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OPERATION ORBAN Model 8400
The 8400 gives you control over the multiplex power threshold (in the Input/Output
Utilities screen). This allows you to compensate for overshoots in the signal path up-
stream from the 8400, preventing excessive reduction of the multiplex power.
Power control is applied to all outputs, not just the composite output.
Patents are pending on this system.
Two-Band Purist Processing
In addition to five-band processing, suitable for pop music and talk formats, the 8400
offers a very high-quality two-band algorithm. This is phase-linear, and features the same
AGC as the five-band processor, followed by a two-band processor with look-ahead lim-
iting. Sophisticated multiband high frequency limiting and distortion-cancelled clipping
complete the chain.
We believe that this is the ideal processing for classical music because it does not dy-
namically re-equalize high frequencies; the subtle HF limiter only acts to reduce high
frequency energy when it would otherwise cause overload because of the FM pre-
emphasis curve. We have heard four-band, allegedly “purist” processing that caused dy-
namic HF lift. This created a strident, unnatural sound in strings and brass. In contrast,
the 8400’s two-band phase-linear structure keeps the musical spectrum coherent and
natural.
The look-ahead limiter prevents speech from being audibly clipped, and prevents similar
audible problems on instruments with rapidly declining overtone structures like grand
piano, classical guitar, and harp.
Digital Radio Processing
The HD (“High Definition Digital Radio”) output is the de-emphasized output of the
8400’s two-band or five-band compressor/limiter (depending on the preset in use), as
processed through an advanced-design look-ahead limiter. This limiter minimizes IM
distortion in addition to harmonic distortion. The resulting peak limiting is almost always
undetectable when used with reasonable amounts of gain reduction (i.e., frequently reoc-
curring gain reduction of 3-4 dB).
Certain unusual program material may cause infrequent instances of gain re-
duction as high as 12 dB with the above settings. This occurs on isolated
transients and is no cause for alarm unless it is frequent.
Except for the fact that its input has been de-emphasized, the HD look-ahead limiter re-
ceives the same processing as the FM peak limiting section. Earlier processing has often
been adjusted to help compensate for the inevitable high frequency loss caused by pre-
emphasis limiting in the FM peak limiter. Therefore, the HD output can be excessively
bright without further adjustment.
The 8400 offers this adjustment in the form of a parametric high frequency shelving fil-
ter, which can supply a high frequency rolloff to tame excessive brightness in the HD
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