Ethereal Harmonizer 🎸✨

A high-fidelity, zero-latency, multi-scale guitar pitch tracker and interval harmonizer built for the Electro-Smith Daisy Seed.

Ethereal is designed to bring robust, artifact-free intelligent harmony to the Daisy Seed platform. By employing advanced signal processing techniques like Cortex-M7 floating-point denormal flushing and custom Schmitt-Triggering, Ethereal tracks your guitar's exact fundamental pitch and instantly synthesizes diatonic or pentatonic harmonies without the dreaded tracking glitches, zipper-noise, or subnormal CPU crashes common to embedded guitar DSP.

Features

• Intelligent Pitch Interval Tracking: Dynamically synthesizes intervals (3rds or 5ths) based on the current musical scale.
• 4-Octave Quantization: Intelligently locks synthesized harmonies to the closest in-key interval across a massive 4-octave range.
• True Analog-Style Dry Bypass: The pure instrument signal passes completely unaffected by the DSP gating when mixed.
• Smart Noise Gate Hysteresis: Decoupled VCA attack/release and Schmitt Triggering allows the harmony to tail off organically like an acoustic compressor.
• High-Frequency Transient Rejection: Ignores rapid pick-attacks to prevent the pitch detector from octave-jumping or choking.

Documentation

Comprehensive documentation on building, wiring, and understanding the DSP algorithms powering the pedal:

• Hardware Setup & Wiring Table: Complete pinout guide, breadboard wiring, and AC-coupling instructions for hooking up the Daisy Seed.
• Noise Mitigation & DSP Algorithms: An in-depth look into the custom DSP fixes, including the DC blockers, SVF envelope trackers, and FPU denormal logic.

Source Code

The primary DSP engine and audio routing logic for the Ethereal Harmonizer is located entirely within a single source file:

• src/harmonizer.cpp

Harmony Generation Logic

When the pedal detects a solid pitch and opens the noise gate, it simultaneously synthesizes a secondary harmony note to accompany the fundamental guitar tone. This harmony is not fixed; it intelligently adapts based on the user-selected musical Scale.

The generated interval is derived directly from the fundamental note's detected pitch before being mathematically forced (quantized) into the nearest legal scale degree.

• Major & Minor Scales (Diatonic): The pedal defaults to adding a Major 3rd (+4 semitones) on top of the original note. Because this new raw pitch is immediately forced through the quantization matrix, the 3rd will automatically flatten into a Minor 3rd when musically appropriate for the key.
• Pentatonic & Blues Scales: In these sparser scales, a 3rd is less desirable as it often clashes or resolves poorly. When the scale knob is set to Pentatonic or Blues (Scale type $\ge$ 3), the pedal switches to adding a Perfect 5th (+7 semitones) to create powerful, open sounding harmonies heavily used in rock.

Building & Flashing

Ethereal is built using the standard libDaisy toolchain.

# Compile the firmware
make

# Flash via USB DFU to the Daisy Seed
make program-dfu

License

This project is licensed under the MIT License - see the LICENSE file for details.

Author

• Robert Jones - rljonesiii

Citation

If you use this library in your research, please cite:

@misc{jones2026ethereal,
  author = {Jones, Robert},
  title = {Ethereal: A high-fidelity, zero-latency, multi-scale guitar pitch tracker and interval harmonizer},
  year = {2026},
  publisher = {GitHub},
  journal = {GitHub repository},
  howpublished = {\url{https://github.com/rljonesiii/ethereal}}
}