MP3 Basics
Background
- MPEG (Moving Picture Experts Group) was established in 1988 by the ISO (International Standards Organization) and the IEC (International Electrotechnical Commission).
- In 1993, standards for audio compression were released. 3 layers of complexity were established, known as MPEG-1 Audio Layers 1, 2, and 3 respectively.
- Layers 1 and 2 were based on the MUSICAM technology. Layer 3, the most complex, was based on ASPEC (Adaptive Spectral Perceptual Entropy Coding). MPEG-1 Audio Layer 3 is now known simply as MP3.
- ASPEC was developed by the Fraunhofer Institute for Integrated Circuits, who with their partners Thompson Mulltimedia, still hold many patents for MP3 encoding and decoding technology.
Basic Information
Goal: To compress files as much as possible while retaining the same perceived audio quality as the original signal.
- Uses lossy audio coding, also known as perceptive coding, to take advantage of the imperfections in human perception. Also uses traditional compression techniques, such as Huffman Coding.
- MP3 is a standard. It suggests encoding methods and standardizes file formatting and decoding, but there are many different encoding schemes.
- Very popular form of compression for music, especially downloading over the internet, playing on portable music players, and storing large amounts of music.
- Other types of audio files, such as WAV, AAC, WMA, and OGG are also popular.
Perceptive Coding
There is much more information in a signal than the human ear and mind process. This extra information is eliminated to make gains in compression.
A detailed model of human perception must be developed so only the extra information is eliminated.
