In the world of the computer, where information must be communicated in a digital form, there occurs a conversion of sound waves, in the form of changes in air pressure, into an analogous change in voltage. This means that sound waves are turned into electric voltages, which are then converted into numerical data to be stored on a memory device, such as a hard drive. The resulting size of these files tend to be quite large , and in most cases, far too large to be conveniently stored on our MP3 devices in sufficient quantity. This is where data compression comes into play. Data compression,or bit-rate reduction, is the encoding of information using less bits than the original, which results in a smaller file size. Bits are the basic building blocks of information in the digital world, consisting of either a 1 or a 0. When a file size is reduced using compression, a certain number of bits are removed from the original file, resulting in a smaller and more manageable file for storage and streaming purposes. There are 2 main forms of data compressions: i) Lossy compression ii)Lossless Compression.
i) Lossy compression:
The aim of lossy compression in audio, is to compress a file as much as possible, whilst still allowing it to be as close to human perception as possible. This means that the ranges of sounds that the average ear cannot hear or distinguish are removed. This done by “sampling” the audio, that is, creating many discrete numbers that represent the amplitude of the wave form, at a lower rate than that of the original, thereby reducing the quality and the file size significantly. Examples of formats that are created using Lossy compression are MP3’s, AAC, WMA, and Dolby AC-3.
ii) Lossless compression:
This form of encoding is aimed at preserving the audio’s fidelity, and does this by creating an exact reproduction of the compressed data. For people that do not wish to compromise their audio’s quality, lossless compression is way of reducing file size by up to 50%, through the removal of redundant bits, much like ZIP compression. Examples of formats that use lossless compression are WAV, FLAC, M4A and ALAC.
Though the use of compression is common when storing or archiving media files, music found on CD’s are uncompressed, and in some cases, you may want to preserve your original, unaltered files. There are different forms forms for this, such as AU, AIFF, CDA and WAV