Last installment I talked about VCAs, which are important in analog synthesis because of their versatility. This time around I'm going to discuss a type of module with a more narrow focus: the voltage-controlled filter (VCF). Voltage control is so ubiquitous in modular-synthesizer filters that we normally expect something called just a "filter" to really be a VCF unless it is explicitly described as a fixed filter. Filters in modular synthesis are nearly always used to set the timbre of a sound.
Back in Part 3 of the "intro to modular" series I said it would cost about US$1000 to US$2000 to get started in modular synthesis, and I said that although there are ways to economize, they are really ways to keep the price tag in that range, not ways to lower the low end further. This week, let's look at a couple of them.
It's been an exciting week here at North Coast. Since selling out the first batch of Leapfrog filters, I've been busy making more. That's still in progress. Then just yesterday I gave a talk at Frequency Freaks, here in Toronto, and that seemed to be well-received. At least, they asked me plenty of questions. I've also been playing a lot with the Roland D-05 I got as a present for the winter holidays, trying to learn how to program it. Somewhere in the middle of all this I'm trying to make progress on the development of the next North Coast module, the MSK 011 Transistor Mixer. There's been Spectre/Meltdown mitigation to do and a move of one of my backend servers to another data centre. And I have a couple of other super secret projects on the go.
All this hasn't left much time for preparing a proper Web log posting, but I'm trying to stick strictly to one every Sunday, so here are some thoughts on negative resistance.
The Leapfrog VCF does not actually go "ribbet," at least not without some effort. But after being told by one friend I showed it to that most people don't want to make real music on their modulars but just want something that goes "uuuuuuuuuuuLAAAAAAAAAAAAARGH" (which, let's face it, is true), I've added a demo highlighting that. Uulargh? Yeah, we've got this.
You've probably noticed that although resistors and capacitors come in many different values, some of which seem like they could be randomly chosen, there's nonetheless some sort of logic to it. You'll see power-of-ten sizes like 1kΩ, 10kΩ, 100kΩ and it's understandable that those would be "round" numbers it might be convenient to use and manufacture... but for instance there also seems to be something special about the number 47, so you see many resistor values like 4.7kΩ, 47kΩ, 470kΩ, and capacitors like 0.47µF and 470pF. Why 47? Why not 46 or 48 - especially when 47 is a prime number and 48 has many small divisors, which would seem more useful? Here are some notes on the commonly-used numbers and where they come from.