Also called Nyquist's Theorem. Before sound as acoustic energy can be manipulated on a computer, it must first be converted to electrical energy and then transformed through an analog-to-digital converter into a digital representation. This is all accomplished by sampling the continuous input waveform a certain number of times per second. The more often a wave is sampled the more accurate the digital representation. Nyquist's Law, named in 1933 after scientist Harry Nyquist, states that a sound must be sampled at least twice its highest analog frequency in order to extract all of the information from the bandwidth and accurately represent the original acoustic energy. Sampling at slightly more than twice the frequency will make up for imprecisions in filters and other components used for the conversion.

For example, human hearing ranges from 20Hz to 20,000Hz, so to imprint sound to a CD, the frequency must be sampled at a rate of 40,000Hz to reproduce the 20,000Hz signal. The CD standard is to sample 44,100 times per second, or 44.1 kHz.

Digital sound vs Analog sound

What is digital sound?

 Digital sound is stored as bytes of information on the media which are made into sound by computer like processing. Exact copies can be made of the original.

What is analog sound?

Digital sound is stored as bytes of information on the media which are made into sound by computer like processing. Exact copies can be made of the original. 

COMPARISON CHART

ANALOG SOUND

-Signals: Analog signal is a continuous signal which represents physical measurements.

-Waves: Denoted by sine waves

-Representation: Uses continuous range of values to represent information

-Example: Human voice in air, analog electronic devices.

-Technology: Analog technology records waveforms as they are.

-Data transmissions: Subjected to deterioration by noise during transmission and write/read cycle.

-Response to noise: More likely to get affected reducing accuracy

-Flexibility: Analog hardware is not flexible.

-Uses: Can be used in analog devices only. Best suited for audio and video transmission.

-Applications: Thermomete

-Bandwidth: Analog signal processing can be done in real time and consumes less bandwidth

-Memory: Stored in the form of wave signal

-Power: Analog instrument draws large power

-Cost: Low cost and portable

-Impendance: Low

-Errors: Analog instruments usually have a scale which is cramped at lower end and give considerable observational errors.

DIGITAL SOUND

-Signals: Digital signals are discrete time signals generated by digital modulation.

-Waves: Denoted by square waves

-Representation: Uses discrete or discontinuous values to represent information

-Example: Computers, CDs, DVDs, and other digital electronic devices.

-Technology: Samples analog waveforms into a limited set of numbers and records them.

-Data transmissions: Can be noise-immune without deterioration during transmission and write/read cycle.

-Response to noise: Less affected since noise response are analog in nature

-Flexibility: Digtal hardware is flexible in implementation

-Uses: Best suited for Computing and digital electronics.

-Bandwidth: There is no guarantee that digital signal processing can be done in real time and consumes more bandwidth to carry out the same information. 

-Applications: PCs,PDAs

-Power: Digital instrument drawS only negligible power
-Memory:Stored in the form of binary bit

-Cost: is high and not easily portable

-Errors: Digital instruments are free from observational errors like parallax and approximation errors. 
-Impendance: High order of 100 megaohm

What is sample rate?

In developing an audio sound for computers or telecommunication, the sample rate is the number of samples of a sound that are taken per second to represent the event digitally.

The more samples taken per second, the more accurate the digital representation of the sound can be. For example, the current sample rate for CD-quality audio is 44,100 samples per second. This sample rate can accurately reproduce the audio frequencies up to 20,500hertz, covering the full range of human hearing.

what is a bit rate?

 describes the rate at which bits are transferred from one location to another. In other words, it measures how much data is transmitted in a given amount of time. Bitrate is commonly measured in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps)