[sdiy] Simple MIDI-syncable LFO...?

[Fredrik Carlqvist]

Why not make a regular analog LFO that is reset every NNth MIDI clock
message? Keep the LFO rate knob and use it to adjust the waveform. The WASP
LFO is very simple and has at least 4 different waveform outputs. 

The MIDI clock message is 0xF8, so perhaps you need a UART and a logic
circuit to detect the message. A PIC would have the UART and counters built
in, together with plenty I/O to adjust the rate, but it could be done
without a microcontroller. 

Fredrik C


-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Blandon Ray
Sent: Wednesday, October 13, 2004 20:37
To: Synth-DIY List
Subject: [sdiy] Simple MIDI-syncable LFO...?

Hi everyone,

I've been on and off this list for a few years now, and I managed to
get my feet wet in the DIY world by building a few things from kits,
and assembling a few unambitious projects.

Now I've got a project shaping up in my head for a compact modular
sound-processing rig, for use with external sources (e.g. electric
guitar). For a long time I've wished for an analog LFO that could be
synchronized to MIDI clock in a way that would be musically useful for
things like tremolo, filter effects, panning, and so on.

I know you can get MIDI-CV converters that have this function, but
most of them are pretty pricey and don't fit in a module form
factor... and besides, isn't it more fun to try to make something that
does exactly what you want?

One idea I had was to start with John Blacet's MIDI-to-SYNC PIC chip,
divide the 24PPQ pulse down, and find some way to convert the
resulting square wave to sawtooth, triangle, etc. But I can't locate a
circuit that does that reliably at very low frequencies... then again,
it doesn't have to be perfect, just good enough to be useful as a
modulation source.

So I'm hoping it would be possible to build a simple device that does
nothing but produce an LFO that synchronizes on different multiples of
the MIDI tempo. I would think that in this application you don't have
to worry about things like running status, and so it could be done in
hardware, without my having to learn to write code for an AVR or some
other microcontroller.

Any thoughts would be appreciated (be gentle, I'm new at this :)

Thanks
Blandon