Undoubtedly the biggest format revolution of the last few years have been MP3, now present in every corner of online and digital life, one of the most frequently searched terms on the internet search engines, but what is it?

MP3 Explained

MP3 stands for MPEG layer 3 audio, MPEG being a form of compression used in both video and audio, so why compress why not just capture digitally, well its all down to size, in this case size of captured files a WAV file (the standard for CD) produces massive files which even with the event of broadband connections are just too big, for example a 1 minute file equates to 10mb of storage.

CD's provide a high quality recordings that faithfully reproduce the music but in ones and zeros (digits) it does this by sampling 44,100 times a second and storing the value of each sample this is a from of compression as it means the whole analogue signal is not stored but the human ear can't really tell the difference between a sampled version. Plus digital recordings do not suffer from noise or degradation which allows copies to be made without losing quality much to the annoyance of the music industry.

MP3 uses far more aggressive compression this goes beyond sampling and actively loses some data that can be re created on replay by use of mathematical algorithms. The first stage is to get rid of frequencies that the human ear can't really hear anyway, the ear can only pick up between 20hz and 20khz, as you age the top end of the spectrum that you can actually hear drops by the age of 20 most of us can't hear over 15khz.

MP3 uses a psycho acoustic model it works on the fact that the most sensitive frequency range is between 2 and 4khz this destructive compression actually throws away data relating to the full frequency spectrum, this immediately reduces the amount of data stored to record a 3 minute track.

The second stage is to reduce the bit rate or sampling rate, the most common bit rate for MP3 is 128kbps this means that when audio is captured to file the already compressed frequency spectrum is sampled at 128kbps not the 44,100 of a CD, this does lead to a loss in quality but as the human ear is quite forgiving and a number of other mathematical tricks are used.

Like other forms of compression data that is repeated can be removed and replaced with markers, it is easy to explain this with  JPEG compression on images, if a picture has a consecutive number of pixels are the same shade of green the JPEG system sends the first pixel as "green level one repeat until" and then only stores the point where the image changes.

This way the data file does not contain the repeated data of what colour each pixel is, a similar system is used in MP3 and MPEG compression redundant data is thrown away and mathematical algorithms (codec's) piece the audio waveform back together during playback. The bit rate at which the MP3 is encoded selects how much data will be discarded and it is generally accepted that a good quality MP3 codec can produce files which are comparable to CD quality audio at 192kbps, MP3 is however a lossy compression system and once files are shrunk to a tenth of their original size they cannot be reversed.

The befits are however compelling especially for internet and mobile applications, a CD which could hold one album (650mb) can now hold ten and a portable MP3 player can hold your entire CD collection on a 20gb hard drive, of course transferring files gets easier too now a one minute audio file is only 1mb which isn't a long download even on a 56k modem.

And so the revolution has begun, audiophiles may sneer at the new upstart format but its spreading like wildfire, MP3 enabled Napster to start an online file sharing business that has changed the way the music industry distribute music and has allowed new artists to become known without even selling a single CD. MP3 is changing society too MP3 players are the gadgets of the moment, MP3's are widely available some legally some not all over the internet, a club in London even invites wannabe DJ's to bring their MP3 player along and play a set of 3 tracks while the audience vote throughout the night for their favourite.

MP3 continues to prove that for once less is more.

Take a look at the MP3 players reviewed in our AV technology section