Panasonic EURO 4 Chassis Technical Manual page 62

3DQDVRQLF
To switch the TV set to the actual sound mode,
control information on the NICAM mode and bit error
rate are supplied by the NICAM - Decoder via
2
I C bus 1 to the microprocessor IC1101. The
microprocessor IC1101
processing, initiates the required switching and OSD
display for user information. From the output of the
NICAM decoder the left and right channels in digital
format are fed to the DFP processor stage.
20.2.5.FM Processing
After the FM signal has been demodulated the
signal is fed to a Mute stage which is controlled by
the carrier detector circuit. If no FM carrier is
detected in channel 2 of the MSP then the
subsequent FM1 output is muted by the muting
stage in that channel. Like wise if no FM2 carrier is
detected in channel 1 the FM2 output will be muted.
This muting stage is provided to prevent the
processing of a noise signal to the loudspeaker
system.
From the output of the muting circuit the signal is
also fed to the DFP after passing a lowpass filter,
here the demodulated FM / AM signals are
decimated to a final sampling frequency of 32KHz.
The usable bandwidth of the baseband signal being
about 15KHz.
20.2.6.MSP3410 Audio Baseband Processing
By means of the DFP processor all audio functions
are performed by digital signal processing. The DFP
functions being grouped into three processing parts
then, as mentioned for FM
1. Input Pre-processing
2. Channel Selection
3. Channel Post-processing
The input pre-processing is intended to prepare the
various signals of all input sources in order to form a
standardised signal at the input to the channel
selector. The signals are adjusted in volume, by the
prescaler, before being processed with the
appropriate de-emphasis. When transmitting an FM
stereo signal, sound carrier1 is made up of L + R/2
while the second sound carrier FM2 is made up of
just right hand signal. To produce a stereo signal the
R/2 has to be removed from the 'Left', this is
performed in the FM matrix stage.
Having prepared all the input signals to a
standardised level it is now possible with the aid of
the channel selector to distribute all possible signal
sources to the desired outputs.
All input and output signals can be processed
simultaneously with the exception of FM2, which
cannot be processed at the same time as NICAM.
This is due to the fact that NICAM and FM2
processing use SIF channel 1 in the demodulator
section. The processing of the NICAM and FM2
signals follow different paths controlled by an
internal switch, used to switch between the two
processing paths. When switching between the two
signal processing paths, a delay is created while the
de-emphasis circuits in the DFP stage switch to the
require de-emphasis for the particular signal
processing required.
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