MSP3401G datasheet(13/104 Pages) MICRONAS

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PRELIMINARY DATA SHEET

MSP 34x1G

Micronas

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 Vrms

– Loudspeaker output 0 dBr = 1.4 Vrms

Fig. 2–4: Simplified AVC characteristics

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

−30

−24

−18

−12

−6

input level

−18

−24

output level

[dBr]

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