Sound Propagation, Complex Waves, and Decibels

Amplitude (A)

Amount of pressure variation about the mean (or zero point)

Frequency (f)

How quickly a sine wave repeats itself

Frequency

Number of cycles completed in 1 second

Frequency Unit

Hertz

Period (T)

How long it takes to complete 1 cycle

Period Unit

sec, ms

Waveform

Amplitude as a function of time

Pure tone

Sine wave

Periodic sound

Sound that repeats itself every T seconds

Peak Amplitude (A)

Distance from 0 to the maximum along the y-axis

Peak-to-Peak Amplitude

Distance between the maximum and minimum

RMS Amplitude

Proportional to its peak amplitude, calculated as RMS = 0.707*A

RMS

Best measure of average amplitude

Root-Mean-Square

Mathematical operations applied to waveform in reverse order: square-mean-root

Frequency (Hz)

Expressed as cycles/second

High-frequency pure tones

Not necessarily more intense than low-frequency tones; have a higher pitch

Phase

Where in its amplitude cycle the waveform starts

Sine wave representation

Can be considered as a point spinning on a wheel or circle

Amplitude at a given moment

Depends on where the point is within a cycle

Phase location

Along the unit circle in terms of angle (unit: radians or degrees)