6
such a signal is called a
square
wave. As the knob is rotated
in either direction from vertical, the pulse becomes wider (to
the right) or narrower (left).
3. When this switch is moved to the right, VCO 2 is SYNCHRO-
NIZED to the frequency of VCO 1. VCO 1 is not affected by this
switch regardless; but VCO 2, when it is "sync'd" to VCO 1, can
produce only harmonics of the frequency to which VCO 1 is set.
When the switch is off the two oscillators are completely inde-
pendent.
4. These are the three MANUAL CONTROLS for the filter. The
smaller knob at the lower right determines whether the filter
will act as a
bandpass filter
(at the click-stop position
labelled "BP"
), lowpass filter
(immediately clockwise from the
click-stop, labelled "LP"),
notch filter
(vertical, at the word
"notch"), or
highpass filter
(extreme clockwise, labelled
"HP"). Do not try to turn the knob clockwise past the highpass
stop.
The large vernier control at the upper left determines the fre-
quency at which the filter begins to take effect, or the
center
frequency
of the bandpass and notch modes. In the low- and
high- pass modes the frequency at which the filter begins to
have some effect on a signal passing through it is called the
cutoff frequency
of the filter.
The large single knob labelled RESONANCE determines the filter
resonance at its cutoff frequency. When this knob is fully
counterclockwise the filter resonance is at a minimum; as it is
rotated to the right the resonance increases. RESONANCE is a
term for the gain (i.e. roughly,
loudness)
of the filter at or
near its cutoff frequency. At maximum resonance, for example,
the filter amplifies strongly any components of the input sig-
nal that lie within a semitone or so of the cutoff frequency,
but virtually ignores components that are not near the cutoff
frequency.
In other words, a pronounced "peak" occurs in the filter fre-
quency response as the resonance is increased, which grows
higher in amplitude as it grows narrower in width. When the
center of this peak is exactly at the frequency of an audio
input to the filter, a relatively weak signal can drive the
filter to produce a quite strong output.
5. The switch selects one of three sources for a control input
to the filter. The left and right positions are self-explana-
tory;
the center position carries a signal from the SAMPLE/HOLD
section of the mini-sequencer panel. This signal is independent
of any of the routing and assignment switches in the
