What is granular synthesis? Explained with grains you can move

Granular synthesis chops a recording into grains, fragments only a few milliseconds long, and fires hundreds of them a second in an overlapping stream. Rather than rolling the sample from end to end, the engine reads those grains from one movable point in the file, which is how a finished recording turns into something you can hold still, stretch out or smear.

A lot of modern sound design runs on that one idea without ever naming it: time stretching that leaves pitch alone is grains under the hood, and so is the freeze button on your reverb. The panel below is the whole mechanism in one picture, and you'll have driven every part of it by the time you reach the bottom of this page, so move things while you read. You can't break it.

One playhead, many grains

Load a sample into a granular engine and nothing plays yet, which throws people the first time. What you get instead is a read position, a point in the file the engine pulls from. Each grain is a short copy of the audio around that point, gone in less time than a blink; by the time one dies another has already taken its place, and the stream of them is the sound.

Drag the amber line across the strip and the scatter follows it, because grains only ever come from wherever the playhead happens to sit. Park it on one of the loud hits and every grain carries a piece of that hit; park it in the quiet gap after one and the cloud pulls from near silence. Now stop moving. The grains keep coming, and the sound they stand for holds still, one instant of the recording kept open for as long as you care to hold it. That's sample freeze, and no one had to design it in.

Something else happened there without announcing itself. You moved through the file at whatever speed you felt like, or sat still, and pitch never entered into it, whereas an ordinary sampler welds speed and pitch together so that slowing a file down drags its pitch down with it. Grains break that weld, which is why the playhead can crawl through two seconds of audio over a full minute while every grain still plays at the pitch it was recorded at. Every decent time stretch you've used works this way.

Grain size

Grain size is how long each fragment lasts, and it decides how much of the source survives the chop. Murmur's dial runs from 10 ms to 500 ms; most engines cover something similar. Up at 150 ms you're hearing recognisable slivers of the recording, so the drum hit is still a drum hit and the word is still a word. Below about 20 ms the source gives up its identity and dissolves into granular dust, nearer a hiss or a tone than the thing you sampled. Short is clicky and broken up, long smears into a pad.

Pull SIZE down under 20 ms and the dots shrink to fine grit; push it past 150 ms and each grain swells and hangs about a while, powder turning to pebbles. The visual trade is the audible one. Small grains give you texture that forgets where it came from, big grains give you texture that still remembers.

Density

Density is how many grains land per second, and it's where granular shows its two personalities. Keep it low and each grain reads as its own little event, a few pinpricks of sputtering pointillism. Raise it until the grains start overlapping and they fuse instead: what was a rhythm becomes a wash with no seams in it. Most granular pads live up there, a dozen or more grains deep at any instant.

Drag DENSITY past 60 and the scatter thickens into a solid cloud; drop it under 10 and it falls apart into single, countable dots. Somewhere in between you stop being able to count them, and that's the same crossing where an ear gives up on events and hears texture instead. Worth sliding back and forth a few times.

Jitter

So far every grain has come from exactly the playhead, and that precision turns out to be a problem: identical grains fired at a fixed rate buzz like a picket fence. Jitter randomises where each one starts, so no two are quite alike any more, and a few percent is usually enough to melt the buzz into something that breathes. Crank it and grains get flung from a whole region of the file, until the position stops meaning a point and starts meaning a neighbourhood.

Set JITTER to 0 and every dot rises off the same line; nudge it to 20 and they spray. Keep going and the playhead turns into a centre of gravity rather than a position.

Windowing, the part nobody mentions

One detail keeps all of this from clicking. Literally clicking. A grain is a slice cut out of a longer waveform, and a raw cut almost never lands on a zero crossing, so it starts and ends with a click; at hundreds of grains a second those clicks fuse into a buzzsaw. The fix is the window, a volume envelope that fades each grain in from silence and back out again so the cut points disappear. Watch any single dot in the panel above: it brightens, then dims away. That ramp is the window. Shapes vary, from a smooth bell to a flat top with quick edges, and each one tints the texture differently, but there isn't a granular engine worth using that skips it. In Murmur it's the SHAPE dial: fully down is a rounded fade, the centre is a flat top that leaves the middle of each grain untouched, and past the centre it rounds back off into a soft bell.

Where it came from

The idea is older than the gear by decades. In 1947 the physicist Dennis Gabor argued that any sound at all could be described as a swarm of acoustic quanta, tiny packets of energy in time and frequency, which stayed a theory until Iannis Xenakis started splicing tape into grains by hand in the late 1950s. Curtis Roads spent the decades after that turning it into working computer programs and eventually into the book Microsound. Work that once took a room full of tape machines now runs a few hundred grains at a time on a laptop, in a plugin window, while you do something else.

Where Murmur fits

Murmur is my granular instrument, and the playground on this page is a sketch of its engine. The free version is the real thing rather than a demo. It's not a trial; nothing counts down, and it never goes quiet on you. Load any sample and POS, SIZE, DENSITY and JITTER are the same controls you just moved, joined by the slice grid, a scale lock, and a dice button that rolls the grain controls to something random (right-click it to undo the roll if it lands somewhere you don't like). If this page made sense, you already know how to play it; the free download is on the Murmur page, no email required.