User Manual
CHOPPL
by positiveppl
Visual drum machine and video sampler. Load clips, slice them into pads, build patterns, apply visual effects, and export as MP4 — all in the browser.
Browser-based
No install (Lite)
MP4 export
MIDI + OSC
Mac app (Pro)
01
Overview
CHOPPL runs entirely in your browser — no install, no plugins, no account required for the Lite version. The app is organized into tabs. This manual walks through each one.
Two Versions
CHOPPL Lite
Free · try.choppl.com
Core pads (up to 8), sequencer, FX, and export. Exports include a watermark. No MIDI Learn, Audio Routing, or Layers.
CHOPPL Pro
One-time purchase · Native Mac app
Full feature set — 16 pads, all banks, MIDI, OSC, Audio Routing, Layers, scenes, and clean watermark-free exports. Works offline.
Keyboard Shortcuts
| A S D F | Pads 1–4 |
| G H J K | Pads 5–8 |
| Z X C V | Pads 9–12 |
| B N M L | Pads 13–16 |
| Space | Play / Stop sequencer |
02
LIB — Clip Library
Your media storage. All clips live here first and persist in the browser between sessions via IndexedDB.
Loading Clips
- Tap the drop zone or drag files directly onto it.
- Accepted: video (MP4, MOV, WebM), audio (MP3, WAV, AAC, FLAC, M4A), and images.
- Multiple files can be loaded at once.
- CHOPPL auto-detects the musical key of audio and video clips on load for use with MATCH KEYS.
Using the Clip Grid
- Tap any clip to preview it in the monitor.
- To assign a clip to a pad: tap SELECT on the clip — the app navigates to PADS. Tap any pad (loaded or empty) to assign the clip. Loaded pads are hot-swapped instantly.
- The X button removes a clip from the library and clears it from any pads using it.
- CLEAR (top right) wipes the entire library.
Special Pad Types
| + CREATE PAD | Adds a blank pad slot beyond the standard grid. Pro only. |
| + CAMERA PAD | Creates a pad using live camera input. |
Clips are stored in your browser's IndexedDB — local to each device and browser profile. Clearing browser storage clears your library.
03
PADS — Drum Pad Grid
The main performance surface. Trigger pads by tapping, keyboard shortcuts, or MIDI notes.
Pad Count & Banks
- 8 / 12 / 16 buttons set how many pads are visible. Lite: 8 only.
- BANK ◀ / BANK ▶ or the bank letter buttons (A, B, C...) switch between pad banks. Each bank is an independent grid of pads.
Toolbar Buttons
| AUTO LOOP CLIPS | When on, a pad loops until another pad fires or STOP is pressed. Toggle off for one-shot playback. |
| LAYERS ON | Enables multi-layer compositing. Each pad can have multiple clips composited together. Pro only. |
| AUTO FILL PADS | Assigns library clips to pads in order. |
| FRESH RANDOM KIT | Randomly picks clips from your library for all pads. |
| RANDOMIZE KIT | Re-randomizes current pad assignments. |
| SHUFFLE PAD CLIPS | Swaps clips between pads without removing any. |
| MATCH KEYS | Finds the most common key across loaded pads (confidence ≥ 40%) and pitch-shifts all others to match. Works without a backing track. Low-confidence detections like speech and dialogue are excluded and left untouched. |
| MUTE ALL AUDIO | Silences all pad audio globally without stopping visual output. |
| CLEAR PADS | Removes all clip assignments from the current bank. |
Hot-Swap During Performance
To swap a clip onto a pad mid-set: go to LIB, tap SELECT on the clip you want, then tap any pad — even a loaded one. The clip replaces whatever was there instantly without interrupting other pads.
