A LITTLE ABOUT SOUND
While 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 humans is useful.
Here is a somewhat oversimplified explanation;
Imagine whistling a single note. What happens is that air being exhaled fills the
space inside your mouth and passes through your parsed lips. Put another way;
Your cheecks and your parsed lips act as a resonator.
The resulting turbulence is pressure waves that exhale from your parsed lips.
For each high pressure wave, there is a low pressure wave just behind it. 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 the whistler.
If you were to tap into
the amplified voltage at
any point in the PA
system and display it
(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, audio tape and digital files are some examples of storage methods
used for Live Sound or Analog Audio that is converted to electrical signals and
ultimately into amplified sound by your home stereo equipment.
© Corey Bailey Audio Engineering
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Image courtesy of: JISC digital media, UK