Orban OPTIMOD-AM 9300 Operating Manual Download

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OPTIMOD-AM DIGITAL

OPERATION

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crease in the loudness of soft sounds. It cannot make loud sounds seem louder.
Compression reduces dynamic range relatively slowly in a manner similar to riding
the gain: Limiting and clipping, on the other hand, reduce the short-term peak-to-
average ratio of the audio.

Limiting

increases audio density. Increasing density can make loud sounds seem

louder, but can also result in an unattractive busier, flatter, or denser sound. It is im-
portant to be aware of the many negative subjective side effects of excessive density
when setting controls that affect the density of the processed sound.

Clipping

sharp peaks does not produce any audible side effects when done moder-

ately. Excessive clipping will be perceived as audible distortion.

Loudness and density

The amount of

gain reduction

determines how much the loudness of soft passages

will be increased (and, therefore, how consistent overall loudness will be). The
automatic gain control (AGC) and the multiband limiter both provide gain reduction,
although their effects are quite different.

In a competently-designed processor, audibly objectionable distortion occurs only
when the processor is clipping peaks to prevent the audio from exceeding the peak
modulation limits of the transmission channel. The less clipping that occurs, the less
likely that the listener will hear distortion. However, to reduce clipping, you must
decrease the drive level to the clipper, which causes the average level (and thus, the
loudness) to decrease proportionally.

Receiver high frequency rolloff

introduces further complications. A typical

receiver’s severe HF rolloff reduces the headroom available at high frequencies and
makes it difficult to achieve a bright sound. This is because bright sound requires
considerable high frequency power to appear at the output of the receiver, thus
requiring a very large amount of high frequency power to be transmitted so that a
sufficient amount will survive the receiver’s rolloff.

To increase brightness and intelligibility at the receiver, the 9300’s NRSC preemphasis
boosts the treble at 6dB/octave starting at 2.1 kHz.

URVE

settings from

produce more severe preemphasis than NRSC, boosting at 18dB/octave with 2 kHz up
about 3 dB. Without very artful processing, this preemphasis will radically increase the
level of the peaks and force you to decrease the average level proportionally. Orban's
high frequency limiting and distortion-cancelling clipping systems greatly ease this
trade-off, but cannot eliminate it. Therefore, you can only increase brightness by
reducing average modulation (loudness)



unless you accept the increased distortion

caused by driving the final clippers harder.

In processing, there is a

direct trade-off

between loudness, brightness, and distortion.

You can improve one only at the expense of one or both of the other two. Thanks to
Orban's psychoacoustically-optimized designs, this is less true of Orban processors than
of any others. Nevertheless, all intelligent processor designers must acknowledge and
work within the laws of physics and psychoacoustics as they apply to these trade-offs.