My Midi controlled VCF module

Jeroen Proveniers J.Proveniers at
Wed Aug 2 15:19:53 CEST 2000


I've written some preliminary software to test if it's possible what I want,
and as things look now, it will be possible.
The unit will have 3 LFOs with 5 different waveforms (ramp up,ramp
down,saw,square and random). Each LFO has a speed and depth control.

Each LFO's output can be routed to one destination but each destination can
have up to 3 sources. The destinations are LFO 1/2/3 speed or depth, filter
cutoff and filter resonance.
It possible to have all 3 LFO to modulate the filter cutoff frequency. This
must give interesting filter sweeps!

LFO outputs are bipolar.

Each parameter has its own potentiometer, this will give 8 pots. Each pot
sends out MIDI controller data, which the unit can also receive. Of course,
when a controller message changes a parameter, the physical pot position
does not reflect the actual parameter value, a LED above each pot will light
up to indicate this.

The modulation matrix (I don't really have a good name for this, maybe
virtual patching?) uses two buttons, and the waveform select for each LFO
uses one button.

No LCD or so will be provided.

I will use an Atmel AT89C52 microcontroller, with an AD7945 12 bit DAC that
is also used for AD for the pots. (SAR principle). The uC has 8K flash
memory, and needs no support logic.

Performance analyses show that calculating the LFO samples take the most of
the processor time, approx. 40%.

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