Sounds are available in two formats, MP3, which is smaller but may not play in older browsers, and AIFF, which will play in almost every browser, but is larger.
A sound spectrogram, or sonogram, is a graph that shows the frequency and intensity of a sound over a period of time. The lower frequencies are at the bottom of the graph, and the high-pitched frequencies at the top. The intensity is shown by changes in color, with black being no sound at all, and louder sounds progressing from light blue through yellow to red.
Making sonograms used to be very complex and expensive, but within the past ten years, low-cost and free software has made use of computers and their sound cards to bring sound analysis within the reach of everyone. These sonograms were created with Gram 5.0 by Richard Horne. The current version, Spectrogram Version 8, is even more capable. The site also provides examples of sonograms from other sounds.
Catfish sounds on the other pages are copyright by John P. Friel and used by permission.