Orban OPTIMOD-FM 8600S, Руководство по эксплуатации

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OPERATION ORBAN MODEL 8600S
instead allowing the codec to use its entire bit budget to encode the desired pro-
gram material.
The 8600SHD’s look-ahead limiter implements “true peak” control by oversampling
the HD peak limiter’s sidechain at 256 kHz. This allows the 8600S to prevent clipping
in a playback device’s analog signal path by predicting and controlling the analog
peak level following the playback device’s reconstruction filter to an accuracy of
better than 0.4 dB. For typical program material, accuracy is 0.2 dB
Thanks to true peak control, sample rate conversion, unless it removes high fre-
quency program energy or introduces group delay distortion, cannot cause sample
peaks to increase more than 0.4 dB. For example, sample rate con-version from 48
kHz to 44.1 kHz is highly unlikely to cause sample peak clipping of the 44.1 kHz au-
dio data.
The look-ahead limiter includes a parametric high frequency shelving equalizer that
can be placed either before or after gain reduction. You can use it to equalize tex-
ture disparities between the FM and HD channels and to reduce codec artifacts at
high frequencies. You can also use the
HD B
AND
M
IX controls and/or HD compression
threshold to achieve this.
The HD output is designed to feed digital channels without pre-emphasis, which in-
clude almost all such channels. The only high-quality digital channels using pre-
emphasis of which we are aware are NICAM channels (which use J.17 pre-emphasis)
and some older CDs (which use EIAJ—50µs/15µs shelving pre-emphasis). If you use
the HD output to feed a digital channel with pre-emphasis, you must allow extra
headroom to compensate for the unpredictable peak level changes that the pre-
emphasis induces.
If the HD output is driving a channel without pre-emphasis but using a lossy codec,
you may want to allow headroom to compensate for data reduction-induced peak
overshoots at the receiver, which might otherwise cause clipping. In our experience,
2 dB is typically adequate.
Delay Difference between HD and FM Outputs
To make the receiver analog/digital crossfade free from comb filtering, the time de-
lays in the HD Radio’s FM and HD channels must have a fixed and predictable offset,
correctly implementing the HD Radio receiver’s “time diversity” processing.
This “diversity delay” is part of the HD Radio system specification. The availability of
the delay in the 8600S eliminates the need to use the delay line built into the HD
Radio exciter. In turn, this allows you to connect any output receiving the analog-
FM-processed signal to the input of the analog FM exciter. This includes the 8600S
composite output, allowing you to use the 8600S’s stereo encoder and composite
limiter during HD Radio broadcasts.
The MX presets have an input-to-output delay of approximately 265 ms, while the
8500-style presets typically have delays below 20 ms. To ensure a smooth transition