NEC DTE-29U1TH, Service Manual, Page: 21 / 71

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Service Manual CP-785F
DSP-Section (Audio Baseband Processing)
- flexible selection of audio sources to be processed
- performance of terrestrial de-emphasise systems (FM, NICAM)
- digitally performed FM-identification decoding and de-matrixing
- digital baseband processing: volume, bass, treble
- simple controlling of volume, bass, treble
Analogue Section
- two selectable analogue pairs of audio baseband input (= two SCART inputs) input level: <2 V
RMS, input impedance: >25 k‰
- one selectable analogue mono input (i.e. AM sound): Not used in this chassis
- two high-quality A/D converters, S/N-Ratio: >85 dB
- 20 Hz to 20 kHz bandwidth for SCART-to-SCART copy facilities
- loudspeaker: one pair of four-fold oversampled D/A converters
output level per channel: max. 1.4 VRMS output resistance: max. 5 k‰
S/N-ratio: >85 dB at maximum volume max. noise voltage in mute mode: < 10 V (BW: 20 Hz...
16 kHz)
- one pair of four-fold oversampled D/A converters supplying a pair of SCART-outputs.
output level per channel: max. 2 V RMS, output resistance: max. 0.5 k‰
S/N-Ratio: >85 dB (20 Hz... 16 kHz)
Application Fields of the MSP 341
x
In the following sections, a brief overview about the two main TV sound standards, NICAM 728
and German FM Stereo, demonstrates the complex requirements of a multistandard audio IC.
NICAM plus FM/AM-Mono
According to the British, Scandinavian, Spanish, and French TV-standards, high-quality stereo
sound is transmitted digitally. The systems allow two high-quality digital sound channels to be
added to the already existing FM/AM-channel. The sound coding follows the format of the so-
called Near Instantaneous Companding System (NICAM 728). Transmission is performed
using Differential Quadrature Phase Shift Keying (DQPSK. Table below offers an overview of
the modulation parameters.
In the case of NICAM/FM (AM) mode, there are three different audio channels available:
NICAM A, NICAM B, and FM/AM-mono. NICAM A and B may belong either to a stereo or to a
dual language transmission. Information about operation mode and about the quality of the
NICAM signal can be read by the controlling software via the control bus. In the case of low
quality (high bit error rate), the controlling software may decide to switch to the analogue
FM/AM-mono sound. Alternatively, an automatic NICAM-FM/AM switching may be applied.
German 2-Carrier System (DUAL FM System)
Since September 1981, stereo and dual sound programs have been transmitted in Germany
using the 2-carrier system. Sound transmission consists of the already existing first sound
carrier and a second sound carrier additionally containing an identification signal. More details
of this standard are given in Tables below. For D/K very similar system is used.