Panasonic EURO 4 Chassis, Technical Manual

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20.4. Audio Output
20.4.1.Loudspeaker Output Path
When a signal source has been selected by the user
for output via the loudspeaker the signal is fed via a
Stereo separation circuit which is used only when
processing an FM stereo signal, at any other time
the circuit is switched off. From the output of this
circuit the signal is then fed to a Bass, treble,
Loudness and spartial effects stage.
20.4.2.Bass and Treble adjustments
The Bass and Treble adjustments consist of two
separate filters. The control range for both filters is
+20/-12dB, the adjustment of -12dB to +20dB is
carried out via the OSD. The two filters coefficients
for the selected range are set to the required value
via the I
2
C bus 1. The volume modifications which
occur during bass and treble adjustments are
stabilised by limiting the internal volume, to prevent
clipping, this limitation is carried out via software.
20.4.3.Loudness
The audio signal fed to the loudness stage is
examined for loudness and aurally compensated for.
Loudness increases the volume of low and high
frequency signals while keeping the amplitude of the
1KHz reference frequency constant.
As the loudness is set according to the actual
volume setting, the required filter coefficients must
be established first, before the signals are acted
upon with varying degrees of severity according to
the volume.