FX Class: Limiter

Interactive example

Overview

Limiter with only 32 samples latency and less than 1 kb memory allocation. This effect can boost the perceived volume while keeping the maximum level below a limit. It can be used to prevent overload or reduce dynamic range.

Implementation example

The limiter is is an FX class, it expects both an input and output buffer. The process() method should be called on every loop of the audio processing block.

class SuperpoweredLimiterProcessor extends SuperpoweredWebAudio.AudioWorkletProcessor {

    // Called when the AudioWorklet is ready to start processing audio
    onReady() {
        this.limiter = new this.Superpowered.Limiter(
            44100 // The initial sample rate in Hz. -
        );
        this.limiter.enabled = true;
    }

    // Runs before the node is destroyed.
    // Clean up memory and objects here (such as free allocated linear memory or destruct Superpowered objects).
    onDestruct() {
        this.limiter.destruct();
    }

    // The shape of the message we pass from our main thread is up to you
    onMessageFromMainScope(message) {
        // Here is an example of how to apply changes to the Three Band EQ instance
        if (typeof message.bits !== 'undefined') this.limiter.bits = message.bits;
        if (typeof message.frequency !== 'undefined') this.limiter.frequency = message.frequency;
    }

    // This is the process loop which is passed pointers to buffers
    // from the WebAudio API (inputBuffer and outputBuffer), with the buffersize (128 samples when running as a native AudioWorklet)
    processAudio(inputBuffer, outputBuffer, buffersize) {
        // Ensure the samplerate is in sync on every audio processing callback
        this.limiter.samplerate = this.samplerate;

        // Render the output buffers
        if (!this.limiter.process(inputBuffer.pointer, outputBuffer.pointer, buffersize)) {
            for (let n = 0; n < buffersize * 2 ; n++) outputBuffer.array[n] = inputBuffer.array[n];
        }
    }
}

#include "SuperpoweredLimiter.h"

void initLimiterEffect() {
    const unsigned int sampleRate = 44100;
    limiter = new Superpowered::Limiter(sampleRate);
    limiter->enabled = true;
}

void configureEffect() {
    limiter->ceilingDb = 0;
    limiter->thresholdDb = -16;
    limiter->releaseSec = 0.2;

}

void processAudio(float *interleavedInput, float *interleavedOutput, unsigned int numberOfFrames, unsigned int samplerate) {
    // Ensure the samplerate is in sync on every audio processing callback
    limiter->samplerate = samplerate;

    // Render the output buffers
    bool outputChanged = limiter->process(interleavedInput, interleavedOutput, numberOfFrames);
    ...
}

Properties

Number

float

Number

float

Number

float

Boolean

bool

Number

unsigned int

Methods

• constructor

  METHOD

  Creates a Limiter instance.

  Parameters

  Name	Type	Description
  samplerate	Number	The initial sample rate in Hz.

  Returns

  Type	Description
  Superpowered.Limiter	The constructed instance.

• constructor

  METHOD

  Creates a Limiter instance.

  Parameters

  Name	Type	Default	Description
  samplerate	unsigned int		The initial sample rate in Hz.

  Returns

  Type	Description
  Superpowered::Limiter	The constructed instance.

• getGainReductionDb

  METHOD

  Returns the maximum gain reduction in decibels since the last getGainReductionDb() call.

  Parameters

  None

  Returns

  Type	Description
  Number	Reduction in db.

• getGainReductionDb

  METHOD

  Returns the maximum gain reduction in decibels since the last getGainReductionDb() call.

  Parameters

  None

  Returns

  Type	Description
  float	Reduction in db.

• destruct

  METHOD

  Destructor to free Linear Memory.

  Parameters

  None

  Returns

  None

• process

  METHOD

  Processes/renders the audio. Always call it in the audio processing callback, regardless if the effect is enabled or not for smooth, audio-artifact free operation. It's never blocking for real-time usage.

  Parameters

  Name	Type	Description
  input	Number (pointer in Linear Memory)	32-bit interleaved stereo input.
  output	Number (pointer in Linear Memory)	32-bit interleaved stereo output.
  numberOfFrames	Number	Number of frames to process. Recommendations for best performance: multiply of 4, minimum 64.

  Returns

  Type	Description
  Boolean	If process() returns with true, the contents of output are replaced with the audio output. If process() returns with false, it indicates silence. The contents of output are not changed in this case (not overwritten with zeros).

• process

  METHOD

  Processes/renders the audio. Always call it in the audio processing callback, regardless if the effect is enabled or not for smooth, audio-artifact free operation. It's never blocking for real-time usage. You can change all effect properties on any thread, concurrently with process().

  Parameters

  Name	Type	Default	Description
  input	float *		32-bit interleaved stereo input.
  output	float *		32-bit interleaved stereo output.
  numberOfFrames	unsigned int		Number of frames to process. Recommendations for best performance: multiply of 4, minimum 64.

  Returns

  Type	Description
  bool	If process() returns with true, the contents of output are replaced with the audio output. If process() returns with false, it indicates silence. The contents of output are not changed in this case (not overwritten with zeros).