Figure 5-1 Sine Waveform - Commodore Amiga Hardware Reference Manual

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Figure 5-1: Sine Waveform
In electronic sound recording and output devices, the attributes of sounds are
represented by the parameters of amplitude and frequency. Frequency is the number of
cycles per second, and the most common unit of frequency is the Hertz (Hz), which is 1
cycle per second. Large values, or high frequencies, are measured in kilohertz (KHz) or
megahertz (MHz).
Frequency is strongly related to the perceived pitch of a sound. When frequency
increases, pitch rises. This relationship is exponential. An increase from 100 Hz
to
200
Hz results in a large rise in pitch, but an increase from 1,000 Hz to 1,100 Hz is hardly
noticeable. Musical pitch is represented in octaves. A tone that is one octave higher
than another has a frequency twice as high as that of the first tone, and its perceived
pitch is twice as high.
The second parameter that defines a waveform is its amplitude. In an electronic circuit,
amplitude relates to the voltage or current in the circuit. When a signal is going to a
speaker, the amplitude is expressed in watts. Perceived sound intensity is measured in
decibels (db). Human hearing has a range of about 120 db; 1 db is the faintest audible
sound. Roughly every 10 db corresponds to a doubling of sound, and 1 db is the smal-
lest change in amplitude that is noticeable in a moderately loud sound. Volume, which
is the amplitude of the sound signal which is output, corresponds logarithmically to deci-
bel level.
Audio Hardware 133