1. The Motion Picture Experts Group (MPEG ) audio compression algorithm is an International Organization for Standardization (ISO) standard for high fidelity audio compression. It is one of a three-part compression standard, the other two being video and system. The MPEG compression is lossy, but nonetheless can achieve transparent, perpetually lossless compression.

2. MPEG-Audio allows three sampling rates : 32 kHz, 44.1 kHz, or 48 kHz. The compressed bit stream can support one or audio channels. The compressed stream can have one of several predefined fixed bit rates ranging from 32 kbps to 244 kbps , per channel. Depending on the audio sampling rate, this translates to compression ratios ranging from 2.7 to 24

3. Because MPEG-Audio only removes inaudible parts of the sound, perceptually it is lossless compression, although original audio data cannot be reconstructed bit to bit after compression. The MPEG-Audio committee conducted extensive subjective listening tests during the development of the standard.

4. The tests showed that even with a 6:1 compression ratio and under optimal listening conditions, expert listeners could not distinguish between coded and original audio clips with statistical significance. The audio clips used in the tests were chosen as difficult to compress.

5. MPEG-Audio is not a single compression algorithm but a family of three audio compression schemes. They are called MPEG-Audio layer 1, layer 2, and layer 3. The complexity of the algorithm increases with the layer ember. Thus layer 3 is the most complex.

6. In general, increased complexity produces a higher compression ratio. These three layers are hierarchically compatible; that is, a layer 2 decoder can decode Bit streams encoded with a layer 1 encoder, and a layer 3 decoder can decode bit-streams encoded with layer 2 and layer 1 encoders.

7. Using MPEG audio coding you can compress the original audio on a CD by a factor of 12 without losing the sound quality. Factors of 24 or even more are also possible, but these are achieved only by getting a sound output of reduced sampling rate and reduced resolution of the samples.

The family of audio coding schemes that achieve compression without losing the CD sound quality , along with their compression ratios are:

• MPEG Layer 1 (corresponds with 384 Kbps of data transferred to the player in case of a stereo signal) compression ratio is 1:4.
• MPEG Layer 2 (corresponds with 256 -192 Kbps of data transferred to the player in case of a stereo signal) compression ratio is 1:6 -1:8.
• MPEG Layer 3 (corresponds with 128-112 Kbps of data transferred to the player in case of a stereo signal) compression ratio is 1:10 -1:12.