Fretscope

Real-time pitch and key detection with guitar fretboard visualization. Runs as a VST3/CLAP plugin (load in any DAW) or as a standalone app.

Cross-platform: Linux, macOS, and Windows. Built for guitar players who want Scaler-style detection with a fretboard-first workflow.

Features

Pitch Detection

• Real-time chromatic detection via McLeod algorithm, optimized for guitar (50-2000 Hz)
• 2048-sample window with 50% overlap (~23ms latency at 44.1kHz)
• Configurable confidence threshold
• Listen/Pause toggle (spacebar shortcut)

Key Detection

• Krumhansl-Schmuckler algorithm with exponential decay weighting
• Floating mode (auto-updates as you play) or locked mode
• Click any detected alternate key to select it
• Manual root note selection (all 12 notes)

Fretboard Visualization

• Resizable window with responsive layout
• Configurable fret count (8-30 frets) for extended range playing
• Color-coded scale overlays (root = amber, scale tones = blue)
• Active note glow/pulse animation
• Fret markers, proportional string thickness, nut rendering
• Display options:
  • Flip — swap low/high string orientation
  • Notes — show/hide note labels
  • Glow — show/hide glow effects
  • Fret numbers — show/hide fret numbers
  • Open Fret — show fret 0 as a column on the board
  • Label mode — cycle between note letters (A B C), scale degrees (1 2 3), or both
  • Degree filters — toggle individual scale degrees (1st, 2nd, 3rd, ...) to isolate patterns

Tuning Support

• 13 preset tunings:
  • 6-string: Standard, Drop D, Drop C, Open G, Open D, DADGAD, Half/Full Step Down
  • 7-string: Standard, Drop A
  • 8-string: Standard
  • Bass: 4-string, 5-string
• Custom tuning — any number of strings (1-12), per-string semitone adjustment

Scale & Chord Browser

• 15 scale types: major, natural/harmonic/melodic minor, pentatonic major/minor, blues, whole tone, diminished, and all 7 modes (dorian, phrygian, lydian, mixolydian, aeolian, locrian)
• 11 chord types: major, minor, dom7, maj7, min7, dim, aug, sus2, sus4, add9, power
• Dropdown selectors for quick access

Tuner

• Cents offset display with color-coded accuracy (green/amber/red)
• Visual needle bar (-50 to +50 cents)

Note Log

• Timestamped detection history with phrase grouping
• Deduplication (only logs on note change)
• In-key/out-of-key color coding
• Scrollable with clear button

Multi-Instance

• Run multiple independent instances in your DAW
• Each instance has its own tuning, scale, display settings

Install

Download a pre-built release from the Releases page or build from source.

From release (recommended)

Download the archive for your platform, extract, and copy to your plugin directory:

Platform	VST3 Location	CLAP Location
Linux	~/.vst3/	~/.clap/
macOS	~/Library/Audio/Plug-Ins/VST3/	~/Library/Audio/Plug-Ins/CLAP/
Windows	C:\Program Files\Common Files\VST3\	C:\Program Files\Common Files\CLAP\

From source (Linux/macOS)

make install      # build + copy to standard plugin dirs
make uninstall    # remove
make clean        # wipe build artifacts

From source (any platform)

cargo xtask bundle fretscope --release
# Bundles appear in target/bundled/

Usage

As a plugin

1. Open your DAW (e.g., Carla, REAPER, Bitwig, Ableton, FL Studio)
2. Rescan plugins if needed
3. Add Fretscope to a track
4. Route audio input to the plugin

Standalone

fretscope --backend jack   # JACK (Linux)
fretscope --backend alsa   # ALSA (Linux)
# macOS/Windows: uses default audio backend

Keyboard Shortcuts

Key	Action
Space	Toggle listen/pause

Build from Source

Requires Rust 1.70+ and standard Linux audio development headers.

# Development build
cargo build

# Bundle VST3/CLAP/standalone
cargo xtask bundle fretscope --release

# Run tests
cargo test --lib

Architecture

Audio Thread (real-time)          GUI Thread (egui)
┌──────────┐  ┌──────────┐      ┌─────────────────────┐
│ Plugin   │─>│ Pitch    │─────>│ Fretboard Canvas    │
│ process()│  │ Detector │ ring │ Key/Scale Panel     │
└──────────┘  └──────────┘ buf  │ Tuner               │
                    │           │ Note Log             │
                    v           └─────────────────────┘
              ┌──────────┐
              │ Key      │
              │ Detector │
              └──────────┘

• Audio thread: Real-time safe. Pitch detector accumulates samples internally across process blocks.
• Key detection: Pearson correlation of rolling pitch class histogram against Krumhansl-Kessler major/minor profiles.
• GUI: egui immediate-mode rendering with custom-painted fretboard. Dark pro-audio theme.

Dependencies

Crate	Purpose
nih-plug	VST3/CLAP plugin framework
nih-plug-egui	GUI via egui
pitch-detection	McLeod pitch detection algorithm
atomic_float	Lock-free float for tuner data

Vibe Coded

This entire project was vibe coded with Claude Code. Architecture, implementation, UI design, music theory engine, pitch detection pipeline — all of it. No hand-written code.

License

Distributed under the MIT License. See LICENSE.