Klark Teknik DN530 ユーザーズマニュアル

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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.

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.

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.