Sound waves and frequency

Sound is vibrations in the air. Stand close to a speaker playing bass — you can feel the vibrations in your chest. On a screen, sound is visualised as a wave curve that moves up and down.

• High frequency (many waves per second) = high pitch (e.g. a whistle or a treble note).
• Low frequency (few waves per second) = low pitch (e.g. bass or a deep voice).
• Large amplitude (tall wave) = higher volume. Small amplitude = lower volume.

A microphone measures variations in air pressure thousands of times per second and converts them into digital data. This is how a voice assistant or a transcription programme ‘hears’ and processes your speech.

Try this: Open a free tool that displays sound waves in real time, such as Audacity on your computer or an oscilloscope app on your phone. Whistle — you will see dense waves. Hum — the waves become sparser. Clap your hands — you will see a short, high spike.

Say the sound ‘a’ and then ‘s’. ‘a’ produces a smooth, repeating wave pattern. ‘s’ looks like noise with irregular peaks. Computer programmes can distinguish between sounds and letters by analysing these patterns in the waveform.