Sound is the audible band of the
mechanical wave spectrum, similar to the band of visible light
within the electro-magnetic wave spectrum.
Hearing is mainly concerned
with two parameters of sound : its frequency (wave/sec = Hertz),
which allows differentiation of pitch, and its pressure level
(dB), which allows differentiation of intensity.
The period is the inverse of the
frequency (T=1/F) :
short periods (high frequencies)
are representative of high pitch tones, and long periods (low
frequencies) are representative of low pitch tones.
You can activate the next 3 drawings
and hear: a) a 3 kHz sound; b) a 300 Hz (low pitch) sound; c)
the same low pitch (300 Hz) modulated in intensity.