Auto Fills User Manual

Auto Fills is a random drum-fill generator for iOS: it builds a polyphonic drum fill from a kit you define, then sends it out as MIDI to whatever drum app, synth, or hardware you route it to. It's available as a standalone app, which includes an optional built-in drum sampler so it can make sound entirely on its own, and as an AUv3 MIDI plugin, which is a pure MIDI processor with no sound engine of its own — inside a host, it always needs its output routed to an instrument.

Overview

A drum fill is a short, denser burst of hits that breaks up an otherwise repeating drum pattern — usually right before a section change. Auto Fills builds one for you automatically: you define a drum kit (which parts it has and how likely each one is to play), and Auto Fills randomizes a polyphonic fill from it, on a loop, so a new-feeling fill keeps showing up at the same spot in your track every few bars.

Because it only sends MIDI, Auto Fills works with any drum machine, sampler, or hardware synth that accepts MIDI notes — an iOS drum app, a hardware groovebox over MIDI, or another AUv3 instrument hosted in the same session.

Interface Overview

The main screen has three areas:

• Mode column (left) — switches what the step grid below is editing: Kit, Duration, Ratchets, Velocity, Note, and Channel.
• Step grid (center) — one column per drum part in your kit. What each column controls depends on the selected mode. A + / − / # column at the right edge adds, removes, or directly sets the number of parts.
• Bottom bar — the current pattern's number, the Variety, Density, Voices, and Rate knobs, the Random and Generate buttons, and the Settings button.

While a fill is playing, the step grid flashes to show which parts are firing on each hit.

Getting Started

1. Build a kit: switch to Kit mode and use the + button to add drum parts (up to 32), or open Settings → Template to load a ready-made kit for a specific drum app or piece of hardware.
2. In Note and Channel mode, set each part's MIDI note and channel to match your drum destination (a template does this for you automatically).
3. Adjust each part's probability fader in Kit mode — higher faders make that part play more often.
4. Tap Generate to roll a new fill, or Random to reshuffle every part's probability first and then generate.
5. Press play. The fill repeats on the cycle set up in Duration mode (by default: 3 bars of waiting, then a 1-bar fill).
6. Route Auto Fills' MIDI output to your drum app, synth, or hardware (see MIDI Routing).

Kit Modes

The step grid's meaning changes with the selected mode. Every mode shares the same set of drum parts — you're only changing what property of that part you're editing.

Mode	What each step controls
Kit	The part's probability (0–100%). The randomization engine favors parts with higher probability, so they play more often in the generated fill.
Ratchets	The part's ratchet probability (0–100%). Higher values increase how often — and how many times — that part repeats rapidly within a single hit, up to 4 repeats.
Velocity	The part's fixed MIDI velocity (0–127), used as the base loudness for every hit of that part.
Note	The part's MIDI note number, shown as both a pitch name and a raw number. This is what needs to match your drum app's or hardware's note mapping.
Channel	The part's MIDI output channel (1–16), letting you spread parts of one kit across multiple destinations or drum apps at once.
Duration	Not part-specific — see Duration Mode below.

Use the +, −, and # buttons next to the step grid to add one part, remove the last part, or type an exact part count (1–32). Adding, removing, or resizing the kit regenerates the fill.

Generating a Fill

• Density — how many of the generated hits actually play. Turning it down thins the fill out without changing its underlying rhythm.
• Voices — the maximum number of parts that can sound at the same instant (i.e. how polyphonic the fill gets).
• Rate — the grid the fill is built on, from 1/2 down to 1/32, including triplet subdivisions (1/8T, 1/16T, etc.). Faster rates produce denser fills.
• Variety — how much each hit's velocity randomly deviates from that part's fixed Velocity-mode value, so repeated hits of the same part don't all sound identical.
• Generate — rolls a brand new fill using the current probabilities, ratchets, density, voices, and rate.
• Random — first randomizes every part's Kit-mode probability, then generates a new fill from those probabilities.

Changing Density, Voices, Rate, or any part's probability/ratchet fader automatically regenerates the fill — you don't need to press Generate after every tweak.

Duration Mode

Switch to Duration mode to configure the fill's timing:

• Wait Before the Fill — how long the pattern plays nothing before the fill starts, in Bars or Beats.
• Fill Duration — how long the generated fill itself lasts.
• Wait After the Fill — how long the pattern plays nothing after the fill ends, before the whole cycle repeats.
• Block incoming MIDI during the fill — if you're routing your regular drum sequencer's MIDI through Auto Fills instead of straight to your drum app, enabling this makes sure only the generated fill reaches your drum app while it's playing, and your sequencer's own MIDI passes through everywhere else in the cycle.
• Randomise the fill every cycle — when on, Auto Fills rolls a brand-new fill (new rhythm, new parts, new ratchets — using your current probabilities) every time the cycle repeats, instead of playing the same fill on loop.

