Granular synthesis: a sample under the microscope
Cut a recording into 20–400 ms windows and fire them in a stream. Position, size, density and spray are the four numbers that decide what the stream sounds like.
The last lesson's stretch machine cut a recording into short pieces and tried to hide the seams. Granular synthesis keeps the pieces and hands you their controls. Cut a short window out of a recording, fade its edges so it does not click, and fire windows one after another fast enough that they overlap. Each window is a grain. The source recording never changes; what changes is that you now choose where in it to read, how much to take each time, and how often. The toy below grains a 2-second chord texture built from three detuned sawtooth pairs on A2, E3 and A3, deliberately dull material so the grain controls are the only thing moving.
What one grain is
A grain has a start point in the recording, a length, and an envelope of its own. The toy's grain envelope is a trapezoid: it ramps up over the first 30% of the grain, holds flat, then ramps down over the last 30%. At the default 100 ms grain that reads 30 ms up, 40 ms flat, 30 ms down. The ramps keep each grain from starting and ending on a click, and they scale with the grain, so a 20 ms grain gets 6 ms of ramp at each end and a 400 ms grain gets 120 ms. Grain length runs 20 to 400 ms here. Long grains keep enough of the source to recognize it; a 20 ms grain of the texture's 110 Hz bottom note holds barely two cycles, near the shortest fragment the ear can still read as a pitch, so at that end you are mostly hearing the window's own shape.
One grain, twice. Above, a 100 ms grain marked on the 2-second recording with the POS marker at 50%, where the toy starts. Below, the same window enlarged, carrying the envelope the toy actually applies: up over 0–30 ms, flat to 70 ms, back to zero at 100 ms.
The four handles
- Position — 0 to 100% of the recording, drawn as the bright vertical marker. At the default 50%, every grain starts 1.0 s into the 2-second texture.
- Size — 20 to 400 ms, the grain length from the section above.
- Density — 2 to 40 grains per second. This is the gap between grain starts: 2 per second is one every 500 ms, 40 per second is one every 25 ms.
- Spray — 0 to 50%, a random offset applied to position, drawn fresh for every grain.
Density and size are not independent in what you hear. Multiply them and you get the average number of grains sounding at the same moment. The defaults, 12 per second at 100 ms, give 1.2: grains barely overlap and the stream runs continuous. Push both to maximum, 40 per second at 400 ms, and 16 grains sound at once, a solid wash in which no individual grain is findable. Pull both down to 2 per second at 20 ms and the product is 0.04, so the output is 96% silence with a tick in it. The toy compensates behind your back, dividing each grain's peak level by the square root of the overlap, because grains land at unrelated phases and add up like independent sources rather than copies of one. Without that correction, sweeping density would read as a volume knob.
Position: standing still inside a recording
Position is what makes granular feel unlike every other machine in this course. Everything else plays a recording forward. Here you choose a point and stay on it. Park position at 50% with spray at zero and every grain reads the same 100 ms of the same chord, so the note sustains indefinitely out of material that was two seconds long and never sustained at all. Move position slowly and you walk through the recording at whatever speed your hand picks, with the source's pitch unaffected by how fast you move. That is the frozen swell behind a decade of ambient records, and it is the gesture worth practising first.
Standing still has one side effect. With spray at zero every grain is identical, so the output repeats exactly at the grain rate. At 40 grains per second that repetition is 40 Hz, above the twenty-per-second line lesson 1 drew, and the stream picks up a low hum of its own that has nothing to do with the recording. Spray is the fix, and it does more than smooth. It adds a random offset to position, uniform across a window of plus or minus its percentage of the whole recording: on a 2-second buffer, 10% is ±200 ms and the 50% maximum is ±1 second, which from a centred position covers everything. Small amounts break the grain rate's periodicity and the hum goes. Larger amounts pull in material from parts of the recording you are not pointing at, so the sound becomes an average of the whole thing. The offset is clamped rather than wrapped, so with position near an edge and spray wide open, grains pile up against that edge.
Twenty-six consecutive grains at three spray settings, placed with the toy's own jitter rule. Spawn order runs down each band and the bright line is the position marker at 50%. At 0% every grain reads from the marker. At 10% they fall inside a ±200 ms window. At 50% that window is the whole 2-second recording.
The amber flecks are the grains, drawn at the buffer position each one was actually read from. Work one control at a time. Park position, then shrink size from 400 ms down to 20 and listen to the chord dissolve. Then raise density from 2 to 40 with spray still at zero, until the grain rate itself turns into a pitch. Then open spray a little and hear that pitch go. Finish with a slow position sweep at high density.
Tonverk's GRAINER is the only machine in this catalog that hands you grain controls directly, and it reaches further than the toy. POS, SIZE, DENS and SPRD are the four handles; SPRD is printed as Spread and runs 0 to 127, from every grain starting at POS to every grain starting somewhere random in the sample. SIZE covers 10 ms to 2 seconds, five times the toy's ceiling. Three controls with no equivalent above are worth finding early. SCAN moves the read position on its own, forward or backward at a speed you set, so the position sweep runs with no hand on the knob. MODE decides how grains are triggered: RAND scatters them around the position, SYNC ties their timing to the tempo and turns DENS into a note division, OSC overlaps them so DENS becomes an overlap amount. FADE and SHAPE are the grain envelope this lesson drew, FADE setting how much of the grain the window covers and SHAPE tilting it from plucky at 0 to reversed at 127.