attack; the drop will become more gradual as the decay time
i n c r e a s e s .
5 ) The SUSTAIN LEVEL control (22) determines the frequency at which
the contour levels off after the initial rise and fall. The
frequency of the sustain level can be as high as the initial peak,
in which case there is no decay after the initial rise, or it can
be as low as the frequency at which the contour began. To hear
this most effectively, set the filter controls for CUTOFF FREQUENCY
of -2, high AMOUNT OF CONTOUR, and medium DECAY TIME. Now repeatedly
depress and hold down a key while setting control (22) at various
levels. Set at 0, the contour decay effectively wipes out the signal;
set in the middle, the brightness levels off at a frequency some-
where below the initial peak, and set at 10, the brightness of the
note rises to an initial peak and remains there.
6 ) The EMPHASIS control (18) introduces a sharp resonance in the
response of the filter at the cutoff frequency. The effect of this
control can be heard very easily. To observe it, turn the AMOUNT
OF CONTOUR fully to the left to shut off the contour signal, and
turn the EMPHASIS control to 7
1
/2*. Depress a key, and turn the
CUTOFF FREQUENCY control slowly throughout its range. You should
hear the individual overtones of the oscillator waveform being
emphasized one by one as the resonance passes over them. Now set
the CUTOFF FREQUENCY to about -2, turn the AMOUNT OF CONTOUR all
the way up, and repeatedly hold down a key while changing the
settings of controls (20), (21), and (22). Notice how the filter
contour is now heard as a sweep of the overtone series when (20)
and (21) are turned up to about 7 seconds and (22) is set low.
We have seen how the filter cutoff frequency may be controlled
manually and using the filter contour controls. These are in
addition to other means of controlling the filter.
7 ) The MODULATION MIX (3) of Oscillator 3 and the Noise Source may be
used to modulate the filter cutoff frequency in exactly the same
way it employed to modulate the pitches of the oscillators. To
direct the Modulation Mix to the filter, the FILTER MODULATION
switch (J) must be turned on. Then the MODULATION wheel (29) can
be moved forward with the left hand to introduce the desired amount
of modulation as the keyboard is played with the right hand. To
test this, turn (18) and (19) all the way down and set (17) to about
1 or 2. Make sure that the Oscillator Modulation switch (A) and
Osc. 3 Control Switch (B) are off, and turn on switch (J). Set the
MODULATION MIX control all the way to the left. Oscillator 3’s
RANGE switch should be set to LO. You will observe as you did when
applying the Modulation Mix to the oscillators that the modulation
contour depends on the settings of the FREQUENCY and WAVEFORM controls
of Oscillator 3. A more complex sound can be made by adding the
effects of controls (18) and (19).
12
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