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HOW DO MP3 WORK?

MP3 relies on the fact that the human ear dosen't work as well as you might have thought. Your brain can't process a lot of the information that the ear picks up, so why bother with it? Several years ago, a group of specialists worked out which types of sounds you can & can't hear using a technique known as psycho-accoustic modelling.

They found that the human ear is good at hearing mid-range noises, while not so good at high & low pitched noises. Your ear can hear these noises, but you can't make anything out of them. Thus these noises can be heavily compressed without you noticing. This is called perceptual coding.

The MP3 standard divides the frequency spectrum into 576 frequency bands & compresses each band according to how much information you can hear in that band. Low & high noises are highly compressed, while the mid-range noises not as much. Sounds are also compressed in stereo- if a sound is identical on both stereo channels, it's stored only once in the MP3, but it's played back on both channels when the file is decompressed & played.

All this put together gives you small sized yet high quality audio files known as MP3. Although there is some loss of quality, but most people can't tell the difference between a CD & an MP3 track.

BITRATES AND QUALITY

There are several bitrates in the MP3 format, beginning from a mere 16kbps to the huge-sized 256kbps. Generally, a higher bitrate (measured in kbps e.g. 128kps) translates into a higher quality of sound, truer to its original, but also larger in size. Currently, the most common used bitrate is 128kbps.

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