Crumar Spirit - Filter Resonance and Tracking; Resonance, Slope, and KB Amount

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UPPER FI
I
- RESONANCE :-
, _ _ _ -.J
4 , 6
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a
LOWER FI
RESONANCE always determines the amount of resonance, or "Q" on the
Lower Filter. It also determines the amount of Upper Filter resonance when
the LOW-VARIABLE switch is to VARIABLE, for both 12dB and 24dB
modes.
The LOW-VARIABLE RESONANCE switch determines whether the Upper
Filter response will be "low resonance" (low Q), or whether its Q will be
determined by the rotary RESONANCE control.
The 12 dB-24 SLOPE switch changes the slope of the Upper Filter. When
switched to 24dB the Upper Filter becomes a 24 dB/Octave Lowpass Filter.
To create the "typical" synthesizer high-resonance filter sound, the LOW-V A-
RIABLE switch must be placed to VARIABLE so resonance, or filter Q can
be increased.
LTER U
D
-SLOPE-
.0.
OUT • • HIGH
PASS
OVE~ w IiIANO-
O~IVE PASS.
LTER L
The LOWER FI L TER SLOPE switch is most important in filter mode selec-
tion on the Spirit. Its positions provide filter responses as follows:
OUT removes the Lower Filter from the signal path . This leaves a standard
lowpass resonant filter with "two-pole" or "four-pole" response, selectable
by 12 dB or 24 dB position respectively on the Upper Filter SLOPE switch.
OVERDRIVE introduces a soft distortion circuit between Lower and Upper
Filters, giving a fuzz-y, raunchy sound quality. This mode also places the
Lower Filter into Parametric Boost mode; that is, a peak is introduced at its
cutoff without attenuation of frequencies far from this cutoff. This peak will
occur below the Upper Filter cutoff frequency when the LOWER ONLY
CUTOFF setting is less than 8. The height of this peak is increased as the
Lower Filter RESONANCE control setting is increased.
The BANDPASS position puts the Lower Filter into the same Parametric
Boost mode, but the distortion circuit is not connected. This filter response
may be described as "double-peak", lowpass-resonant. (The MASTER
CUTOFF control sets the high peak; the LOWER ONLY CUTOFF sets the
location of the lower peak relative to the higher peak. When the MASTER
CUTOFF is moved, both peaks will move; the distance between peaks is set
by the LOWER ONLY CUTOFF. The sharpness of the lower peak is always
determined by the RESONANCE control; the sharpness of the upper peak is
determined by the same control only when the associated switch is set to
VARIABLE.)
The HIGHPASS position puts the Lower Filter into Hi .ghpass-resonant mode.
I n this case the "lower peak" attenuates frequencies lower than its cutoff
frequency. The overall response is double-peak, highpass-Iowpass.
KB AMOUNT determines the extent to which the keyboard voltage is used
to control the cutoff (s) of the filter sections. Filter cutoff frequencies
"track" oscillator pitch perfectly at a setting sl ' ightly less than 10. That is,
when this control is set to 10, the filter cutoffs move slightly more than one
octave when you play one octave on the keyboard. (When the TRACKI NG
switch in the Lower Filter is set to FORMANT, the Lower Filter does not
track the keyboard. This lets you use the Lower Filter to create a formant
- - which does not move as pitch changes. This formant, or filter peak does
not track the keyboard.)