Moog-music Slim Phatty User Manual download pdf (Page 63)

Page 64

Slim Phatty User’s Manual - Appendices

Page 65

Slim Phatty User’s Manual - Appendices

Returning to our Subtractive Synthesis model, the rst of the auxiliary components is the keyboard. The

keyboard provides a familiar musical instrument ‘interface’ that produces a control voltage and trigger signal

whenever a key is pressed. The level of the control voltage signal is a function of which key is pressed - the

higher up on the keyboard you play, the higher the level of the control voltage.

The keyboard’s control voltage signal is commonly routed to the oscillators to control the pitch, and it can also

be routed to other voltage-controlled components like the lter, to vary the cutoff frequency. The keyboard

trigger signal is routed to the Envelope Generators to trigger the envelopes.

The second auxiliary component is the Envelope Generator, or EG. The

EG makes no sound by itself. Rather, it creates a time-varying control

voltage that is typically used to control the gain of the amplier, or the

cutoff frequency of the lter. Many synthesizers, including the Little

Phatty, provide several EG’s for independent envelope control of the

amplier and lter circuits.

The EG is triggered from a Gate signal that is generated every time a

key is pressed on the keyboard. Once triggered, as long as the key is

held down (i.e. the Gate signal is present), the EG envelope will evolve

according to the control settings.

The SP’s Envelope Generators have four stages that can be set individually:

Attack – The time to go from zero volts to the maximum voltage (the fade in time).

Decay – The time to go from the maximum voltage to the Sustain level.

Sustain – The maximum level of the envelope after completing the attack and decay stages (if the

key is held). If the sustain time is zero, the envelope consists of just the attack and decay

stages, and the Release control has no effect.

Release – The time to go back to zero volts when the key is released (the fade out time).

The last auxiliary component is the Low Frequency Oscillator, also known

as the LFO. The LFO operates like the main oscillators in almost all

respects, but generally at a much lower frequency. LFO’s are typically used

to send modulation control signals to the main components. For example,

if you route a 6Hz LFO signal to an oscillator, it will produce vibrato by

varying the pitch of the oscillator. If you send that same LFO signal to

the amplier, and you’ll get tremolo. LFO’s are used to create cyclical

variations in the sound, making the sound more dynamic and interesting.

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Moog-music Slim Phatty User Manual Page 63