Pad Settings (gear icon)
Tap the gear icon on any loaded pad to open its settings sheet. The sheet is scrollable on smaller screens.
| Bar Length | Sets playback region to 1, 2, 4, or 8 bars at the current BPM. |
| Start / End | Manual trim — only the region between these points plays. |
| Clip BPM | Shows detected BPM. Updates reactively as you move the Pitch slider, showing the effective BPM at that pitch. Correct manually if detection is off. |
| Volume | Per-pad volume 0–150%. |
| Pitch | Semitone pitch shift from -12 to +12. Displayed as key name if a source key is detected. |
| Source Key | Detected musical key of the clip. Can be overridden manually. |
| Look | Visual filter applied to the clip in the monitor. |
| Transition | How the clip cuts or blends when triggered. |
| Layer | Which compositing layer this pad occupies. |
| Choke Group | Assign to group A, B, C, or D. When this pad fires, all other playing pads in the same group stop (6ms fade). All of a pad's layers stop together as a unit. Pads with no group are unaffected. |
| Fade In | Audio and visual attack time in ms — how long the pad takes to reach full volume and opacity from silence. |
| Hold | How long the pad stays at full volume and opacity before fading out. |
| Fade Out | Audio and visual release time in ms — how long the pad takes to fade to silence and invisible after the hold phase. |
| MATCH KEY | Pitch-shifts this pad to match the loaded track's key. Requires a track with a detected key. |
| LOOP | Loops this pad continuously. |
| AUDIO LINGER | Audio continues playing after the visual ends. |
| VIDEO ONLY | Plays the visual without audio. |
| MUTE | Silences audio for this pad while keeping the visual active. |
Fade In, Hold, and Fade Out apply to both the audio gain envelope and the visual opacity envelope simultaneously.
MIDI Quick Control
A compact MIDI base note slider sits at the bottom of the PADS view. Default is 36 (C1 in GM standard / C2 in Ableton naming). Pads map chromatically upward from the base note. To align with Ableton's Drum Rack default layout, use note 36 and octave down on your keyboard.
04
SLICE — Video Slicer
Chop a single clip into regions and send them directly to pads. The fastest way to build a playable kit from a music video or long sample.
Controls (single row, left to right)
| Source dropdown | Select which library clip to slice. Video clips render as a filmstrip; audio-only clips render as a waveform. |
| Slices dropdown | How many equal slices to cut: 4, 8, 12, or 16. Independent of your global pad count. |
| AUTO button | Divides the clip into equal regions and places markers automatically. |
Manual Markers
- Tap anywhere on the filmstrip to drop an amber slice marker.
- Drag existing markers to reposition them.
- CLEAR MARKERS removes all markers at once.
TO PADS — Smart Fill
- First looks for a consecutive run of N empty pads and fills from there.
- If no consecutive run exists but N or more empty pads are scattered, a confirm dialog appears. Confirming fills whatever is open in index order.
- If fewer than N empty pads exist, an alert cancels the operation.
Stack multiple sliced clips across banks — slice 8 clips to Bank A, switch to Bank B, load a second clip, slice 8 more. Full 16-pad performance across two banks.
05
SEQ — Step Sequencer
Programs pads to fire automatically on a rhythmic grid. Steps can be toggled freely during playback — changes take effect immediately on the next loop pass.
Controls
| Pattern buttons (A–D) | Four independent patterns, each with its own step data. Switch freely during playback. |
| CLEAR PATTERN | Hold for 1.5 seconds to clear all steps in the current pattern. A fill animation shows progress. Release early to cancel. |
| Swing | Delays odd steps to create a shuffled feel. 0% = straight, higher = more shuffle. |
| BPM slider | Global tempo 60–200 BPM. Always visible in the bottom strip. |
| Space bar | Play / Stop from anywhere in the app. |
06
TRACK — Backing Track
Load a full audio file to play behind your pads. Syncs with the sequencer transport and runs through the master audio FX chain.
Loading a Track
- Tap the waveform area (when empty) or the LOAD button to open a file picker. Accepted: MP3, WAV, AAC, M4A, FLAC.
- Once loaded, the waveform renders — tap anywhere on it to seek.
- CLEAR (top right) removes the track and resets the area.
