Lossy compression is a technique used for data which reduces the size of the data and also modifies the data in some way, so that an approximation to the original data can be achieved by a decoding process. When decoded the data has lost information, and is likely not to be of the same perceived quality as the original. However some lossy compression methods do manage to maintain most of the perceived quality of the original source data.

For audio use the following formats are commonly used lossy compression formats: