KOOROW
Serum 2 added a granular oscillator, and it is one of KOOROW’s favourite ways to make sound: perfect for FX, textures and pads in psytrance and hitech. Granular synthesis sounds complicated, but the idea is simple. This lesson explains what granular synthesis is, how to read what the oscillator shows you, and what each of its random controls does to a sample.
The video is in Persian. This article walks through every step in English.
Granular in one sentence
A granular oscillator takes any sample you give it, cuts it into hundreds or even thousands of tiny pieces called grains, and plays those grains back with a timing, pitch, pan and level that you control, often with randomness.
What granular synthesis is
Granular synthesis is a way of building sound, just as wavetable synthesis is. In a wavetable, think of the table as a picture and a magnifying glass: wherever you point the glass, you hear that part. Granular is another approach to sound design, and the name comes from “grain”.
Whatever audio you feed it, a sample or any sound at all, is turned into many very small slices. The oscillator plays them back with a spacing in time. How it plays them is what you set with the controls below. It is much less complicated than it sounds.
Step 1: Load a sample
Switch the oscillator to granular mode and drop a sample into it. In the video KOOROW loads a recorded sound into the granular oscillator and starts from there. Any source works. Different material gives very different results.
Step 2: Read the display
When you play a note, you see two kinds of lines on the waveform:
- The yellow line is the main read position: it shows where the oscillator is reading the sample.
- The white lines next to it are the grains being played in that moment. Each one is read and finishes, then the next one is read and finishes, while the yellow line keeps moving through the sample.
Each grain also has its own envelope, a shape that sets how its volume rises and falls. You can change that shape, and with it the character of the whole sound.
Step 3: Choose how the sample is read
The play mode decides how the yellow line moves through the sample:
- One-shot reads the sample once, to the end, and stops. For an evolving texture you usually do not want this.
- Loop keeps reading. You can loop forward, in reverse, or back and forth. KOOROW shortens the loop region so the oscillator keeps working on a smaller part of the sample.
Step 4: The random controls
Under the display are the controls that make granular so useful. Most of them have a random amount, which varies the value from grain to grain.
| Control | What it does |
|---|---|
| Scan | The direction the read position moves: left to right or right to left. In the centre the position stays where it is. These settings only mean something once you move it away from the centre. |
| Scan random / direction | Adds randomness to the movement. Turned up, the read position moves in both directions instead of only one. |
| Density | How many grains play at once: from sparse to very dense. |
| Pitch random | Gives each grain its own pitch offset in semitones. KOOROW uses this one a lot. |
| Length | How long each grain is. With randomness, some grains are very short and others much longer. |
| Pan | Places grains left and right. With random pan, every grain lands in a different position. |
| Level | The volume of each grain, which can also be randomised. |
Step 5: Shape it into a texture
Play with the combinations. In the video, adding random length and pitch to a looping sample immediately turns it into a moving texture, and lowering the density while keeping a lot of randomness makes it sparser and more scattered. Then add space:
- Put a reverb after the oscillator. KOOROW already had one on while testing, and switches it off to hear the dry grains first.
- Add a delay as well.
- Move the scan away from the centre and listen to how the texture travels through the sample.
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