The Tao of FM Synthesis #5 ~ Envelope recipes

This is already the fifth episode of The Tao of FM Synthesis and we haven’t heard a single bell sound yet.. unforgivable! Here it is...

In this bell patch the short envelope for oscillator D provides a ‘realistic’ attack while a subtle LFO adds a bit of movement to oscillator F. The change in color is caused by a constantly varying aftertouch, assigned (in the modulation matrix) to the level of oscillator E, which provides most of the bell-like color in the sustain-part of the sound.

For some people FM means bell sounds, for others it’s more like a candy shop. When you’re tweaking an FM-patch you’ll sometimes stumble upon a whole range of settings that produce one amazing sound after another. The problem is you can’t choose which one to ‘save’ because there are too many wonderful sounds... the solution: next time this happens try to make the whole range accessible by assigning something like key velocity, aftertouch or any other modulation source to the magic ingredient that’s producing all these interesting variations. This way you can have it all :-)

While it’s nice to just tweak around, exploring some of the possibilities of FM without having a plan or a goal, it can also be a little frustrating because in the end you might return empty-handed from your sonic trip (unless you hit 'save' every now and then).

So you say to yourself: “OK, I’m gonna do a nice fat string pad” but you end up with an awesome bass sound… If you’re happy with that type of result, that’s excellent. If you like things a bit more structured and predictable you could also try the yin~yang approach of ‘sonic opposites’. It’s like having a recipe before you start cooking, but with some room to improvise. Here are some ideas:


These are just some examples of pairs of opposite qualities that a sound (or a piece of music) might have. If you can identify some of the characteristics you want a sound to have before you start tweaking that will give you a better general sense of direction and you’ll also know when to stop for a moment and save a patch.

Qualities like long~short, soft~hard, straight~wiggly and simple~complex are related to the use of envelope generators like the ‘classic’ LFOs, ADSRs and gates and the so-called sophisticated envelope-tools you’ll find in some of the more recent synth designs.

As you probably know, envelopes are used to shape the basic form of the overall sound, to define the attack part and the sustain part and to give a sound internal movement. For example the basic sonic shape of a guiro, a handclap and a cymbal are all very different. They’re all good starting points for creating a new FM sound.

With only two of the envelopes that were used to create the bell, but using different waveforms and ratios here’s a cheap noisy crash cymbal imitation. Note that oscillator F wobbles itself fully (100% feedback) to produce lots of extra noise. Oscilllator E does not kick in immediately because it is still being controlled by the aftertouch, which is once again producing a range of subtly varying sounds within one patch. The sine wave-shaped LFO again produces a bit of extra movement (a.k.a. tremolo).

Internal movement in a sound can be as simple as vibrato or tremolo, but almost any sonic quality can be shaped or accentuated with envelopes to give the overall sound more liveliness. In FM you’d typically be playing around with levels of operators/oscillators, with pitch or ratios. Maybe to have a bright attack and a dull sustain or maybe to have a ‘varispeed’ wobble somewhere in your sound.

A recognizable attack and sustain is crucial for sounds that imitate ‘real’ instruments but if you’re into abstract, electronic sounds this is far less important. Instead you’ll want unnatural or mechanic envelopes. The biggest difference between weird sounds and realistic sounds is the way you play them or use them in a tune. The realistic types of sounds are good for basslines and melodies and the weird electronic stuff is better for soundscapes.

In practice, if you’re working on abstract sounds using extreme settings you’ll often end up with something so bent out of shape you can’t really say where it begins or ends. If you’re an experienced dub scientist you’ll say that’s a good thing, but if you’re a beginner in sound design this can also be a bad thing :-)

For beginners I’d say that the most important thing, even while creating those ‘weird’ sounds, is some overall sense of sonic cohesion in each patch you create. Because when you’re working with extreme envelope settings in FM-synthesis, there’s always a kind of turning point where one sound starts to fall apart and either splits up in multiple seemingly unrelated components, or where the overall character of the patch changes radically, to the point where you either get something completely different and new, or some vague sonic debris. Stop! Hammertime!

And remember that the patch you’re creating is not necessarily the finished ‘product’. You can always add some kind of effect at a later stage to make things weirder if that’s really necessary. George Clinton says “there's nothing that funk will not render funkable” but I‘d like to add that there's nothing that DUB will not render DUBABLE.

Dynamic envelopes

If you’re into lively sounds, variable dynamic envelopes can be much more interesting than static, repetitive envelopes. Dynamic envelopes are really about imitating the lively character of natural sounds. Anything from acoustic guitars to raindrops. The ‘envelopes’ of the individual notes played on a guitar or raindrops ticking on a roof are never exactly the same.

semi-random dynamic envelope using the FM8 modulation matrix

Try to use dynamic envelopes without losing a basic sense of coherence and sonic character in the sound. And usually, you’ll have to bend the rules a little to get dynamic envelopes.

[switching to rant mode now…]

Some of the new FM synths don’t have ‘classic’ envelopes on board anymore. Stuff like a basic LFO, ADSR etc. That’s sooo 20th century, don’t you think? Nowadays manufacturers prefer the extremely sophisticated multi-stage, multi-curve, infinitely expandable, amazingly versatile, not-so-easy-to-use envelope generators we’ve all come to know and love...

So why haven’t they figured out yet how to do variable dynamic envelopes with these stupid things!!? It’s so much fun to have sounds with variable attack times, release times etc. Sound designers who are into that kind of stuff actually have to buy an oldskool modular synth with ‘classic’ VCLFOs or VCADSRs...

[switching back to normal mode now…]

Tip for advanced sound designers: ‘free running’ LFOs, randomizers (possibly combined with sample-and-hold) or some ‘external input’ (like an envelope follower that accepts external input) might help. Avoid sync options like key or bpm sync for maximum variation.

Next time we’ll check out more practical examples of envelopes.