Corey Bailey
           Audio Engineering
USEFUL INFORMATION        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 second (or Hertz).   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 sine wave. 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 on an oscilloscope, (Right) you would observe a sine wave! What I have just described can be divided into two categories: LIVE SOUND: Is the experience of listening to the whistler without any electrical amplification. ANALOG AUDIO: The PA system: It converted the Live Sound into electrical signals and back again to pressure waves via the loudspeakers. Records and analog audio tape are two examples of storage methods used for Live Sound that was converted to electrical signals and then back to amplified sound by your home stereo equipment. If you found this interesting and would like to learn more about the subject, there are some excellent articles at the JISC Digital Media website. Return to TOP of page © 2012 Corey Bailey
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                Image courtesy of: JISC digital media, uk