*02 Sound,Light(46-102).qxd
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3:33 PM
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Musical notes
WAVES, SOUND, AND LIGHT Key words
1 Waveform
amplitude frequency fundamental harmonic
1 Waveform ● Musical
2 Waveform of 440 Hz note
Displacement
Piano
Displacement
Violin
Time
Time
instruments produce a range of notes, often due to vibrating strings or vibrating columns of air. The same note played on different musical instruments sounds different because, unlike a tuning fork, musical instruments do not produce pure notes. ● A musical instrument produces a fundamental frequency together with a series of overtones at lower amplitudes. The fundamental has the lowest frequency and the overtones have frequencies that are multiples of this fundamental. ● The number and amplitudes of the overtones determine the quality of the sound and are typical of the particular musical instrument thus middle “C” on a violin sounds different from the same note played on a piano. ● The fundamental frequency is also called the first harmonic. If this is equal to f then the overtones have frequencies of 2f, 3f, 4f, etc. They are called the second harmonic, third harmonic, fourth harmonic and so on.
2 Waveform of 440 Hz note ● It
is possible to analyse the frequencies and amplitudes of the harmonics which combine to produce a note on a musical instrument. ● When a note of frequency 440 Hz is played on a violin and a piano the mixture of harmonics is very different.
3 Frequency spectrum of 440 Hz note
1
2 3 Frequency in kHz
4
3 Frequency spectrum of 440 Hz note ● The
0
1
2 3 Frequency in kHz
4
amplitude of the second and fifth harmonics on the violin is much higher than the corresponding harmonics on the piano. This difference contributes significantly to the different sound of this note on the two instruments.
© Diagram Visual Information Ltd.
0
Piano
Amplitude
Amplitude
Violin