it’s all good, good opportunity for me to verify I’m not misunderstanding something.
What is happening with the span control is that there is a linear offset that is applied to the LOW and HIGH frequencies relative to the CENTRE frequency. At fully CCW this offset is 0…at CW. I’m basing this off trent’s livestream where he recreated the span control with crow, which was very interesting. From the three sister’s technical map, I believe my understanding is confirmed.
In the locked mode, the left filter on blades is equivalent to CENTRE, and the right is equivalent to LOW or HIGH (depending on if that frequency knob is set less or more than 12 o’clock). From Blade’s manual
I. Filter cutoff coupling. When this button is pressed and illuminated, filter 2’s cutoff frequency is set relatively to filter 1’s cutoff frequency. For example, when filter 2’s FREQUENCY knob is at 12 o’clock, both filters share the same cutoff frequency. With the knob past (or before) 12 o’clock, filter 2’s cutoff frequency will follow filter 1’s, but transposed up (or down).
The formant mode can be emulated by setting both filters to bandpass. You could implement a crossover with setting the two filters to LP and HP…though the 3 bands are a bit key in three sisters crossover as CENTRE is like a variable width bp filter (which I hadn’t really thought about until seeing this technical map diagram…which is pretty sweet.
The CCW quality stuff is wild on three sisters, I still don’t full wrap my head around it, I do know that sounds tend to punch out what you go towards CCW which can be pretty sweet in a mix. I have no idea if you could emulate the !Q VCAs the technical map talks about with Blades.
I can’t speak to any of these other synths you are talking about, as I’ve never tried them. I do love my three sisters though, I’m very excited to have both of these once Blades comes.