Orban OPTIMOD-FM 8600Si, Руководство по эксплуатации

Страница: 179 / 356

OPTIMOD-FM DIGITAL OPERATION
3-13
harmonics as if they were L–R information and the decoded harmonics appear at
new frequencies not harmonically related to the original frequency that generated
them.
While the processing never clips the pilot tone, the extra spectrum generated by the
processing can fall into the 19 kHz region, compromising the ability of receivers to
recover the pilot tone cleanly. Therefore, the 8600Si’s composite processor has a 19
kHz notch filter to protect the pilot tone. This filter does not compromise stereo sep-
aration in any way.
We still prefer to use the 8600Si’s main clipping system to do the vast majority of the
work because of its sophisticated distortion-controlling mechanisms. This means that
the 8600Si does
not rely on composite processing to get loud. Consequently, broad-
casters using its left/right-domain AES3 digital output can enjoy the loudness bene-
fits of the 8600Si’s processing—the 8600Si gets competitively loud without compos-
ite clipping. However, it is also possible to reduce the drive level to the 8600Si’s
left/right domain overshoot compensators and to increase the composite limiter
drive by a corresponding amount. This arrangement uses the overall composite lim-
iter (with or without the composite clipper’s being active) to provide overshoot
compensation. It has a different sound than using the left/right domain overshoot
compensators—the sound is brighter but has more aliasing distortion (as discussed
above). If the composite clipper is active, stereo separation will decrease.
ITU-R 412 Compliance for Analog FM Broadcasts
ITU-R 412 requires the “average multiplex power” to be limited to a standard value.
The 8600Si contains a defeatable feedback multiplex power limiter that constantly
monitors the multiplex power according to ITU-R 412 standards. The power control-
ler automatically reduces the average modulation to ensure compliance. It allows
you to set the “texture” of the processing freely, using any preset. If a given process-
ing setting would otherwise exceed the multiplex power limit, the power controller
automatically reduces the drive to the peak limiting system. This action retains the
compression texture but reduces distortion while controlling multiplex power.
The 8600Si gives you control over the Multiplex Power Threshold (in the In-
put/output Utilities screen). This allows you to compensate for overshoots in the sig-
nal path upstream from the 8600Si, preventing excessive reduction of the multiplex
power.
Power control is applied to all outputs, not just the composite output.
See ITU-R Multiplex Power Controller on page 3-80.
Two-Band Purist Processing
In addition to five-band processing, suitable for pop music and talk formats, the
8600Si offers a very high-quality two-band algorithm. This is phase-linear and fea-
tures the same AGC as the five-band processor, followed by a two-band processor