Onset Gate
Overview
onset_gate is a specialization of noise_gate that adds a slope guard for gating out slow attacks. It has two independent thresholds:
onset_threshold-
An absolute level, as in
noise_gate. slope_threshold-
The required envelope rise over
attack_width.
The gate opens if the signal is either unambiguously loud or rising fast:
-
open if env > onset_threshold OR slope(env) > slope_threshold
Above onset_threshold the level alone opens the gate at once, so a loud note need not wait for (and clip) its attack. Below it, the slope guard governs: only a fast rise passes, so slow moving signals such as noise or bleed are rejected. Release is unchanged: the gate closes when the level drops below the release threshold.
The constructor parameters attack_width and sps specify the slope’s delta time. For example, given an attack width of 500 µs and a slope threshold of -30 dB, the difference in amplitude over a period of 500 µs must exceed -30 dB to pass the slope guard.
Declaration
struct onset_gate : noise_gate
{
onset_gate(
decibel onset_threshold
, decibel slope_threshold
, decibel release_threshold
, duration attack_width
, float sps
);
using noise_gate::operator();
bool operator()(float env);
void slope_threshold(decibel t);
float slope_threshold() const;
};Expressions
As a subclass of noise_gate, onset_gate inherits all the publicly accessible member functions, member variables, and types of its base class.
In addition to valid expressions for noise_gate, onset_gate allows these expressions.
Notation
g-
Object of type
onset_gate. ot,rt-
Object of type
decibelrepresenting onset (level) and release thresholds, respectively. st-
Object of type
decibelrepresenting the slope threshold. aw-
Object of type
durationrepresenting attack width. sps-
Floating point value representing samples per second.