digital control of analog component question...

[Harry Bissell]

Er... I'm not sure that I'm getting this...
There was a mail about the Juno 106 method of digitally controlling an "almost
correct"
VC ramp... but that still needs the analog ramp.

Some circuits (the twin-tee oscillator/filter for instance) and be "triggered"
to produce a wave... but not over any wide range. It might work for a percussive
sound of something like that... but probably not for a pitch source...

Or I don't get it...???

:^) Harry

Rob wrote:

> Well, one nifty thing I have seen is that ANY capacitive element in a
> circuit can usually be replaced by a trigger spike.
> So, for example, if you were to take the cap out of a VCO and replace it
> with a periodic trigger spike, the standard VCO circuit should just become a
> sort of waveshaper with the trigger determining the frequency. Then you dont
> even NEED a stinking D/A..
>
> Now THIS is some food for thought. Imagine the possibilities of a perfectly
> in tune VCO, with the same harmonics but without the pesky drift.
> I have been meaning to try this for some time, as I saw this very example in
> a project at my work and it worked well. Really intriguing, I about yelled
> outloud when I came across it in the circuit I was troubleshooting.
>
> Rob
>
> ----- Original Message -----
> From: Harry Bissell <harrybissell at prodigy.net>
> To: The Proteus <proteus at xmission.com>
> Cc: <synth-diy at mailhost.bpa.nl>
> Sent: Wednesday, January 12, 2000 9:44 PM
> Subject: Re: digital control of analog component question...
>
> > I believe that the major difference between the DCO and the VCO is that
> most DCO's
> > produce a waveform that starts over from the beginning of the wave with
> each change
> > in frequency...  sort of an unintended reset function. Most samplers work
> this way.
> >
> > VCO's respond with a continuous waveform... even a jump between octaves is
> a smooth
> > transition... and glide etc is always smooth, not a series of steps...
> >
> > And some circuits are halfway inbetween... but few... very few...
> >
> > VCO's... because I can taste the difference....
> >
> > :^) Harry
> >
> > The Proteus wrote:
> >
> > > Gents,
> > >
> > >         This opens up a whole new topic of discussion on how to
> interface
> > > the D/A to the analogue circuit. I was grilled on a question about the
> > > difference between VCO's and DCO's in an interview for my current
> > > employer, and the only difference I could think of is that a DCO is a
> VCO
> > > with D/A on all the CV inputs. Then it got me to thinking, how many
> > > current output DACs there are out there, and even some of them having
> > > logarithmic current output. Why have an I->V converter on the output of
> a
> > > DAC, then go trhough another V->I converter on the input of the VCO?
> Since
> > > most VCO's I've worked with and built have an OTA current-control gain
> > > cell at its core, this could prove to be an advantage both in noise and
> > > parts cost. Anyone care to followup on this thread? Any other
> differences
> > > between a VCO and a DCO that people have noted over the years?
> > >
> > > The Proteus - Morphing the convergence of technology and passion.
> > > -- Musician - Producer - Engineer  -  UNIX Admin Extrordinaire --
> > > "...the best workaround for a bug in a UNIX utility is to install
> > >  the GNU version" - Kragen Sitaker
> > >
> > > On Wed, 12 Jan 2000, Magnus Danielson wrote:
> > >
> > > >
> > > > Yes, this is one of many popular ways of doing it.
> > > >
> > > > Then there are more ways to control curcuits by digital meants, like
> CMOS
> > > > switches and such. There are also all kind of hybrid solutions by
> which the
> > > > frequency generation is done digitally but waveshaping is done by
> analog etc.
> > > >
> > > > Cheers,
> > > > Magnus
> > > >
> >
> >