About The Pro-One Basic Operation Front Panel Back Panel Routine Maintenance Service

Section 2: Front Panel

2—6 Filter

figure 2-5

The FILTER module contains controls for the filter itself and for its envelope generator.

CUTOFF knob: Sets cutoff frequency for the 24 db/octave (4-pole) low-pass filter. It is rather like a tone control. Cutoff is the frequency below which all elements of a signal are let through. The higher-frequency components of the signal (i.e. all those above the cutoff frequency) are suppressed. The higher the knob is set, the higher the frequencies that are allowed through the filter.

RESONANCE knob: Determines the amount of filter resonance. As the setting is increased from 0 to approximately 7 the amount of resonance (“emphasis”, “regeneration”, or “Q”) applied to those signal components at the cutoff frequency will increase. The components far below the cutoff frequency will be less audible relative to the frequencies being resonated. As the setting is increased beyond 7, the filter breaks into oscillation and will act as a sine-wave audio source whose pitch is determined by the cutoff frequency.

ENVELOPE AMOUNT knob: Sets amount (not the shape) of ADSR filter envelope CV controlling the filter cutoff frequency. The filter envelope generator is discussed below.

KEYBOARD AMOUNT knob: Determines the amount of KYBD CV controlling the filter cutoff frequency. When set between 7 and 8, the filter cutoff frequency is maintained at a constant point relative to the notes played on the keyboard, creating consistent tone. When set to 10, notes played higher on the keyboard will have less of their overtones suppressed than those played on the lower end of the keyboard. As a result, the higher notes will have a brighter timbre. When reduced or off, notes played higher on the keyboard will have more of their overtones suppressed than noted played lower. As a result the higher notes will have a duller timbre.

figure 2-6

Figure 2-6

The filter envelope generator contours timbre by controlling the filter cutoff frequency. The entire contour pattern is initiated when a key is struck, producing a GATE. The initial appearance of the GATE “triggers” the envelope generators to proceed through their ATTACK and DECAY periods. After the ATTACK and DECAY periods set for each envelope generator have elapsed, it will produce a steady control voltage (CV) at the level set by the SUSTAIN knob for as long as the GATE is present. When the key is released, the GATE goes off and the envelope generator output voltage drops to zero at a rate set by the RELEASE knob.

ATTACK knob: Varies time for envelope to increase from zero to maximum, from 2 milliseconds to more than 6 seconds.

DECAY knob: Varies time for envelope to decrease from maximum to SUSTAIN level, from 2 milliseconds to more than 6 seconds.

SUSTAIN knob: Varies level from zero to maximum. Remember, this is a level control, not a time control. (SUSTAIN time is the period between the end of the DECAY and when the key is released.)

If SUSTAIN is set at maximum then the DECAY knob setting is irrelevant.

RELEASE knob: Varies time for envelope to decrease from sustain level to zero, from 2 milliseconds to more than 6 seconds. If the key is released before either the ATTACK or DECAY periods have elapsed, this knob controls the time taken for the output to drop to zero from its level when the key was released.

If the ATTACK and DECAY periods have elapsed and SUSTAIN is set to 0, the RELEASE knob setting is irrelevant.

vintage synth synth museum logo custom synth