A audio noise filter in JavaScript quantile based

Dec 03, 2016 Audio JavaScript

I am a little bit interested in the possibilities of reading audio input from the web browser. So I have written a small audio noise filter based on frame wise speech / non-speech classifcation a few days ago. This filter was based on the research of the paper Quantile based noise estimation for spectral subtraction and Wiener filtering. The paper contains also an other approach, a quantile based noise spectrum estimation.

Quantile based noise spectrum estimation

This approach is just using the history of the audio input and for every frequency band we calculate the quantile with a given constant. This value will be the value of the noise frequency band. The JavaScript library quickselect from Vladimir Agafonkin helped me to calculate the quantile quickly. I guess the result looks very promising, but I have to create strategy to clean up the audio input history after a while.

JavaScript

Here is the JavaScript code behind the noise spectrum estimation based on quantiles. Please note that this code requires the JavaScript library quickselect as mentioned above.

function qbNoiseFilter(qValue) {
    this.qValue = qValue;
    if (this.alpha === undefined) {
        this.alpha = 0.55;
    }
    this.noiseHistory = null;

    this.getNoise = function(input) {
        if (this.noiseHistory === null) {
            this.noiseHistory = [];
            for (var i = 0; i < input.length; i++) {
                this.noiseHistory[i] = [];
            }
        }
        var noise = [];
        for (var i = 0; i < input.length; i++) {
            this.noiseHistory[i].push(input[i]);
            var k = Math.floor(this.noiseHistory[i].length * this.alpha)
            quickselect(
                this.noiseHistory[i],
                k,
                0,
                this.noiseHistory[i].length - 1,
                defaultCompare
            );
            noise[i] = this.noiseHistory[i][k];
        }
        return noise;
    };
}

You just have to create a instance of qbNoiseFilter and can call getNoise with the given audio data from getByteFrequencyData function for example.

// Create analyser and check for navigator.getUserMedia
navigator.getUserMedia = (
    navigator.getUserMedia ||
    navigator.webkitGetUserMedia ||
    navigator.mozGetUserMedia ||
    navigator.msGetUserMedia
);

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var source;
var stream;

var analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;
analyser.smoothingTimeConstant = 0.85;
analyser.fftSize = 128;
var bufferLength = analyser.frequencyBinCount;

var distortion = audioCtx.createWaveShaper();
var gainNode = audioCtx.createGain();
var biquadFilter = audioCtx.createBiquadFilter();
var convolver = audioCtx.createConvolver();

var noiseFilter = new qbNoiseFilter();

// Bind function readAudioData to navigator.getUserMedia
if (navigator.getUserMedia) {
    navigator.getUserMedia(
        {audio: true},
        function(stream) {
            source = audioCtx.createMediaStreamSource(stream);
            source.connect(analyser);
            analyser.connect(distortion);
            distortion.connect(biquadFilter);
            biquadFilter.connect(convolver);
            convolver.connect(gainNode);
            gainNode.connect(audioCtx.destination);
            readAudioData();
        },
        function(err) {
            console.log(err);
        }
    );
} else {
    console.log('UserMedia not supported on your browser');
}

var readAudioData = function() {
    requestAnimationFrame(readAudioData);
    var dataArray = new Uint8Array(bufferLength);
    analyser.getByteFrequencyData(dataArray);
    var noise = noiseFilter.getNoise(dataArray);
    console.log(noise);
}