V O R S I S H D P 3 G U I
page 2 – 33
HD P3 / Aug 2006
Multiband Limiter - “Airchain”
No bones about it, and no pre-
tence: this processing section’s sole
reason for being is to make things
LOUD. As with the three-band
compressor, it was felt that ulti-
mately the user is better served by
having all the “handles” on the pro-
cessing available. There are a dif-
ferent set of controls for this Multi-
band Limiter, although the two truly
important ones operationally remain
similar to the “Production” style processor: “Drive” which adjusts overall
depth of limiting and gain-reduction, and “Output Level” which sets the
overall output from the multiband stage.
These two, assuming that initial operation is going to be from an
existing preset, are the only ones of concern, at least until confidence has
risen and the control screen no longer seems as intimidating as Concorde’s
flight deck. The specific controls for the three bands are ranged horizon-
tally across the GUI screen:
DRIVE — Yes, Virginia, there are four controls called “Drive” on the
GUI. The top one is the important one - it is the master drive for the whole
three-band section. The three below it are for the high-frequency, mid-
frequency, and low-frequency processing bands. These allow the relative
amounts of signal drive into each band to be varied; the range is +8dB to
-20dB, more than enough to (over) emphasize a band, or effectively
remove it. In practice these should rarely be more than a very few dB adrift
of the nominal 0dB.
ATTACK — The period of time an applied signal within the band must
instantaneously exceed the threshold in order to reduce the output signal
down to the threshold. 0.5mS is recommended for zero-overshoot limit-
ing. Free-form range is 0.2mS to 1Sec.
RELEASE — The time the band’s limiter’s gain takes to recover from
a typical degree of limiting once the signal no longer exceeds the threshold.
50mS is recommended for transparent zero-overshoot limiting. Overall
range is 33mS to 1Sec.
BACKOFF (CLIP BACKOFF) — The discussion on “Backoff” as
applied to the Output Limiter (on page 3-17) is hereby set as homework.
Review is strongly recommended since it is directly appropriate to the
limiters used in this section. For the recommended zero-overshoot / zero-
attack settings, “Backoff” should be set at 0dB.
In short, “Backoff” is the amount that the limiter’s threshold is reduced
below it’s downstream zero-attack-time “clipper” threshold. It becomes
relevant if the attack time is made greater than approximately 2mS. Slower
attack times allow greater peaks to ‘escape’ through a limiter; reducing its
threshold with “Backoff” can prevent too much signal being clipped,
which could potentially sound unpleasant. The range is 0dB to -10dB.
