MOTM

At 2:29 AM +0000 11/10/01, sucrosemusic@... wrote:
>
>The "Oscillator Helper"

Talk to Larry, he's the Stooge in charge of voltage processing :)

>Too Much Stability?

Oh not again!!

>   I've always thought that the quirkiness of analog synths is part
>of the charm.

It is, but it has less to do with VCO instability than you might think.

>I'm almost wondering if there's a tangible difference
>between a nearly perfect VCO and a Digitally Controlled one.

Yes, there are tangible differences in the way changes in frequency can be
implemented.  A VCO has an infinite number of frequencies.  A DCO has a
finite number of frequencies.  In many synths, including any analogue synth
with MIDI, you have an analogue VCO controlled by the output of a DA
converter.  In some cases the VCO is controlled entirely by the DA (eg.
Matrix 12), and in other cases it receives a mix of DA output and analogue
modulation, including analogue portamento (eg. SH-101).

>Don't confused DCO with DO, though.  My understanding (which might be
>flawed) is that a DCO is an analog oscillator tightly paired with a
>digital circuit that maintains the tuning of the oscillator, while a
>DO is just a digital oscillator, using a DAC I guess.

A DCO may be defined as an analog oscillator synced to a digital clock
(Roland calls this a "rectangular of audio frequency" :).  You have a
digital master oscillator that is divided to clock analogue "oscillators".

Apparently, I don't like DCO's since I've sold every DCO synth I've ever
had (Juno 106, Juno 60, Matrix 6, MKS-10, etc.).  Then again, I've never
owned an EDP Wasp.

Otoh, you can have set of twelve analogue VCO's (one for the top octave of
each note) divided digitally (eg. Korg PS-3100), or a digital divider to
produce a sub-oscillator.  You can also have a wavetable driven by an
analogue VCO (eg. an MOTM-300 driving a Blacet Mini-Wave).  While I'm
typing, why is a PPG called a PPG??  If it stands for "Palm Products
Germany" wouldn't it be PPD??

I don't think the term "DO" is ever used, and many digital synths do not
even have a part that functions as a VCO.

>So back to the point, if these VCOs are so stable, what's the difference
>>between using them and using a DCO?  Wouldn't it be more practical
>>(although some purists would be mad) to have a modular, voltage
>controlled
>DCO?  Ahh, there's a problem there, I see, since you couldn't have
>the unit really respond to a CV signal for tuning, since the digital
>circuit wouldn't know where to tune it to be "correct"... although
>you could do it anyway (on the assumption that the Midi->CV converter
>or your CV keyboard is 100% accurate), or just have a MIDI equipped
>DCO.

Listen, you can get a MIDI controlled DCO in a number of polysynths, but it
has no place in a modular!!  In order to have a DCO module, you would need
a master clock (using a crystal or somesuch), an AD converter for every CV
input, a CPU to process all of this data, a system of clock dividers, and
the analogue circuitry required to generate the different waveshapes.
After all that, it would be much more expensive and still inferior to a
free-running analogue VCO.  Worse for more money is just bad engineering.

>Anyway, I'm not saying that I prefer DCOs at all.  I just wonder if
>having a super-stable VCO takes a bit of the warmth out of a modular
>synth?  Again, I'm not sure just HOW stable these VCOs are, if they
>vary by +/- .5 hz

If they varied by that much they'd be useless for FM and bass patches.

>then that's one thing, but if it's +/- .001 hz it's
>another.  So, if these VCOs are uber-stable, why not add a goofiness
>factor to the unit I made above, controllable with a pot, CV control
>being probably quite useless.

You can add "goofiness" by modulating the VCO with a random voltage.