Controls
| Volume | Track volume 0–150%, independent of master. |
| LOOP | Loops the track continuously (default on). |
| Detected BPM | Auto-detected from the track using onset autocorrelation. |
| 1/2 · x2 | Halves or doubles the detected BPM to fix octave errors in detection. |
| USE BPM | Snaps the global sequencer BPM to the detected track tempo. |
| Key | Detected musical key. Override manually if needed. |
| MATCH ALL PADS | Pitch-shifts all loaded pads to match the track key. Requires a track with a detected key. For key matching without a track, use MATCH KEYS in the PADS toolbar. |
07
MIDI Control
PROConnect a MIDI controller to trigger pads, switch banks, load scenes, toggle effects, and control parameters live. Requires Chrome or Edge. Enable MIDI via the MIDI pill in the bottom status bar.
MIDI Monitor
| Input Device | Select which MIDI device to listen to. 'All inputs' listens to everything connected. |
| Base Note | MIDI note that maps to Pad 1. Default 36 (C1/GM standard). Pads map chromatically upward. |
| Velocity Sensitivity | On: pad volume scales with hit velocity. Off: all triggers at full volume. |
| Velocity Curve | Linear, exponential, or logarithmic velocity-to-volume mapping. |
MIDI Learn
- Select an Action, target Pad/Effect/Scene/Bank, and Mode.
- Tap LEARN then move a control on your MIDI device. CHOPPL captures the note or CC.
- Tap SAVE MAPPING to store it.
Available Actions
| Trigger pad | Fires a pad on note-on. |
| Stop pad audio | Stops a specific pad's audio. |
| Toggle pad mute | Mutes or unmutes a pad. |
| Trigger / Toggle effect | One-shot or toggle a visual effect. |
| Toggle strobe | Enables/disables the strobe effect. |
| Trigger scene | Loads a saved scene by index. |
| Prev / Next / Load bank | Navigates between pad banks. |
| Blackout | Cuts visual output to black. |
| Start/stop recording | Toggles export recording. |
| Opacity / Speed / Scale / Rotation | Maps a CC knob or fader to a visual parameter. |
08
SCENES
PROSnapshots of the full CHOPPL state — pads, patterns, FX, BPM, VFX — that can be recalled instantly. Use scenes to switch between different songs or set sections live.
- Type a name and tap SAVE NEW to create a snapshot.
- UPDATE ACTIVE overwrites the current scene with your current state.
- Tap any scene in the list to load it.
- Import / Export scenes as JSON for backup or sharing between sessions.
Scenes can also be triggered via MIDI using the 'Trigger scene' MIDI action.
09
AUDIO Modulators
PROControls how CHOPPL analyzes audio and uses it to drive visual effects reactively in real time.
Input
| Master output | Analyzes CHOPPL's own audio output. Default mode. |
| Uploaded track / master | Analyzes the loaded backing track mixed with pad audio. |
| Mic / external input | Analyzes a mic or external audio device — for example, a virtual audio driver receiving your DAW's output. |
| RECORD EXT AUDIO | When on, external audio is captured in exports. Required if you want your DAW's audio in CHOPPL recordings. |
Tuning
| Gain | Amplifies input before analysis. |
| Smoothing | How much meters average over time. |
| Threshold | Minimum level to trigger beat detection. |
| Sensitivity | How strongly beats register against background noise. |
| Attack / Release | How fast analysis responds to rising and falling signal. |
Routes
| BASS → SCALE | Bass energy controls visual scale. |
| MID → GLITCH | Mid frequencies drive glitch intensity. |
| HIGH → BRIGHT | High frequencies drive brightness. |
| PEAK → FLASH | Peaks trigger flash events. |
| RMS → OPACITY | Average loudness controls opacity. |
10
LAYERS
PROStack multiple clips on top of each other in the visual output, each with its own blend mode and opacity. This is what makes CHOPPL a full VJ tool.
- When Layers mode is on, each pad can have a primary clip plus additional layers composited on top.
- Triggering the pad plays all its layers simultaneously. Choke groups stop all layers of a pad together as a single unit.
- Tap a preset to instantly configure a multi-layer layout — the fastest way in.
- Keep Layer 1 as the main clip and use upper layers for fades, hits, and blends.
