Sound Wave
Light, Sound and Waves

Pitch and frequency - an activity

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

The aim here is to bring together the concepts of pitch and frequency. Pupils are encouraged to relate what they hear (high and low pitched sounds) to more precise measurements of high and low frequency.

What to Prepare

  • various pairs of sounds: these might be recorded onto a small music player. You'll need to be able to jump from sound to sound pretty smartly. Most should be a pure note – a single frequency. Some of the pairs of sounds should be very close in frequency; others more clearly separated. For the sake of clarity of demonstration it is probably best not to have the same computer playing the music and analysing it.
  • three cards marked pitch higher, pitch lower, and same pitch: can't tell.
  • three cards marked frequency higher, frequency lower, and same frequency: can't tell.
  • a microphone linked to a computer running sound-analysis software.

The software should produce a near full-screen display like this (Audacity (on Windows, Linux or Mac OSX) currently offers the required facility and more for free).

What Happens During this Activity

Start with pairs of sounds. Play the first one and ask the pupils to indicate with the pitch cards whether the second sound is of higher, or lower or the same pitch.

We think it a really good idea to draw on a wide range of sounds, not just, for example, using musical instruments or the human voice.

Then introduce the computer display, showing how the rise and fall in pitch is matched by the rise and fall in the frequency display. Refer to the numbers up the vertical scale as values of frequency.

To introduce the idea of frequency, go back to counting the to and fro motion of the wobble board. Carefully move through one complete cycle: from the board being as close to you as possible to as far away as possible and then back to as close as possible again. Then introduce the frequency as the number of to and fro movements each second.

Now introduce the frequency cards, asking pupils to make judgements about pairs of sounds in terms of frequency and seeing how they match with the display.

To take it further: plenty of fun can be had with pitch-bending software, which alters the playback rate. This can be used to reinforce the connection between the number of to and fro motions a second and the pitch. Before computers you would have played tape recordings speeded up. Beware of cleverly designed software that alters the rate of playback without altering the pitch: lots of mathematical processing goes into that!

Teacher: The sound we can hear comes from lots of to and fro movements of the speaker and the air each second. There are too many for us to count, so we get the computer to do the counting for us.

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