Daewoo DTC-20T2, DTZ-29U7/U3, DTZ-2881/28W8, DTY-21U7/21B4, DTC-21Y1/21Y2, DTZ-2481 Nicam AUTO-MUTE

CP-520/520A/520F Service Manual

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.

DTV R&D Europe 48