As an example I'm still a bit wooly in terms of Modulation and Envelopes e.g. I can understand (and hear!) what the amp envelope does, but have yet to understand the filter envelope and it's applications and anything beyond things like simple vibrato effects via the modulation section is just guess work at the moment

Syntorial has caught my eye, and I've worked through the free part which covers the basics, and was useful - anyone care to comment on the content you get once you actually buy it?
Any suggestions welcome!
Regards