Subtractive synthesis is not as complicated as most beginners think is, there really is very little you actually need know, once you’ve got the basics the rest comes naturally in very short time just by playing around and having fun with synths.
In all synths all the modules of the same type are similar and follow the same principles and once you’re familiar with the basics you can normally start programming a new synth in minutes.
First learn about the foundation modules: Oscillators and Filters and Amplifiers. Understand how sounds are generated and what can be obtained before you do anything else to the audio.
Then go on to understand modulation and how it’s applied, this is where the real fun starts: Low Frequency Oscillators ( LFO ) and Envelopes ( sometimes referred to as EG or ADSR ).
Of course there are a lot of other ancillary module types but you don’t need to understand them until you’ve got to grips with the above mentioned.
The concept of Subtractive Synthesis hasn’t changed through the past decades so just because a resource is old doesn’t make it irrelevant. Articles on hardware synths, particularly modular synths often give you a wealth of information which is equally applicable to soft synths.
If I have any advice at all it is “Never be afraid to twiddle”. You aren’t going to break anything! Turn a knob and listen to what happens, if nothing happens twiddle another one. Occasionally you will lose all sound and a synth will remain stubbornly silent. When that happens simply reload the preset and start twiddling afresh. Alternatively a good challenge is to see if you can work out why it went silent and when you do that you will gain a lot of satisfaction when you realise what’s going on. In fact, if you can work out how a synth is making it’s sound by examining it’s parameters you’ve reached the destination!
Finally, a quick YouTube search brings up a wealth of videos
How to make a noise - Simon Cann -
Sound Synthesis Theory - WikiBooks -
The Complete Synthesizer - David Crombie -
Synth Secrets - Sound On Sound, in the process of being updated but you can follow the links on the page -
Sound Design: Stack Exchange (More Advanced)
If you have any more to add to this list please reply to the thread and leave your links…