MULTIMEDIA

1.Multimedia is just two or more media.
2.Generally, the multimedia is the combination of two or more continuous media, that is, media that have to be played during some well-defined time interval, usually with some user interaction.

An audio (sound) wave is a one-dimensional acoustic (pressure) wave. When an acoustic wave enters the ear, the eardrum vibrates, causing the tiny bones of the inner ear to vibrate along with it, sending nerve pulses to the brain. These pulses are perceived as sound by the listener.
In a similar way, when an acoustic wave strikes a microphone, the microphone generates an electrical signal, representing the sound amplitude as a function of time. The representation, processing, storage, and transmission of such audio signals are a major part of the study of multimedia systems.
The frequency range of the human ear runs from 20 Hz to 20,000 Hz but the useful range falls between 20 Hz to 4,000 Hz.

The ratio of two sounds with power A and B is conventionally expressed in dB (decibels) according to the formula.
dB=10 log10(A/B).
Audio waves can be converted to digital form by an ADC (Analog Digital Converter). An ADC takes an electrical voltage as input and generates a binary number as output.
To convert the analog audio into digital audio, we should know the highest frequency of the analog signal. According to the Nyquist Sampling Theorem, the analog signal is sampled at a rate of twice or greater than the highest frequency of the analog signal per second. E.g. If an sine signal has a frequency of 300 Hz i.e. sine(300), then this signal must be sampled at least 600 times per second. The sampling interval is 1/sampling rate.