zetaSID: A Chat with Developer, Peter Knoblach

Thanks for chatting with us Peter, I'm excited to hear all about midiphy - how did it all begin and what products led up to zetaSID?

It all started way back with MIDIbox, a brainchild of Thorsten Klose, who invented one of the first great hardware SID synthesizers as a DIY project (check out MBSID and MB6582), and then built a very powerful hardware step sequencer (check out MIDIbox SEQ v4) - i joined the MIDIbox community in ~ 2009. In 2017, together with Andy, whom i met in the community and with Thorsten's support, we founded midiphy - and created commercial DIY kits for MIDIbox based developments. We're incredible thankful to Thorsten, both for his inventions and that he let us create commercial kits based on his inventions, this was the start. 

We'll get to the nitty-gritty fun stuff in a mo, but first - the SID has had a huge and varied history in music making...original C64 hardware/software, modern C64 solutions like MSSIAH, synth modules that transplant the original chips (Sidstation, Midibox SID) and a huge amount of emulative hardware/software - why do you think SID is still so revered? Pure Nostalgia? Synth Engine? The analogue VCF?

Everyone probably has a different story and idea about this, but here's mine: as a typical computer kid, starting with a "home computer" at the age of five, I grew up only with few friends (the ones i had were geeks with computers as well, we were treated like aliens in the classroom). So i had my C64 and its software, mostly games, which were pirated on the schoolyard :) - That C64 was on in the afternoons, every afternoon. Its sounds, from the masters like Rob Hubbard, Chris Huelsbeck, Jeroen Tel and many others probably burned too often, too deep into my brain :) - and seemingly did the same to other computer freaks of that time as well. I think it is the imperfection of the SID chip that makes it perfect - it is not a hi-fi device, the original 6581 has a really high noise floor and there are some chip bugs (ADSR envelopes anyone?) - nevertheless, this chip reached solid gold fame status when comparing early sound creation systems. I've lived through the full era, starting with Atari's TIA and Pokey sound chips, the SID, Amiga's Paula (for the also famous Soundtracker .mod files), Ad Lib, SoundBlaster and Gravis Ultrasound PC sounds, all the way to modern 192khz 32bit DACs (who can hear that?) - and for me, the SID chip is a favourite, because of its character.

(Rob Hubbard & Ben Daglish - Auf Wiedersehen Monty)

In 2009 i began building my first MIDIbox SID and when it was done, i was blown away by the power of its engine. I knew the SID chip, but what the engine offered was more than i understood at that time. I've used my MB6582 since 2010 and in the first ten years I still discovered new features. So maybe to understand it better, but probably more to preserve it, zetaSID was built - with Thorsten's blessing, it is a modern recreation of his original, mindblowingly powerful SID engine, that he originally built in pure PIC microcontroller assembly back in the 2000s.

Wow! So zetaSID, tell me a little about it. 4HP I see (nice and compact!) how is the SID engine implemented (it uses state of the art sound chip emulation, I understand). Also, does it have any unique features?

For this I'd better link to zetaSID's web editor, which contains all the parameters on one page: https://www.midiphy.com/en/zetasid-webedit/
I've not counted the number of engine parameters, but it must be a few hundred :). We have classical synth sections for the three SID oscillators, LFOs, filter, but also notable stuff like two complex parametric envelopes, a modulation matrix with 8 paths and algorithmic and bitwise operations (i.e. XOR a parametric envelope with an LFO), three independent arpeggiators (one per oscillator) an extensive trigger matrix and four independent wave sequencers, which implement what the C64 scene often calls "wavetables". These are basically step sequencers that can manipulate every patch parameter (very quickly, if needed) over time. In the C64 scene this is often used to very quickly cycle through the SID chip waveforms, to create pseudo-waveforms that are normally not available. 

In short, Thorsten built MIDIbox SID v2 in a way that allows to create sounds that are not typical SID-like, but would be more fitting to a VA digital synthesizer. As far as i can recall, with the PIC microcontrollers he managed to update the original SID registers with a higher rate than that was normally possible with the original 1MHz C64 CPU, but i may have to revise that statement, when looking at what modern demos do :-)

Yeah, more C64 audio limits are broken each year, it seems! On your instrument I spotted six(!) LFO's - a modulation monster, then?

Yes. :) But do not worry, in conjunction with the web editor, it is very manageable - and not every feature needs to be used for every patch. You can create a nice-sounding typical C64 SID patch, e.g. with pulse width modulation and slightly de-tuned pulse wave oscillators via the module user interface really quickly. Every parameter can be controlled via the native user interface - and we added visual feedback to see what is going on, i.e. you have animated envelopes, LFOs and modulation waves that you can see on the OLED - you'll also get an approximate filter response curve graph and see the arpeggiator notes flying by. Also, having more than one zetaSID available allows sharing of the UI, dedicating each module to a specific task, i.e. for a live performance you can leave one zetaSID assigned to filter cutoff manipulation and another to change the release time of the SID envelopes - it's a dynamic UI and every user can set it up in a way that suits them best.

Ah yes, owning more than one! You've advertised the module as expandable, I see images of multiple zetasids lined up in a rack - great for polyphony or multi-timbrality I imagine! Tell me more about how this works - CV/Gate but with an optional MIDI expander, right?

For the expandability of our modules we created phybus - this is a reason why the development of zetaSID took over two years: creating this framework was utterly complex. It is a backplane high-speed data bus, that allows not only polyphonic expansion but also user interface interactions and virtual routing of MIDI, CV and gate/trigger signals throughout the system. With phybus, it is possible to reuse "unused" ports for other functions in the system, by "splicing" them. How does this work? Just push the LEDome button next to an unilluminated (and thus yet unused) modular port - and all port-compatible phybus connected modules will ask the user how that remote port should be internally wired up. Like this you can virtually patch MIDI signals e.g. from nexusMIDI into zetaSID and back out again.

This system also allows "total recall" of internally spliced connections - say you have a live set and want to quickly switch from one zetaSID setup to another - where many modules should reconfigure themselves, load different patches, rewire their spliced virtual phybus connections. In a classic modular system, you'd have to remove and re-insert a lot of patch cables - for a phybus system that uses internal connections, you can do that by just switching the session on one module - all other phybus modules will follow the switch command and rewire themselves. If you have found a nice "setup", you can save that as a recallable session for the future, then switch to another session without worrying of losing it. 

Recallability and Eurorack have never made good bedfellows, but your system sounds really neat, contained, tweakable. How can our readers find out more about zetaSID?

Have a look over at midiphy! We have created a free-to-use emulator of the full zetaSID engine - you can listen to all patches in the ROM patch bank, even attach a MIDI keyboard, play with it and listen to the sounds. While it has some processing latency and the occasional audio glitch, we think it is a good way to test-drive a new module before buying it. We did not manage to go to any trade shows yet, but think that his might be a fair alternative for anyone interested in the module to judge and test-drive it.

Try it out over here: https://www.midiphy.com/en/zetasid-emulator/

For more information: https://www.midiphy.com/en/zetasid/

Thanks Peter and good luck with zetaSID!