The Science/ Technology
MP3 is short for MPEG-1 Layer 3.
MPEG is short for Moving Picture Expert Group which works as part of ISO (International Standards Organisation) and IEC (International Electro-Technical Commission). These standards relate to the encoding or compression of video and associated audio. The first standard, MPEG-1 was completed as long ago as 1992 and part 3 of the standard is about encoding audio. There are 3 layers defined and the higher the layer, the more complex the encoding but giving more audio quality per encoded bit. The algorithm is so effective as it focuses on the the audio parts that the human ear is most sensitive to and heavily compresses the rest which cannot be discerned by the human ear. See the diagram (courtesy CSET) below for the encoding system. The encoder analyses the spectral components of the audio signal and applies a psychoacoustic model to estimate the just noticeable quantisation noise level. The net result is audio that sounds CDROM quality, but is in fact rather distorted or noisy - but you just can’t hear it, and uses only about 60 kb/s per channel.
The technology has matured now (although there is still more progress possible) and MP3 encoded audio (music) is readily available for download on the
internet as are the decoders you need to listen to it.
An MP3 stereo encoder would typically use a DSP (Digital Signal Processor) chip and requires a performance of around 12 MIPs (12 million instructions per second), and internal storage of about 11kwords each of at least 20 bits.
|
