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3-8
Operation
MX presets use an advanced peak limiting structure that uses additional "intelligence," novel processing structures,
and other strategies to produce lower perceived distortion with "difficult" program material. This peak limiter also
offers substantially improved transient impact and high frequency power handling capability compared to the
"intelligent" clipping in the non–MX presets.
For more information on the MX clipper technology, see Appendix D.
Speech Mode: You can set many of the processing parameters separately for speech signals, as detected by the
5750's speech/music detector. This allows you to tune the processing separately for speech and music.
A SPEECH DETECT control allows you to force the 5750 into Music mode, overriding the Speech/Music detector. This
control is contained in the processing preset. In fiveband presets, it is found in the Speech Mode screen (Advanced
Modify 6) and in two-band presets, it is found in the Two Band screen (Advanced Modify 4).
Note that the speech detector will detect most speech mixed with music as "music" unless the music is at a very low
level compared to the speech. Speech must also be centered in the stereo sound field to be detected as "speech."
DSP-derived Stereo Encoder: The 5750's stereo encoder is derived from algorithms first developed for the high-
performance Orban 8218 stand-alone encoder. The 5750's stereo encoder operates at 512 kHz-sample rate to ease
the performance requirements of the D/A converter's reconstruction filter, making it possible to achieve excellent
stereo separation that is stable over time and temperature. DSP-based group delay and magnitude equalizers for
the entire composite analog path further improve separation.
The 5750 has two independent composite outputs, whose levels are both software settable. For convenience, two
SCA inputs sum into the 5750's analog composite output amplifier. The second SCA input can be configured to
provide a 19kHz reference output for subcarrier generators that need it. See page 6-2.
The 5750 does not digitize SCAs.
SSB Stereo Encoder Operation: The 5750 allows its stereo encoder's stereo subchannel modulator to operate in an
experimental compatible single sideband/vestigial sideband mode. SSB/VSB operation suppresses the upper
sideband of the stereo subcarrier above 38,150 Hz, which reduces the occupied bandwidth of the FM-modulated RF
signal. In SSB mode, the subchannel modulator acts as a pure SSB generator for L–R material in the frequency range
of 150 Hz to 17 kHz and as a vestigial sideband generator below 150 Hz.
In normal operation, the stereo subchannel modulator produces a double sideband suppressed carrier signal with
pairs of mirror image sidebands around 38 kHz. With respect to an L+R gain of 1, the gain of each sideband is 0.5. In
SSB/VSB mode, the upper sideband is suppressed by at least 80 dB above a modulating frequency of 150 Hz and the
gain of the lower sideband is 1.0. Below 150 Hz, the sum of the gains of the sideband pairs is 1.0. (The conventional
DSB case is a limiting case of this, where the gains of the upper and lower sidebands are both 0.5 and sum to 1.) This
"summation to 1" criterion is necessary to achieve compatibility with normal FM radios that use synchronous
demodulation of the stereo subchannel. Almost every radio manufactured since 1973 works like this. We have
verified that the 5750's SSB generator produces more than 60 dB of separation from 50 to 15,000 Hz when measured
on a Belar FMSA-1 "Wizard" modulation monitor, which was originally designed for convention double sideband
operation.
However, there are consumer-based radios and car audio systems which detect the missing upper sideband and
misinterpret this as a signal issue and blend towards mono. Other systems will develop distortion because of the
increased amplitude in the lower sideband which is needed to allow the system to work at all. This distortion
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