Patterns

The pattern strip at the bottom lets you keep multiple fill setups side by side — different kits, durations, or feels — and switch between them instantly, including live while playing. Tap + to add a new pattern (it starts as a copy of the current one), tap a number to switch to it, and long-press a pattern to Copy, Paste, or Delete it.

Kit Templates

Rather than building a kit note-by-note, open Settings → Template to load a ready-made MIDI note map for a specific drum app or hardware groove box. Loading a template replaces the current kit's parts, notes, and channels (each part starts at 50% probability), so you can start generating fills that speak your drum destination's language immediately.

Templates cover two groups:

App: AR-909, Axon 2, Blip Box, Dadamachines Automat, Digistix, DM1/DM2/Drumlab, Drum Computer, EGDR606, EGDR808, EGDR909, FAC Drumkit, General MIDI 8, General MIDI 16, Hammerhead, Klevgrand Ting, Koala Sampler 2x8, Koala Sampler 4x4, Korg Gadget (Amsterdam, Bilbao, Gladstone, London, Recife, Tokyo), MV08, NS2 Slate, Pure Acid Drums, Ruismaker, Ruismaker FM, SDS-x, Sitala, Splat-to-Clat, VA Drum SM, VA Drum 2 808, VA Drum 2 909, Vatanator.

Hardware: Arturia Drumbrute, Arturia Drumbrute Impact, Korg Electribe EMX, Korg Electribe ER-1, Korg Volca Beats, MFB 522, Roland MC-101, Roland TR-08, Roland TR-707, Roland TR-727, Roland TR-808 (CHD Kit), Roland TR-808 (Kenton Kit), Roland TR-8S, Roland TR-909, Elektron Rytm.

A handful of templates (numeric-pad samplers like the Koala Samplers or Axon 2) label their parts by pad number rather than drum-part name, since those instruments don't have a fixed role-per-pad convention.

Manual Trigger Mode

By default, fills fire automatically on the Duration-mode cycle. Turn on Manual Trigger in Settings → Manual Trigger to fire a fill on demand instead, from an incoming MIDI note or MIDI CC message:

• Trigger Type — Note or MIDI CC.
• Value — the specific note number (shown with its pitch name) or CC number that fires the fill. Defaults to MIDI note 60 (Middle C).
• Channel — the MIDI channel the trigger message must arrive on (1–16).
• Quantization — when on, a trigger is held and the fill starts on the next beat rather than instantly, so it stays in time with your session.

While Manual Trigger is enabled, the Duration mode's Wait Before/Wait After fields are hidden (they don't apply), and only Fill Duration matters.

MIDI Routing

Auto Fills is MIDI-only end to end:

• Virtual MIDI In / Out — Auto Fills creates its own virtual CoreMIDI ports, "Auto Fills In" and "Auto Fills Out", so any other MIDI app on the device can send to or receive from it without a shared physical interface. Toggle these in Settings.
• Physical MIDI In/Out — every other MIDI source and destination visible to the device (Bluetooth, USB, network) is listed in Settings → MIDI In / MIDI Out as an individual on/off switch.
• MIDI In Channel — the channel Auto Fills listens on for pattern-select and manual-trigger messages (Settings → MIDI In Channel).
• Pattern select via CC — sending the configured Patterns CC# (default CC 10) on the MIDI In Channel, with a value of N, switches to pattern N. Handy for driving pattern changes from a hardware controller or another app.
• Per-part channel — each kit part's own output channel is set independently in Channel mode, so one kit can address several MIDI destinations at once.
• MIDI Panic — Settings → MIDI Panic immediately sends note-off messages on every channel, for the rare case a note gets stuck.
• Incoming MIDI not consumed by pattern-select or manual-trigger is passed through to Auto Fills' output untouched (see "Block incoming MIDI during the fill" above for the one exception).

Built-In Sampler (Standalone)

The standalone app includes a small built-in drum sampler so you can hear your fills without a separate drum app — useful for auditioning a kit or a template on the go. It plays whatever MIDI Auto Fills generates internally, independent of your MIDI routing.

• Sampler — enable/disable the built-in sound.
• Sampler Volume — the sampler's output level.

The bundled sound bank covers the core GM percussion range (kick, snare, claps, toms, hi-hats, cymbals, cowbell). Parts mapped outside that range by a template — some numeric-pad templates use notes the bank doesn't cover — will stay silent on the built-in sampler even though they still send correctly over MIDI.

Ableton Link

The standalone app syncs tempo and transport with other Link-enabled apps and devices on the same network. Open Settings → Ableton Link to join a session; once connected, Auto Fills' tempo follows the Link session, and starting or stopping playback in Auto Fills (or any other Link peer) starts or stops the whole group together.

Exporting a Fill as a MIDI File

Settings → MIDI Export → Export Pattern renders the current pattern's generated fill to a standard MIDI file and opens the share sheet, so you can drop it into a DAW, send it to another app, or save it for later — a snapshot of one specific generated fill rather than the live, regenerating pattern.

