The envelope you shaped before had three moves: a rise into the sound, a held middle, and a fall back to silence. A synth envelope adds a fourth move, a short drop between the rise and the held level.
Attack is the rise from silence to the loudest point. Decay is the fall from that peak down to a held level. Sustain is that held level. It is a height, not a length of time: it sets how loud the sound stays while you hold the note. Release is the fall back to silence once the note ends. Plucked and struck sounds spike on the attack, drop fast through the decay, and sit low. Pads do the opposite: a slow attack, a gentle decay, a high sustain, a long release.
Drive that four-stage shape into the loudness of a pad.
Keep headphones at a low volume before you press play. Try a fast attack with a low sustain for something plucked, then a slow attack with a high sustain for a pad that swells in. The sound is the same three notes throughout. Only the shape changes.
That shape has no loudness in it. It rises, holds, and falls, and it will move whatever control you point it at. Point it at pitch and the note bends.
Pitch is how fast a wave repeats. Speed the wave up and the pitch rises; slow it down and it drops. Raising a sound by twelve semitones (the small steps between piano keys, twelve to an octave) doubles how fast it repeats. Pitch can move over the life of a single note, gliding up and back down, and a shape is how you describe that motion.
The Range slider sets how far the pitch travels at the peak, measured in semitones.
A short attack with a high range gives you a quick upward chirp. A long attack is a slow scoop into the note. The same shape you used for loudness is now an instruction for pitch.
You drew one shape by hand with four sliders and sent it to two different controls. A shape can also draw itself and keep going without you. The tool for that is the LFO, a low frequency oscillator, the most common shape maker in any synth or DAW.
An oscillator makes a wave. The ones that make sound repeat fast, hundreds or thousands of times a second, inside the range your ears register: roughly 20 Hz at the low end up to 20 kHz at the top. An LFO is the same kind of wave generator running far slower than that, under 20 Hz, below the bottom of hearing. You never hear the LFO itself. Its wave is still being drawn, cycle after cycle, and you aim that moving shape at a control to let its rise and fall move the control for you.
The shapes an LFO draws are the same four every oscillator uses: the sine you already know, plus triangle, sawtooth, and square.
Because these waves sit below hearing, you read them differently. The peaks and valleys are not sound anymore. They are positions: high, low, and everything between, arriving in time. A sine glides smoothly up and down. A triangle does the same with straight lines. A sawtooth ramps and snaps back. A square sits high, then jumps to low, with nothing in between.
When a wave is fast enough to hear, its frequency is pitch. When it is too slow to hear, that same frequency is felt as a rate: how often the thing happens. A slow LFO is a slow wobble. A faster LFO is a faster wobble. To put a number on it, convert the frequency to a tempo.
A 2 Hz LFO, just barely too low to hear as a pitch, already puts a peak under your finger 120 times a minute. Most expressive LFO motion lives well below that, from a fraction of a hertz up to a few hertz.
Now point an LFO at something. Pick a shape and rate, then send it to pitch or to its stereo position, called pan in software. On pitch the note swings the range above and below where it started, a vibrato; on pan it slides between your ears. The LFO on the left grows with the slider.
On pitch, a slow sine is a gentle vibrato; a square jumps between two pitches. On pan, the same shapes move the sound between your ears. The rate readout doubles as a tempo: multiply by 60 for BPM.
So far the shape has moved things you hear directly: how loud, how high, where in the field. A shape can also move a control on another tool and let that tool change the sound. The classic pairing is an LFO and a filter.
A filter sets which frequencies pass through and which get turned down. A low-pass filter lets the low frequencies through and turns down everything above a point called the cutoff frequency. Slide the cutoff down and the sound gets darker and rounder as the highs leave. Slide it up and the brightness returns. Resonance adds a small boost right at the cutoff, a focused emphasis that makes a sweep sing.
Sweeping the cutoff by hand opens and closes a sound. But the cutoff is just a control with a value, and a shape can move a control. Aim an LFO at the cutoff and the filter sweeps on its own, in time, forever. This is what Ableton's Auto Filter is built around: a filter with a cutoff, resonance, and an LFO wired to drive the cutoff for you.
Auto Filter Live 11 audio effect referenceThis tool wires the whole chain: a pad, a low-pass filter on it, and an LFO driving the cutoff. The left panel is the LFO. The right panel is the filter's response, the curve sliding left and right as the LFO moves the cutoff up and down.
The pad never changes. The LFO never reaches your ears. All it does is move the cutoff, and the filter does the rest. That gap, a shape steering a control that shapes the sound, is the engine behind most movement you hear in electronic music.
Modulation is one control moving another over time. The moving signal stays apart from the sound itself. An LFO or an envelope never reaches your ears; it steers a knob that does. That separation is the trick behind everything on this page: a shape you cannot hear sits behind the sound and pushes a parameter around while the note plays.
Every modulation has two parts: a source that makes the shape, and a destination the shape moves. Envelopes and LFOs are the two sources you will reach for most. An envelope shapes each note once, from press to release. An LFO repeats on its own, as slow or as fast as you set it. The destination is whatever you point the source at: volume, pitch, a filter's cutoff, the position between your speakers.
The same source changes its name with its destination. Point an LFO at pitch and the note bends up and down, a vibrato. Point that same LFO at volume and the note pulses louder and softer, a tremolo. Point it at a filter's cutoff and you get the sweep running under so much electronic music. One source, three effects, and the only thing that moved was where you sent it. You built two of the three in the tools above.
Once routing is in hand, the rest of a synth stops looking like a wall of knobs and starts looking like a small set of sources pointed at a small set of destinations.
If routing one shape into another is the part that grabbed you, there is a whole course in it. MUS 486, Advanced Sound Design II: Synthesis, Modulation & Creative Digital Signal Processing, builds synths from scratch and goes deep on the modulation you just met.
Sound on Sound goes deeper on envelopes and on modulation effects. The Simpler pages are where these same controls live inside Ableton.
Envelopes, gates & triggers Sound on Sound More about envelopes Sound on Sound Modulation effects: a primer Sound on Sound Envelopes in Simpler Live 11 instrument reference LFO in Simpler Live 11 instrument reference Global parameters in Simpler Live 11 instrument reference