SYNTHESIS TUTORIAL
The Filter - Envelopes and Amplifier
When resonance is added, frequencies at the cut off point are boosted in volume.
Cut off frequency Cutoff Volume Volume
Frequency
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 duration of a sound created by a musical instrument often varies greatly according to the type of instrument.
Key "On" Key �On� Key �Off� Key "Off"
Frequency Frequency
Volume 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 frequencies below the cutoff frequency point are removed. Frequencies above that point are passed. When the FREQUENCY knob is set fully anti-clockwise, the filter is set completely open and no frequencies are removed from the raw Oscillator waveforms.
Time
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.
Key �Off�
Key"On" Key �On�
Key "Off"
Cutoff Frequency
Volume Volume
Volume
Time
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.
Frequency
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.
Key �On� Key "On"
Key �Off� Key "Off"
Volume Volume
Cutoff Frequency
Time
Volume
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 duration of a note are controlled by a section known as an Envelope Generator. The KS Rack 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.
Frequency
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 signal passing through the Amplifier is to modulate it by using Amp Envelope controls.
Each envelope generator has four sliders which are used to adjust the shape of the envelope.
