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What we perceive as sound occurs when our ear senses a variation in environmental pressure at set or changing
frequencies. Sound travels through a medium, such as air, or water, as a wave and is a physical phenomenon.
The average person hears sound waves that travel at a frequency of 20 Hz to 20000 Hz (20 KHz). Sound originates as an analog wave, but an electronic device stores sound in digital format. To store sound in a digital form, conversion from analog to digital must occur. This occurs in an analog to digital converter, which takes samples of the wave form with a set resolution, at a set frequency. This resolution and frequency are properties of digital sound files and are known as the following. Sample rate: The amount of samples taken per second. Bit rate: The resolution of the sample taken in a single snapshot at a frequency of the sample rate. For example, files with a resolution of 8 bits can only represent 256 (2^8) amplitude values where as files with a resolution of 16 bits can represent 65536 (2^16) different values. Sound can be sampled in mono or stereo. The difference between mono and stereo is the number of simultaneous channels. Mono is single channel audio where as stereo is dual channel, that is to say, 2 channels of audio sampled at a set resolution at a set rate. In raw form, a collection of these samples becomes large quickly. For example 1 second of stereo audio, sampled at a resolution of 16 bits and at a rate of 44,100 samples per second requires 172.3 Kb. (44100 * 16 * 2) / 8 = 172.265625 Kilobytes. A full minute of audio would require over 10 megabytes in raw form! This file size is very large and unsuitable for distribution. To facilitate quick distribution, sound file compression is used. The following file formats are various implementations of file compression. Not all file compression is created equal, and I will present the advantages and disadvantages of the file formats below: |
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