Echo Cancellation

Overview

AEC stands for Acoustic Echo Cancellation. It reduces the speaker signal bleed into the microphone signal. Popular AEC use-cases are telephony/VOIP and karaoke.

Superpowered AEC has unique characteristics:

• Audio quality is not reduced or limited, therefore it's well suited for musical applications.
• Very low latency: just 32 audio samples (example: less than 0.7 milliseconds at 48000 Hz).

It's independent from the built-in hardware, operating system or web browser specific echo canceler, therefore the sound is identical across all and latency is significantly reduced.

Implementation example

AEC expects an input signal and an other signal that should be "removed" from it. The process() method should be called on every loop of the audio processing block.

class SuperpoweredAECProcessor extends SuperpoweredWebAudio.AudioWorkletProcessor {

    // Called when the AudioWorklet is ready to start processing audio
    onReady() {
        this.aec = new this.Superpowered.AEC();
        this.monoMicrophoneSignal = new this.Superpowered.Float32Buffer(4096);
        this.monoSpeakerSignal = new this.Superpowered.Float32Buffer(4096);
        this.cleanMicrophoneSignal = new this.Superpowered.Float32Buffer(4096);
    }

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

    // 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) {
        ... // some code to produce an output for the speaker, placed into outputBuffer

        // convert the speaker signal and the microphone signal to mono
        this.Superpowered.StereoToMono(outputBuffer.pointer, this.monoSpeakerSignal.pointer, 1, 1, 1, 1, buffersize);
        this.Superpowered.StereoToMono(inputBuffer.pointer, this.monoMicrophoneSignal.pointer, 1, 1, 1, 1, buffersize);

        // remove the speaker signal from the microphone signal
        this.aec.process(this.monoSpeakerSignal.pointer, this.monoMicrophoneSignal.pointer, this.cleanMicrophoneSignal, buffersize);

        ... // do something with the cleaned microphone signal, such as record to disk
    }
}

#include "SuperpoweredAEC.h"
#include "SuperpoweredSimple.h"

void initialize() {
    aec = new Superpowered::AEC();
    monoMicrophoneSignal = malloc(sizeof(float) * 4096);
    monoSpeakerSignal = malloc(sizeof(float) * 4096);
    cleanMicrophoneSignal = malloc(sizeof(float) * 4096);
}

void processAudio(float *interleavedInput, float *interleavedOutput, unsigned int numberOfFrames, unsigned int samplerate) {
    ... // some code to produce an output for the speaker, placed into outputBuffer

    // convert the speaker signal and the microphone signal to mono
    Superpowered::StereoToMono(interleavedOutput, monoSpeakerSignal, 1, 1, 1, 1, numberOfFrames);
    Superpowered::StereoToMono(interleavedInput, monoMicrophoneSignal, 1, 1, 1, 1, numberOfFrames);

    // remove the speaker signal from the microphone signal
    aec->process(monoSpeakerSignal, monoMicrophoneSignal, cleanMicrophoneSignal, numberOfFrames);

    ... // do something with the cleaned microphone signal, such as record to disk
}

Properties

Superpowered.AEC.MicToSpeakerDistance_Handheld (Telephony, speaker to mic distance is very short (example: mobile phone).
Superpowered.AEC.MicToSpeakerDistance_Close (Speaker to mic distance is short, very little room sound (example: studio).
Superpowered.AEC.MicToSpeakerDistance_Room (Speaker to mic distance is moderate, the mic picks up some room sound (example: living room).
Superpowered.AEC.MicToSpeakerDistance_Large (Speaker to mic distance is large, the mic picks up reverberation (example: large room, hall).

Superpowered::AEC::MicToSpeakerDistance_Handheld (Telephony, speaker to mic distance is very short (example: mobile phone).
Superpowered::AEC::MicToSpeakerDistance_Close (Speaker to mic distance is short, very little room sound (example: studio).
Superpowered::AEC::MicToSpeakerDistance_Room (Speaker to mic distance is moderate, the mic picks up some room sound (example: living room).
Superpowered::AEC::MicToSpeakerDistance_Large (Speaker to mic distance is large, the mic picks up reverberation (example: large room, hall).

Number

float

Number

float

Number

unsigned int

Methods

• constructor

  METHOD

  Creates an instance of the AEC class.

  Parameters

  None

  Returns

  Type	Description
  Superpowered.AEC	The constructed instance.

• constructor

  METHOD

  Creates an instance of the AEC class.

  Parameters

  None

  Returns

  Type	Description
  Superpowered::AEC	The constructed instance.

• destruct

  METHOD

  Destructor to free Linear Memory.

  Parameters

  None

  Returns

  None

• process

  METHOD

  Processes the audio. It's never blocking for real-time usage. Simplified explanation: output = mic - loudspeaker.

  Parameters

  Name	Type	Description
  loudspeaker	Number (pointer in Linear Memory)	32-bit mono audio, typically sent to the speaker/headset. AEC will remove this signal from the mic signal. VOIP: the "far" signal, audio incoming from the network. Karaoke: the backing track.
  mic	Number (pointer in Linear Memory)	32-bit mono microphone input that should be cleaned (VOIP: "near" signal).
  output	Number (pointer in Linear Memory)	32-bit mono output. The "cleaned" mic audio.
  numberOfFrames	Number	Number of frames to process.

  Returns

  None

• process

  METHOD

  Processes the audio. It's never blocking for real-time usage. Simplified explanation: output = mic - loudspeaker.

  Parameters

  Name	Type	Default	Description
  loudspeaker	float *		32-bit mono audio, typically sent to the speaker/headset. AEC will remove this signal from the mic signal. VOIP: the "far" signal, audio incoming from the network. Karaoke: the backing track.
  mic	float *		32-bit mono microphone input that should be cleaned (VOIP: "near" signal).
  output	float *		32-bit mono output. The "cleaned" mic audio.
  numberOfFrames	unsigned int		Number of frames to process.

  Returns

  None