Noise Gate

Dynamic range gate

• 

Libraries:
Audio Toolbox / Dynamic Range Control

Description

The Noise Gate block performs dynamic range gating independently across each input channel. Dynamic range gating suppresses signals below a given threshold. The block uses specified attack, release, and hold times to achieve a smooth applied gain curve.

Examples

Gate Background Noise

Apply dynamic range gating to remove low-level noise from an audio file.

• Open Model

Ports

Input

x — Input signal

matrix | 1-D vector

• Matrix input –– Each column of the input is treated as an independent channel.

• 1-D vector input –– The input is treated as a single channel.

This port is unnamed unless you specify additional input ports.

Data Types: single | double

T — Threshold (dB)

scalar

Dependencies

To enable this port, select Specify from input port for the Threshold (dB) parameter.

Data Types: single | double

AT — Attack time (s)

scalar

Dependencies

To enable this port, select Specify from input port for the Attack time (s) parameter.

Data Types: single | double

RT — Release time (s)

scalar

Dependencies

To enable this port, select Specify from input port for the Release time (s) parameter.

Data Types: single | double

HT — Hold time (s)

scalar

Dependencies

To enable this port, select Specify from input port for the Hold time (s) parameter.

Data Types: single | double

Output

Y — Output signal

matrix

The Noise Gate block outputs a signal with the same data type as the input signal. The size of the output depends on the size of the input:

• Matrix input –– The block outputs a matrix the same size and data type as the input signal.

• 1-D vector input –– The block outputs an N-by-1 matrix (column vector), where N is the number of elements in the 1-D vector.

This port is unnamed until you select the Output gain (dB) parameter.

Data Types: single | double

G — Gain applied to each input sample

matrix

Dependencies

To enable this port, select the Output gain (dB) parameter.

Data Types: single | double

Parameters

If a parameter is listed as tunable, then you can change its value during simulation.

Main Tab

Threshold (dB) — Operation threshold

–10 (default) | scalar in the range –140 to 0 inclusive

Operation threshold is the level below which gain is applied to the input signal.

To specify Threshold (dB) from an input port, select Specify from input port for the parameter.

Tunable: Yes

View static characteristic — Open static characteristic plot of dynamic range gate

button

The plot is updated automatically when parameters of the Noise Gate block change.

Tunable: Yes

Attack time (s) — Time for applied gain to ramp up

0.05 (default) | scalar in the range 0 to 4 inclusive

Attack time is the time the applied gain takes to rise from 10% to 90% of its final value when the input goes below the threshold. The Attack time (s) parameter smooths the applied gain curve.

To specify Attack time (s) from an input port, select Specify from input port for the parameter.

Tunable: Yes

Release time (s) — Time for applied gain to ramp down

0.2 (default) | scalar in the range 0 to 4 inclusive

Release time is the time the applied gain takes to drop from 90% to 10% of its final value when the input goes above the threshold. The Release time (s) parameter smooths the applied gain curve.

To specify Release time (s) from an input port, select Specify from input port for the parameter.

Tunable: Yes

Hold time (s) — Time during which applied gain holds steady

0.05 (default) | scalar in the range 0 to 4

Hold time is the period for which the (negative) gain is held before starting to decrease towards its steady state value when the input level drops below the threshold.

To specify Hold time (s) from an input port, select Specify from input port for the parameter.

Tunable: Yes

Inherit sample rate from input — Specify source of input sample rate

on (default) | off

When you select this parameter, the block inherits its sample rate from the input signal. When you clear this parameter, you specify the sample rate in Input sample rate (Hz).

Tunable: No

Input sample rate (Hz) — Specify input sample rate

44100 (default) | scalar

Tunable: Yes

Dependencies

To enable this parameter, clear the Inherit sample rate from input parameter.

Advanced Tab

Output gain (dB) — Gain applied on each input sample

off (default) | on

When you select this parameter, an additional output port, G, is added to the block. The G port outputs the gain applied on each input channel in dB.

