INTRODUCTION TO SYNTHESIZERS - hol.gr

Pitch
The repeat rate of the pattern is called the frequency of the waveform. The frequency determines the pitch of
the sound - a sound with higher frequency will be perceived as a higher tone. To take an example, a female
human voice has a higher frequency than a male voice.
Take a look at the wave in the next illustration. It is also a sawtooth wave, but its frequency is exactly two times
higher than the one in the previous example. The result is a sound exactly one octave higher.
The same wave, but one
octave higher
In physics, frequencies are measured in the unit Hertz (Hz), which is the same as repetitions per second. A
person with normal hearing can perceive sounds with frequencies from around 20 repetitions per second (20 Hz)
to around 18 000 repetitions per second (18 kHz).
If the frequency is lower than 20 Hz, we will no longer perceive the wave as being a sound, but more like a
"throbbing" in the air. These sounds are called "subsonic sounds", or "infrasounds". Even if subsonic cannot be
heard by humans, they can cause some strange phenomena, like shopping windows starting to vibrate by no
apparent reason. Quite often these vibrations are caused by trucks passing by, or aircraft taking off many miles
away. Many animals, like elephants and manatees actually use these sounds to communicate with each other.
On the other side, frequencies beyond the top border are called "ultrasonic sounds", or "ultrasounds".
Ultrasounds can not be perceived by humans at all, but as you probably know, the hearing of many animals can
stretch way into the ultrasonic range. Dog-whistles emit ultrasonic sounds at around 40 kHz, which are easily
heard by our four-footed friends. Bats also use ultrasounds to localize their prey in flight.
To be able to perceive the pitch and the timbre of a sound, the waveform must be periodic - otherwise we can't
tell how often the waveform is repeating. Of course there are also non-periodic, or random waveforms. These
are perceived by the human ear as noise - such as the sound of a distant waterfall or radio static.
Noise
Other waveforms are of course not as simple as the ones in the examples above, but far more complex. Well,
here is a beautiful one taken from the Korg X3 synthesizer!
Volume
A more complex waveform
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