11
FX — Audio FX Chain
Global audio processing applied to all pads and the backing track.
| Master | Global output volume 0–150%. |
| Drive | Waveshaper distortion — subtle saturation at low amounts, grit at high. |
| Lo Cut | High-pass filter, removes low-frequency rumble (20–800 Hz). |
| Hi Cut | Low-pass filter, rolls off highs (1200–20000 Hz). Use for lo-fi feel. |
| Delay | Wet/dry mix for the delay effect. |
| Feedback | How much delay signal feeds back — higher = longer cascading echoes. |
12
VFX — Visual Effects
Canvas overlay effects that render on top of your video output in real time. All effects are beat-reactive and respond to pad hits and audio input.
Effects
| SCAN | Horizontal CRT scanline overlay. |
| GLITCH | Digital corruption — pixel displacement and color splitting. |
| BLOOM | Amber glow on bright areas. Flares on pad hits. |
| VHS | VHS tracking artifacts — horizontal jitter, color bleed, noise. |
| STUTTER | Full-frame white flash strobe. Use sparingly — it is intense. |
| KALEIDO | Kaleidoscope mirror effect — reflects the image across axes. |
| FEEDBACK | Video feedback loop — trails and recursive echo of the canvas back into itself. |
| TILE GRID | Tiles the visual output into a repeating grid pattern. Works well combined with KALEIDO. |
Global Controls
| Amount | Master intensity of all active effects (0–100%). |
| Beat | How strongly pad hits spike effect intensity. |
| Energy | Overall visual energy — drives motion and chaos across all effects. |
| Shake | Screen shake intensity on pad hits. |
| Color | Shifts color grading across effects. |
Overlays
| BORDER | Color border frame around the canvas. |
| TEXT | Burns a text label onto the visual output. |
| REC BUG | Small REC indicator dot in the corner — classic camcorder style. |
All overlays are visible in exports. Disable them before recording for a clean export.
Random FX on Hit
In each pad's settings sheet, assign any combination of VFX to trigger momentarily each time that specific pad fires. Independent of the global VFX toggles.
13
REC — Record & Export
Captures your session as a video file — visual canvas plus audio output, synchronized from the moment you hit START.
Aspect Ratio
| 9:16 | Vertical — TikTok, Instagram Reels, YouTube Shorts. |
| 1:1 | Square — Instagram feed. |
| 16:9 | Horizontal — YouTube, desktop, widescreen. |
Quality
| Standard | 30fps, balanced bitrate. Smallest file. Good for most sharing. |
| High | 30fps, higher bitrate. Sharper image. |
| Ultra | Maximum quality at 30fps. Best for archiving. |
| MAX | 60fps, highest bitrate. Smoothest motion. Largest file, most CPU. |
Lite exports include a CHOPPL Lite watermark. Pro exports are clean.
Recording Flow
- Tap START — sequencer and backing track start and sync automatically.
- Play pads live while recording to add hits over the pattern.
- Tap STOP in the top bar to end. The sequencer and track stop automatically.
- A download link appears in the Exports list when processing completes.
- CHOPPL prefers browser-native MP4 encoding, with WebM fallback. ffmpeg.wasm converts WebM to MP4 in the background on first use (10–30 seconds to load from CDN).
14
Integrations
Max for Live Bridge (Ableton)
CHOPPL receives controls from Ableton Live via a Max for Live device and a local WebSocket/OSC bridge. The OSC BRIDGE READY indicator in the bottom status bar confirms the bridge is active.
01
Open CHOPPL first. The bridge starts automatically. Wait for OSC BRIDGE READY before Ableton sends controls.
02
Add the device. Create an empty MIDI track in Ableton and drop the CHOPPL Max for Live device onto it.
03
Choose MIDI From. In the track's input dropdown, select the track you want CHOPPL to receive MIDI from.
04
Monitor ON. Set Monitor to In/ON so MIDI passes through the Max for Live device.
05
Trigger CHOPPL. Use device controls or routed MIDI to send pads, BPM, record, FX, and bank changes.
06
Show visuals. Use OUTPUT in the top bar for a pop-out visual window. Fullscreen it or capture in OBS.
