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

[Scott Gravenhorst]

harrybissell at wowway.com wrote:
>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

I finally "got" what Harry just described moments before this message arrived.  I read it
and then tried to visualize it - and "oh yeah" happened.

My $0.02 on Walsh - I wasn't thinking of 8 coefficients when I proposed using an FPGA for a
Walsh-based synthesizer.  I was thinking of MANY more than 8.  No - it's a bit hard to put
a knob on all of them, but then it would be a digital synth.  I'll add this to my already
too long list of "things I gotta try".





>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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>> > > > Synth-diy at dropmix.xs4all.nl
>> > > >
>> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
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>> > 
>> > 
>> > Harry Bissell & Nora Abdullah 4eva
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>
>
>Harry Bissell & Nora Abdullah 4eva
>
>
>
>
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-- ScottG
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