'audio' - description

audio: A digital representation expresses the pressure wave-form as a sequence of symbols, usually binary numbers, which permits digital signal processing. Whilst all real-world audio signals are continuous-time and continuous-level analog signals, the frequency range of these signals is limited by physical effects, and human ears cannot perceive frequencies below approx. 20 Hz or above approx. 18 kHz (strongly depends on the age of the listener). Therefore, there is no significant loss of information when the analog signal is sampled using a high enough sampling rate (see: sampling). In addition, the dynamic range of audio signals is limited by Noise (sound). More than 130 dB Signal-to-noise ratio is almost impossible to achieve. Therefore, quantization also does not result in significant loss of information either, if done appropriately. Both sampling and quantization must be applied to convert the continuous-time analog signal to a discrete-time digital representation. Although such a conversion is more or less lossy, most modern audio systems use this approach as the techniques of digital signal processing are much more powerful and efficient than analog domain signal processing.
Source: Wikipedia (http://en.wikipedia.org/wiki/Audio_signal_processing)