Most psytrance FM leads are tight, hard and aggressive. This one is looser. It sits halfway between a lead and an FX layer, and it gets its movement from an LFO that modulates the oscillator pitch at audio rate. Here is the full patch, step by step, starting from an init preset in Serum 2.
What you will build
- An FM tone made with LFO 1 running at about 45 Hz on Oscillator A’s coarse pitch
- Random movement from a sample-and-hold LFO 2 that changes LFO 1’s rate
- Notes from Ableton’s Arpeggiator and Random MIDI effects
- A band-pass filter, chaos LFO panning and light effects for space
- Recorded gate and cutoff automation for a performance that feels alive
What FM means here
FM, frequency modulation, means modulating the frequency of one oscillator with another signal. Serum 2 gives you two ways to do it. You can use the built-in FM option, where another oscillator (B, noise or sub) becomes the modulator for Oscillator A. Or you can use an LFO as the modulator.
For this sound KOOROW uses the second route. The reason is control: an LFO’s rate can be moved by hand, mapped to a MIDI knob, recorded as automation or modulated by other sources. That flexibility is what gives the lead its unstable, organic character.
Step 1: LFO 1 on coarse pitch
- Start from an initialized preset.
- Assign LFO 1 to Oscillator A coarse pitch.
- Keep the modulation depth under 10%. Around 7% is a good starting point. More depth quickly turns the tone harsh and uncontrolled.
- Set LFO 1 to free mode and its rate to roughly 40–45 Hz. At audio rate the LFO stops sounding like vibrato and becomes part of the tone.
Step 2: Randomize the LFO rate with LFO 2
Instead of only moving LFO 1’s rate by hand, let another modulator do it:
- In the mod matrix, set LFO 2 as the source and LFO 1 rate as the destination.
- Use a negative amount, around −20%. Starting at 45 Hz, you want the rate to drop as well as rise, not only climb higher.
- Set LFO 2 to sample and hold so every step gives a new random value.
The result is an FM tone that keeps shifting slightly, which is exactly what makes it useful in darkpsy and forest arrangements.
Texture, movement and notes
KOOROW splits sound design into three stages: the texture of the sound, its movement, and the notes. Texture and movement are made inside the synth. The notes are how the instrument is played, and they matter as much as the patch. Some producers write notes first, others design the sound first. Use whichever order fits your workflow, but do not treat the notes as an afterthought.
Step 3: Write the notes with MIDI effects
Put Ableton’s Arpeggiator and Random MIDI effects before Serum. In the video the arpeggiator runs at 1/16, with the random effect adding variation, which creates evolving patterns from a single held note. Write that note on the root of your track. In the example the bassline is in D, so the note is D2.
Step 4: Tighten the tone with a band-pass filter
Bending the waveform a little more removes some of the growl and muddiness and makes the sound brighter and tighter. Then add movement with the filter, the most common tool for it:
- Use a band-pass filter.
- Add a little drive.
- Keep resonance low, around 15–25%. Too much resonance makes the sound hollow, as if it has been squeezed.
Step 5: Chaos LFO on pan
Assign LFO 3 to pan and reduce its range. Then switch it to one of Serum 2’s new chaos modes. These generate a new random path every time a note is triggered, with values on both the X and Y axes. Pan responds to the X axis here, but you can choose Y for a completely different motion.
Step 6: Distortion, delay and space
| Effect | Setting in the video | Why |
|---|---|---|
| Distortion | Tube mode | Fuller body and harmonics |
| Delay | 1/8 dotted, ping-pong, low feedback, very low mix | Width and rhythm without washing the lead out |
| Hyper/Dimension | Low mix, small size | Depth. A large size gives a strange reverb-like smear |
Step 7: Record gate and cutoff automation
Map the arpeggiator gate and Serum’s filter cutoff to two knobs on your MIDI controller, make sure the clip covers the whole loop, and record while you play both. Controlling note length with the gate creates choppy rhythmic patterns, and riding the cutoff shapes the phrase. You can also map LFO 1’s rate to a knob and move it during the take.
Step 8: Note-On Random on the release
Serum 2’s Note-On Random source creates a new random value for every note. Assign it to an envelope’s release and some notes get longer tails than others, which gives the lead a springy feel.
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