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

Carrier

Parameter Range What it does
f_b 20 – 100 Hz Base carrier frequency (the pitch)
d_b 1 ms – 2 s Carrier amplitude decay
A_f 0 – 1000 Hz Pitch-sweep amount at the attack
d_f 1 ms – 2 s Pitch-sweep decay time

Modulator

Parameter Range What it does
use_ratio_mode off / on Switch modulator frequency between Hz and ratio-to-carrier
f_m 40 – 2000 Hz Modulator frequency (when ratio mode is off)
mod_ratio_index 0 – 63 Modulator ratio preset (when ratio mode is on)
I 0 – 10 Modulation index (modulator amplitude into carrier)
b_m 0 – 16 Modulator self-feedback
d_m 1 ms – 2 s Modulator amplitude decay
mod_env_sync off / on Sync modulator frequency envelope to carrier

For punchy techno kicks: low f_b, short d_b, short d_m, moderate I, short A_f pitch sweep. For FM bass lines: higher f_b, ratio mode on, longer d_b.

See also

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