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CP-520/520A/520F Service Manual
DTV R&D Europe
48
number of sound sample errors, resulting from parity checking, that occurred in the past 128ms
period. The Bit Error Rate (BER) can be calculated using the following equation;
During NICAM mode a switchable J17 de-emphasis is supplied.
NICAM AUTO-MUTE
If the Auto Standard Detection (ASD) or the Static Standard Detection (SSS) feature is activated
the following auto mute function is in effect.
If NICAM B/G, I, D/K is received, the auto-mute is enabled and the signal quality becomes poor,
the built-in control automatically switches the output signal (DEC output) to FM channel 1. The
automatic switching depends on the NICAM bit error rate. The auto-mute function can be
disabled via the control bus.
This function is enabled by setting bit NIC_AMUTE to 0. Upper and lower error limits may be
defined by writing appropriate values to the corresponding control bits (NICLOERRLIM and
NICUPERRLIM). When the number of errors in a 128 ms period exceeds the upper error limit the
auto-mute function will switch the output sound from
NICAMtowhateversoundisonthefirstsoundcarrier(FM or AM). When the error count is smaller than
the lower error limit the NICAM sound is restored.
The auto-mute function can be disabled by setting bit NIC_AMUTE to 1. In this condition clicks
become audible when the error count increases; the user will hear a signal of degrading quality.
For NICAM L applications, it is recommended to demodulate AM sound in the first sound IF. The
demodulated AM is provided by the internal IF processor. For applications with external IF
processing the external demodulated AM signal can be connected to the SCART/Mono input of
the TV Sound Processor. By setting the EXTAM bit, the auto-mute function will switch to the
audio ADC input signal named EXTAM instead of switching to the first sound carrier. The ADC
source selector should be set to internal AM mono signal or to the external SCART/mono input,
where the AM sound signal should be connected.