LFOs

[Magnus Danielson]

From: "Paul Maddox" <paul.maddox at ndirect.co.uk>
Subject: LFOs
Date: Tue, 4 Jul 2000 14:57:38 +0100

> Dear All,

Paul,

Just some random thougths collected, please ignore at the level of pleasure...

>  Ok couple of questions regarding LFOs..
> 
>   Im developing a polysynth (with the interest of a certain synth
> manufacturer) and I intend to make it
> 8 voice poly. Now couple of questions about LFOs,
> 
>   1) Should I have 8 seperate LFOs or one global? I dont want both.

If you have LFOs triggable to gate/trigg, then you really want separate LFOs.
Also, if you run in splitt-mode a common LFO will be an annoying resource
problem. Separate triggable LFOs, you could have voice or common trigger
thougth.

>   2) Midi Syncable LFO, Ive been advised that this is something they would
> like to see,
>         someone explain to me what it is, Im guessing that with each
> successive midi clock received the LFO is
>         stepped through its waveform. am I right? and if so how do you tell
> it how many steps it takes to do a full
>         cycle, ie 1 beat, one bar, 8bars??

Isn't this just that the LFO triggers on the MIDI Key message just as if you
would press that key on the keyboard?

>    3) I would like the LFO to be voltage controlled (its going to be
> programmable) and have a sine wave (if the
>         above point is true then it doesnt matter as its going to have to be
> a lookuptable anyway).

Oh, sinewave LFO is really nice to have.

>   oh, I also want it done with just 2 opamps (ie ONE TL072), I need this
> thing to be compact if Ive got to build
> 8 voice cards. Trying to find an easy way to do 3 EGs under CV/DIGITAL
> control. All with as few chips as
> possible..

You really should check out the EH SmallStone LFO. It uses a single CA3094
for it's LFO. Sure, it also uses two 2N5087 trannies, but CV control is really
the default action of it, so you should just drop in a resistor to the current
input to have a simple voltage control. Its a interesting LFO concept to
meditate over.

Cheers,
Magnus