$(document).ready(function() {
         var ctx = new window.AudioContext(),
                 osc = undefined,
                 prev = undefined,
                 freqs = {E: 82.4, A: 110, d: 146.8, g: 196, h: 246.9, "e'": 329.6};
         $('input[type=button]').click(function() {
                 var act = $(this);
                 if (osc)
                         osc.stop(0);
                 if (prev)
                         prev.removeClass('highlighted');
                 if (prev === undefined || act.val() !== prev.val()) {
                         prev = act;
                         osc = ctx.createOscillator();
                         osc.connect(ctx.destination);
                         osc.frequency.value = freqs[prev.val()];
                         osc.start(0);
                         prev.addClass('highlighted');
                 } else
                         prev = undefined;
         });
 });