About The 8300' Shd / Digital Radio Processing - Orban Optimod-FM 8300 Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
If your setting of a given D R control would otherwise create a release
ELTA ELEASE
slower than "slow" or faster than "fast" (the two end-stops of the M
ULTIBAND
R control), the band in question will instead set its release time at the appro-
ELEASE
priate end-stop.
B1/B2 Xover (Band 1 to Band 2 Crossover Frequency) sets the crossover frequency
between bands 1 and 2 to either 100 Hz or 200 Hz. It significantly affects the bass
texture, and the best way to understand the differences between the two crossover
frequencies is to listen.
About the 8300's HD / Digital Radio Processing
The 8300 HD ("High Definition Digital Radio") output is designed to feed streaming,
netcasting, and digital radio channels, either Eureka 147 or the iBiquity® High Defi-
nition Radio system (formerly known as "IBOC"—"In-Band On-Channel") approved
for use in the United States.
The signal at the HD AES3 output is processed by a look-ahead limiter that operates
in parallel with the analog FM peak limiting chain. The look-ahead limiter (which
receives the 8300's "monitor" signal) is optimized to make the most of the limited
bit-rate codec used in the High Definition Radio system's digital channel. By eschew-
ing any clipping, the digital-channel output prevents the codec from wasting pre-
cious bits encoding clipping distortion products, instead allowing the codec to use its
entire bit budget to encode the desired program material.
The look-ahead limiter is fed by a parametric high frequency shelving equalizer. You
can use it to equalize texture disparities between the analog and digital channels
and to reduce codec artifacts at high frequencies.
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, it will control peak lev-
els with an uncertainty of approximately 2 dB. However, you may want to allow
headroom to compensate for data reduction-induced peak overshoots at the re-
ceiver, which might otherwise cause clipping. In our experience, 2 dB is typically
adequate for this task.
The ultra-low latency structure does not support HD processing. If an ultra-low-
latency preset ("UL") is put on-air, the HD output will emit the de-emphasized, FM-
processed output. Because of the diversity delay that is a part of the HD Radio sys-
tem, ultra-low-latency processing has no advantages in this context and we would
expect stations transmitting HD FM to always use a normal latency 5-band or a 2-
band preset.