SoundConverter (Mac, $10) is a sound-file conversion utility from software designer Steve Dekorte (www.dekorte.com/software/osx/SoundConverter). It handles uncompressed formats such as AIFF, WAV, and SDII, as well as compressed formats such as MP2, MP3, and SND. You can download a free version that converts files under 500 KB; paying the license fee removes that limitation. In an interesting twist, SoundConverter will also convert a variety of ringtone formats to either other ringtone formats or to most audio formats. Because ringtone formats are based on musical notes, conversion from audio to ringtone formats is not possible.
SoundConverter will convert individual files as well as batches. In either case, you launch SoundConverter, choose an output format from a drop-down menu, and then drag the file or files to be converted from the Finder to the SoundConverter application. You can also drag folders for batch conversion, which will convert all files at any level of nesting. Care is advised when doing batch conversions, because the conversion process can be lengthy.
SoundConverter lets you to set conversion parameters appropriate to the output format. For example, for MP3 conversion, you can choose mono or stereo and set sampling and bit rates. SoundConverter supports a huge number of input and output file formats. You're probably unfamiliar with most of them, but if you happen upon a Web site with audio files in some little-used format, then you'll be covered. (Mac OS X 10.2 or above is required for some conversions.) Whether you need to frequently convert large batches of audio files or occasionally convert an off-the-wall format, SoundConverter can save you time and frustration.