MSP4458 datasheet(12/85 Pages) MICRONAS

12 / 85 page

MSP 44x8G

PRELIMINARY DATA SHEET

Micronas

2.3. Preprocessing for SCART and

I2S Input Signals

The SCART and I2S inputs need only be adjusted in

level by means of the SCART and I2S prescale regis-

ters.

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.

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.

2.4.1. Mixing Unit

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.

After adding up both channels, the signal is fed back

and is available as source 15 (Mix output) of the

Source Selector.

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.

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

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

– Main and Aux output 0 dBr

= 1.4 V

rms

Fig. 2–4: Simplified AVC characteristics

−30

−24

−18

−12

−6

input level

−18

−24

−12

output level

[dBr]

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