Apple Logic Express 7 - Manual (Page 31)

Chapter 4 Dynamic 31
The three rotary knobs (at the top) influence the dynamic response of the noise gate. If
you want the gate to open extremely quickly, say for percussive signals such as drums,
set the Attack knob to the lowest value by turning it as far as it will go counter-
clockwise. If the signal fades in a bit more softly, as is the case with string pads and the
like, a noise gate that opens too quickly can wreak havoc with the signal, causing it to
sound unnatural.
For this type of sonic scenario, set the Attack knob so that the gate emulates the attack
of the original signal. Much the same holds true for the Release phase of signals. When
you’re working with signals that fade out gradually or have longer reverb tails, you
should turn the Release knob up, allowing the signal to fade naturally.
The Hold knob determines the minimum amount of time that the gate stays open. This
knob avoids the dreaded chattering effect caused by a rapidly opening and closing
noise gate. The Hysteresis slider provides another option for avoiding chatter, without
needing to define a minimum Hold time.
Let’s back up a bit for a brief explanation: Noise gates often begin chattering when the
level of a signal fluctuates slightly, but very rapidly, during the attack or release phase.
Instead of clearly exceeding or falling short of the Threshold value, the signal level
hovers around the Threshold. The Noise Gate then rapidly switches on and off to
compensate, producing the undesirable chattering effect. If you were able to tell the
Noise Gate to open at the determined Threshold level and remain open until the level
drops below another, lower, predefined Threshold level, you’d be able to avoid
chatter—as long as the sonic window formed by these two Threshold values is large
enough to contain the fluctuating level of the incoming signal.
This is exactly what the Hysteresis feature enables you to do—the value determined by
the Hysteresis slider is actually the difference between the Threshold values that open
and close the gate. This value is always negative. Generally,
−
6 dB is a good place to
start.
If you’re dealing with audio material featuring extremely sensitive transients, or attack
phases that are critical to the overall sound, you may find it beneficial to have the Noise
Gate open up a tad before the useful signal fades in. This is what the Lookahead slider
is designed for. The program analyzes the signal level ahead of time, and anticipates
the point at which it can open the gate before the signal actually reaches the Threshold
value. When you choose to use this feature, please make sure you set the Attack, Hold
or Hysteresis controls to appropriate values.