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MP3 is a very popular format for the encoding and compression of audio files, one that's contributed heavily to a rapid increase in availability of digital music online and helped usher in great changes in the way we consume music. Its proper name is MPEG-1 Audio Layer III. MPEG stands for Motion Picture Experts Group (MPEG), a group established in 1988 to set standards specifically for digital audio and video encoding and related technologies. MPEG is a branch of the International Standards Organization (ISO), a Geneva-based group that sets voluntary standards for a large variety of industries worldwide. MP3 can compress mono or stereo digital audio down to around one-tenth its original size, digitally speaking, for easy transfer over the Internet, or for storage of large numbers of songs onto computer hard drives, CDs, DVDs or MP3 players (such as the iPod) without compromising audio quality to any great extent (although it does lose a little quality, sound-wise).
An MP3 encoder quantizes audio data into numbers, which can be scaled down by dividing them all by another number and rounding. Individual bands can be scaled differently to adjust precision. The encoder then uses something called Huffman coding to convert these numbers into even shorter binary strings of information using search trees (in reality, tables of the possible numbers and their binary codes). These tables have the shorter, less precise numbers at the top so that they can be located first. If a sound element is easily perceptible, it will be encoded with more precision than one that is harder to hear to keep the sound quality as high as possible while reducing data file size.
Along with the above, MP3 also takes advantage of some psychoacoustic (how people perceive sound) phenomena to compress audio files down to smaller sizes. For one, it discards the data for any sounds that are below or above what the human ear can actually hear. We can hear frequencies in approximately the 20 Hz to 20,000 Hz range (although the average adult can't hear much above the 16 KHz level due to hearing damage from loud noise exposure that happens naturally throughout life). MP3 encoding also uses the Haas effect, where two identical sounds arriving at nearly the same time but from different directions are perceived as a single sound from one direction, and frequency masking, where a louder sound at a similar frequency to a quieter sound will be the only one heard if both are playing at the same time, to get rid of data. This penchant for discarding audio data is why MP3 is called a lossy compression method, although it uses some lossless methods, too, like Huffman coding. MP3 encoding uses other more traditional compression methods for simpler or more audible sounds that don't fall prey to these psychoacoustic effects, as well.
The creation of MP3 files has come in handy, allowing us to send music over the Internet with ease and to carry around hundreds or thousands of songs on our phones or digital music players. MP3 has become a pervasive music encoding standard. Read on to find out from whence it came.