[sdiy] Really Low, LFO

[Kyle Stephens]

Prof. Lanterman said the PWM out of a PIC, heavily filtered, would work. I know Tom Wiltshire's VCLFO is PIC-based and does just that, so it's possible alright.

http://www.electricdruid.net/index.php?page=projects.lfo9

Maybe the universe is trying to get me order a PIC developer's kit and start cracking, heh.

Pixels have their place, though not in this given app, so I dig that analogy (hm, analogy, analog... ;) ).

I'm making an panner (between dif FX, not an L/R deal) with the LFO btw, for anyone's reference.


_Kyle

--- On Fri, 4/2/10, dancemachine at gmail.com <dancemachine at gmail.com> wrote:

> From: dancemachine at gmail.com <dancemachine at gmail.com>
> Subject: Re: [sdiy] Really Low, LFO
> To: "cheater cheater" <cheater00 at gmail.com>
> Cc: "Kyle Stephens" <lightburnx at yahoo.com>, "synth-diy at dropmix.xs4all.nl" <synth-diy at dropmix.xs4all.nl>
> Date: Friday, April 2, 2010, 4:32 PM
> really? that's where I would be more
> worried about it. think about it. the finite changes in
> output could be stretched to the point where you have enough
> time to hear each one. analog has no steps.
> 
> for the graphic art mind it is pixels va vector art when
> dealing with enlarging
> 
> =aliasing
> 
> --
> sent from phone
> 
> On Apr 2, 2010, at 5:15 PM, cheater cheater <cheater00 at gmail.com>
> wrote:
> 
> > Leakage current of your capacitor and off-resistance
> of the transistor
> > used for resetting the core are going to be the
> issues, I think.
> > 
> > If you want an infrasonic LFO I suggest doing it in
> DSP, there's no
> > advantage to using analog at those frequencies that I
> can think of.
> > 
> > 
> > On Fri, Apr 2, 2010 at 22:51, Kyle Stephens <lightburnx at yahoo.com>
> wrote:
> >> Can anyone point me to some reading material on
> infrasonic oscillator design? I want to build a really low,
> low LFO, with a period of around half an hour (yes, _that_
> slow!).
> >> 
> >> As HF designs have their share of issues that get
> worse in that spectrum, infrasonic has its problems too I
> would imagine - I just don't know what exactly they might
> be.
> >> 
> >> For my app, accuracy isn't as important as
> precision/repeatability, though if both are possible then
> both are welcome.
> >> 
> >> Closest I've found so far is this:
> >> 
> >> http://tinyurl.com/yf9wzp3
> >> 
> >> I reckon I can tailor it if I make the integrator
> cap several decades larger, to shift that 0.1Hz to 100KHz
> range several decimal places downward.
> > 
> > Eh, not really about the size of the cap, it's more
> about being able
> > to control the current accurately enough.
> > 
> >> I've a copy of AD's Nonlinear Circuits Handbook,
> which has some material on the topic, though nothing too
> specific on freqs beneath 1 Hz (half an hour is ~ 0.0001
> Hz).
> >> 
> >> I spoke to Prof. Lanterman about this a while
> back, and he recommended a microcontroller based solution,
> > 
> > Yep, I second that. DSP options (and for an lfo you
> don't even need a
> > dedicated dsp uC such as a 56k) give you accuracy AND
> repeatability;
> > but they're easy  to badly implement on their own
> (aliasing, ...)
> > although, comparing the typical sampling frequency
> you'd run this at
> > to the frequency you expect, the error in pitch coming
> from aliasing
> > on the discontinuity (which gives you only an error of
> +-1 sample,
> > maybe 2) will be minuscule. Your biggest problem will
> be implementing
> > an accumulator register big enough, I think.
> > 
> > D.
> > 
> >> and while that's something I want to break into,
> it's a whole 'nother can of worms too. If this can be done
> in analog, it'd be a cool achievement and an enrichment
> exercise if nothing else... :]
> >> 
> >> 
> >> 
> >> _Kyle (so slow it Herz?)
> >> 
> >> 
> >> 
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> >> 
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