Noise Gate

Overview

A noise gate is an audio tool that reduces unwanted noise by muting or attenuating signals below specified thresholds. It is typically used to eliminate background noise or hum. The noise_gate class implements a Q-flavored noise gate processor following Q’s Dynamic processor design. Unlike typical noise gates, noise_gate has no parameters for attack and release and does not process audio waveform samples directly. Instead, it operates on the envelope of the audio signal. The objective is separation of concerns and the flexibility to use various envelope followers.

There are two thresholds. On onsets, the noise_gate opens up if the signal envelope goes above the specified onset threshold. On note release, the noise_gate turns off if the signal goes below a specified release threshold.

Include

#include <q/fx/noise_gate.hpp>

Declaration

struct noise_gate
{
               noise_gate(decibel onset_threshold, decibel release_threshold);
               noise_gate(decibel release_threshold);

   bool        operator()(float env);
   bool        operator()() const;

   void        onset_threshold(decibel onset_threshold);
   void        onset_threshold(float onset_threshold);
   void        release_threshold(decibel release_threshold);
   void        release_threshold(float release_threshold);

   float       onset_threshold() const;
   float       release_threshold() const;
};

Expressions

Notation

g, a, b

Objects of type noise_gate.

env

Floating point value for the current envelope value.

ot, rt

Object of type decibel representing onset and release thresholds, respectively.

Constructors and Assignment

Expression Semantics

noise_gate(rt)

Construct a noise_gate with specified release threshold, rt.

noise_gate(ot, rt)

Construct a noise_gate with specified onset threshold, ot and release threshold, rt.

noise_gate(b)

Copy construct a noise_gate from b.

a = b

Assign b to a.
C++ brace initialization may also be used.

Function Call

Expression Semantics Return Type

g()

Get the current state.

bool

g(env)

Process the input envelope env, compute and return the state.

bool

The noise_gate state is a boolean flag that is true if the noise_gate is open or false if the noise_gate is closed.

Mutators

Expression Semantics Return Type

g.onset_threshold(ot)

Set the noise_gate onset threshold.

void

g.release_threshold(rt)

Set the noise_gate release threshold.

void

Accessors

Expression Semantics Return Type

g.onset_threshold()

Get the noise_gate onset threshold.

decibel

g.release_threshold()

Get the noise_gate release threshold.

decibel