[sdiy] top octave gneration

[adam at hoodmusic.net]

i could do it with AVRs, but i want to make an organ and keep it as simple as
possible, and and AVRs would require investment in new equipment and learning
them, so that kills the simplicity for me.

adam

Theo wrote:

> As I suggested earlier;
> you can do that with a AVR.
> Or rather 12 AVRs that are also the dividers.
>
> Theo
>
> Cross tread remark:
> PIC have other applications ;)
>
> From: Don Tillman <don at till.com>
>
> > Brock Russell wrote:
> >
> > > Just happen to have the 9 bit top octave divide list on my desk.
> > > (2 MHz typical input)
> > > Equal tempered scale; a few Just scales from Vanessa Else (Polyphony May
> 84)
> > > C (hi)  239             210     360     630     24
> > > B       253             224     384     672     26
> > > A#      268             240     400     720     27
> > > A       284             252     432     756     28
> > > G#      301             270     450     810     30
> > > G       319             280     480     840     32
> > > F#      338             330     512     900     33
> > > F       358             315     540     945     36
> > > E       379             336     576     1008    39
> > > D#      402             360     600     1080    40
> > > D       426             378     640     1120    42
> > > C#      451             405     675     1225    44
> > > C (lo)  478             420     720     1260    48
> >
> > I'm sure I've said it a couple times before whenever the topic of top
> octave
> > generators comes up, but it's been a while...
> >
> > The divide-by-239 to divide-by-478 is the classic top octave chip, like
> the
> > 5024.  It has roughly twice the error of the gear-based Hammond organ tone
> > generator (that's 1938 technology!)
> >
> > The reason is that instead of a 1/N approach the Hammond uses a pair of
> gears
> > for each note, and thus an M/N approach, which gives you bettter accuracy
> with
> > smallish integers.
> >
> > This suggests a couple things.  One is that you might want to aim for
> better
> > accuracy than a 1938 organ.  Another is that it might be fun to copy the
> Hammond
> > ratios exactly with twelve 4046 PLLs and 24 dividers.
> >
> >   -- Don
> >
> > --
> > Don Tillman
> > Palo Alto, California, USA
> > don at till.com
> > http://www.till.com
> >
> >
> >