[sdiy] Divide down question

[Tom Wiltshire]

On 25 Aug 2009, at 15:09, cheater cheater wrote:

> What about this:
> start out with a normal square divide down, and then when you're e.g.
> playing C1, then actually what is output is:
> C1+ 1/2 C2 + 1/4 C3 + 1/8 C4
>
> Each of the higher tones would have to go through a latch. That latch
> would only let through one pulse of C2, C3, etc, but it would be reset
> on C1's rising slope. Maybe this could be a little bit difficult,
> maybe not.

Actually you don't need the latches. You're dead right with the rest  
of it; C1+ 1/2 C2 + 1/4 C3 + 1/8 C4 + etc gives you a steppy saw. Try  
it on graph paper, graphics calculator, or maths package (in  
ascending order of techno-overkill). Since it's a bright buzzy sound  
with even as well as odd harmonics, it actually sounds pretty much  
like a saw even with fairly few steps. A good substitute, anyway,  
even if not enough for perfectionists.

> Actually, couldn't you do a big part of square-based divide down
> topology in FPGA?

Yes. Wasn't someone on this list doing a top-octave chip on an FPGA?  
That's the hard part! The rows of flip-flops would be a good  
"beginner's FGPA project" I'd have thought!

T.