User Guide

LOUDNESS AND PITCH
When the air pressure is constant there is no sound.You perceive constant air
pressure as silence. When something causes a sound, the air pressure around
your eardrum changes above and below the normal atmospheric level. You
perceive the amount of change as the loudness of the sound.The loudness of a
sound, called its amplitude, is usually measured as a fraction of a standard
level, often in decibels (dB).
You perceive the rate of change in the air pressure as the pitch of the sound.
In scientific terms, this term corresponds to the frequency of the wave. The
frequency is usually measured in Hertz (Hz), or cycles per second.
Sounds in nature are not as simple as the above sine wave. In reality, a sound
would look something like the one below. This irregular waveform does not
have a periodic amplitude or frequency.
TIMBRE
Complex waveforms like the one shown above are constructed by combining
a number of simple waveforms (like the one in the first drawing) of different
amplitudes and frequencies. This is why we perceive both high and low
pitched sounds at once when we hear most natural sounds.
The characteristic sound of a waveform (be it produced by a grand piano or a
violin) is called its timbre. Timbre, also referred to as tone color, is said to be
rich or full when there are many different frequencies in a sound. Most people
consider a sound from a sine wave dull since it only has one frequency.
INTRODUCTION
8