MSP3417G datasheet(12/81 Pages) MICRONAS

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MSP 34x7G

PRELIMINARY DATA SHEET

Micronas

2.3. Preprocessing for SCART

The SCART input need only be adjusted in level by

means of the SCART prescale register.

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

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 demod-

ulated 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 27).

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 Vrms

– Loudspeaker output 0 dBr = 1.4 Vrms

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

−30

−24

−18

−12

−6

input level

−18

−24

output level

[dBr]

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