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Application Notes
DN530
30 Operator Manual
Chatter
Chatter can normally be eliminated by increasing the hold time, but this may allow the
gate to stay open longer than is desirable. Adding hysteresis to the threshold control
helps enormously and allows hold times to be reduced without signal chatter. The
DN530 has 4dB of i-TS hysteresis built in, which is enough to eliminate chatter on all
normal instrument types.
Clicking
The key to silent gating is the shape of the gain transition curve that is used to fade up
the signal level when the gate opens (attack) and fade it back down when the gate
closes (release). Many gates use linear transitions that, when applied to low frequency
signals, generate high order harmonics that sound like extra clicks (in time with the
music source). The ideal shape is logarithmic (like an audio fader) so that the initial
transition from shut to mostly open is fast and the final adjustment to fully open is
progressively slower and slower. The exact reverse applies to the gate closing, which
needs to start slowly and then speed up to close the gate fully. With these shapes no
harmonics are produced during an attack, only a fundamental frequency (quarter cycle)
that can be controlled by the attack time.
The tonality of the gate opening transition can be adjusted using the attack control to
be slightly higher in pitch than the LF content of the sound it is processing to accentuate
the start of each note. Or it can be set to be the same, in which case the transition will
not be heard at all. If the attack is made slower still, the start of each note will be
softened, which may be useful as an effect. Release times are, typically, much slower
so audio frequency clicks are rarely heard, but the logarithmic shape is still the best
because it makes the fade out much less noticeable. The attack and release
characteristics in the DN530 are logarithmic and fully adjustable to ensure effective
gating that can be tonally transparent or used to add (or reduce) punch and definition.
False triggering
Often, mics pick up as much spill from other instruments as the sound they pick up
from the intended source. This causes the gate to open at times when it should be
shut. Traditionally, hi pass and low pass filters have been employed on gate sidechains
in an attempt to limit the frequency spectrum that will trigger the gate to open. This
type of filter seldom works well in this application because they are not easily
manufactured with steep enough transitions from pass band to stop band. Also, set up
is difficult because you typically need to adjust them together to form a band pass filter.
A much better solution is to use a band pass filter in the first place, which is set up with
a high enough Q to make it very selective. Most instruments (especially drums) have a
resonant frequency, and false gate triggering can be massively improved by tuning a
single band pass filter, as described, to find this resonance. False triggering is
eliminated because the frequency spectrum and resonance from the spill does not
produce enough energy at the tuned frequency to open the gate; only the intended
source will.
The DN530 sidechain filters are high Q band pass types as described above. Set up is
made by a simple single control (per channel) and this is made even easier because you
can listen to the filter output (without interrupting the source material) on a separate
solo bus.