Audio Synth via d3-ease

This generates an audio waveform from scratch by combing different waves that have been generated using d3's easing functions. 'Elastic' is created using d3.easeElasticIn(), 'sine' uses d3.easeSinInOut(), 'triangle' uses d3.easeLinear(), and 'square' is generated using Math.round(). Moving the mouse causes the ratio of each wave to change, effecting the timbre.

For more Web Audio fun, check out:

<!DOCTYPE html>
<html>
<head>
    <style>
        body {margin: 0px; overflow:hidden;}
      	svg {margin: 10px;}
      	path {fill: none; stroke: black; stroke-width: 1;}
        rect {fill: none; stroke: steelblue;}
    </style>
    <script src="//d3js.org/d3.v4.min.js"></script>
</head>
<body>
    <svg></svg>
</body>
<script>
    var width = Math.max(940, innerWidth-20),
        height = Math.max(460, innerHeight-20);

var source;
    var playing = false;

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

var sampleRate = 44100,
        frequency = 220,
        waveCycles = 4,
        samples = sampleRate/frequency;

var buffer = audioCtx.createBuffer(1, samples * waveCycles, sampleRate);
    
    var svg = d3.select("svg")
        .attr("width", width)
        .attr("height", height)

var x = d3.scaleLinear().range([0, width]).domain([samples * .25, buffer.length - (samples * .75)]),
        y = d3.scaleLinear().range([height-50, 50]).domain([-1,1]),
        toneScaleX = d3.scaleLinear().range([0,1]).domain([50,width-50]).clamp(true),
        toneScaleY = d3.scaleLinear().range([0,1]).domain([height-50,50]).clamp(true);

var wave = d3.line()
        .curve(d3.curveMonotoneX)
        .x(function(d, i) {return x(i)})
        .y(function(d) {return y(d)})

var waveShape = svg.append("g").append("path")
        .datum([])
        .attr("d", wave)
        .attr("transform", "translate(0,0)");

var elasticLabel = svg.append("text")
        .attr("x", 15)
        .attr("y", 20)
        .attr("text-anchor", "start")
        .text("Elastic: 25%" )

var sineLabel = svg.append("text")
        .attr("x", width - 15)
        .attr("y", 20)
        .attr("text-anchor", "end")
        .text("Sine: 25%")

var squareLabel = svg.append("text")
        .attr("x", 15)
        .attr("y", height - 20)
        .attr("text-anchor", "start")
        .text("Square: 25%")

var triangleLabel = svg.append("text")
        .attr("x", width - 15)
        .attr("y", height - 20)
        .attr("text-anchor", "end")
        .text("Triangle: 25%")

svg.append("rect")
        .attr("width", width)
        .attr("height", height)

svg.on("touchstart", playSound)
        .on("mousemove", update)
        .on("touchmove", update)
        .on("mouseout", stopSound)
        .on("touchend", stopSound)
    
    svg.append("line")
        .style("stroke", "steelblue")
        .attr("stroke-dasharray",[5,5])
        .attr("y1", height/2)      
        .attr("x2", width)      
        .attr("y2", height/2)

document.addEventListener("touchmove", function(e) {e.preventDefault();}, false);    
    
    loadAudio()

function update() {
        var xTone = toneScaleX(d3.event.pageX ? d3.event.pageX : d3.event.touches[0].pageX),
            yTone = toneScaleY(d3.event.pageY ? d3.event.pageY : d3.event.touches[0].pageY);

var elasticVal = yTone * (1-xTone),
            sineVal = yTone * xTone,
            squareVal = (1-yTone) * (1-xTone),
            triangleVal = (1-yTone) * xTone;

loadAudio(xTone, yTone)

elasticLabel.text("Elastic: " + d3.format(",.2%")(elasticVal))
        sineLabel.text("Sine: " + d3.format(",.2%")(sineVal))
        squareLabel.text("Square: " + d3.format(",.2%")(squareVal))
        triangleLabel.text("Triangle: " + d3.format(",.2%")(triangleVal))
    }

function loadAudio(xTone = .5, yTone = .5) {
        for (i=0; i<buffer.length; i++) {
            var thisVal = (Math.abs(((i+samples/4) % samples)/(samples/2)-1))
            
            
            var eased = (((d3.easeSinInOut(thisVal) - .5) * yTone) + 
                        ((d3.easeLinear(thisVal) - .5) * (1 - yTone))) * xTone + 
                        
                        (((d3.easeElasticIn(thisVal) - .5) * (yTone)) +
                        ((Math.round(thisVal) - .5) * (1 - yTone))) * (1-xTone)
            
            buffer.getChannelData(0)[i] = eased;
        }

waveShape.datum(buffer.getChannelData(0)).attr("d", wave)

if (playing == false) playSound();
    }

function playSound() {   
        if (playing) stopSound();
        playing = true;     
        source = audioCtx.createBufferSource();
        source.buffer = buffer;
        source.connect(audioCtx.destination);
        source.loop = true;
        source.start();
    }

function stopSound() {
        playing = false;
        if (source) {source.stop();}
    }
</script>

https://d3js.org/d3.v4.min.js