The files on this page have been digitized at 22kHz sample rate. As the sample rate is decreased, a file will contain fewer high frequencies. In theory, any sample rate is supported, but most commercial software will select from the following sample rates: 48kHz, 44.1kHz (CD-quality), 22kHz, 11kHz, 7kHz and 5.5kHz. Typically, when the software opens a sound file with a non-standard sample rate, it selects the nearest supported rate and plays it. Sometimes the result is an audible pitch shift.
These files are set up so that when you click on a file, it will either open in a new window and play, or it will be downloaded to your computer and played using a helper app. The method of playback depends on how you have configured your applications in the "Preferences" window of your browser.