The Threeler and Filter Foundry

via Scott Stites:
"Here's something that doesn't come along every day. A few years back, I built a dual version of PCB pattern for René Schmitz's "late" MS20 VCF, which René had designed using CA3080s and green LED's for the resonance limiter. This particular rendition of the circuit has the marvelous capacity of creating strong harmonics above and below the fundamental while feeding it a sawtooth into it while in HP mode, which creates a sound not unlike two or more oscillators operating simultaneousy (the effect is not the same a simple sub-oscillator). I'd posted some samples that happened to include the filter, and the sound of the thing caught Ian Fritz's ear. The chaotic non-linearity of the the filter, and the resulting timbres interested him. To make a long story short, he came up with a filter based on the concept that does some amazing things, which he calls the "Threeler". It actually contains three six dB blocks in cascade, each of which can be configured either in HP or LP mode. He includes a version of the resonance limiter, which helps to impart the nonlinear response, to which the timbre of the the output owes much.

There's a thread at electro-music about it here.

The threeler operates in four modes. Here the links to a couple of samples:

Mode 1

Mode 2 (I especially like this one!)

If anyone is unfamiliar with Ian Fritz and his work, he's a well-seasoned author in the Electronotes series, and has a site here.

Cheerio,
Scott"