4 Vrms
Any source can be selected as the input for the two
channels of the Mixing unit. The mixer channel matri-
ces and the scaling factors can be programmed sepa-
rately for each channel.
output level
[dBr]
After adding up both channels, the signal is fed back
and is available as source 15 (Mix output) of the
Source Selector.
−12
−18
−24
−30
−24
−18
−12
−6
0
+6
input level
[dBr]
Fig. 2–4: Simplified AVC characteristics
12
Micronas
MICRONAS [ MICRONAS ]
