[sdiy] Auto Center waveforms

[Jerry Gray-Eskue]

The arbitrary wave shapes part is talking about wave shapers such a one
sided clippers or wave folders that do not act symmetrically.

The idea about using a tracking filter has merit.

One could use a VCHP filter to get an acceptable level of DC rejection. As a
VCHP filter inherently scales the Time Constants to the control voltage and
waveform frequency is also a result of control voltage, the result would be
the least amount of latency for each frequency.

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Kyle Stephens
Sent: Tuesday, July 14, 2009 3:47 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Auto Center waveforms



How are the arbitrary wave shapes being generated btw?

And here's my (inexpereinced) $0.02 worth of a solution/guess: tracking
filter tied to the CV controling the arbitrary VCO?


_Kyle

--- On Tue, 7/14/09, Jerry Gray-Eskue <jerryge at cableone.net> wrote:

> From: Jerry Gray-Eskue <jerryge at cableone.net>
> Subject: [sdiy] Auto Center waveforms
> To: Synth-diy at dropmix.xs4all.nl
> Date: Tuesday, July 14, 2009, 6:45 AM
>
> I have been thinking about centering arbitrary wave shapes
> on 0 volts.
>
> Wave shapers and some VCO waveforms tend to create
> waveforms with a dc
> offset and it would be nice to have a circuit that would
> "balance" these so
> that the sum of the + voltage = the sum of the - voltage.
>
> To do this it would seem that if you took the sum of one
> waveform cycle
> using a simple integrator you would have a voltage that
> represents the DC
> offset. Using the proper scaling you could then subtract
> this voltage from
> the waveform to remove the offset. A pair of voltage hold
> circuits would
> store the voltage of the previous cycle and remove the
> offset from the
> current cycle. The integrator (s) would reset each cycle
> after the voltage
> hold circuits were updated.
>
> The problem that I am having with this scheme is that it
> appears the period
> of the waveform must be used to scale the resulting
> voltage. Now it is
> simple enough to use a constant current into a second
> integrator to derive a
> voltage representing the time period, and it would appear
> that using this
> voltage and a multiplier in the feed back of an op amp will
> allow division
> of the total voltage / period voltage.
>
> The issue with this approach is cost and complexity. It
> seems like there may
> be a "Slick" way to do this without resorting to expensive
> ICs and still
> give good offset removal performance.
>
> Any thoughts, or ideas on a better method ?
>
> - Jerry
>
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