[sdiy] Thoughts on a Polyphonic Synth

[jure zitnik]

that digisound voice card is very interesting, but if i'll ever design
something like a voice card it'll be discrete. i mean... don't all the
synth-purpose ICs (like those curtis chips on the digisound) extinct
after some time? as i can see the CEM3340 are going for 40$!

i know a totally discrete voice card would be fairly big... you guys
think too big? it actually doesn't need all that i wrote above... i'd
like it to offer something unusual... a few ideas:

-the 2x 2pole SV filter could be used as an oscillator. so you
wouldn't need 2 VCOs per voice. or is that a stupid idea? how good is
the tracking on such filters? (like the ray wilson's) with some
clipping you could get a squarish VCO and detune it from the main VCO
to get some fatness.

-a few dividers (like 2) that could be used (simultaneously) instead
of the second VCO (i know, synced all the time) which i think could
sound quite good with...

-waveshapers don't consume that much space right? 2 x pulse and one
SQR->TRI->SIN shapers could be used for both the subosc (sqr or pulse)
and the main osc (pulse, sqr, tri, sin)


what bothers me the most is that it would be necessary to have an
exponential voltage converter on each card. but i guess you can't
avoid that huh?

so - how big you reckon the card would be?

jure

On 3/24/06, Dave Kendall <davekendall at ntlworld.com> wrote:
> Hi Jure.
>
> > that's exactly what i've been thinking about for the past weeks.
> > my idea is to design voice modules that include something along the lines of
> > - 2x VCO with saw/tri/sqr/sin + SUB (shaped?)
> > - 2x 2pole SV VCF that can be cascaded into 4pole (with variable spacing)
> > - 3x ADSR EG (for each VCO and for VCF)
> > - 2x LFO
> > - 2x VCA
>
> For the sake of a few extra circuits, It might be a good idea to have some
> global modulation sources that affect all voices - another LFO ( even with
> just a simple triangle wave for sweeping VCFs or whatever),  sample + hold,
> and maybe overdrive/distortion.
>
> A global EG with external triggering is useful too... pulsed chords, or that
> trancey stuttering gated chord thang, without tying up an external dual
> noise gate..... :-)
>
> The uCapps stuff is amazing, and the possibilities are huge. If you can live
> with 4 note poly, then the PolyDAC as a kit gives a whole load of MIDI
> controllers too for about the cost of a midibox CV+ AOUT, once the MAX525s
> are figured in, and includes CC64 sustain, which is pretty important for
> chord work IMO.
>
> cheers,
>
> Dave
>
> >
> > and then you could stack as many as you want to get polyphony of your choice.
> >
> > i've got a whole bunch of ideas but since i'm a total n00b i'll learn
> > some more before writing about it :)
> >
> > jure
> >
> > On 3/24/06, harrybissell <harrybissell at prodigy.net> wrote:
> >> You would need to duplicate all the modules that you wished for
> >> in one voice.  8 eg for the VCF is probably a bare minimum.
> >>
> >> You probably would like 2 VCO per voice...
> >>
> >> And a way to keep them all in tune. Usually they use a computer
> >> to measure the frequency error and compensate per MIDI note number.
> >> Lookup table kind of thing...
> >>
> >> One thing that is NOT obvious... making a very complex single
> >> voice (like for a mono patch) will not be so satisfying in a poly.
> >> It will either get 'muddy' sounding... or blend so well that it
> >> is totally smooth
> >>
> >> H^) harry
> >>
> >> Benjamín Velasco wrote:
> >>>
> >>> Hi list!!!
> >>>
> >>> After looking the amazing midi projects at www.ucapps.de i was
> >>> wondering how difficult it would to build for example a 8 note poly
> >>> synth. With the MIDI to CV from this page you could have 8
> >>> independent for each oscillator. Then you would need perhaps 8 EG
> >>> and 8 VCA for each note's volume? What other module you i have to
> >>> repeat? Maybe 8 EG for VCF??
> >>>
> >>>
> >>
> >
>
>
>