index.html

<html>
<head>
    <meta content="text/html;charset=utf-8" http-equiv="Content-Type"/>
</head>
<body>
<input id="play" type="button" value="⏯"/>

<div>
    Primary frequency: <input type="range" min="30" max="80" value="50" style="width: 400px" id="primary_input"/>
</div>

<div>
    Modulation frequency: <input type="range" min="0" max="3" value="0" step="0.05" style="width: 400px" id="fm_freq"/>
</div>

<div>
    Modulation amount: <input type="range" min="0" max="3" value="0" step="0.05" style="width: 400px" id="fm_amount"/>
</div>

</body>
</html>