Understanding the properties of sound involves separating the physical properties from the perceptual properties. Physical properties are things we can measure. Perceptual properties describe how humans perceive specific physical properties. In general, human perception is exponentially related to physical properties.
Frequency and Pitch
Frequency is the measurement of the rate of sound vibrations, measure in cycles per second (cps) or Hertz (Hz). Pitch is how we perceive frequency. For example, the pitch A that an orchestra tunes to has a fundamental frequency of 440 Hz. For every octave increase in pitch you have a doubling of frequency. So the octave above that is A has a fundamental frequency of 880 Hz (2 x 440). And the next octave increase takes you to 1760 Hz (2 x 880).
Amplitude and Loudness
Amplitude measures the deviation in air pressure of sound. Amplitude can be an instantaneous measurement (peak amplitude), or it can refer to an average over time. Humans perceive amplitude as loudness. Amplitude can be measured in a few ways. One way to measure is in terms of a percentage of maximum, with 100% being maximum amplitude. Another was to measure amplitude is with decibels (dB). Decibels are designed to help map amplitude in a linear fashion to loudness. If you double the amplitude, you increase the decibel level by 6 dB. From 25% to 50% is a 6 dB increase. From 50% t0 100% is also a 6 dB increase. Humans perceive both increases as the same increase in loudness.
Spectrum and Timbre
Spectrum is the frequency content of a tone – specifically the frequencies present and their relevant amplitudes. Almost all tones have more than one frequency component present. We hear spectrum as timbre, or tone color.
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