[sdiy] New TOG board: $0.02 needed / Walsh

[harrybissell at wowway.com]

Oops... this was in response to the 'digital pots' and the CLPD
part of the thread, quite a bit further down. I was pointing out that the
"multiply" needed for Walsh function coefficients could be as simple as
an analog switch and a CV source. Of course it might be more controllable to
use a big FPGA for total computer control... but a TOG/Walsh synth could be
much simpler. The functions are square so the fancy multiply becomes
quite trivial.

~not~ a suggestion for you to add to your TOG :^)

H^) harry




On Wed, 7 Jan 2009 12:23:18 -0800 (PST), Tim Ressel wrote
> Harry, I don't understand. How would that work? What would that be 
> useful for?
> 
> --Tim (thick as a brick) Ressel
> 
> --- On Wed, 1/7/09, harrybissell at wowway.com <harrybissell at wowway.com> wrote:
> 
> > From: harrybissell at wowway.com <harrybissell at wowway.com>
> > Subject: Re: [sdiy] New TOG board: $0.02 needed / Walsh
> > To: madhun2001 at yahoo.com, synth-diy at dropmix.xs4all.nl
> > Date: Wednesday, January 7, 2009, 9:56 AM
> > You could use simple analog switches as multipliers for a
> > Walsh
> > coefficient system... the square waves (or Walsh functions)
> > drive the
> > control input, the analog outputs are summed, and control
> > voltages fed into
> > the analog input. No digital pot needed, CVs can be input
> > directly
> > 
> > H^) harry
> > 
> > 
> > 
> > 
> > On Wed, 7 Jan 2009 09:25:06 -0800 (PST), Tim Ressel wrote
> > > FYI:
> > > 
> > > Cheap digital pot: MCP4231-103E/P-ND (DigiKey)
> > > Dual 10K (other values available) $0.68 in 100 pcs
> > > 
> > > That's $0.34 per pot. Not bad. 12 notes * 8 Walsh
> > coefs per = 96 
> > > pots = $32.64.
> > > 
> > > Another cool thing: since all notes will have the same
> > timbre (?)
> > >  the digital pots can be tied together and all clocked
> > at once.
> > > 
> > > Of course that is going to be one nightmare board to
> > lay out....
> > > 
> > > --TimR
> > > 
> > > --- On Tue, 1/6/09, Nicholas Gregorich
> > <nicksdsu at mac.com> wrote:
> > > 
> > > > From: Nicholas Gregorich <nicksdsu at mac.com>
> > > > Subject: Re: [sdiy] New TOG board: $0.02 needed
> > > > To: music.maker at gte.net
> > > > Cc: synth-diy at dropmix.xs4all.nl
> > > > Date: Tuesday, January 6, 2009, 8:08 PM
> > > > Scott Gravenhorst wrote:
> > > > > Scott Nordlund <gsn10 at hotmail.com>
> > wrote:
> > > > >> I've always wanted to retrofit a
> > TOS-based
> > > > synth with something that output Walsh functions
> > instead of
> > > > simple 2'/4'/8'/16' squares. Of
> > course this
> > > > would require all the octave dividers to be
> > replaced (with
> > > > CPLDs?) 
> > > > > 
> > > > > IMO, an FPGA would be more appropriate, lots
> > more
> > > > logic to play with.  Then you can go completely
> > > > > nuts with the design.  Also, a CPLD has no
> > dedicated
> > > > multipliers, AFAIK, a Walsh synth would need
> > > > > multipliers so that each logic output can be
> > amplitude
> > > > controlled rather than simply on/off.  An
> > > > > FPGA has this capability.
> > > > > 
> > > > 
> > > > If you control amplitude in the FPGA then you
> > need a DAC
> > > > (rather than just an output pin) and a way to
> > control the
> > > > amplitudes (MIDI or ADC).
> > > > 
> > > > I think part of the beauty of a Walsh generator
> > is that you
> > > > can actually put it in a small CPLD and build a
> > mixer,
> > > > that's it. No development kits  needed.
> > > > 
> > > > Nicholas
> > > > _______________________________________________
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> > 
> > 
> > Harry Bissell & Nora Abdullah 4eva
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Harry Bissell & Nora Abdullah 4eva