Noob question here. What, fundamentally, is the difference between an LFO and an envelope? An envelope has a funny shape? It gets triggered? Or are they really just two different kinds of same thing?
LFO is a type of VCO a Low Frequency Oscillator that can be one of various wave shapes like a square or pulse wave form. Envelopes are not oscillators. In other words, they are fixed shape but that can vary with different stages: attack, sustain, decay and release. Here is a good comparison:
https://www.musicradar.com/how-to/LFOs-and-modulation-for-beginners
Now where LFOs and envelopes share they are both modulation sources that can affect parameters of an oscillator. For example, if you want to affect the duration of a note, both can vary that to some degree.
The difference between modulating a parameter with an LFO vs. an Envelope is that LFO’s are intended to continuously repeat at a certain rate or frequency, whereas envelopes are usually triggered events based on some user input like a key press. The envelope generates data based on the duration of the event.
Now the fine line gets blurred in function generator modules like Maths and Quadrax that combine LFOs with envelopes. These super modulators let you configure LFO and envelopes in combos. Acid Rain Labs Maestro is a super duper modulator that I recently obtained which lets you mix wave shapes, LFOs and envelopes in six channels. Quadrax can do similar things.
Hope this helps!
Yes, the easiest way to think of it is that an envelope is a triggered one-shot event while an LFO is a continuously cycling event.
They can be the same shapes (sine, triangle, square, oddly shaped ADSR, bouncing ball, etc.), but the envelope only goes through the cycle once per trigger. LFOs can be synced with a clock, but repeat the shape over and over.
Have fun and good luck!
One other point: you can use an LFO as a clock as long as the waveform has a sharp leading edge (saw, square, pulse). An EG, not so much.
One other module where the lines get blurry would be the 4ms PEG. It can loop or act as a pair of one-shots, but it uses some timing tricks similar to their QPLFO to let timing signals OR tap tempo govern the cycle duration. And in both cases, they're capable of insanely long cycle durations, making them excellent for generative purposes.
Lugia is correct and I am a bit of an LFO and envelope junkie with all sorts of modulation modules: Quadrax, Kermit, Batumi, Radar, Malekko Quad Envelop, Acid Rain Technology Maestro. Many have combo modes that do LFO and EG in button settings. Some are pure LFO or pure envelope like my basic Doepfer LFO and Doepfer ADSR modules. I like do cool modules bang for buck so a super modulator like Kermit can output 4 LFOs or envelopes or random voltages or combo of these things. Some advanced clock modules like Pamela's New Workout even have LFO and envelope mode features as well. For learning as a beginner, I recommend getting a simple LFO module and a simple envelope generator module and clock. Figure out how to use LFO with envelopes and VCAs to modulate things. Then move to a do cool combo super modulator like the ones I mentioned above. Most important: have fun! Eurorack is a super expensive hobby so if you are not having fun then you are doing it wrong :-)
Thank you so much for all the thoughtful and informative responses. I think I understand better now, and have some venues for further research.
And yeah, it was screwing around with MATHS that made me ask this question!
Also, check the "Too Many LFOs?" thread...I put quite a bit of info in there about how to work with LFO signals via other modules, and many of those tricks work just as well with envelope generator outputs.
