Using Surround Sound Processors; The Ssp Must Not Come After The Preamp; The Ssp Must Not Come Before The Preamp - Mark Levinson 380 Owner's Manual

the SSP must not
come after the preamp
the SSP must not
come before the preamp
Using Surround Sound
Processors
The Nº380 Preamplifier incorporates a special surround sound proces-
sor mode which makes it uniquely capable of integrating the highest
performance audio with surround sound—that is, dual-purpose music
and movie systems. In order to better understand the value of this de-
sign, it is essential to understand a bit about the nature of a surround
sound processor.
One obvious and fundamental difference between stereo listening and
multichannel listening is the number of channels that must be con-
trolled. When listening to two-channel stereo, one must have a two
channel volume control so both speakers increase or decrease in vol-
ume in concert with one another. Similarly, when listening to six- or
eight-channel surround sound recordings (whether movies or music),
one must have a corresponding six- or eight-channel volume control.
This simple fact has made combining a high quality two-channel
preamp with an outboard surround sound processor extremely diffi-
cult over the years. In fact, until the Mark Levinson Nº38 was intro-
duced in 1993, it was virtually impossible to combine the two and have
the system work reliably well.
Dolby Pro Logic decoders incorporate a form of Dolby noise reduction
similar to the Dolby B one finds in cassette decks. This form of noise
reduction is level-sensitive. That is, Dolby noise reduction intentionally
treats strong signals differently than weak signals. In order to operate
correctly, the signal strength of the source must be "calibrated" to the
expectations of the Dolby noise reduction circuitry. (It is for this rea-
son that one finds "Record Calibration" features on better-quality cas-
sette decks.) It is therefore inappropriate to feed a surround sound de-
coder with the variable output of a preamplifier. Were you to do so, every
change of the volume control on the preamplifier would cause the
Dolby circuitry to mistrack. In extreme cases, severe distortion can re-
sult as the Dolby circuitry overloads.
The next logical alternative might be to use the Pro-Logic decoder
ahead of the preamplifier, sending its Left and Right outputs through
the preamplifier as a selectable Source. Sending the Right and Left Out-
puts from a surround sound decoder to a pair of inputs on a conventional
preamplifier is also inappropriate, since any change of the preamp's vol-
ume control would then throw the carefully calibrated output levels of
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