FX Class: Reverb

Interactive example

Overview

This CPU-friendly reverb audio effect outputs adds depth to the sound, putting the audio into a virtual enclosed space, reflecting in all directions, decaying in amplitude, and eventually dying off as the sound is absorbed by the surfaces of objects in the space. One instance allocates around 120 kb memory.

The mix property is used to edit and control the balance of the original signal ("dry") and the affected signal ("wet") leaving the reverb, however they can also be adjusted in detail using dry and wet.

The roomSize property controls the scale of the decay time and reflections found in the physical characteristics of living spaces, and studios. A large room size results in longer reverb time, providing the illusion of a physically larger space. The predelayMs property is the length of time it takes for a sound wave to leave its source and create its first reflection is determined by the pre-delay. This property controls an offset of reverb from the dry signal. An increase in pre-delay can result in a feeling of a bigger space too.

The damp property is used to control the absorption of high frequencies in the reverb. More absorption of high frequencies means higher damping values. The tail of the reverb will lose high frequencies as they bounce around softer surfaces like halls and result in warmer sounds. The lowCutHz property controls the low frequency build up generated from the reverb. This can be used to shape the output of the reverb, and to limit the rumbling sound of low frequency content.

Implementation example

class SuperpoweredReverbProcessor extends SuperpoweredWebAudio.AudioWorkletProcessor {
    onReady() {
        this.reverb = new this.Superpowered.Reverb(
            this.samplerate, // The initial sample rate in Hz.
            44100  // Maximum sample rate (affects memory usage, the lower the smaller).
        );
        this.reverb.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.reverb.destruct();
    }

    onMessageFromMainScope(message) {        
        if (typeof message.dry !== 'undefined') this.revberb.dry = message.dry;
        if (typeof message.wet !== 'undefined') this.reverb.wet = message.wet;
        if (typeof message.mix !== 'undefined') this.reverb.mix = message.mix;
        if (typeof message.width !== 'undefined') this.reverb.width = message.width;
        if (typeof message.damp !== 'undefined') this.reverb.damp = message.damp;
        if (typeof message.roomSize !== 'undefined') this.reverb.roomSize = message.roomSize;
        if (typeof message.predelayMs !== 'undefined') this.reverb.predelayMs = message.predelayMs;
        if (typeof message.lowCutHz !== 'undefined') this.reverb.lowCutHz = message.lowCutHz;
    }

    // This is the process loop which is passed pointers to audio buffers
    // from the WebAudio API (inputBuffer and outputBuffer), with the buffersize
    processAudio(inputBuffer, outputBuffer, buffersize) {
        // Ensure the samplerate is in sync on every audio processing callback
        this.reverb.samplerate = this.samplerate;

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

#include "SuperpoweredReverb.h"

void initReverbEffect() {
    const unsigned int sampleRate = 44100;
    const unsigned int maxSampleRate = 96000;
    reverb = new Superpowered::Reverb(sampleRate, maxSampleRate);
    reverb->enabled = true;
}

void configureReverbEffect() {
    reverb->dry = 0.987;
    reverb->wet = 0.587;
    reverb->mix = 0.4;
    reverb->width = 1;
    reverb->damp = 0.5;
    reverb->roomSize = 0.8;
    reverb->predelayMs = 0;
    reverb->lowCutHz = 0;
}

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

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

Properties

Number

float

Number

float

Number

float

Number

float

Number

float

Number

float

Number

float

Number

float

Boolean

bool

Number

unsigned int

Methods

• constructor

  METHOD

  Creates a Reverb instance.

  Parameters

  Name	Type	Description
  samplerate	Number	The initial sample rate in Hz.
  maximumSamplerate	Number	Maximum sample rate (affects memory usage, the lower the smaller).

  Returns

  Type	Description
  Superpowered.Reverb	The constructed instance.

• constructor

  METHOD

  Creates a Reverb instance.

  Parameters

  Name	Type	Default	Description
  samplerate	unsigned int		The initial sample rate in Hz.
  maximumSamplerate	unsigned int	96000	Maximum sample rate (affects memory usage, the lower the smaller).

  Returns

  Type	Description
  Superpowered::Reverb	The constructed instance.

• 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).