- Three Filter Modes: Lowpass, Highpass, Allpass
- Two frequency ranges (10:1 ratio)
- Series/Parallel Switching
Here is the article: MIF.pdf
Here is a mirror on Mediafire in case the link above doesn't work for you. I've been told that some web browsers (or their extensions) flag this as a dangerous site. It's not but the page does have a lot of extraneous links and other junk that can make it confusing to navigate. To start the actual download of the pdf file click on the big green "DOWNLOAD" button that also has the file size in smaller letters: MIF pdf
Craig was in top form—this is one tricked-out VCF.
Update 2017.2.26 Note that this design is not optimal. More work has to be done to get the stages to "behave" properly. This has been discussed on the Synth DIY list on multiple occasions. There is a searchable archive here: SDIY Archive
And there's some really good news: a clone of the 3320 has been fabbed. It's available here and the price is very reasonable. The datasheet is here.