Drums

Bass Drum

A self-contained bass drum voice: a self-resonating sine body, a pitch-sweep punch, and a noise click for transient bite.

Try one in your browser →

What is a Bass Drum?

A bass drum voice is a single self-contained module that synthesizes a kick drum from scratch, the way every classic drum machine since the Roland TR-808 has. It does not sample a real kick. It builds one out of an oscillator, a couple of envelopes, and a transient generator - which is why it has knobs for things like Pitch, Decay, and Punch, and not a list of WAV files.

The architecture every TR-style kick descends from is the bridged-T resonator: a passive analog network that, when hit with a fast trigger pulse, rings out a decaying sine wave at its resonant frequency. The pitch you hear is just that ringing tone - typically in the 40-90 Hz range - and the natural amplitude decay of the resonator gives the kick its tail. To get the characteristic 'thump' on the attack, the original 808 also fast-sweeps the resonator's pitch downward at the start of every hit: high for a few milliseconds, then settling to the body pitch. That sweep is the pitch envelope, and it is what your ear hears as punch.

There is one more ingredient. Real kick drums have a sharp transient at the very front of the hit - the sound of the beater striking the head. Synthesized kicks recreate this with a noise burst or click mixed into the attack, just a few milliseconds long. Take that away and the kick goes blunt; turn it up and it gets clicky and aggressive. Body, pitch sweep, click - that is the whole anatomy of a synth kick drum.

Our Bass Drum

Webrack's Bass Drum is free in the browser. The body is a pure-sine oscillator driven by two exponential envelopes - one for amplitude, one for the pitch sweep - plus a short noise click for the transient and a tanh waveshaper for drive. Architecturally it is faithful to the 808 lineage; the voice stays tight and punchy with no glitching even when triggered fast.

Eight knobs, three inputs, two outputs. Pitch and Decay set the body. Punch and P.Dcy shape the pitch envelope - punch is how high the sweep starts, P.Dcy is how fast it collapses. Click adds the transient noise burst. Drive runs the whole signal through tanh saturation for harmonics and squash. Tone is a one-pole lowpass you can use to soften the click. There's also a V/Oct input for tuned-kick basslines and an Env output for sidechain patches.

It will not perfectly match a real 808 - that's an analog circuit and we are a digital sine plus envelopes - but the architecture, the response to the controls, and the way it sits in a mix are all in the right ballpark, and you have it instantly with no plugin install.

In a patch

A bass drum voice is one of the simplest modules to patch: send it a gate or trigger and route its output to your mixer. The trigger source is almost always a Clock for a four-on-the-floor pulse, or a step sequencer or Euclidean generator for syncopated patterns. You do not need a separate envelope or VCA - those are baked in.

Two patching tricks are worth knowing. First: most bass drum voices have an accent CV input that boosts level and slightly extends decay for emphasized hits, and an envelope output that follows the kick's amplitude shape - patch that into a VCA on a pad or bass to get the classic sidechain ducking effect every time the kick fires. Second: feeding 1V/Oct into the V/Oct input turns the kick into a tuned percussion voice, which is how a lot of techno bassline-and-kick hybrids are made - the same module plays the bassline.

Inputs

Trig (gate) — Trigger input. Each rising edge above 2.5V fires the drum. Pulse width does not matter - it's strictly edge-triggered.
Acc (cv) — Accent CV. 0-10V scales the hit volume and slightly extends decay for emphasized hits. Patch the AC1 output of Euclidean here for accented patterns.
V/Oct (cv) — 1V/octave pitch input. Adds to the Pitch knob for tuned kicks and bass-drum melodies. 0V = no offset.

Outputs

Out (audio) — Audio output. Eurorack-level kick drum signal.
Env (cv) — Envelope output following the kick's amplitude shape. Patch into a VCA CV input for classic sidechain "ducking" of pads or bass against the kick.

Controls

Pitch — Body fundamental, 30-240 Hz. 30-50 Hz for sub-heavy 808 kicks, 60-80 Hz for techno punch, 100+ Hz for high tom-like hits.
Decay — Body decay, 50-800 ms. 50-150 ms = tight, 250-500 ms = boomy and full, 800 ms = tom/long sub.
Punch — Pitch-sweep amount, 0-100 Hz added to base pitch at attack. Gives the kick its initial "thump" - 40-80 Hz is the sweet spot.
P.Dcy — How fast the pitch sweep collapses, 1-50 ms. Short = clicky attack; longer = sweeping bend.
Tone — One-pole low-pass after the body, 200-8000 Hz. Roll down to soften the click, open up for brighter kicks.
Drive — Tanh saturation amount. Adds harmonics and squashes the transient. 0.2 default; push to 0.6+ for distorted industrial kicks.
Click — Noise burst at the attack for transient definition. Helps the kick cut through a busy mix.
Gain — Output level, 0-1. Trim to taste against the rest of the kit.

Inspired by

The architecture is the classic 808 lineage - a bridged-T-style resonator that rings out a decaying sine when struck, plus a fast pitch sweep for the attack 'thump'. Our DSP refactors that into a pure-sine oscillator driven by two exponential envelopes (amplitude and pitch) and a noise click, written in TypeScript at 44.1 kHz inside an AudioWorklet. Same musical intent, modern signal path.

Roland TR-808 BD
Roland TR-909 BD
Jomox MBase11

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