Orban OPTIMOD-FM 5700i, Руководство по эксплуатации

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OPTIMOD-FM DIGITAL INSTALLATION
2-35
od for matching the loudness of the analog and HD1 channels in HD Radio
transmission.
If the BS.1770 Safety Limiter is active, the
DO 100%
control does not affect
loudness, only peak headroom. Refer to the explanation in step (12.A) on
page 2-35.
In a transmission system using a lossy codec, it is usually wise to leave 1 to
2 dB of headroom to accommodate codec overshoots.
If the transmission system uses linear PCM, we recommend setting the
DO
100% control to –0.2 dBFS. Because the peak limiter is a “true peak” lim-
iter whose sidechain is oversampled to 256 kHz, setting the DO 100%
control to –0.2 dBFS or lower will prevent overshoots following the
transmission system’s final D/A converter if the D/A converter is phase-
linear (i.e. introduces no group delay distortion). This setting will also
prevent overshoots caused by phase-linear sample rate conversion unless
the sample rate converter removes a significant amount of spectral en-
ergy, which is typically true when the output sample rate is 32 kHz. To
prevent overshoots in 32 kHz transmission systems, set the 5700i’s
HD
B
ANDWIDTH
control to 15 kHz.
12. Set up and activate the BS.1770 Safety Limiter (optional).
The BS.1770 Safety Limiter applies only to the digital radio processing. It prevents
the BS.1770-3 integrated loudness from exceeding a value set by the
L
OUD THR
control. If your country requires that the integrated loudness of your digital ra-
dio broadcast to be constrained according to the BS.1770-3 loudness measure-
ment algorithm, execute the steps below.
If your country does not require this,
leave the BS.1770 Safety Limiter off. It must be OFF if you are transmitting HD
Radio.
A) To use the BS.1770 Safety Limiter, assign the output source of one of the Digi-
tal Outputs to HD. See step (11.I) on page 2-34. We suggest using Digital Out-
put 1 to drive the digital radio transmitter.
To facilitate error-free loudness calibration through your transmission
system, activating the BS.1770 Safety Limiter changes the behavior of the
Digital Output 100%
P
EAK
L
EVEL
control. Normally, changing the setting
of this control changes both the loudness and peak level of the signal
appearing at the Digital Output driving your digital radio transmitter.
However, when the BS.1770 Safety Limiter is turned
ON , the Digital Out-
put becomes the "Loudness Reference Output" and the Digital Output
100% P
EAK
L
EVEL
control sets only the peak level, not the loudness . In this
case, the output loudness is always calibrated correctly with respect to
0 dBFS.
( Note: If both Digital Output 1 and Digital Output 2 are sourced from
“HD,” then Digital Output 2 becomes the “Loudness Reference Output”
instead of Digital Output 1.)
For example, setting the Digital Output 1 100% PEAK LEVEL control to
–3 dBFS always constrains the maximum peak level appearing at Digital
Output 1 to –3 dBFS, but changing the setting of the Digital Output 1
100% P
EAK
L
EVEL
control does not change loudness. This is because when
the BS.1770 Safety Limiter is turned ON, a second “hidden” gain control