[sdiy] Low Frequency Square to Sine Waveshaper

[Tom Wiltshire]

A couple of thoughts about this:

If you're going for the weighted-squares approach, you ought to be  
able to do it to pretty much whatever degree of accuracy, simply by  
adding more squares waves. It's a bit like the weighted-squares  
approach to building a ramp wave. 4 or 5 square waves gives you a  
staircase that is obviously getting towards a ramp wave, but not  
quite there yet. A few more improves the quality quite a bit.

Secondly, if you're going for a design based on triangle waves, you  
can use precision rectifier circuits to double the frequency of a  
triangle wave. Starting with one really low triangle wave , then  
following it with rectifiers to get each octave, and then shaping the  
triangles with the standard triangle-to-sine waveshaper circuits  
should work nicely.

T.

On 26 May 2008, at 15:51, Paul Perry wrote:

> I'd agree that the idea of a high frequency clock divided down &  
> driving a
> kind of sine construction - the approach made famous by Don  
> Lancaseter, eg
> at www.tinaja.com/glib/stepsynt.pdf is very good indeed for audio
> applications.
>
> But is there a problem when it comes to LFOs? When a very low  
> frequency LFO
> is modulating an oscillator, a discontinuity that would be quite
> unnoticeable in an audio signal, is only too obvious. LFOs are  
> definitely a
> special - and very awkward - case.
>
> That is why I think a phase locked method is more promising.  
> Although, even
> there it won't be without problems, when if comes to settling times  
> in the
> PLL. At LFO frequencies, the settling time might be embarrassingly  
> long.
>
> The more I think about it, the better triangles look.
>
> Paul Perry melbourne australia
>
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