Appendix. The Synthesizer Sound Seminar - Casio HT-6000 Operation Manual

Appendix. The Synthesizer Sound Seminar
8
Sound
Every day, we hear a greater variety of sounds. Tones, the noise of car engines, doors opening and closing,
footsteps, rain .. . and music. In other words, we live our lives surrounded by sound. We can't see sound,
so how can we describe it?
Physics tells us that "Sound is vibration". Taking· the sound of a bell •as an example, we will try to pursue
the basics of sound as it is produced and as it is heard.
When kinetic (motive) energy is applied to a bell with a bell hammer as shown in figure 1, a "deformation"
of the bell occurs causing energy to work trying to restore the bell to its original state. A periodic repetition
of deformation and restoration commences. This is called vibration.
This vibration causes pressure changes in the air. These are called compressional waves. They are similar
to the ripples that occurs when a stone is thrown into water.
These compressional waves are transmitted to the human ear where they cause the eardrum to vibrate. These
vibrations are picked up by nerves so we hear them as "sound". If the vibrating body differs, so will the
vibrations, meaning that we also hear a different kind of sound. Outer space, where there is no air, is a world
altogether without sound.
I
:~ne
Remember
f - - - - - - - - - - - - - ~
Sound is vibration of the air.
(fig.
1)
2
Wave Forms
- Seeing Sounds With Our Eyes -
, I '
As explained above, sounds cannot actually be seen since they are ,vibrations of the air. However you will
often hear expressions such as , " the w~ve form is different" or "this is almost a pure sine wave" c~ncerning
sounds. What is meant by "sound waves"?
,,
' Condensed
))))) ) ) ilil'i)'°;"')'i')));"i')i'»J'it'"~~•E!),~
"T;m,
dense
J
dense
J
dense Rarefied
l
non -dense non-dense (low atmospheric ..
8
-1 cycle
---l
pressure)
Let's consider t~e mechani_sm o_ f a micro?hone which is used as a means for picking up sound. A microphone
~onvert~ sound. into electrical s'.gnals_ which can be then transmitted to an amplifier and' speakers. As shown
~n the 1llustr~t1on, these _electrical ~1gna~s are simple conversions of the vibrations of the air ( the changes
m atmo~pheric pressure) into electrical (±) and
8 .
When these changes are presented graphically they
d
ean_ be interpreted as "wa~e and displays then as waveforms on a television screen. If we use this kind of a
ev1ce, we can see sounds with our own eyes. ,
What we see are "waveforms" These waveforms diff ti d'
teristics. These points will be e~plained later on in th;r;~~:n~i:~cor mg to the sound and have various charac·
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