[sdiy] All-pass filters, was: Screwing with Square Waves

[cheater00 .]

Hi,

On Thu, Oct 31, 2013 at 7:02 PM, Donald Tillman <don at till.com> wrote:
> Folks,
>
> Please enjoy an article I just wrote about some strange and beautiful aspects of Square Waves:
>
>     Square Wave Variations
>     http://www.till.com/articles/squares/index.html
>
> (This presentation relies heavily on the MATHML feature of modern browsers. I'm interested in hearing of any cases where it doesn't work correctly.)
>
>   -- Don


I've been looking into phase and frequency shifts in standard waves
for some time now. Does anyone have a practical circuit to perform a
pi/2 (tau/4) phase-shift on an oscillator waveform?

Cheers,
D.