ReaBeat

Neural beat detection and tempo mapping for REAPER. State-of-the-art machine learning meets professional audio workflow.

Why ReaBeat?

REAPER has no built-in beat detection. ReaBeat adds it as a native extension: one file in UserPlugins, zero dependencies. It uses beat-this (CPJKU, ISMIR 2024) - the neural network with the best published F1 scores for beat and downbeat tracking.

No Python. No server. No installer. Drop one file, detect beats.

Features

Detection

• Neural beat detection - beat-this model (ISMIR 2024, state-of-the-art accuracy)
• Automatic downbeat detection - neural downbeats, not naive every-4th-beat
• Time signature detection - from downbeat spacing (2/4 through 7/4)
• BPM from filename - parses "120bpm" patterns, shows hint if different from detected
• Per-item cache - switch items without re-detecting, shows "(cached)"

Three Action Modes

• Match Tempo - adjust playrate to target BPM (pitch preserved). Match to project tempo or to another detected item for multi-track sync.
• Insert Tempo Map - sync REAPER's grid to audio. Constant, variable-bars, or variable-beats. Only tempo markers inside the item are replaced (existing markers elsewhere in the project are preserved), and the item is locked to time so the audio doesn't stretch when the grid changes.
• Insert Stretch Markers - quantize audio to grid with four modes:
  • Straight - mathematical grid from detected BPM (default, best for modern music)
  • Bars - downbeat subdivision with variable bar lengths (live recordings)
  • Project grid - snap to REAPER's project grid (multi-track sync)
  • Strength slider (0-100%) - partial quantization, industry standard

Interactive Waveform Editor

• Beat editing - drag, add (double-click), delete (right-click), toggle downbeat
• Marker editing - after Apply, edit individual stretch markers directly in REAPER
• Gap highlighting - red tint over missing-beat regions with teal suggestion lines at the strongest transients; an on-canvas hint shows the N shortcut to jump to the next gap
• Seek - click waveform to set REAPER cursor (accounts for stretch markers)
• Zoom/scroll - mouse wheel, shift+scroll, trackpad swipe
• Playhead tracking - auto-follow during playback

Multi-Track Sync

• Select reference item from "Match to:" dropdown
• One click: tempo map + playrate + downbeat alignment + stretch markers on both tracks
• Single Ctrl+Z undoes the entire operation

Quality

• Onset refinement - snaps each beat to nearest audio transient (+/-30ms, sample-level precision). Currently disabled past 10 minutes of audio to avoid a multi-gigabyte spectral buffer; the neural model alone still gives ~20 ms precision in that case. A streaming rewrite that lifts the length cap is on the roadmap.
• Beat interpolation - fills gaps in quiet sections using sub-threshold model hints
• Consistency pass - removes isolated false-positive beats
• Octave correction - [/2] [x2] buttons, 78-185 BPM range
• Editable BPM - click to override detected tempo

Keyboard Shortcuts

Action	Shortcut
Play/Stop	Space
Apply action	Enter
Next gap	N
Undo	Cmd+Z / Ctrl+Z
Redo	Cmd+Shift+Z / Ctrl+Shift+Z

Installation

ReaPack (recommended)

1. Install ReaPack if you haven't already
2. Extensions > ReaPack > Import repositories...
3. Paste: https://raw.githubusercontent.com/b451c/ReaBeat/main/index.xml
4. Extensions > ReaPack > Browse packages > search "ReaBeat"
5. Right-click > Install
6. Restart REAPER

Manual Install

Download both files for your platform from Releases and place them in REAPER's UserPlugins folder. Both files must be in the same folder.

macOS (Apple Silicon) — ~/Library/Application Support/REAPER/UserPlugins/

Download from Release	Save as
reaper_reabeat-arm64.dylib	reaper_reabeat-arm64.dylib
libonnxruntime-macOS-arm64.dylib	libonnxruntime.1.24.4.dylib

macOS (Intel) — ~/Library/Application Support/REAPER/UserPlugins/

Download from Release	Save as
reaper_reabeat-x86_64.dylib	reaper_reabeat-x86_64.dylib
libonnxruntime-macOS-x86_64.dylib	libonnxruntime.1.16.3.dylib

Intel builds bundle ONNX Runtime 1.16.3 - the last release that runs on macOS 10.15 (Catalina) - so older Macs are supported. Apple Silicon builds use ORT 1.24.4 (macOS 11+).

