Variable ramp generator

[Steven Cook]

Hi,

I've been following this with interest as I've recently created a variable
ramp generator in Csound (i.e. cheating!). My method is similar to Don
Tillman's, but arrived at independently.

1) Start with a positive sawtooth and a CV, both with the same range, say 0 to 1.

2) Send the sawtooth into a VCA whose gain is controlled by the CV. Gain
should equal 1 / CV.

3) Send the output of the VCA into a limiter/clipper (precision rectifier?)
set to 1 (the sawtooth's peak). The output from this should be a variable ramp
from 0 to 1 followed by a DC level of 1.

4) Send the sawtooth also into a 2nd limiter/clipper set to limit downward
excursions to the level of the CV. Subtract the CV from the output of this.
Send into a 2nd VCA whose gain is equal to 1 / (1 - CV). The output from this
should be a DC level 0f 0 followed by a variable ramp from 0 to 1.

5) Subtract the second ramp from the first ramp.

6) Go to the pub :-)

No idea if this is practical or not.

Steven Cook.

mbartkow at ET.PUT.Poznan.PL wrote:

> First of all I need a variable ramp waveform, i.e. a waveform,
> whereby the ratio of the rising edge to the falling one is
> freely adjustable without affecting the frequency.
> I know, it is possible to independently control the charge and
> discharge times in integrator by using a pair of diodes or
> a CMOS switch. AFAIR, Juergen described such operation of KORG
> LFOs. The problem is if one applies this control scheme to VCO
> it leads to severe tracking problems.
>
> My idea was to generate a stable saw or triangle and shape it
> using a switched gain circuit. I must say I tried to design such
> a circuit, but either I am too narrow minded or blind - I just
> cannot come up with anything. I hope somebody invented this before
> and would not mind to share.