In this patch we are using the Gemini in Cascade Mode, so the Dual/Cascade and Invert switches are both in the up position.
By feeding a signal first through a LP (low pass) filter, and then feeding it through a second filter set to HP (High pass) we
create a BP (band pass) filter. The first question would be.... why bother? We already have a BP filter on each of the individual
filters........BUT the individual fiters are each 6dB slope when set to BP filter, wheras if we combine the two filters together we
can get a BP filter with a 12dB slope, which has a higher Q and covers a narrower band. And of course we also have the option
of fading from LP response (VCF 1 only) and BP responce (VCF1 and VCF 2 in series) by using the AUDIO MIX control, and we
can automate this cross fading by patching an external CV to the MIX CV jack.
We are feeding the audio into IN 1, however do note that there is no patch cable in the IN 2 input - it is not needed as in
CASCADE mode OUT 1 is normalised (connected) to IN 2 internally, so the single input is automatically patched to both VCF 1
and VCF 2.
The D-FCV IN input is fed from the contour generator, and here we have the D-FCV Mix control at mid point, so that the D-FVC
control signal is being sent equally to VCF 1 and VCF 2.
We have also included a variant on this patch (lower picture) which shows the inverse output from an envelope generator
being used as the control voltage to automate the control of the Audio mix from Low Pass to Band pass response, obviously
other modulation sources can also be used for this, and the effective range of the control is 0V to +5V to cross fade fully when
the Audio Mix control is set to fully clockwise. .
Note: The numbers used to illustrate control knob positions do not relate to the markings on the module itself, but are simply a scale from zero to 10 with 5
being the control centre position. For attenuverters the control positions are -10 to +10, with zero being centre position for the control knob.
GEMINI 2412 - PATCHING EXAMPLES
3 - Cascade Mode - creating a 12dB BP filter by combining LP and HP filters
0
1
3
3
0
0
10
Gate 1
Output 1
10
10
0
0
0
3
5
3
8
8
1
0
5
2
0
0
4
5
5
5
10
16’
0
0
HP
LP
CASCADE
VCF 2
5
0
0
0
0
0
0
Cascade Mode - creating a 12dB BP filter by combining LP and HP filters
With added CV control of AUDIO MIX
Cascade Mode - creating a 12dB BP filter by combining LP and HP filters
10
10
Gate 1
Output 1
10
0
0
0
3
5
3
8
8
1
0
5
2
0
0
4
5
5
5
10
16’
0
0
HP
LP
CASCADE
VCF 2
5
0
0
0
0
0
0
1V/Oct IN
1V/Oct IN
