At least I don’t know about any video tutorials on this topic …sorry about that, I would love to share. Maybe others know. What I can share is some of my humble experience gained from various recources (textbook style) and trial and error.
Example … if you apply AM or FM you can create pretty disharmonic sounds, which might have at least two bands of frequencies, which are non-harmonic. This generates those metallic or wooden timbres. If you then sync such a modulated oscillator to another oscillator, the sound will be forced to the pitch of the syncing oscillator and the AM/FM modulated part of the sound becomes sound color only.
Now change the AM/FM modulation frequencies or intensity and you will get very interesting and differnent sounds at a fixed pitch. It is very rewarding to change the frequencies of the FM/AM modulation source and the AM/FM modulated oscillator until a sweet-spot is found. But there is some searching involved. Sometimes detuning the modulation frequency a third, or fifth apart gives more interesting results than an octave. Most important - listen carefully for sounds, which seem to converge to a less gritty, wobbly, or noisy timbre - from here it could be only a little fine tuning that is needed to hit one of the sweet-spots.
Example: On the A4/AK you can use a LFO (with or without keyboard tracking) as FM-modulator, VCO1 as the FM-destination and then sync this to VCO2. For a performance you can use the joystick to modulate the frequency of the VCO1, or the LFO, or the modulation depth …
Concerning the envelopes… In the old days, when envelopes were generated by real analog circuits, we had so called RC circuits, which had an exponential/logarithmic behaviour. This often is overlooked, if a sound is supposed to be “old-school-analog”. At the end it’s only about how an attack will rise, or a decay, or a release will fall - and how our hearing perseives the sound. Our hearing is logarithmic and if an envelope is linear, the modulated effect (pitch, volume, brightness) of the sound will be perceived more smooth, if it’s exponential it will be more punchy.
For many more interesting details I would recommend the great series we have on sound-on-sound …
http://www.soundonsound.com/sos/allsynthsecrets.htm
And there is more