Orban OPTIMOD-FM 8700, Руководство по эксплуатации

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OPTIMOD-FM DIGITAL INTRODUCTION
1-27
Using the monitor output is appropriate for both HD Radio and non-HD Radio oper-
ations, while using a non-MX preset on-air is only useful in non-HD Radio operations
where no diversity delay has been applied to the analog FM transmission.
Because of their higher performance, we recommend using MX presets in HD Radio
operations. In this context, the preset delay becomes part of the HD Radio diversity
delay and the 8700i automatically compensates for the preset delay to ensure that
the diversity delay always agrees with the value you specified when setting the
8700i up.
With non-MX presets, the normal delay through the 8700i (from input to FM out-
puts) is about 18 ms when
H
ARD
or M
EDIUM
bass clipping is selected, as it is in all non-
MX factory presets other than those with “LL” (“low latency”) or “UL” (“ultra-low
latency”) in their names. An 18 ms delay is workable for most talent (although it
may require some acclimatization) because 18 ms is below the psychoacoustic “echo
fusion threshold,” which means that talent will not hear discrete slap echoes in their
headphones. This means that they can monitor comfortably off-air without being
distracted or confused. Moreover, off-air cueing of remote talent is routine.
Some talent moving from an analog processing chain will require a learning period
to become accustomed to the voice coloration caused by “bone-conduction” comb
filtering. This is caused by the delayed headphone sound’s mixing with the live voice
sound, which introduces notches in the spectrum that the talent hears when he or
she talks. All digital processors induce this coloration to a greater or lesser extent.
Fortunately, it does not cause confusion or hesitation in the talent’s performance
unless the delay is above the psychoacoustic “echo fusion” (Haas) threshold of ap-
proximately 20-25 ms, where the talent starts to hear slap echo in addition to fre-
quency response colorations.
Two lower-delay options are available. “Low latency” reduces input-to-FM-output
delay to 13 ms and “ultra-low latency” reduces delay to about 3.7 ms. The trade-off
for this reduction is approximately 1 dB decrease in loudness compared to the
8700i’s full look-ahead processing for low latency and about 2.5 dB loudness de-
crease for ultra-low latency.

When using a non-MX preset, you can invoke the low latency mode by setting
the B
ASS
C
LIP
M
ODE
control (in the C
LIPPERS
page of A
DVANCED
C
ONTROL
) to
LLH
ARD
.
You can also recall a preset with “LL” as part of its name.
LLH
ARD
differs in two ways from the normal H
ARD
mode of the bass clip-
per:
LLH
ARD
automatically defeats the compressor look-ahead. (This action is functionally
equivalent to setting the
L
OOK
-
AHEAD
control to
O
UT
, except that it reduces in-
put/output delay by 5 ms).
LLH
ARD
prevents the bass clipper from switching to Medium mode whenever speech is
detected. By constraining the system in these ways, it ensures that the delay is always
13 ms.
Switching the B
ASS
C
LIP
M
ODE
to LLH
ARD
(from any other mode) removes
five milliseconds of delay from the signal path. If it occurs during pro-
gram material, switching can cause audible clicks, pops, or thumps (due
to waveform discontinuity). If you have some presets with
LLH
ARD
bass