Oscilloscopes and sound

An oscilloscope is a machine that shows the wave shape of an electrical signal. When connected to a microphone they can show the wave shapes of sounds. These diagrams show oscilloscope traces of three sounds:

Trace one: peak heights half unit, peak to peak distance 1.5 units. Trace two: peak heights one unit, peak to peak distance 1.5 units. Trace three: peak heights one unit, peak to peak one unit.

Sounds 1 and 2

  • The sound waves have the same frequency, so the sounds have the same pitch.
  • Sound 2 has a greater amplitude than sound 1, so sound 2 is louder.

Sounds 2 and 3

  • The sound waves have the same amplitude, so the sounds have the same loudness.
  • Sound 3 has a greater frequency than sound 2, so sound 3 is higher pitched.

The frequency of a sound is the number of oscillations (waves) per second and is measured in hertz (Hz). It can be calculated by:

frequency = \frac{1}{time~period}

The time period is the time taken to complete one oscillation and is measured in seconds. So if the time period of a sound wave is 0.01 seconds, then the frequency is calculated as:

frequency = 1 ÷ 0.01

= 100 hertz

This would make a low pitched sound (low frequency) as this is towards the bottom of our audible range.