How does an MP3 work?

The MP3 format allows large music files to be compressed, without compromising on quality. We aim to learn the science behind this compression, and whether or not MP3 audio is comparable to that of a CD.

The basics

The MP3 format aims to compress a music file without reducing the sound quality. But why do we need to compress our files, and how can an MP3 rival a CD? The average uncompressed song (CD track) is 32 megabytes in size. An MP3 can factor this number down to approximately three megabytes. This allows users to store ten times the amount of MP3 files in the same space as a CD track. Also, download speeds of compressed files are a fraction of their uncompressed equivalents. Music tracks consist of multiple sound layers, varying in frequency. MP3 compression algorithms operate by deleting unnecessary data from these layers. If two sounds are playing simultaneously, louder sounds can drown out the quieter sounds. The quieter sounds can be deleted without noticeably impacting the track. Similarly, some sounds are inaudible to the human ear, and are subsequently deleted. This makes the compression algorithm particularly interesting, as it has been tailored to us.

Further reading

There are varying degrees of compression in MP3 files. The lower the “bit rate”, the more data is deleted. Very low bit rates (96 Kbps is most commonly the lowest) may sound noticeably different to their CD counterparts. Low bit rates conserve memory by lowering the threshold for louder sounds to be considered loud enough for deletion of other layers. 128Kbps is recommended for radio sound quality, and 160Kbps is equivalent to uncompressed CD tracks. If the bit rate is high enough, even the most discerning audiophile cannot make a distinction. MP3 files are designed with home users in mind. They have made it substantially easier to edit and manipulate files using online software, as well as computer to computer sharing over the internet . They can be recorded easily and for free, allowing more artists to flourish. The compression algorithm is complicated but the concept is simple. The MP3 format has revolutionised online music sharing, allowing easy storage without compromising on quality.