When Sonic Foundry"s ACID was introduced in 1998, it threw the music production community for a loop-literally. It could seamlessly combine loops (pieces of music that play in a repeating pattern) in almost any tempo, and this ability revolutionized music creation and remixing. * ACID 2.0 can play back an unlimited number of tracks (independent musical sounds from a piece of music). It includes a CD full of tasty, royalty-free audio files that cover a range of styles, from funk to country. It also lets you record and incorporate your own audio. The DirectX-compatible mixer includes plug-ins that let you customize your mixes with sound effects and synthesizers, and you can export your work to MP3, RM, WAV, and WMA files or burn it directly to CD, * This powerful, near-professional program is exceptionally easy to learn. Using the efficient interface, you build songs by dragging specially encoded WAV files to the Arrange window. You can record such files on your PC or use those that come with the program. ACID 2.0"s ability to match tempos is better than that of most other programs; you really have to stretch a file (extend its length without changing its tempo) for its sound quality to suffer. You can cut loops into individual segments and rearrange their order or change the pitch (nondestructively, without altering the original files). Loops can be positioned freely or snapped to a musical value (such as an eighth note or the beginning of a bar).