Representing sound

Sound is the continual vibration of air particles and is an analogue signal. Therefore, we need to convert sound into binary to be able to process and store it using a computer.

A sound card translates between the outside world's analogue information and a computer's digital information. It uses an analogue to digital convertor (ADC) to change sound into a digital format the computer can understand, and a digital to analogue convertor (DAC) to change digital information into sound that you can hear.

Flowchart of how sound input to a microphone goes through an analogue to digital convertor

How is sound stored?

Digital sound is broken down into thousands of samples per second.

Sampling is when we record sound at set time intervals and is measured in hertz. 1 hertz = 1 sample taken per second.

Sample frequency is the frequency at which a sample in a sound file is taken. Most music CDs have a sample frequency of 44,100 hertz (samples per second). Each sound sample is stored as binary data.

Sample frequency is influenced by both bit rate and bit depth.

  • Bit rate: How accurate each sample will be. It is the number of bits used per second of audio
  • Bit depth: The number of bits of information in each sample, (the higher the bit depth, the higher the quality of the audio)

Analogue to digital conversion

A computer's sound card contains:

  • An analogue-to-digital converter (ADC) converts the analogue signal from a microphone to a digital signal for the computer to process
  • A digital-to-analogue converter (DAC) converts the computer's digital signal to an analogue one for the listener