DAW Audio into CHOPPL (Virtual Audio Driver)
To feed your DAW's audio into CHOPPL's analysis or export capture, use a virtual audio driver — BlackHole (Mac, free) or VB-Cable (Windows, free).
| Install driver | BlackHole: existential.audio/blackhole — VB-Cable: vb-audio.com. Both free. |
| Mac setup | In Audio MIDI Setup, create a Multi-Output Device with your speakers and BlackHole checked. Set Mac system output to that device. |
| Your DAW | Set audio output to the Multi-Output Device or route audio to the virtual driver. |
| CHOPPL | In AUDIO tab, set Input to Microphone / external input, select the virtual driver, enable RECORD EXT AUDIO ON. |
Live Output (OBS, Projector, Second Display)
| Pop-out window | Tap OUTPUT in the top bar — opens a clean window with only the visual canvas. |
| Fullscreen | Click the pop-out canvas to request fullscreen, then drag to a projector or second display. |
| OBS capture | Add a Window Capture or Display Capture source in OBS pointed at the CHOPPL pop-out. |
15
Common Workflows
Workflow A — Chop a Music Video
01
Drop a video into LIB. Tap SLICE.
02
Select the clip from Source. Set Slices to 8. Tap AUTO.
03
Tap TO PADS. Pads load with the sliced regions.
04
Go to PADS, tap any pad to preview. Adjust via gear settings.
05
Go to SEQ, program a pattern by toggling step cells.
06
Go to REC, pick aspect and quality, tap START.
07
Tap STOP in the top bar. Download the export link when it appears.
Workflow B — Live Mix with Backing Track
01
Load multiple clips into LIB. Assign to pads or use AUTO FILL PADS.
02
Go to TRACK, load an audio file, tap USE BPM.
03
Use MATCH KEYS in the PADS toolbar to pitch-align all clips.
04
Play pads live over the track or program the sequencer.
05
Record from the REC tab.
Workflow C — Beat-Reactive Visual Performance (Pro)
01
Install a virtual audio driver and route your DAW's output through it.
02
In CHOPPL AUDIO tab, set Input to external input and select the driver.
03
Enable RECORD EXT AUDIO ON if you want your DAW's audio in exports.
04
Turn on audio Routes (BASS → SCALE, PEAK → FLASH, etc.).
05
Set up MIDI Learn to map DAW controls to CHOPPL pads and effects.
06
Use OUTPUT for a pop-out window — capture in OBS or send to projector.
16
Troubleshooting
Export is WebM, not MP4
Requires COOP/COEP headers configured on the server. These are set on try.choppl.com. Running locally without a proper server setup won't have these headers — WebM only.
ffmpeg.wasm is slow on first use
Downloads from CDN on first load (10–30 seconds). Cached after that.
No sound from pads
Tap a pad manually first to unlock the AudioContext — browsers require a user gesture before audio can play.
Clips sound lower pitched than expected
BPM sync no longer auto-applies on load. If a clip sounds slow, check the Pitch slider in pad settings and reset it to 0 semitones if needed.
MATCH KEYS shifts everything wrong
One clip may have a low-confidence key detection (speech, dialogue, noise). MATCH KEYS excludes clips with key confidence below 40%. If most clips are non-musical, no match will run — adjust pitch manually per pad.
Filmstrip is slow to generate
Frame extraction is CPU-intensive on long clips. On low-end mobile a timeout may fire and show an incomplete filmstrip. Use shorter clips for faster extraction.
iOS recording drops frames
iOS Safari has limited canvas capture support. Use Chrome on Android or desktop for full recording support.
MIDI not showing up
Use Chrome or Edge (Web MIDI API required). Enable MIDI via the MIDI pill in the bottom bar. Connect your device before opening the browser.
Library disappeared
Clips are stored in IndexedDB — local to each device and browser profile. Clearing browser storage or switching browsers clears the library.
OSC bridge not ready
Refresh the page. Always open CHOPPL before launching the Ableton Max for Live device.
Pad settings sheet is cut off
The sheet scrolls internally — swipe up within the sheet to access controls below the visible area.