Sampling Sound

The KS3 National Curriculum for Computing requires that students know how sound is stored inside the computer. In addition, GCSE Computer Science also requires that you understand the impact of sampling rate and sample size on the recorded sound.

When a sound is recorded for storage on a digital device, the sound wave is sampled at regular intervals and the height of the wave is stored as a number. The number of times per second that the wave is measured is called the sampling frequency and is measured in Hertz. The number of bits used to stored the sample is called the sample size, or sometimes the bit depth. A bit depth of n bits can represent 2ⁿ different values - e.g. CDs use 16-bit samples with 65,536 (i.e. 2¹⁶) possible values.

The width of the display below represents one second of sound. You can adjust the controls at the bottom to see the impact on the samples taken and how closely the track the original sound wave. Note the strange things that can happen if the sampling frequency is lower than the audio frequency.