INTRODUCTION TO SYNTHESIZERS - hol.gr

The volume of the sound the same as the amplitude of the waveform. The amplitude is the "height" of the
waveform, or the height difference between the lowest and the highest part of the wave. The higher the
amplitude, the louder the sound. The roar of a jet engine has for instance a much higher amplitude than a
whispering voice.
It's just like the difference between a pebble that your through in the pond, and a boulder. Trust me, the
boulder will make much higher ripples!
The amplitude of a sound is also a measurement of its energy state - the louder the sound is, the more energy it
carries. It is probably hardly a surprise that sound waves with very high energy can damage your ears. And not
just your ears: the roar of a jet engine from at close range can destroy the blood vessels in the human body.
Extremely high-energy sounds can even be used to shatter rocks.
But since our goal is not rock shattering, let us instead look at how a synthesizer works to create artificial
sounds!
The oscillators
Now we understand the principle behind our sonic environment. Let's see how we can create artificial sounds
with a synthesizer.
First of all we need something to generate a soundwave with. A device to create a wave with is usually called an
oscillator.
The first synthesizers used analog electronic oscillator circuits to create waveforms. These units are called VCO's
(Voltage Controlled Oscillator). More modern digital synthesizers use DCO's instead (Digitally Controlled
Oscillators).
A simple oscillator can create one or two basic waveforms - most often a sawtooth-wave - which we have
already looked at in the previous chapter - and a squarewave. Most synthesizers can also create a completely
random waveform - a noise wave.
Sawtooth-wave
Square-wave
Noise
These waveforms are very simple and completely artificial - they hardly ever appear in the nature. But you
would be surprised to know how many different sounds that can be achieved by only using and combining these
waves.
A synthesizer has a function to "map" the wave over the entire keyboard range, and make the frequency of the
wave shift from one key to another. Since the frequency of a soundwave is the same as its pitch, we can use the
keyboard to play the wave as an instrument.
Filters
To be able to vary the basic waveforms to some extent, most synthesizers use filters. A filter is an electronic
circuit, which works by smoothing out the "edges" of the original waveform.
If you listen to a sawtooth wave, you will find it rather "harsh" - because the waveform has a lot of sharp
"edges". These edges are in the acoustic terminology called overtones.
Now, if we apply a filter to the waveform, some overtones will be removed - and the waveform will become
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