Sound is a physical phenomenon by which matters are vibrated such as a violin string, guitar, and block of woods. As the matter vibrates, pressure variation is created in the surrounding air. This low and high air pressure is propagated through a air in a wave light motion. Which when reaches to human ear, a sound is heard. The propagations of oscillation which is called a wave form.
The wave form repeats the same shape at regular intervals which is called period.(one complete cycle)
The natural sounds are not perfectly smooth or uniformly period. The sounds which have recognizable periodicity tend to be more musical then non periodic sounds.
Example of periodic sounds sources are musical instrument, vowel sounds whistling wind, bird songs, etc
Non periodic sounds are coughs, sneezing, rousing water etc.

Some terms:

Frequency:

The number of periods per second or number of cycles completed by a wave form in a second is called the frequency of sound or wave. It is measured in hertz (HZ)
1000 hz à 1khz
1000 khz à 1mhz
1000 mhz à 1ghz
1000 ghz à 1thz
The frequency range of sound in divided into four groups. a) infra sound:à from 0 to 20 HZ
b) human hearing or audio sounds:à 20HZ to 20 KHZ
c) ultra sound:à 20KHZ to 1 GHZ
d) hyper sound:à 1 GHZ to 10 THZ
Multimedia system uses 20hz to 20khz frequency range. This range of sound is called audio and wave as acoustic signal.
Beside speech and music, any other audio signal is treated as noise for example, aero plane, falling water.

Amplitude:

The maximum displacement of the air pressure wave from its mean or quit scent state in vertical direction is called amplitude of the wave or sound. It measures of the strength of a signal such as sound or voltage. Representation of sound in computer:The smooth continuous wave from sound is not directly represented in computer. The computer measures the amplitude of wave from at regular intervals of time to produce a series of numbers. Each of these measurements is a sample, or digitally sample wave form.
The process by which audio signal converted into digital signal is the analog to digital converter ADC and digital to analog is DAC.
AM79C30A, digital subscriber controller chip is an example of ADC available in SPARC station tm , it include built in speaker for audio output. Similarly DAC is available in UNIXTM device.

Sampling rate:

The rate at which a continuous wave form is sample is called sampling rate. It is also measured in hertz. The CD standard sampling rate is 44100 Hz that is the wave form is sample 44100 times per seconds. According NYQUIST sampling theorem the sampling rate should be at least twice of the maximum frequency responses.

Quantization:

It is the process by which the sample values from the wave form are taken at discrete time. Since sample values are taken at discrete time so its resolution or quantizations of sample values are also discrete, it depends on the number of bits used in measuring the height of the wave form. An 8 bit quantization can have 2^8=256 possible values. Similarly to 16 bits can have 2^16=65536, the lower the quantization, the lower the quality of the sound.

Sound hardware:

It includes input/outpurt devices. For eg: Microphone jacks and built-in speakers are devices connected to an ADC and DAC respectively for the input and output of audio.

Audio formats:

AM79C30A, digital subscriber controller provides voice quality audio. This converter uses 8 bits meu law, encoded quantization and a sampling rate of 8000 Hz; it is fast and accurate for telephone quality speech input. CD quality audio is uses 44100 samples per second with 16 bits linear PCM, encoded quantization.