[sdiy] Re: Spiral Waveforms

[Scott Gravenhorst]

Ian Fritz <ijfritz at earthlink.net> wrote:
>Hi Scott --
>
>At 08:49 AM 4/11/2004, Scott Gravenhorst wrote:
>>Ian's description notes that a constant angular velocity yeilds a constant
>>output frequency, which is a good thing for tonal music.  But this doesn't
>>seem all that easy to do in analog electronics.  Sawtooth and triangle
>>oscillators try to do this by using a linear current to charge a capacitor.
>>  The sawtooth has the nasty reset time that perturbs constant angular
>>velocity.  I'm not sure, but triangle oscillators may also exhibit this to
>>a lesser degree at ramp direction reversal time due to the finite amount of
>>time it takes to switch the current source's polarity.  Once we get away
>>from linear ramps, things get difficult.  Someone correct me if I am wrong,
>>but sinewave oscillators don't operate by following a dot as it goes around
>>a circle with constant angular velocity.  Of the difficulties involved, it
>>seems to me that there are two main requirements: 1) a circuit to establish
>>and maintain the spiral and 2) a circuit that can provide a projection of
>>the spiral placing a "light source" at a given angle.  One way to approach
>>this might be the use of quadrature, would simple panning provide the
>>projection?  If one distorts the quadrature outputs, the angular velocity
>>is maintained, but would panning still give a (variable) projection?  It
>>seems that this idea might be more easily implemented using DSP or other
>>digitally computed methods.  I can't envision how much different this would
>>be from what we already do with oscillators and waveshapers.
>
>Thinking in terms of directly generating spiral waveforms I agree with 
>you.  It would be tricky.  But using the waveshaper approach -- starting 
>with a sine and distorting it with various algebraic manipulations -- isn't 
>difficult in principle.  I would say that the important question is whether 
>a simple circuit could give a useful range of dynamic waveforms.  It seems 
>worth thinking about a bit.

I don't see this as conceptually different from what people already do with
modulars, i.e., sine wave to waveshaper, or any-wave to waveshaper for that
matter.  If the output is to be a single waveform, generated from a single
waveform, how does the spiral come into play?


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