Post

yes it makes more sense to me too

well filter is one of the things that maths can't do - here is what it can do (which is a lot): https://w2.mat.ucsb.edu/mat276n/resources/systems/CREATE_teachingSynth/manuals/8c_Maths2013-V1.11-printable.pdf

I would spend some time on youtube and forums researching filters - they all sound different etc...

I'd definitely look at doepfer filters though - as they are inexpensive and decent - mostly based on classic synth filters, as are most others to be honest, to a greater or lesser extent

maybe get a couple so that you can have some variation - one for the sub and one for the main output - maybe a wasp style (gritty) and a smoother moog style one - send each to a different cascading vca channel, but with a different rhythmic envelope going to each and different modulation to the filters and you suddenly get 2 voices from your single vco - buy doepfer and the pair together are cheaper than a lot of other filters - and just as good!

I'd be tempted to get a stages - it'll give you envelopes (from simple decay up to 36 stages if you chain 6 together), lfos, and a host of other functions as and when you need them - including a harmonic oscillator

I'd also recommend something for mixing (copies of) the outputs together to make more interesting patterns - a simple unity gain mixer with no controls will do the job - or a matrix mixer - which will do a much better job, but will be more expensive and take up more space

if the lfos you do get are uni-polar (stages is, for example) you might also want to consider adding something like shades - atttenuversion, offset, precision adder (for accurately adding v/oct signals) and mixer rolled into one

you may be thinking why do I need so many mixers?
(multed and) mixed modulation = (more) complex modulation
mixed lfo and envelope = tremolo effect
mixed v/oct and a tiny tiny bit of modulation (may require multiple levels of attenuation to get the right level) = vibrato
mixed vcos before filter = fatter (due to detuning etc) or accents one vco tuned an octave higher than the other - open filter more for accent
feedback
transposition - precision adder
etc etc

and all that may be for a single voice before hitting a final audio mixer - and most of those might want vcas and you probably want vcas for modulation on top of that - hence the saying - you can never have too many vcas - which should also be extended to mixers imo

as you are planning on playing from a midi keyboard - I'd get the midi converter asap and plan on adding as many simple adsr envelopes (as i suspect this is what you will expect to hear) as the midi converter has gate outputs - doepfer and frequency central both make great dual adsrs that are both reasonably small and inexpensive