A LITTLE ABOUT SOUND
Very few of us actually think about how we hear sounds.
A basic understanding of how sound gets transmitted through the atmosphere
and subsequently heard by us mortals is useful.
Here is a somewhat oversimplified explanation:
Imagine whistling a single note. What happens is that air being exhaled passes
up through your throat, fills the space inside your mouth and passes through
your parsed lips. What actually creates the sound is that the exhaled air inside
your mouth builds up pressure and it is released several hundred times a second
or, to put it another way, your mouth acts as a resonator. The resulting
turbulence is pressure waves that exhale from your parsed lips. For each “high”
pressure wave there is a void just behind it or “low pressure wave.” Each high
pressure wave and subsequent low pressure wave constitutes a cycle.
If a person is whistling a Concert Pitch ‘A’ note, they are creating 440 cycles per
Because each cycle is created
over time, the rise and fall from
zero (no pressure) to high, back to
zero, then to the low pressure
zone and back to zero pressure
creates what is known as a
Our ear drums respond (vibrate,
actually) to the changes in air
pressure, and those vibrations are then converted into tiny electrical signals and
transmitted to our brain via our nervous system.
Now, imagine that someone is standing on a stage whistling a single (A) note
into a microphone. The microphone works somewhat like the ear drum and
converts the pressure waves into tiny electrical pluses and minuses. Those tiny
electrical signals are then amplified about a thousand times by the sound system
amplifiers, and the resultant voltage is applied to loudspeakers. If the PA system
is connected correctly, every high and low pressure wave created by the whistler
is faithfully reproduced by the loudspeakers and the audience hears the changes
in air pressure from a hundred feet away or so, as if they were seated in front of
If you were to tap into the
amplified voltage at any
point in the PA system and
display it on an
, (Right) you
would observe a sine wave!
What I have just described can be divided into two categories:
Is the experience of listening to the whistler without any electrical amplification.
The PA system: It converted the Live Sound into electrical signals and back
again to pressure waves via the loudspeakers.
Records and audio tape are two examples of storage methods used for Live
Sound that is converted to electrical signals and ultimately to amplified sound by
your home stereo equipment.
© Corey Bailey Audio Engineering
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Image courtesy of: JISC digital media, uk