Kit VCV Rack module panel, a physically modelled drum with a drawn head you can strike with the mouse and four rows of trimpots

Kit is a struck membrane, modelled mode by mode.

A drum head is a 2D wave equation on a disc, and its solutions are the Bessel modes. Rather than run a mesh over the disc, Kit runs one resonator per mode. That is cheaper, and much more importantly it puts every parameter you would want to play in plain sight: strike position becomes a per-mode gain you can evaluate in closed form, and muffling becomes the same evaluation used subtractively.

One instrument covers tom, timpani, kick, snare, gong, steel pan, frame drum and tabla, because those differ in shell depth, head stiffness and air cavity rather than in kind.

22 HP.

The one thing to know about the controls

For an ideal membrane, radius and tension scale every mode by the same factor and leave the ratios untouched. Acoustically, SIZE and TENSION are therefore the same control, and shipping both as separate knobs would be shipping a duplicate.

What breaks that scale invariance is bending stiffness, the air cavity, and damping that depends on size. That is why MATERIAL and AIR exist, and it is why SIZE is allowed to sit alongside TENSION. A small tight drum and a large slack one at the same pitch are different instruments, and those three controls are where the difference lives.

AIR closes the bottom of the shell. At zero it is an open shell with a resonant head across it, which is a tom or a kick. Wound up it bellies into a sealed bowl, which is a kettledrum. A kettledrum is exactly what the harmonic series AIR imposes belongs to.

Controls

The panel is eight columns by four rows. Every control is a trimpot, on one pitch, so sixteen of them read as one instrument rather than as four ideas competing for the same panel.

Tooltips report quantities, not percentages. A drum has a diameter, a head has a pitch, a beater has a weight and a contact time.

What the drum is

Control	Range	What it does
SIZE	6 to 22 inches	Reads inches and centimetres.
TENSION	±8.4 semitones	Head tension, read as a pitch offset.
MATERIAL	drum head to gong	Bending stiffness. Pushes the modes from a membrane’s inharmonic ratios toward a plate’s.
AIR	open shell to sealed kettle	Closes the bottom of the shell.
DECAY	80 ms to 7 s	Scaled by SIZE as well, and the tooltip says so.
TONE		How much faster the high modes die than the low ones.
EXCITER	soft felt to hard stick	Reads as a beater name and a contact time, for example “hard mallet, 3.4 ms contact”.
MUFFLE	0 to 100%	A hand on the head. Subtracts the modes that are live at that spot.

How it is played and dressed

Control	What it does
COUPLE	How much the batter head drives the resonant head.
RESO	Resonant head tuning, as a ratio to the batter head.
BEND	Pitch drop after the hit, from the head being driven hard.
WEIGHT	Beater mass, 10 to 70 g.
WIRES	Snare wire amount.
TIGHT	Wire tightness, loose buzz to tight snap.
LEVEL	Output trim.
HIT	A momentary strike. A button, not a value.

The third row is CV: one jack per control in the row above, directly underneath, so a cable hangs under the thing it modulates.

Inputs

The fourth row is the transport row: performance data in and out, nothing else.

Input	What it does
GATE	Strikes on a rising edge.
V/OCT	1V per octave.
VEL	Velocity, 0 to 10V.
X, Y	Strike position, ±5V, summed with the panel’s strike position.

Outputs

Output	What it does
HEAD	The membrane alone.
WIRES	The snare wires alone.
MIX	Both, at LEVEL.

Taking HEAD and WIRES separately is how you put the wires through their own compressor or reverb, which is what a close-miked snare gets in practice.

The display

The head is drawn as it moves. Rings and spokes trace the modal displacement, excited areas warm toward orange, and the strike mark sits where X and Y put it. Click or drag on the head to strike it, and the position you click becomes the strike position.

Three details are load-bearing rather than decorative:

The grid redistributes with TENSION. A taut head pulls its rings out toward the rim; a slack one lets them gather in the middle. That is what tension does to a real head’s response.
AIR closes the bottom, and you watch the open shell belly into a sealed bowl.
The snare wires appear one at a time as WIRES comes up, and they buzz while the drum sounds. They are drawn as straight lines rather than as coils. A coil is the more accurate picture, and at this size it read as a braid wrapped round the shell, so the accurate drawing was the wrong one.

A small spectrum in the corner answers the one question the head cannot: which modes are actually sounding.

Head view: flat or 3D.

Instruments: Tom, Floor tom, Timpani, Kick, Snare, Brush snare, Gong, Steel pan, Frame drum, Tabla. These are the instruments the engine was measured against while it was being built, so they are also the shortest route to hearing whether something has broken.

Patch ideas

A kit from one module. Three instances loaded with Kick, Snare and Floor tom, clocked from Beat. They share nothing, so they detune and decay independently the way a real kit does.

Timpani that follow a line. Load Timpani, patch V/OCT from Note or Chance, and put a slow LFO on TENSION CV. The pedal glide comes from tension rather than from pitch, so it bends the way the instrument does.

Playing the head. An LFO into X and another, slower, into Y. The strike position walks around the head and the timbre moves with it, because position is a per-mode gain rather than a filter.

Gongs. Load Gong, wind MATERIAL up, DECAY long, and strike hard with velocity. MATERIAL is bending stiffness, so a high setting is genuinely a plate rather than a membrane with a longer tail.

Kit