MSP34X1G Datasheet, PDF (13/104 Pages) Micronas – Multistandard Sound Processor Family with Virtual Dolby Surround

PRELIMINARY DATA SHEET
MSP 34x1G
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 (loudspeaker, headphone, etc.). All input and out-
put signals can be processed simultaneously. Each
source channel is identified by a unique source
address.
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.
If Automatic Sound Select is on, the output channel
matrix can stay fixed to stereo (transparent) for
demodulated signals.
2.5. Audio Baseband Processing
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.
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 33).
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
– SCART input/output 0 dBr = 2.0 V_rms
– Loudspeaker output 0 dBr = 1.4 V_rms
output level
[dBr]
−18
−24
−30 −24 −18 −12
−6
0
Fig. 2–4: Simplified AVC characteristics
input level
[dBr]
2.5.2. Loudspeaker and Headphone Outputs
The following baseband features are implemented in
the loudspeaker and headphone output channels:
bass/treble, loudness, balance, and volume. A square
wave beeper can be added to the loudspeaker and
headphone channel. The loudspeaker channel addi-
tionally performs: equalizer (not simultaneously with
bass/treble), spatial effects, and a subwoofer cross-
over filter.
2.5.3. Subwoofer Output
The subwoofer signal is created by combining the left
and right channels directly behind the loudness block
using the formula (L+R)/2. Due to the division by 2, the
D/A converter will not be overloaded, even with full
scale input signals. The subwoofer signal is filtered by
a third-order low-pass with programmable corner fre-
quency followed by a level adjustment. At the loud-
speaker channels, a complementary high-pass filter
can be switched on. Subwoofer and loudspeaker out-
put use the same volume (Loudspeaker Volume Reg-
ister).
2.5.4. 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
Micronas
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