OPTIMOD-PC
OPERATION
3-5
Look-ahead limiting
is limiting that prevents overshoots by examining a few milli-
seconds of the unprocessed sound before it is limited. This way the limiter can an-
ticipate peaks that are coming up.
In Dolby Digital transmission channels, appropriate setting of the
D
IALNORM
metadata parameter will allow enough headroom to keep peak
levels below the threshold of the 1101’s look-ahead peak limiters. The
best sounding limiting is no limiting at all.
Loudness control
prevents the subjective loudness from exceeding a preset thresh-
old.
Distortion in Processing
In a competently designed processor, distortion occurs only when the processor is
controlling peaks to prevent the audio from exceeding the peak modulation limits
of the transmission channel. The less peak control that occurs, the less likely that the
listener will hear distortion. However, to reduce the amount of peak control, you
must decrease the drive level to the peak limiter, which causes the average level
(and thus, the loudness) to decrease proportionally.
Loudness and Distortion
In processing, there is a direct trade-off between loudness and distortion. You can
improve one only at the expense of the other. Thanks to Orban’s psychoacoustically
optimized designs, this is less true of Orban processors than of any others. Neverthe-
less, all intelligent processor designers must acknowledge and work within the laws
of physics as they apply to this trade-off.
In AM and FM processing, we have long said that there is a direct trade-
off between loudness,
brightness
, and distortion, However, because DAB
and netcasting systems don’t use preemphasis, there is no problem get-
ting the audio to sound bright and the trade-off is only between loud-
ness and distortion.
Perhaps the most difficult part of adjusting a processor is determining the best
trade-off for a given situation. We feel that it is usually wiser to give up ultimate
loudness to achieve low distortion. A listener can compensate for loudness by simply
adjusting the volume control. However, a listener cannot make an excessively com-
pressed or peak-limited signal sound clean again.
If processing for high quality is done carefully, the sound will also be excellent on
small playback systems. Although such a signal might fall slightly short of ultimate
loudness, it will tend to compensate with an openness, depth, and punch (even on
small speakers) that cannot be obtained when the signal is excessively squashed.
If women form a significant portion of the station’s audience, bear in mind that
women are more sensitive to distortion and listening fatigue than men. In any for-
mat requiring long-term listening to achieve market share, great care should be tak-
en not to alienate women by excessive stridency, harshness, or distortion.
Summary of Contents for Optimod-PC 1101
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