It is and isn’t obvious.
Obvious:
To assign an envelope to modify the level of an oscillator, setup a ‘wire’ in the modulation matrix. E.g. “WIRE 1: source: ENV1 +63 dest: Osc1Lvl”
Less obvious:
To hear the affect of level modulations, you will probably need to lower the oscillator’s level parameter, to zero typically. This is because the modulation ‘wires’ are additive/subtractive. So in the setting above, the envelope’s values are added to the oscillator’s level parameter. If your oscillator’s level parameter is already at full, adding the envelope’s values will have no affect; there’s no headroom for the level parameter to go any higher. (Alternatively, you could set the wire’s modulation to -63, to subtract from the oscillator’s level, but then you need to imagine your envelopes upside down… )
Obvious, but easy to forget:
ENV4 multiplies the levels of all oscillators. E.g. if an individual oscillator has a wire that gives it a fast attack, but ENV4 is set to a slow attack, the overall level of the patch will have a slow attack.
Not so obvious:
This one always throws me: The arguably mis-named ‘MOD’ parameter modifies the waveshape of each waveform type in different ways, but by default, has nothing to do with other modulations in the matrix or elsewhere. On the NF-1, envelopes 1-3 are ‘hardwired’ to the ‘MOD’ parameter of oscillators 1-3. (And, the affect of each envelope on each oscillator’s MOD parameter is multiplied by each oscillator’s ‘ENV’ parameter.) So, unless you’re starting from an INIT patch, you might want to check the MOD and ENV parameter on each oscillator in question, and set them to zero, so that the waveform isn’t changing shape while you’re modulating it’s level; unless that’s what you want!
Obvious until it’s not obvious:
The 7-stage envelopes can confuse things if you’re not expecting them. When doing complex modulation, I usually start with them at standard ADSR shape (L1 & L2 to full, and T1 to zero.) to keep things simple, at first anyway.
Hope that helps!