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

[harrybissell at wowway.com]

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