[sdiy] More new Alfa chips - CEM3394

Mattias Rickardsson mr at analogue.org
Fri Apr 5 22:19:58 CEST 2019


Or unless you wanted to make it possible to sequence parameters differently
for different notes.

Same timbre or not - that is the question.

:-)

/mr

Den tors 4 apr. 2019 20:53 <paula at synth.net> skrev:

> Unless you wanted to make it multi-timbral.
>
> ;)
>
>
> On 2019-04-04 19:29, Richie Burnett wrote:
> > Very true.
> >
> > And Neil has a good point that not all CVs are unique to each synth
> > voice in a polysynth, so they can be connected to a common analogue CV
> > line. It would make little sense writing the same value multiple times
> > to the same parameter register in each voice chip if everything was
> > handled digitally over something like SPI.
> >
> > -Richie,
> >
> > Sent from my Xperia SP on O2
> >
> > ---- Tim Ressel wrote ----
> >
> >> you can get an 8-channel 8-bit DAC with SPI for about $2. no need to
> >> muck about with muxes.
> >>
> >> --timmers
> >>
> >> On 4/4/2019 5:14 AM, Neil Johnson wrote:
> >>> Hi Rich,
> >>>
> >>>> When I saw "Microprocessor controllable..." in the datasheets for
> >>>> these
> >>>> CEM chips I was initially expecting to see an SPI interface! :-(
> >>> Indeed not, as they say (AS3394E):
> >>>
> >>>> Thus interface to a microprocessor system may be accomplished simply
> >>>> with a single DAC, 4051-type CMOS multiplexer, and 8 hold
> >>>> capacitors.
> >>> That said, for a polyphonic synth it is actually quite useful to have
> >>> voltage control of these parameters, in EGs for example, where each
> >>> parameter is common across all voices so you hang the controls off a
> >>> voltage bus.  For example this is how the Siel Opera6 does things,
> >>> with all the SSM EGs driven off common voltages for the A, D, S and
> >>> R.
> >>> If you did this with SPI then you would either need some sort of
> >>> addressing scheme (in that case use I2C), OR you end up with a huge
> >>> mass of slave select lines!!  And you've now increased the cost of
> >>> the
> >>> silicon by putting logic (another voltage rail) and some number of
> >>> DACs plus reference on the die.
> >>>
> >>> Cheers,
> >>> Neil
> >>
> >> --
> >> --Tim Ressel
> >> Circuit Abbey
> >> timr at circuitabbey.com
> >>
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