PURPOSE: To demonstrate the relation between "consonance" (musical intervals) and frequency ratios.
DESCRIPTION: Two identical oscillator/loudspeaker setups are sounded and simultaneously input into the two axes of an oscilloscope to produce a Lissajous figure. Two pitches which are related by simple rational whole numbers such as 3:2 or 5:4 are musical intervals and produce stationary figures. Beats between two close frequencies are also visibly evident by this technique. Try two close frequencies and two related by a small whole number interval for contrast. Let your students judge their consonance.
SUGGESTIONS:
REFERENCES: (PIRA unavailable.)
EQUIPMENT: Two oscillators with loudspeakers and oscilloscope with scope/TV cart.
SETUP TIME: 5 min.
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