Click left buttons to play/stop sounds (check your volume is not maximised first, or you might get a shock).[br]The sliders or input boxes let you change the frequency of the two sounds.[br]Click Show Sum (and turn of the other two) to see the mathematical sum of the functions on the graph.[br][br]Try making the two frequencies really close (say 440, and 444), and adjusting the x-axis zoom by shift-dragging the x-axis. On zooming out you'll see the 'beats' that you can hear in the joint sound as a 'wobble'.