Raven Lite is a wonderful software program for visualizing birdsong or just about any other sound. It's available free from the Cornell Laboratory of Ornithology and can use sounds from a number of different sources, including audio CDs.

As the image above shows, Raven Lite presents two views of a sound. The top panel shows the changing volume over time for the sound you're hearing. The bottom panel shows you the sound frequencies or pitch of the same sound. For birdsong, in particular, these views help spot such features of the sound as harmonics or the simultaneous production of sound from both branches of the songbird's y-shaped dual voicebox, the syrinx.

You can also use Raven Lite to slow down sounds and do other simple sound editing tasks.

Raven Lite is available free for both Windows and Mac OS. (There is also a professional version called Raven Pro for which you must pay.)

To learn more about Raven Lite from the Cornell Laboratory of Ornithology, or to download the software, visit their website: Raven Lite.