Introducing Pas-Isel: A classic, done in a new way

     Everyone knows and loves the voltage-controlled resonant lowpass filter. It's the great staple of popular electronic music, from the dawn of the Moog modular to the present. It's certainly the component of a synth that gets the most love.

    It's pretty easy to understand why - The filter is the 'heart and soul' of a synth more than any other part. It's what imparts a particular synth's 'colour' onto the sound. There's a reason nobody's celebrating the Minimoog's envelope generator or the MS20's LFOs quite as much as their filters.

    However, looking at the synth market as it currently stands, there seems to be maybe only a handful of distinct VCF cores that get recycled a lot, usually derived from the original giants of the industry back in the 60s and 70s. Most 'new' VCFs are still variations on classic OTA-based designs, transistor ladders, Sallen-Key topologies, or other tried and tested technologies. Either that, or the innovation happened decades ago (such as the EDP Wasp or Polivoks filters), and have only recently been brought to the attention of the synth community. With so much innovation going on particularly in the Eurorack scene, why has there been relatively little by way of filter cores?

    Well, that's why I came up with Pas-Isel.

    Pas-Isel (Welsh for 'low-pass') is my attempt at creating a filter core that isn't clone of a classic. My intention was to implement a classic lowpass VCF in a way that hadn't quite been done before, experimenting with underused, forgotten and obscure filter topology, and hopefully achieving a whole new character of sound in the process. I think I managed it!

    Being my first ever synth module, I've opted to keep it simple - No voltage-controlled resonance, no resonance insert loop, no pole mixing... That's what future revisions are for. For now, it's a straightforward four-pole lowpass, that will give a life and colour to your signal like no other filter can.

    In my next blog post, I'll go into the technical details of how and why it works, and how the topology of the filter is derived.