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

[cheater00 .]

Phil,

On Fri, Nov 1, 2013 at 4:10 PM, Phil Macphail
<phil.macphail at liivatera.com> wrote:
> That depends on what you want - do you want a 90-degree shift on the harmonics too?

Yes, definitely. Can you see any other options? Or do you mean the
alternative would be to shift the starting phase of the oscillator by
tau/4, i.e. a quarter cycle? That's not what I had meant.

> If so then a polyphase network will do that. There is a trade-off between bandwidth, ripple and number of stages so these days they are probably best implemented digitally.

I'm kind of hoping there's a way to do this with and have it work well
even when the oscillator changes pitch rapidly. Naturally it has to be
analogue, otherwise we cannot use the oscillator for many things that
require immediate reaction time.

I wonder if shaping a triangle wave might create a wave that's good
enough an approximation of the "hilbert wave".

Cheers,
D.