# What are sine waves

## Pure tones as opposed to real tones

A pure tone is a tone with a sinusoidal waveform. A sine wave is characterized by:

• Their frequency: the number of cycles per second. Your unit is Hertz (), for example.
• Their amplitude (in terms of loudness for sounds): the size of each cycle.

These properties are deciphered by the human ear in order to perceive a sound. Humans can hear pure sounds from to (for the best ears), but this audible range decreases with age. In comparison, the light we see is made up of sine waves of up to.

You can check the hearing range of your ears with youtube videos like the following, which plays all the pure tones from to. Chances are you're not hearing anything.

The human perception of volume depends on the frequency of the pure sound. For example, a pure tone at the amplitude of the frequency is quieter than a pure tone at the amplitude of the frequency. Human ears follow a psychoacoustic model (for those interested an article on Wikipedia with further information: Psychoacoustics).

Note: This fun fact will have interesting ramifications by the end of the article.

### Pure sine wave at 20 Hz

In this figure we see the representation of a pure sine wave of frequency and amplitude.

There are of course no pure tones, but every sound in our world is the sum of several pure tones at different amplitudes.

Composition of sine waves

This illustration shows a more realistic sound made up of several sine waves:

• a pure sine wave of frequency and amplitude
• a pure sine wave of frequency and amplitude
• a pure sine wave of frequency and amplitude
• a pure sine wave of frequency and amplitude

A real sound can consist of thousands of pure tones.