FLAC 
Free Lossless Audio Codec 
This open-source codec compresses audio by about 50 percent, but the good news is that it does not lose a single bit during the process. Like other lossless codecs, FLAC works in mysterious ways, by finding parts of an audio file with a bunch of 1s or 0s in a row and describing 11111 as five 1s. The details are much more complicated, but that's the basic idea. FLAC is a favorite of audiophiles because it sounds exactly as good as the original CD.