3-14
OPERATION
ORBAN MODEL 8600Si
with look-ahead limiting. Sophisticated multiband high frequency limiting and dis-
tortion-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
dynamic HF lift. This created a strident, unnatural sound in strings and brass. In con-
trast, the 8600Si’s two-band phase-linear structure keeps the musical spectrum co-
herent 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
Only the phase rotator, highpass filter, and AGC are common between the FM ana-
log and digital radio processing chains. The processing chain splits into two paths af-
ter the AGC. Each path contains a structurally identical but independently adjustable
equalizer and multiband compressor. Each preset has an
FM
Æ
HD
C
ONTROL
C
OUPLING
control that
determines if audio controls affecting the HD equalizer and HD multi-
band compressor/limiter will follow their counterparts in the FM analog processing
chain or if the HD and FM controls can be adjusted independently. (See
The peak limiter in the digital radio processing chain is a mastering-quality look-
ahead limiter. This limiter minimizes IM distortion in addition to minimizing har-
monic distortion. The resulting peak limiting is almost always undetectable when
used with reasonable amounts of gain reduction (i.e., frequently recurring gain re-
duction of 3-4 dB).
Certain unusual program material may cause infrequent instances of gain reduction
as high as 12 dB with the above settings. This occurs on isolated transients and is no
cause for concern unless it is frequent.
Except for the fact that its input has been de-emphasized, the HD look-ahead limiter
receives the same processing as the FM peak limiting section if the
FM
Æ
HD
C
ONTROL
C
OUPLING
is set to
FM
Æ
HD.
Earlier processing has often been adjusted to help com-
pensate 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.
In
FM
Æ
HD
mode, you can use the 8600Si’s parametric high frequency shelving filter
to supply a high frequency rolloff that tames excessive brightness in the HD output.
Simultaneously, this HF rolloff may reduce high frequency artifacts in the relatively
low bite-rate codec used in the iBiquity HD Radio system.
Summary of Contents for OPTIMOD-FM 8600Si
Page 1: ...Operating Manual OPTIMOD FM 8600Si Digital Audio Processor Version 2 5 Software...
Page 7: ...Operating Manual OPTIMOD FM 8600Si Digital Audio Processor Version 2 5 Software...
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