When resonance is added, frequencies at the cut off point are boosted in
volume.
In addition to the traditional Low Pass Filter type, there is also a High
Pass and Band Pass Filter. The type of Filter used is selected by using
the front panel Filter TYPE button.
The High Pass Filter is similar to the Low Pass Filter except that frequen-
cies
below
the cutoff frequency point are removed. Frequencies
above
that point are passed. When the FREQUENCY knob is set fully anti-clock-
wise, the filter is set completely open and no frequencies are removed
from the raw Oscillator waveforms.
When the Band Pass Filter is used, only a narrow band of frequencies
centered on the cutoff frequency point are removed. It is not possible to
fully open this type of Filter, allowing all frequencies to pass through.
Envelopes and Amplifier
In earlier paragraphs, it was determined how the pitch and timbre of a
sound are synthesized. This final part of the Synthesis Tutorial describes
how the volume of sound is controlled. The volume throughout the dura-
tion of a sound created by a musical instrument often varies greatly
according to the type of instrument.
An Organ sound quickly attains full volume when a key on the keyboard is
pressed. It stays at full volume until the key is released, at which point the
volume level falls instantly to zero.
A Piano quickly attains full volume when a key is pressed and gradually
falls back down to zero after several seconds, even if a key is held.
A String Section emulation attains full volume gradually when a key is
pressed. It remains at full volume while the key is held down, but once the
key is released, the volume level gradually falls to zero.
On an Analogue synthesizer, changes which occur throughout the dura-
tion of a note are controlled by a section known as an Envelope
Generator. The KS 4 / KS 5 has two Envelope Generators. The circuit of
one of these is always connected to an
Amplifier,
which controls the
Volume of the sound when a note is played.
Note that there are no controls in a section on the front panel which deal
with the Amplifier directly. The only way to hear and control an audio sig-
nal passing through the Amplifier is to modulate it by using Amp Envelope
controls.
Each envelope generator has four controls which are used to adjust the
shape of the envelope. The Envelope controlling the Amplifier uses slid-
ers.
Volume
Frequency
Cutoff
Frequency
SYNTHESIS TUTORIAL
The Filter - Envelopes and Amplifier
•
12
•
Volume
Frequency
Frequency
Volume
Cutoff
Frequency
Cut off
frequency
Frequency
Volume
Cutoff
Frequency
Key "On"
Key "Off"
Volume
Key “On”
Key “Off”
Volume
Time
Key "On"
Key "Off"
Volume
Key “On”
Key “Off”
Volume
Time
Key "On"
Key "Off"
Volume
Key “On”
Key “Off”
Volume
Time
