Input and output of sound

Key points

1. In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium, such as a gas, solid or liquid.
2. In computer science, all type of information has to be in binary form(digitized) so that it can be stored and manipulated by computer.
3. The input of sound is a process of digitizing sound.
4. The output of sound is a process of converting digital signals to analog signals.

Input

For input, microphone is needed. Microphone converts sound into electronic signal. A microphone has a diaphragm. The diaphragm vibrates when subjected to pressure. The diaphragm is connected to a circuitry. The vibration causes a change in electrical signal.
Two types of microphone:

1. Condenser microphone
   Condenser is the old name of capacitor. The condenser microphone uses capacitances change as the mechanism.
2. Piezoelectric microphone
   It uses the phenomenon of piezoelectricity, that is, the ability of some materials to produce voltage when subjected to pressure. In such a way, the vibration of diaphragm is converted to electrical signal.
   NOTE: the electrical signal has to be converted to digital signal before it can be stored and manipulated by computer. That is what an ADC (Analog-to-Digital Converter) does.

Output

The output of sound is the revers process to that of input. A DAC (Digital-to-Analog Convert) is used to convert the digital signal generated by computer to analog signal. The analog signal is used to produce vibration to generate sound.

For output, usually a speaker is needed. The main components of a speaker are: a coil, a magnet, a diaphragm. The analog signal is passed to the speaker. The current flows through the coil which is suspended in the magnetic field provided by the permanent magnet in the speaker. As the direction of current keeps reversing, the coil moves backwards and forwards. This movements control the vibration of diaphragm to produce sound.