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Appendix B Synthesizer Basics 474
Other waveform properties
In addition to frequency, other properties of sound waves include amplitude, wavelength, period,
and phase.
Amplitude
Wavelength
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Amplitude: The amplitude of a waveform indicates the amount of air pressure change. It can
be measured as the maximum vertical distance from zero air pressure, or “silence” (shown as a
horizontal line at 0 dB in the illustration). Put another way, amplitude is the distance between
the horizontal axis and the top of the waveform peak, or the bottom of the waveform trough.
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Wavelength: The wavelength is the distance between repeating cycles of a waveform of a
given frequency. The higher the frequency, the shorter the wavelength.
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Period: The wave period is the amount of time it takes to complete one full revolution of a
waveform cycle. The higher and faster the frequency, the shorter the wave period.
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Phase: Phase compares the timing between waveforms and is measured in degrees—from 0 to
360.
When two waveforms begin at the same time, they are said to be in phase or phase aligned.
When a waveform is slightly delayed in comparison to another waveform, the waveforms are
said to be out of phase.
Note: It is dicult to discern a constant phase dierence over the entire wave period, but if
the phase of one of the waveforms changes over time, it will become audible. This is what
happens in common audio eects such as anging and phase shifting.
When you play two otherwise identical sounds out of phase, some frequency components—
harmonics—can cancel each other out, thereby producing silence in those areas. This is known
as phase cancelation, and it occurs where the same frequencies intersect at the same level.
Phase: 180°
Phase: 0°