FM Kick / Bass
Synthesised FM kick drum / bass voice — punchy electronic kicks with a distinctive metallic/plucky edge, plus tuned bass notes.
Available on: Track 2
Built on: Custom CTAG FM kick voice — two-operator FM synthesis with dedicated decay envelopes.
Character
A classic two-operator FM topology: a carrier at the fundamental frequency, modulated by a modulator whose frequency, amplitude, feedback and decay you can dial in independently.
- Short modulator decay + high modulation index → plucky, metallic kick transient.
- Low fundamental + gentle pitch sweep → deep sub kick.
- Higher fundamental + more feedback → tuned FM bass lines (perfect for playing melodic bass on a sequencer track).
The modulator can run either on a free Hz frequency or on a ratio to the carrier, giving you either arbitrary inharmonic metallic tones or harmonically-locked musical tones.
Parameters
The fmb-allparams macro exposes all ten FM-drum parameters across three pages:
| Page | Knob 1 | Knob 2 | Knob 3 | Knob 4 |
|---|---|---|---|---|
| Carrier | carFrq | carDec | atkPit | swpDec |
| Modulator | modFrq | modDec | modFB | index |
| Mode | ratio | envSync | — | — |
Carrier
| Parameter | Range | What it does | DSP |
|---|---|---|---|
| carFrq | 20 – 100 Hz | Base carrier frequency — the fundamental pitch of the kick | f_b |
| carDec | 1 ms – 2 s | Carrier amplitude decay — how long the body sustains | d_b |
| atkPit | 0 – 1000 Hz | Pitch-sweep amount at the attack — initial pitch deviation before settling | A_f |
| swpDec | 1 – 100 ms | Pitch-sweep decay — how fast the attack pitch settles | d_f |
Modulator
| Parameter | Range | What it does | DSP |
|---|---|---|---|
| modFrq | 40 – 2000 Hz | Modulator frequency (Hz mode) — tonal character of the FM | f_m |
| modDec | 1 – 500 ms | Modulator amplitude decay — transient brightness length | d_m |
| modFB | 0 – 16 | Modulator self-feedback — distortion / resonance amount | b_m |
| index | 0 – 10 | FM modulation index — depth of the modulation (0 = no FM) | I |
Mode
| Parameter | Range | What it does | DSP |
|---|---|---|---|
| ratio | off / on | When on, modFrq locks to a harmonic ratio of carFrq instead of running as free Hz — enables clean musical FM bass lines | use_ratio_mode |
| envSync | off / on | Sync the modulator frequency envelope to the carrier — cleaner retrigger for sequenced bass | mod_env_sync |
For punchy techno kicks: low
carFrq, shortcarDec, shortmodDec, moderateindex, shortatkPitsweep. For FM bass lines: highercarFrq,ratioon, longercarDec.
See also
- Synth Kick — Plaits-based electronic kick on Track 1.
- Analog Bass Drum — warm analog-style kick on Track 1.
- Parameter Locks — per-step pitch and modulation-index variation.
Origin & credits
Custom CTAG FM kick voice (synthesis/FmKick.hpp / .cpp) by Robert Manzke (CTAG, GPL 3.0). Uses Mutable Instruments Plaits’ FM operator (plaits/dsp/fm/operator.h, MIT) as the oscillator core.
The design is inspired by the Elektron Machinedrum SPS-1 EFM Kick concept and shares ideas with the open-source md-drum-synth research project, but this voice is a separate CTAG implementation — not a port.
- DSP sources:
synthesis/FmKick.hpp/.cpp,plaits/dsp/fm/operator.h - TBD-16 wrapper:
rack/RackFMB.hpp/.cpp