This wave has the largest, what we call, amplitude which is this distance from this imaginary middle line up to the peak. All these other waves have smaller amplitudes. It’s this amplitude of the wave that controls the loudness and the loudness of a sound is measured in something called decibels.>>So, is amplitude the only way a wave can be different?>>Well, you tell me. Amplitude affects the volume of a sound. Is volume the only property of sound that we can hear?>>Well, no, some are really low and some are really really high, like high pitch voices compared to low pitch voices.>>Exactly, and you’ve said yourself. You used the word pitch and pitch is actually controlled by what’s called the frequency of a wave.>>Well, Andy, what exactly is frequency?>>Well, remember have we said that waves will be caused by these little vibrations?>>Yeah.>>Well, frequency just measures how many vibrations are happening each second. So, if something’s vibrating slowly, or if it’s vibrating quickly. And we measure this with a unit called Hertz. So, if these vibrations are slow, we get a low frequency wave. If they’re fast, we get a high frequency wave.>>I see.