Since three of the filters in this shootout were coded by me, I thought I'd contribute a little clarification about their differences.
The CA Ladder, VM2500 Filtamp, and Mood 904 are all 4-pole, 24db/oct, Moog-style ladder filter designs with subtle differences between them. I don't know what's in the CA Filter or the S100 Dual Filter. The Laboratory VCF is quite different being a multi-mode state-variable design.
Ladder type filters are capable of a maximum Q*** (resonance) of 4 before they go into self oscillation. This makes for a very useful and musical sounding filter, but is hardly appropriate in many applications. For instance, if you try to cascade them to make speech sounds or simulate instrument resonances, they fail miserably. For those two applications, higher Qs (in the 10 to 50 range) and 2-pole designs are required. Also, if you want to bang the input and listen to the filter ring, you need even higher Q. The Lab VCF is capable of Q values up to 2000. It's actually clamped there and could probably go much higher, but I had to limit it somewhere. 2000 is plenty. The VM2500 1047 filter not featured in this shootout is similar and capable of Qs up to 500.
If you have the Lab Bundle, find the Talky preset which is programmed to say "Cherry Audio" and you'll quickly realize that that patch could never work with ladder filters. The VCFs' Qs are all set somewhere in the 20 range to simulate human vocal tract resonances. There's also a preset here
viewtopic.php?t=1100 that shows percussive physical modeling using high-Q filters.
While this filter shootout was informative, in many ways it's an apples and oranges comparison. However, I would have loved to have heard some bwwwwaaah sweeps of all of them just to get a quick idea of the differences. Maybe somebody will do that.
Well, I didn't mean to write a manifesto, but I didn't have time to make it any shorter. I hope it was informative.
--mb
*** The Q of a resonant peak is equal to its frequency divided by its bandwidth (F/bw). Since both of these values are measured in Hz, Q has no unit and is a dimensionless figure. The Q literally stands for "quality", and you can see that the narrower (smaller) the bandwidth, the higher the Q. Additionally, unless compensated for, the gain of the filter at the peak is equal to the Q. Now you can see why I put an input level control and a meter on the Lab VCF in an attempt to save the planet from flying speakers!