AUv3 Plugin

Auto Fills also ships as an AUv3 MIDI plugin (a MIDI-effect/processor, not an instrument) for use inside a compatible host such as AUM or GarageBand:

• MIDI output: a single output cable, "Auto Fills Out".
• Transport & tempo: the plugin follows the host's transport and tempo automatically — there's no separate Link connection to make inside a host.
• Automation: Pattern, Mode, Density, Voices, Rate, Generate, Random, Variety, the three Duration fields, Block-incoming-MIDI, and Randomise-every-cycle are all exposed as host-automatable parameters, alongside a fader per kit part that mirrors whatever mode's step grid is currently showing.
• Presets: choosing a factory preset loads the matching kit template (one preset per template, plus a Default preset); your own kit setups save as user presets through the host's normal preset UI.
• State saving: the full kit, pattern, and settings state is saved and restored with the host session.

The built-in sampler is a standalone-only convenience — inside a host, route the plugin's MIDI output to an instrument track the same way you would any other MIDI source.

Settings Reference

Setting	Location	Effect
BPM	Settings (standalone)	Sets the Ableton Link tempo.
Sampler / Sampler Volume	Settings (standalone)	Built-in sampler on/off and level.
Ableton Link	Settings (standalone)	Opens the Link session panel.
Virtual MIDI In / Out	Settings	Toggles Auto Fills' own virtual CoreMIDI ports.
MIDI In / MIDI Out	Settings	Per-port enable switches for every visible MIDI source/destination.
MIDI Panic	Settings	Sends note-off on every channel.
Patterns CC#	Settings	The CC number used to select a pattern remotely.
MIDI In Channel	Settings	The channel Auto Fills listens on for pattern-select/manual-trigger messages.
Template	Settings	Loads a kit template (see Kit Templates).
Manual Trigger	Settings	Enables trigger-on-demand mode (see Manual Trigger Mode).
MIDI Export	Settings	Exports the current pattern's fill as a .mid file.
Knob Control Style	Settings	Changes how the on-screen knobs respond to touch (horizontal/vertical/both/rotary drag).

Tips and Starting Points

• Start from a Kit Template that matches your drum app or hardware, then tweak probabilities in Kit mode rather than building a note map from scratch.
• Keep Voices low (1–2) for sparse, tasteful fills; raise it for busier, more chaotic ones.
• A high Rate (1/32 or a triplet subdivision) with low Density often reads better than a low rate at full density — the fill stays interesting without turning into a wall of notes.
• Turn on Randomise the fill every cycle for a pattern you loop for a long time, so the fill doesn't become predictable.
• Use Manual Trigger with Quantization on when you want to drop a fill in live from a MIDI controller without worrying about hitting the beat exactly.
• If you're layering Auto Fills over an existing drum sequencer, route the sequencer through Auto Fills' MIDI In and turn on Block incoming MIDI during the fill, rather than running two separate MIDI paths into your drum app.

Troubleshooting

No sound at all. In the standalone app, check that Sampler is enabled in Settings and its volume isn't at zero. If you're relying on an external drum app/synth/hardware instead (or you're using the AUv3, which has no sound engine of its own), confirm that destination is actually receiving on the port and channel each kit part is set to send on, and that its own instrument/sound is loaded correctly.

No MIDI reaching my other app. Check that Auto Fills' Virtual MIDI Out is enabled and that the receiving app has "Auto Fills Out" enabled as an input. For physical/network MIDI, confirm the destination port is toggled on under Settings → MIDI Out.

Stuck notes. Use Settings → MIDI Panic to force every channel's notes off. If it recurs, check whether a part's Duration or Rate setting is producing overlapping ratchets on a device that doesn't handle rapid repeated notes well.

The fill won't start. If Manual Trigger is enabled, the fill only fires from the configured note/CC on the configured channel — confirm your trigger source matches all three, and that Quantization isn't making it look delayed. Otherwise, check the Duration-mode Wait Before value isn't longer than expected.

Fill sounds different than expected after a settings change. Density, Voices, Rate, and any part's Kit/Ratchet fader all regenerate the fill automatically — this is expected, not a bug. Use Randomise the fill every cycle off if you want a fill to stay fixed once generated.

Pattern select via CC isn't switching patterns. Confirm the incoming CC number matches Patterns CC#, and that it's arriving on the configured MIDI In Channel.

AUv3: host doesn't see Auto Fills, or it's silent in the host. Auto Fills' AUv3 is a MIDI processor, not an instrument — it won't appear in an audio-instrument slot, only wherever your host lists MIDI effects/processors, and it needs its MIDI output routed to an instrument track to produce sound.

Sampler is silent for some kit parts. The built-in sampler only covers the core GM percussion note range; parts mapped to notes outside that range (common on some numeric-pad templates) won't sound on the sampler even though they still transmit over MIDI correctly.

Ableton Link won't sync. Confirm both devices/apps are on the same Wi-Fi network and that Link is enabled on both sides — Auto Fills only syncs tempo/transport with other Link-enabled peers, not with arbitrary MIDI clock sources.

Links

• Auto Fills Website
• Auto Fills on the App Store
• All Cem Olcay Apps