Lossless coding halves data size while leaving the signal bit-identical

Evidence

Lossless audio coding systems: In these systems, the data rate, or data quantity, is reduced but in such a way that no information is lost. That is, after coding and subsequent decoding, the signal that comes out is identical to the signal that went in. This is like audio computer data file “zip” compression. Examples of such systems are: Shorten, an early lossless format; MPEG-4 ALS, FLAC, Apple Lossless, which are newer ones; and Direct Stream Transfer (DST) and Meridian Lossless Packing, which are proprietary methods that are used in the SA-CD and DVD audio formats, respectively. Lossless methods typically achieve a compression ratio of around 2 to 1. That is, the data size after compression is typically half the size of the input. The actual amount of compression achieved is dependent on the nature of the input audio signal itself (i.e., what kind of music it is or if it is speech) and can vary from about 1.5 to 1 to 3 to 1. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2580

Categorization

• DEFINE: Defines lossless coding by its invariant: output equals input. The 2-to-1 ratio and the naming of FLAC/ALS/DST give concrete anchors.