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08.06.2009

MP3: You can't stop the music...

With all the controversy currently surrounding the digital-audio format known as MPEG Layer III, or MP3, you might wonder how the digital-audio industry evolved from tinny-sounding MIDI files into near-CD-quality MP3 files.

With all the technical jargon, it's difficult to figure out why this breakthrough is so revolutionary. The reason is simple: MP3 dramatically reduces file size with only a small loss of quality.

In the late 1980s the digital-music industry stalled. Multimedia was outpacing the computer industry's ability to produce a large enough storage format that would let musicians store their digital work. The dominant compression scheme at the time, JPEG or Joint Photographics Expert Group, was only used for still images, and it couldn't handle the compression of high-quality movies or audio.

MPEG is born
Out of the necessity to provide multimedia creators with better formats and standards, the Moving Pictures Expert Group was formed in 1988.

The group first met in May of 1988 with 25 experts. Since then, the group has grown to enormous proportions. Now, 350 experts from 200 companies and organisations in 20 countries are a part of the MPEG organisation.

When a company or individual wants its technology to become an MPEG standard, it must first produce a verification model and submit it to the MPEG organisation. The verification model explains how the multimedia encoder and decoder work through the use of programming code. This code is later used to test how the technology being proposed as a standard performs under actual conditions. If and when the MPEG organisation believes that the technology has passed the verification model stage, the group producing the technology moves on to the working-draft phase of the process.

The working draft is essentially the proposed technology standard in its final form. The MPEG organisation keeps the draft version of the technology within the organisation for further evaluation. A series of evaluation stages follows. MPEG 1 and MPEG 2 both went through this process to become today's audio and video standards.

MPEG-1
MPEG-1 was born in 1992 after the MPEG organisation met with the International Standards Organisation (ISO) and the International Electrotechnical Commission (IEC). It featured audio encoding in three different layers, with the third layer having the best encoding abilities.

MPEG-2
The same three organisations -- MPEG, ISO, and ITEC -- met again in 1994 to announce the arrival of a new compression format known as MPEG-2. MPEG-2 was designed primarily for video, and it contains a number of new features, such as support for interlaced video signals. As an audio format, MPEG-2 continued to build off MPEG-1. MPEG-2 supports backward and forward compatibility for multichannel audio, so it supports both old audio technology, such as MPEG-1, and emerging digital-audio formats such as Dolby 5.1.

MPEG-2 also added a new feature to the MPEG standard: the ability to encode files with lower sampling frequencies such as 16KHz, 22.05KHz, and 24KHz. This allowed for better coding efficiency with lower bit rates. In other words, you get smaller files with little sacrifice in overall quality.

As MPEG-2 underwent continual evaluation, the MPEG organisation learned that if MPEG-2 did away with backward compatibility and some of the additional features, encoding efficiency would be improved tremendously. As a result, in 1994 MPEG-2 Advanced Audio Coding was born. MPEG-2 AAC continued the trek toward providing digital-audio users with high-quality encoding and a small file size.


Source: news.zdnet.co.uk

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