Beats are an interesting type of interference because the waves have a different frequency.  So far both types of interference we have looked at were the same frequency so the waves always start and end at the same time.  When waves are a different frequency they overlap differently in time.  It is best described in the picture below. Notice how first crests and troughs overlap then a ittle time later crests and crests.  Watch next to learn how to create beats and listen to them in Audacity.