A level revision

Signal frequencies

The frequency of the wave, measured in Hertz (Hz), is the amount of cycles or oscillations made in a second. Recap the features of a wave in our introduction to waves page.

Consider the following signal:

This signal is made up from 3 different waves:

At each point the amplitudes of each wave adds up (bearing in mind negative signs) to give the amplitude of the signal.

Each of the 3 different waves has a different frequency, this presence of a range of frequencies in a signal is called its spectrum.

Plotting the frequency of each wave against the corresponding amplitude gives a graph of the frequency spectrum:

The left most frequency (in this case both the green and orange waves share the same frequency, they are drawn apart for presentation reasons) on the graph is known as the fundamental frequency. This is the lowest frequency which makes up the signal. All other frequencies are known as overtones.