Pitch

Some instruments sound high, a violin sounds sweet, a nearby crash of thunder sounds loud. The features that let the ear tell sounds apart are the characteristics of sound: pitch, loudness and quality.

Activity 4.4

Clamp a hacksaw blade between two blocks of wood, with about 10 cm sticking out from the edge.
Twang the blade and listen to the sound it makes as it vibrates.
Repeat, letting 5 cm more of the blade stick out each time, and listen again.

Figure to be added

Figure 4.28 — a hacksaw blade clamped at the edge of a table and set vibrating: (a) with a short length sticking out, (b) with a longer length sticking out.

The observation

The longer the vibrating part of the blade, the lower its frequency of vibration, and the less shrill the sound becomes. A shorter blade vibrates faster and sounds shriller.

Pitch

Pitch is the sensation the ear feels that depends on the frequency of the sound wave.

The higher the frequency of a vibrating object, the higher the pitch of the note it gives out; the lower the frequency, the lower the pitch. Middle sa has a frequency of 256 Hz and high sa 512 Hz, so the pitch of high sa is double that of middle sa.

Seeing a sound

Connect a microphone to a cathode ray oscilloscope (CRO) and sound a tuning fork near it. The screen draws a graph of how the air particles vibrate against time. The shape of that graph is the waveform of the sound.

Figure to be added

Figure 4.29 — a microphone picking up sound, connected to a cathode ray oscilloscope showing a wave on its screen.

Figure to be added

Figure 4.30 — two oscilloscope screens: a low-pitched sound with few, widely spaced waves (low frequency, long period) and a high-pitched sound with many, closely spaced waves (high frequency, short period).