Casio VZ-8M Operation Manual page 88

; you might imagine, the cyclical changes in air pressure caused by the
7
^oscillation of the bell's surface produced what are known as "compres-
fsfonaJ waves." These waves of air pressure cause our eardrums to vibrate,
f nerves in the inner ear translate these vibrations into "sound."
aturally, the type of vibration produced is dependent on a great number
|6f factors — as the vibrating body differs so will the vibrations, and so
Iwill the sound.
peeing Sounds With Our Eyes: Waveforms
> we discussed in the introduction to this sound seminar, sounds cannot
factually be seen with the human eye. However you've probably heard such
sions as "the waveform is different" "this is almost a pure sine
rave," with regards to sound. But what exactly is meant by these terms
- waveform and wave — and how can they be observed?
f For a moment, let's consider the how a microphone works. As you prob-
I ably already know, a microphone converts compressional waves into elec-
{trical signals, which can then be transmitted to an amplifier and speakers
| for output as sound. As shown in the illustration, these electrical signals
| are simple conversions of compressional waves — with condensed air be
ting output as positive (+) electrical charges and rarefied air being output
I as negative (-) charges. The compressional waves of air are, then, trans
it formed into electrical "waves", which can be viewed on electronic devices
|-such as oscilloscopes. These waves are cyclical, and their form over time
pproduces a visible shape or form which is called — you-guessed it, a
: waveform.
I The Three Basic Elements of Sound
When we hear an individual sound, it can be defined by considering three
ormf different parameters; Pitch, Timbre and Amplitude (loudness).
ELEMENT 1: PITCH
Pitch is the quality of a sound which makes it seem higher or lower than
Vibrational
other sounds. For example, the notes at the top or right-hand end of a
energy
keyboard are "higher in pitch" than those at the left-hand end.
The pitch of a note is determined by the rate at which vibrations are set
up in the air particles — i.e. the rate at which cyclical compression and
rarefaction takes place.
arefied air
If we convert sounds into electrical signals and look at them on an oscil
loscope, we can see that the number of waves per time unit differ between
"high-pitched" and "low-pitched" sounds.
jndensed air
For a moment, let's go back to our bell example. As the bell produces
compressions and rarefactions at a fixed rate, waves of particle vibrations
are generated in the air surrounding the bell. These waves move away from
the fork at a fixed rate — the speed of sound. As waves move away from
our sound source (the bell) at a fixed rate, the length of each wave de
pends on the rate at which the bell's surface vibrates. A single cycle of
I
a sine wave is shown on the right.
condensed
led v^^v
Vibrational (Eardrym) s
Air
Waves of condensation
Kinetic
and rarefaction
energy
(high atmospheric pressure)
condensed „ _. ,
Rarefied ■►©
rarefied (low atmospheric
pressure)
Oscilloscope
IWllBlHlHJfflffl
-Low sounds High sounds -
(low register)
(high register)
Few waves
Many waves
r\
*-1 cycle —!
. ^
-Time