OPTIMOD-FM OPERATION
3-9
The 8400’s bass, midrange, and high frequency parametric equalizers have curves that
were modeled on the curves of Orban’s classic analog parametrics (like the 622B), using
a sophisticated, proprietary optimization program. The curves are matched to better than
0.15 dB. This means that their sound is very close to the sound of an Orban analog para-
metric. They also use very high quality filter algorithms to ensure low noise and distor-
tion.
The 8400 HF Enhancer is a program-controlled HF shelving equalizer that was originally
introduced on Orban’s 2200 OPTIMOD-FM. It intelligently and continuously analyzes
the ratio between broadband and HF energy in the input program material, and can equal-
ize excessively dull material without over-enhancing bright material. It interacts synergis-
tically with the five-band compressor to produce a sound that is bright and present with-
out being excessively shrill.
Multiband Compression: The basic sound of the five-band compressor is similar to the
8200’s five-band compressor. However, in response to user requests we have increased
the number of release time settings from four to seven, doubling the resolution of this
audibly important parameter.
The multiband compressor now uses a “look-ahead” topology, which means that the pro-
gram audio is delayed until the gain control signal has time to attack fully. This signifi-
cantly reduces compressor overshoot and eases the burden on the following peak limiting
stages.
Often, transient response sounds punchier if transients overshoot in the multiband com-
pressor and hit the clippers instead. Consequently, we have made look-ahead operation
defeatable in the multiband compressor. To optimize performance for all program mate-
rial, we also offer an automatic option that turns the look-ahead on for speech material (to
achieve lowest distortion) and off for music (to achieve best transient punch).
Like the 8200, we control high frequencies with distortion-canceled clipping. However,
the clipper in the 8400 operates at 256 kHz-sample rate and is full anti-aliased.
We are well aware of the controversy regarding the audible benefits of anti-
aliasing a digital clipper and we continue to believe that it provides no audi-
ble benefit with program material in a well-designed system at sufficient
sample rate. Nevertheless, we chose to put the issue to rest by adding anti-
aliasing to all primary 8400 clippers.
The 8200 determined the gain reduction in band 5 from the gain reduction in band 4;
these bands are only independent from the viewpoint of the downward expander and mul-
tiband clippers. In the 8400, we have added a high frequency limiter, which causes addi-
tional gain reduction in band 5 when band 5 multiband clipping alone would be insuffi-
cient to prevent HF distortion. The HF limiter uses a sophisticated analysis of the signal
conditions in the 8400’s “back end” clipping system to do this.
We also improved on the embedded bass clipper that protects bands 1 and 2 from tran-
sient overshoot. In the 8400, you can adjust this clipper for “hard,” “medium,” or “soft”
operation. Each step gives a further reduction in audible distortion by means of increas-
ingly sophisticated signal processing. Each step from “soft” to “hard” adds a touch more
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