Tunable: No

Sidechain — Enable sidechain input

off (default) | on

When you select this parameter, an additional input port SC is added to the block. The SC port enables dynamic range gating of the input signal x using a separate sidechain signal.

The datatype and (frame) length input to the SC port must be the same as the input to the x port.

The number of channels of the sidechain input must be equal to the number of channels of x or be equal to one.

• Sidechain channel count is equal to one –– The computed gain, G, based on this channel is applied to all channels of x.

• Sidechain channel count is equal to channel count of x –– The computed gain, G, for each sidechain channel is applied to the corresponding channel of x.

Tunable: No

Simulate using — Specify type of simulation to run

Interpreted execution (default) | Code generation

• Interpreted execution –– Simulate model using the MATLAB^® interpreter. This option shortens startup time and has a simulation speed comparable to Code generation. In this mode, you can debug the source code of the block.

• Code generation –– Simulate model using generated C code. The first time you run a simulation, Simulink^® generates C code for the block. The C code is reused for subsequent simulations, as long as the model does not change. This option requires additional startup time, but the speed of the subsequent simulations is comparable to Interpreted execution.

Tunable: No

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no

Algorithms

The Noise Gate block processes a signal frame by frame and element by element.

1. The N-point signal, x[n], is converted to magnitude:

   $$x_{\text{a}}\text{[}n]=\left|x[n]\right|$$

2. x_a[n] passes through the gain computer. The gain computer uses the static characteristic properties of the dynamic range gate to apply a brickwall gain for signal below the threshold:

   $$g_{\text{c}}(x_{\text{a}})=\{\begin{array}{cc}0& x_{\text{a}}<T_{\text{lin}}\\ 1& x_{\text{a}}\ge T_{\text{lin}}\end{array}$$

   T_lin is the threshold property converted to a linear domain:

   $$T_{\text{lin}}={10}^{\left(\raisebox{1ex}{$T_{\text{dB}}$}\!\left/ \!\raisebox{-1ex}{$20$}\right.\right)}.$$

3. The computed gain, g_c[n], is smoothed using specified attack, release, and hold time parameters:

   $$g_{\text{s}}[n]=\{\begin{array}{cc}{\alpha }_{\text{A}}{g}_{\text{s}}[n-1]+(1-{\alpha }_{\text{A}})g_{\text{c}}[n]& \left(C_{\text{A}}>T_{\text{H}}\right)\&\left(g_{\text{c}}[n]\le g_{\text{s}}[n-1]\right)\\ g_{\text{s}}[n-1]& C_{\text{A}}\le T_{\text{H}}\\ {\alpha }_{\text{R}}{g}_{\text{s}}[n-1]+(1-{\alpha }_{\text{R}})g_{\text{c}}[n]& g_{\text{c}}[n]>g_{\text{s}}[n-1]\end{array}$$

   C_A is the hold counter for attack. The limit, T_H, is determined by the Hold time (s) parameter.

   The attack time coefficient, α_A, is calculated as

   $${\alpha }_{\text{A}}=\exp \left(\frac{-\log (9)}{Fs\times T_{\text{A}}}\right).$$

   The release time coefficient, α_R, is calculated as

   $${\alpha }_{\text{R}}=\exp \left(\frac{-\log (9)}{Fs\times T_{\text{R}}}\right).$$

   T_A is the attack time period, specified by the Attack time (s) parameter. T _R is the release time period, specified by the Release time (s) parameter. Fs is the input sampling rate, specified by the Inherit sample rate from input or Input sample rate (Hz) parameter.

4. The output of the dynamic range gate is given as

   $$y[n]=x[n]\times g_{\text{s}}[n].$$

References

[1] Giannoulis, Dimitrios, Michael Massberg, and Joshua D. Reiss. "Digital Dynamic Range Compressor Design –– A Tutorial And Analysis." Journal of Audio Engineering Society. Vol. 60, Issue 6, 2012, pp. 399–408.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2016a