BassStation Filter: What is it? Digital exponentiation!

[Bjorn Julin]

>If this is the one I'm thinking of... the CPU sets a rough current
>source charging a cap, and the counter tick is the reset pulse to discharge
>the cap...

A interesting analysis aproach to this DCO matter could be:

Se the MCU/counter as the comparator resetting the
integrator (MCU tick) and as a exponential converter
to surge current out or in to the integrator
(MCU driving DAC who setts a voltage(trough mux)
at the - input of the integrator) then let the
MCU do a exponential aproximation of analog exponential
converter by using a time delay lookuptable of the
outputed DAC value to the integrator and there you
have your VCO! :-)

Its all a matter of "resolution"!

And with in resoltution you can and have
controlled random who if properly set by
chosen laged random generator whit a known
time constant you get endless or no analog
VCO phasing whit the phasing time constant
settable by a value in the MCU mamory.

Hmm, maybe i should have patented this!

Reg
BJ( the brutal)

>so this way the sawtooth is pure linear (no steps) and the frequency is
>pure digital...  any errors show up as amplitude variation. Nice way to go.
>
>I have no problem with digital oacillators either, except they are really 
>hard
>to modulate with CV's....  Its funny that it is the imperfections in real 
>analog that
>everyone likes....
>
>For some things I prefer digital... like digital delay lines.  BTW I 
>consider the
>BBD a digital delay, albeit a Sh!tty one. The fact that it has an analog 
>range of
>oh... a couple volts in the Y axis does not cover up the sampled data 
>nature of
>the X axis....  so just saying analog does not mean good !
>
>(if this don't draw some flames then the list is dead....;^)
>
>H^) harry
>
>Bjorn Julin wrote:
>
> > Yeah, there it is,one thing that are missing
> > are the DCO tickers, they are created in a
> > wery odd MCU, from matshusita if i remember right.
> >
> > No wave tables just a counter tick to a integrator
> > who charges in a odinary whay to create sawtoth.
> >
> > I remmber the "OLD and "LIVELY" discussion on diy list
> > about why a DCO was a VCO, and the reverse,in my opinion
> > there is absolutely nothing wrong whit DCO's,in my
> > opinion i prefer them "if" high enough resoulution
> > of the charge ticks are used. Besides DCO'dont soft
> > sync. :-)
> >
> > Thanks for the link!
> >
> > Reg
> > BJ
> >
> > >you are all in luck....
> > >
> > >http://www.asahi-net.or.jp/~WZ4K-TNK/syoyuu/bsk.html
> > >
> > >Rob wrote:
> > >
> > > > Well, I remember way back when, I looked into the unit and I didnt 
>see
> > >the
> > > > telltale signs of a ladder filter ie neat rows of
> > >transistors/capacitors.
> > > > Unfortunately, I don't have one on hand to check out right now.. I 
>am
> > >sure
> > > > once the rack unit I bought comes in, it will prlly only take me an 
>hour
> > > > with my scope to figure the thing out.
> > > >
> > > > Also, a state variable filter would definitely be easier to produce 
>the
> > >2
> > > > pole/4 pole configuration that they used.
> > > >
> > > > As far as the VCO, I question whether it has a VCO at all. I get the
> > >feeling
> > > > that it has a DCO driven from lookup tables in the uP.. I dont 
>remember
> > >it
> > > > ever going out of tune, so this would point to to a uP DCO.
> > > >
> > > > Nothing wrong with this, but you definitely don't get the warmth of
> > >analog
> > > > with the DCO.. Still sounds good, but just a bit too perfect.
> > > >
> > > > Thanks
> > > >
> > > > Rob
> > > >
> > > > ----- Original Message -----
> > > > From: <metamatic at webtv.net>
> > > > To: <synth-diy at node12b53.a2000.nl>
> > > > Sent: Saturday, November 25, 2000 8:51 PM
> > > > Subject: Re: BassStation Filter: What is it?
> > > >
> > > > > cyborg_0 at iquest.net wrote:
> > > > >
> > > > > >Anyone know what kind of filter is
> > > > > >crammed in there? From what I
> > > > > >remember, it was some sort of state
> > > > > >variable filter, but I am not all that sure.
> > > > >  >Perhaps someone has some schematics?
> > > > >
> > > > >  I have the keyboard version. The VCF has two modes, both lowpass. 
>The
> > >2
> > > > > pole mode is meant to suggest a TB-303 filter, somewhat
> > >unconvincingly,
> > > > > IMO. The 4 pole mode, however, does a wonderful job of emulating a
> > >Moog
> > > > > VCF. I think it sounds quite a bit like my ancient Source, and 
>along
> > > > > with the bonus of factory MIDI, I don't have to worry about 
>damaging a
> > > > > rare membrane switch panel.
> > > > >
> > > > >  I'd love to see schematics as well, if only to see how the 
>different
> > > > > cutoff slopes are achieved.
> > > > >
> > > > > Richard Hess
> > > > >
> > > > > metamatic at webtv.net
> > > > >
> > > > >
> > >
> > >--
> > >mark verbos
> > >
> > >"if you want something done right, build it yourself."
> > >
> > >verbos at simple-answer.com
> > >www.simple-answer.com
> > >
> > >watch out for...
> > >on my new label SIMPLE ANSWER "only a danger to myself"  and "Culture
> > >Shock"
> > >out now.
> > >also...
> > >coming soon "World of Illusion" Simple Answer 003 now distributed by
> > >Integrale,
> > >UK
> > >I have moved to Berlin!
> > >
> > >
> >
> > 
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