Other Properties of Sound
In addition to frequency and amplitude, sine waves have several other properties that contribute to the human perception of sound. These properties include phase, timbre, and envelope.
Phase
When two sine waves occur simultaneously, they interact with one another and create a composite sound wave. If the two waves have exactly the same amplitude and frequency, the composite wave will be the sum of the amplitudes—in other words, twice the volume. For example, having two audio speakers instead of one provides double the volume. However, altering the frequency or amplitude of one sine wave would put them “out of phase.”
Decibel Level | Sound |
130 dB | Emergency siren; threshold of pain |
120 dB | Jet airplane |
110 dB | Jackhammer |
100 dB | Heavy thunderstorm |
90 dB | Motorcycle |
80 dB | Lawn mower |
70 dB | Heavy traffic |
60 dB | Loud conversation |
50 dB | Average office |
40 dB | Average household |
30 dB | Quiet conversation |
20 dB | Whisper |
10 dB | A pin dropping |
0 dB | Absolute quiet; threshold of hearing |
Timbre
The timbre of a sound is its tonal character, sometimes called its tone color. Most sounds are not pure, or single, sine waves. Most sounds are composite waves comprised of a fundamental wave (the sound's lowest frequency) and additional frequencies called harmonics. Additional frequencies change the human perception of tonal character and thus the perception of the overall sound. For example, consider a man singing ...
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