[sdiy] Ms20 filter clone PBC?

[Aaron Lanterman]

On Feb 27, 2008, at 8:41 AM, Ian Fritz wrote:

> JH --
>
> Just out of curiosity, why does it say "LP/HP slopes are -12dB/ 
> oct" ?  In the actual MS-20 it looks like the HP is -6 dB/Oct, since  
> the output is taken from the same stage as the input.  Tim  
> Stinchcomb pointed this out some time age in his detailed analysis.  
> Is the MOTM module configured differently?

I remember coming up with similar conclusions, that the HP is actually  
more of a one pole. If I recall correctly it wasn't a straight high- 
pass either - it was like a high-pass band-pass mixture. But I could  
be remembering that wrong.

If you actually start with a regular two-pole highpass and go through  
the exercise of replacing the resistors with OTAs, you get something  
that I haven't actually seen in any synth.

It's been ages since I've done the analysis - so I can't remember for  
sure. I must have my notes somewhere...

- Aaron