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A
basic primer on sound Sound travels
through the air as longitudinal waves.
Molecules of air vibrate, changing their
distances between each other. When they
come closer, they are known as
compressions. When they move further,
they are known as rarefactions. These alternating
rarefactions and compressions of air
reach your eardrum, and cause the
eardrum to vibrate too. Once your
eardrum is vibrating, your ear will hear
the sound. |
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| Audio signals are
measured in Bels, or in the more
convenient Decibels (dB), which are
one-tenth of a Bel. The Decibel or Bel
standard is used to measure sound in the
same way humans judge sound. For
example, if we were to perceive a
doubling of a standard audio volume, the
sound level would have increased by
about 6dB. However, how much extra
energy is required to achieve this
doubling would vary according to how
loud the sound already was to begin
with. |
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Analog electric
audio signals come in various standards,
but typically, they are direct currents
that vary in strength. The quickly
changing high and low voltages in an
audio signal correspond to the
rarefactions and compressions of sound,
though not necessarily in that order. When the diaphragms
of
microphones
vibrate, they create a little current
into the audio cable. The same can be
said for electric guitar pickups that
detect the movement of metal strings
over a magnetic field. This current is
your audio signal. |
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A loudspeaker does
precisely the same thing in reverse. The
current reaches the speaker, and the
coils of wire in the speaker turn it
back into actual movement, that causes
the air surrounding the speaker to
vibrate, which results in sound again. But a microphone produces a very low voltage signal, while a loud speaker relies on a very very high voltage signal to work. The device that sits between the two is an amplifier. The amplifier will increase the voltage in for a higher-power audio signal proportionately to the voltage that it is receiving. Read
more on Page 2 |
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