Using Surround Sound
Processors
The Nº383 Reference Preamplifier incorporates a special surround sound processor mode which makes it uniquely capable of integrating the highest performance audio with surround sound—that is, a dual- purpose music and movie system. In order to better understand the value of this design, 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 volume 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.
Over the years, this simple fact has made combining a high quality two-channel preamp with an outboard surround sound processor extremely difficult. In fact, until the Mark Levinson Nº38 was introduced in 1993, it was virtually impossible to combine the two and have the system work reliably well.
the SSP must not Dolby Pro Logic decoders incorporate a form of Dolby noise reduction come after the preamp 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 reason that one finds “Record Calibration” features on better-quality cassette decks.) It is therefore inappropriate to feed a surround sound decoder 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 result as the Dolby circuitry overloads.
the SSP must not The next logical alternative might be to use the surround sound pro- come before the preamp cessor ahead of the preamplifier, sending its Left and Right outputs
through the preamplifier as a selectable Source. Sending the Right and Left Outputs from a surround sound decoder to a pair of inputs on a conventional preamplifier is also inappropriate, since any change of the preamp’s volume control would then throw the carefully calibrated output levels of the decoder out of adjustment, changing the volume of