Windows 64-bit — %APPDATA%\REAPER\UserPlugins\

Download from Release	Save as
reaper_reabeat-x64.dll	reaper_reabeat-x64.dll
onnxruntime.dll	onnxruntime.dll

Linux x86_64 — ~/.config/REAPER/UserPlugins/

Download from Release	Save as
reaper_reabeat-x86_64.so	reaper_reabeat-x86_64.so
libonnxruntime.so.1-Linux-x86_64	libonnxruntime.so.1

Linux aarch64 — ~/.config/REAPER/UserPlugins/

Download from Release	Save as
reaper_reabeat-aarch64.so	reaper_reabeat-aarch64.so
libonnxruntime.so.1-Linux-aarch64	libonnxruntime.so.1

Important: On Linux, the ONNX Runtime library must be renamed — remove the platform suffix so the file is called libonnxruntime.so.1. ReaPack does this automatically; manual install requires the rename.

Restart REAPER after installing.

Linux Requirements

Linux users may need to install graphics drivers and curl if not already present:

sudo apt install mesa-utils libcurl4

mesa-utils provides the OpenGL context JUCE needs for rendering. libcurl4 is required for model auto-download. Most desktop Linux distributions have these pre-installed.

First Run

On first launch, ReaBeat downloads the neural network model (~79MB) to ~/.reabeat/models/. A progress bar in the plugin window shows the download status; the Detect Beats button is replaced with Downloading model... until the download completes. This happens once; subsequent launches use the cached model.

Portable / offline install: if ~/.reabeat/models/ is not usable (portable REAPER, restricted network), place beat_this_final0.onnx directly in your UserPlugins folder next to the plugin binary. ReaBeat will load the model from there and skip the download. The file is available from the v2.0.0-model release.

Long items: detection has been tested on 30+ minute drum stems and full-length classical material. Items beyond 10 minutes skip per-transient refinement (which would otherwise demand multi-gigabyte spectral buffers) - the neural model alone already gives ~20 ms beat precision.

Usage

1. Select a media item in REAPER
2. Extensions > ReaBeat (or assign to toolbar/shortcut)
3. Click Detect Beats
4. Review beats on the waveform - edit if needed (drag, double-click, right-click)
5. Choose action mode: Match Tempo, Tempo Map, or Stretch Markers
6. Adjust settings (quantize mode, strength, quality)
7. Click Apply
8. In marker edit mode: fine-tune individual stretch markers directly

Building from Source

git clone https://github.com/b451c/ReaBeat.git
cd ReaBeat
git submodule update --init    # JUCE, WDL, reaper-sdk

Download ONNX Runtime to vendor/onnxruntime/ (headers in include/, library in lib/).

mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build .

Copy the built binary to REAPER's UserPlugins folder and restart REAPER.

Architecture

reaper_reabeat.dylib / .dll / .so
    |
    +-- ReaperPluginEntry()       REAPER extension entry point
    +-- JUCE UI                   Window, controls, waveform editor
    +-- MelSpectrogram            PocketFFT, Slaney mel, matching torchaudio
    +-- ONNX Inference            Chunked, 50fps, beat-this model
    +-- Postprocessing            Peak detection, interpolation, onset refinement
    +-- REAPER API                Direct calls (no TCP, no Lua wrapper)

Module	Purpose
BeatDetector	High-level detection orchestration
MelSpectrogram	FFT + mel filterbank (PocketFFT)
InferenceProcessor	ONNX chunked inference with overlap
Postprocessor	Peak detection + deduplication
TempoEstimator	Phase-aware BPM (circular mean + regression)
BeatInterpolator	Fill missing beats in quiet sections
OnsetRefinement	Snap to audio transients (+/-30ms)
ReaperActions	All REAPER API operations (undo blocks)
MainComponent	Full UI with waveform editor
ModelManager	Model download and caching

Tested On

Platform	OS	Architecture	REAPER
macOS	macOS 26.3.1 (Tahoe)	Apple M1 Pro (arm64)	v7.x
Windows	Windows 11 Enterprise	x64	v7.6.8
Linux	Ubuntu 25.10 (Questing Quokka), kernel 6.17.0-20-generic	aarch64 (ARM64)	v7.69

Previous Version (v1.3.1)

The Lua/Python version is preserved on the v1-lua branch and at the v1.3.1 tag. It requires Python + uv + beat-this. See the v1 README for installation.

Support

If ReaBeat saves you time, consider supporting development:

• Ko-fi
• Buy Me a Coffee
• PayPal

License

MIT - ReaBeat is free and open source.

Uses JUCE (AGPL), ONNX Runtime (MIT), PocketFFT (BSD-3), beat-this model (CC BY-NC-SA 4.0).

Links

• REAPER Forum Thread (v2)
• REAPER Forum Thread (v1, Lua/Python)
• GitHub Repository
• beat-this Paper (ISMIR 2024)