Binary and data representation - EdexcelSound

How analogue sound is represented in binary

Computers can only recognise binary. All data must be converted into binary in order for a computer to process it. Sound is no exception. To do this, sound is captured - usually by a microphone - and then converted into a digital signal.

An analogue-to-digital converter will capture a sound wave at regular time intervals. This recording is known as a sample.

For example, a sound wave like this can be sampled at each time interval:

The sound recorded at each sample point is converted to its nearest numeric equivalent:

This data is then stored in a file for later use.

Sample rate

Sample rate is the number of samples recorded in any given period of time. The higher the sample rate the closer the recorded signal is to the original. Sample rate is measured in hertz (Hz).

If the samples recorded above were plotted on a graph, the resulting representation of the sound wave would not be too accurate:

However, if the sample rate is doubled - twice as many samples in the same time period - the resulting representation would be closer:

However, the higher the sample rate, the larger the resulting file. As a result, sound files are often a compromise between quality and size of file. An audio file is usually recorded at 44.1 kilohertz (kHz). This is high enough for good sound quality while keeping file size down to sensible levels.

Bit depth

Bit depth refers to the number of bits used to record each sample. As is the case with images, the higher the bit depth, the more accurately a sound can be recorded, but the larger the file size. Typical bit depths are 16 bit and 24 bit.

Bit rate

Bit rate in the context of sound is simply a measure of how much data is processed for each second of sound. Bit rate is calculated by:

Sample rate × bit depth

As with sample rate, the higher the bit rate, the better the quality of the recorded sound.