Sunday, January 13, 2013

XA-80 Patch Notes

Thanks to Marc Doty, I'm going to make a few changes to my XA-80 plan. I'll also tell you a bit about its progress so far.

As for things I'm not probably totally scrapping:-Brilliance: I was misunderstanding the brilliance control on the CS-80. As it turns out, that's actually a secondary resonant low pass filter after the two voices mix together. So, I'll be adding that.
-IL and AL controls: I was right about how these affect the amount and voltage start point of the filter ADR, however I will still not be using IL. AL is the attenuator I was talking about.

2nd Voice Detuning, Octave/Footing Controls, Keyboard Controls, Touch Response, Footswitch/pedal Controls, and Presets are still being omitted. That seems like a large list...

Things I'm adding:
-MIDI control: yes, I'm making it MIDI controlled (In and Thru). I'll explain why and how later.
-CV outputs: Pitch CV, Gate, and Trigger will have outputs on the rear panel.
-Stereo audio out: just in case. This may also result in a panner, probably VC via the LFO.

External audio input is still in place.

So far, the instrument's plan is going well. And by well, I mean I'm slowly building it virtually. So far it has all the oscillators (except the noise oscillators), filters, amplifiers, attenuators, the ringmod, and current I/O planned.

However, there might be a few changes. I've been speaking with a longtime friend of Nyle Steiner (yes, the guy whose name is plastered on the Steiner-Parker modular, and more recently their filter) about the instrument and things I can do to make it affordable to build yet still playable and somewhat simple. He taught me two things: how to do the duophonic keyboard, and how to make a resonant filter.

As you probably know, I totally suck at building resonant filters. I also am bad at normal filters, so it's really no surprise. However, when he was telling me about the original Steiner filter, I noticed something about it: resonance was induced by increasing the gain on the non-inverting amplifier at the end of the signal chain! Though, when I tried it, I got weird phasing and stuff so I apparently need to work on it, but if this does in fact work then resonance will be a snap!

Now, about the keyboard... it's digital. OMG WHAT DUDE IT'S SUPPOSED TO BE FULLY ANALOGUE AND STU-- Yeah, I know. However, it requires a micro-computer (or a crap load of transistors n stuff) to accurately track two keypresses and send them to the oscillators and such. The XA-80 will actually use a MIDI keybed (with MIDI stuff still attached) and will feed a polyphonic MIDI-CV converter, which will then send out gate, trigger, and polyphonic pitch CVs to the rest of the (fully analogue) synthesizer. So really this will be a digitally played analogue synth. That's ok, right?

However, by using a MIDI keyboard, that means it's MIDI enabled, thus allowing for MIDI input, thus meaning MIDI sequencing is entirely possible!! However, it will only be for pitch, gate, and trigger. I'm not making the whole front panel MIDI-controlled. I'm not Moog :)

So, yeah, that's about it for now. Woot!

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