The sound is a wave generated by the oscillation of the molecules of the air that, compressing the adjacent layers, cause in turn their vibration. The characteristics of the sound are three: pitch, intensity and timbre.
- The intensity is the volume of the sound, and it is greater the larger is the amplitude of the wave (and consequently that of the vibratory motion of the molecules of the air).
- The pitch allows to distinguish between grave and acute sounds, and depends on the frequency of the wave. For example, a female voice is normally more acute (and therefore emits sound waves characterized by a higher frequency) of a male one; also sounds gradually become more acute as you move to the right on the keyboard of a piano.
In practice, the more a sound is acute, the less time is spent by the molecules in a complete oscillation.
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More grave sound  |
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| More acute sound |
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- The timbre is what distinguishes the sound of different musical instruments, even with the same intensity and height, and depends on the shape of the wave. In fact, while electronic instruments can produce sinusoidal sounds (from sinusoid, or sine wave, that is the graph of y=senx), such as those represented in previous figures, the sound coming from a musical instrument (or by the human voice) is the sum of any sinusoidal sounds whose frequency is multiple of one called fundamental frequency (all this sounds forms the harmonic series). The amount of needed harmonics and the respective amplitudes (that, remember, are functions of their intensity, and therefore of their “weight” within the real sound) determine the shape of the wave, and then the timbre of a musical instrument.
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| Example of timbre (1) |
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| Example of timbre (2) |
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N.B. The shape of the wave in the two examples of timbre are purely illustrative, not having been derived from corresponding sound.
