Loudness And Distortion; Processing For Low Bit Rate Codecs - Orban OPTIMOD 6300 Operating Manual

OPTIMOD 6300 DIGITAL

Loudness and Distortion

In processing, there is a direct trade-off between loudness 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 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 radios. 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 speak-
ers) 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 are. In any
format requiring long-term listening to achieve market share, great care should be
taken not to alienate women by excessive stridency, harshness, or distortion.

Processing for Low Bit Rate Codecs

6300's 5-band processing includes PreCode™ technology to minimize codec artifacts.
To exploit PreCode technology fully ( minimizing "phasey" and "underwater" arti-
facts in low bit rate codecs), do not set up OPTIMOD 6300 for very bright sound
(with large amounts of high frequency energy) because this is likely to exacerbate
artifacts. Some appropriate presets include J
the C presets. Avoid presets like C
LASSICAL
sounding presets and are more appropriate for uncompressed channels or com-
pressed channels with relatively high bit rates (64 kbps or higher for the aacPlus V2
codec used in Opticodec-PC, for example).
The 6300 has several controls whose settings determine brightness. To minimize
brightness when using the 5-band structure:

Use little or no high frequency boost in the equalization section.

Set Band 4>5 coupling to 100%.

Set the band 5 compression threshold to match the codec. Adjust the threshold
until you find a good compromise between presence and high frequency codec
artifacts. We find the range from –6.0 to +6.0 dB to be useful.

Use a moderate Band 5 attack time. 25 ms works well.
, S J , G
AZZ MOOTH AZZ OLD
and E
; these are very bright-
RISP DGE
OPERATION
, R S
OCK OFT , and
3-5