3-6
OPERATION ORBAN
MODEL
9400
gle-ended dynamic noise reduction system, which can be activated or defeated
as desired.
The HD AM chain also uses a five-band compressor. However, it has different
crossover frequencies and no embedded clipper.
The fifth stage in the analog processing chain is a clipper with an “intelligent”
distortion controller that reduces the drive to the clipper if this is necessary to
prevent objectionable clipping distortion.
The sixth stage in the analog AM chain is a safety clipper and overshoot com-
pensator. These elements precisely control peak modulation without adding
out-of-band frequencies, as a simple clipper would.
The seventh stage in the analog processing chain is an overshoot compensator
that drives separate transmitter equalizers (TX EQ) for each output. The TX EQ
allows you to pre-distort OPTIMOD-AM's output waveform to compensate for
low-frequency tilt, high-frequency ringing, and high-frequency group delay dis-
tortion in the transmitter and antenna system.
The digital processing chain is simpler. Its fifth (and final) stage is an advanced,
low-IM-distortion look-ahead limiter.
AM Processing: The Art of Compromise
Noise, interference, and narrow bandwidth inherently restrict AM audio quality. Be-
cause of this, purist goals (“the output should sound just like the input”) are not
relevant because receiver design makes them impossible to achieve. Instead, the
goal of processing should be to deliver the highest subjective quality through this
limited transmission channel to the listener's ear. This always requires substantial
compression and limiting to ensure that the received signal will override the noise
and interference over the maximum possible geographical area. It also requires high
frequency boost to compensate for the high-frequency rolloff in all AM radios.
The 9400’s
GEN
MED
factory preset at a
L
ESS
-M
ORE
setting of
7
meets these re-
quirements and provides a sound that is subjectively undistorted even on
high-quality automobile radios. This is the default preset upon initial power-up of
the 9400. You may continue using this preset or choose another preset as you deem
appropriate.
You must also choose a setting of the system bandwidth control (in System Setup).
Depending on whether the bandwidth is 4.5 - 7 kHz or 7.5 - 9.5 kHz (NRSC), the
characteristics of any factory preset will change to complement the chosen band-
width. The wideband and narrowband variations of the factory presets were gener-
ated using a stock formula; they were fine-tuned via exhaustive listening tests with
a wide variety of program material.
To see what the factory programmers have done, use 9400 PC Remote software to
compare the Advanced Control settings while changing the system bandwidth con-
trol. You can also use a text editor with a “file compare” function to compare iden-
Summary of Contents for Optimod-AM 9400
Page 1: ...Operating Manual OPTIMOD AM 9400 Digital Audio Processor Version 1 2 Software...
Page 7: ...Operating Manual OPTIMOD AM 9400 Digital Audio Processor Version 1 2 Software...
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Page 261: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 29...
Page 267: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 35 CPU Module...
Page 273: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 41 RS232 BOARD PARTS LOCATOR...
Page 275: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 43 8300 POWER SUPPLY PARTS LOCATOR...
Page 284: ...6 52 TECHNICAL DATA ORBAN MODEL 9400 DSP BOARD PARTS LOCATOR DRAWING 32170 000 14...
Page 292: ...6 60 TECHNICAL DATA ORBAN MODEL 9400 DISPLAY BOARD PARTS LOCATOR...
Page 293: ...OPTIMOD AM DIGITAL TECHNICAL DATA 6 61 DISPLAY BOARD...