How to add effects to audio

Tony Conway

The modern way

The Web Audio API uses the AudioContext() interface to manage sources, filters, and destinations. Once you’ve created a new AudioContext(), create an audio source node, like an AudioBufferSourceNode or OscillatorNode. As an example, consider a basic oscillator with a low pass filter applied.

Browser Support

Source

Using the `createBiquadFilter()` method

First, create a new AudioContext(). Then create an audio source node, like an AudioBufferSourceNode or OscillatorNode. You'll create a sine oscillator node, for this example, which has a frequency of 420 hertz from the moment it starts playing.

const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
const oscillator = audioCtx.createOscillator()
oscillator.type = 'sine';
 // Value is in hertz.
oscillator.frequency.setValueAtTime(420, audioCtx.currentTime);

Next, create an effect node using createBiquadFilter(). Set the type to lowpass and the frequency to start one second after the start of playback. Then connect the biquadFilter to the oscillator.

const biquadFilter = audioCtx.createBiquadFilter();
biquadFilter.type = 'lowpass';
biquadFilter.frequency.setValueAtTime(200, audioCtx.currentTime + 1);
oscillator.connect(biquadFilter);

Finally connect the biquadFilter to the destination of the audioCtx, before starting the oscillator and stopping it after two seconds of playback.

biquadFilter.connect(audioCtx.destination);
oscillator.start();
oscillator.stop(2);

The sound from the oscillator is passed through the unaffected filter, and on to the destination, which is your computer's speakers. After one second of playback, the lowpass filter comes into effect. After two seconds, the oscillator is stopped.

Other available filters and effects

Other filter nodes can be added to an AudioContext to create different effects:

createWaveShaper() is used to add distortion to a source.
createGain() is used to boost the overall signal of the source it's applied to.
createConvolver() is most commonly used to add reverb to a source.
createDelay() is used to add delay to the start of a source.
createDynamicsCompressor() is used to raise the volume of the quietest part of a source, and lower the volume of the loudest parts.
createPanner() and createStereoPanner() are used for changing the spatial position of sound output.

The classic way

Before the availability of the Web Audio API, there was no way to add effects to audio in the browser. Workarounds using server-side rendering and switching between streams are possible, but this can incur a lot of network overhead.

Using the audio element

The only audio effects that can be directly controlled are playback and volume.

const audio = document.querySelector('audio');
 // Sets audio volume to 50%
audio.volume = 0.5;
// Doubles the playback rate.
audio.playbackRate = 2;