Analog Synthesis: Basic Information

• VCO: a circuit that generates one or more audio/low frequency waveforms, the frequency of which vary in response to the voltage applied to its control voltage input.
• VCA: a circuit that varies the output gain of an input signal in response to the voltage applied to its control voltage input.
• VCF: a circuit that varies a filter parameter (usually cut-off frequency) in response to the voltage applied to its control voltage input.
• Resonance: (emphasis, peak, Q) With filter circuits, increasing the resonance exaggerates an area of frequencies around the cut-off frequency. With maximum Q, the filter will oscillate.
• Cut-off frequency: the filter frequency at which attenuation begins.

Filter types:

1. Low Pass: passes frequencies below a given point.
2. High Pass: passes frequencies above a certain point.
3. Band Pass: a circuit which passes a particular range of frequencies while rejecting higher and lower frequencies than the selected range.
4. Notch: this filter attenuates frequencies within a specific range centered around a frequency of maximum rejection called the notch frequency.
5. Formant filtering: using vowel sound as a model in speech synthesis, formant filtering creates a chain of shifting areas of resonance.

• Attack: the initial phase of an EG. It determines the amount of time required for the EG signal to go from full off to full on.
• Decay: the second phase of an ADSR, this determines the time it takes a signal to fall from maximum voltage attained during the attack phase to an arbitrarily set sustain voltage.
• Sustain: the level at which an envelope will remain while the key is depressed.
• Release: determines time from key release to full off volt.