iGCSE Computer Science - Distance Learning
Representing Digital Sound (2023 Specification Only)
New 2023 Syllabus Only
Representing sound in a computer system requires the data about the sound to be converted into a digital format. Before we understand how to convert the data, we must first understand how a sound wave works.
Sound waves can either be analogue or digital.
An analogue wave is a continuous, smooth wave which replicates the original sound.
A digital wave is a set of discreet steps which represent the meansurements taken from the original analogue sound.
Let’s look an an analogue soundwave in more detail. In the example below, you can see that the height of the wave is labelled amplitude, and the length of the wave is labelled frequency. Both of these measurements are important to capturing the shape of the wave in a digital format.
To create the digital wave, the height (amplitude) is measured and saved as a binary number using a ADC (Analogue to Digital Converter) inside a device such as a microphone. This measurement is known as a sample.
The rate at which these measurements are taken are measured in samples per second and called the sample rate. Later on, if you study the A Level, you may come across a formula that identifies what the sample rate should be – this is known as Nyquist Theorum (Nye-quist). This states that the sample rate should be twice the highest frequency of the sound wave to allow the whole wave to be captured – this is useful theory to know, but not needed at GCSE.
Once the samples have been saved, they can be reconstructed into an analogue wave by passing the measurements back through an DAC (Digital to Analogue Converter) which recreates the soundwave in an output device such as a speaker.
Try out recording a sound for yourself using the online Twisted Wave Sound Editor (or a free program such as Audacity) and adjusting the amplitude, pitch, and sample rate. What does this do to the wave?
Now you have seen what happens to a sound wave when it becomes dititized, download and complete the notes below.