Burt Baccarach's Korg CCO core in the TB 303 essay!

[Magnus Danielson]

From: Haible Juergen <Juergen.Haible at nbgm.siemens.de>
Subject: RE: Burt Baccarach's Korg CCO core in the TB 303 essay!
Date: Thu, 14 Dec 2000 12:33:01 +0100

Hi Juergen, BJ, the list!

I've got this a few days ago, but haven't had the time to ponder over it.

First off I do not particularly like the tone it is written in, there
is no reason for such a tone.

> > I have written an Essay of the TB303 at:
> > http://home.swipnet.se/~w-133242/tb303.htm
> > 
> Sad to say that the "analog master" brings up that same old 
> misinformation about the 303 filter. 

Which missinformation? Please be specific. In the rest of your email
you only discuss generic things in sufficiently detail for comments.
Also, the essay droped of the edge of the web due to the responce, so
I was not able to look at it.

> When a filter has a slope of 345 dB/Oct (fit in any number here) in the
> frequency range of interest, then it is perfectly right to adress it as
> a "345 dB filter", regardless how many poles and/or zeroes are used.

True, but to a certain limit. It is naturally of importance to say
what sort of means of measure the slope one has. If it is from the -3
dB point to the -40 dB point or something. The trouble with slopes and
slope measures is that they are incredibly hard to get accurate to
tell you a good story of what is going on.

They can bring in a minimum requirement such as "in order to get that
lowpass 18 dB/Oct slope will at least 3 poles be required".

What can happend (and happends quite often) is that down the slope is
another pole or zero hidden. The slope measure is those rather limited
but may be usefull, especially in musical terms where we are
interested in how much attenuation overtones experience when they pass
a filter.

> When you're talking about poles, talk about poles. When you're
> talking about slope, talk about slope. If you mix up both concepts,
> you can still be right on textbook designs, but not on more exotic
> filters.

Hum. While correct in theory, this could be written in a nicer way.
I would normally spend more cycles on explaining how this is...

> This should not be in the category of "myth" for someone who is reading
> synth-diy for years.
> 
> (Your description about "bumpy" and "sound" is perfectly right, so why
> not draw the right conclusion?)

Which is? Even if I have been a steady customer to the Synth-DIY I
can't recall all things being said. Searching the archives is not a
very pleasent thing either. It is by discussing things actively that
we keep the knowledge up and learn things. I have been forced to study
details of various things prior to answer emails on Synth-DIY, but
that has raised my knowledge as well as others.

If we look at Synth-DIY lately I have noticed that for some the
tolerance level has gone way down, we have diverted away from
discussing real DIY aspects and run into sidetracks. Some threads have
still been valid stuff. Yeah, I have done my fair share of
diversions. Anyway, I'm not very interested in weither BBDs are BAD
for your health, weither there are americans that can defend themself
or any other sidetrack issue, I want to get back to discussions on
VCOs, VCFs, smart ways of doing expo-converters, waveshapers, phasers,
how to do your own faceplates, PCBs, help onn getting a curcuit
working, and just pure awe when someone done a good job!
So, Synth-DIY is currently not what it used to be... we should be able
to get some of that back before to many run away for the wrong
reasons.

Now, if we back up to the real issues here... we have this filter up
in the TB-303. It has some quirky aspects. I have looked on the
schematic some and made some quick analysis. Can't we discuss this in
a way that I and possibly others gets further insight into it, some
filter theory, ladder filters etc.?

Cheers,
Magnus