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Acoustic Drone Detection

CI License: AGPL v3 Rust 2021 no_std core edge: esp32 / riscv32

A Rust DSP and machine-learning toolbox for detecting drones from sound. A shared no_std signal-processing backbone feeds many task heads - detection, direction-of-arrival, type and vendor ID, blade-pass / RPM, range, and source separation - each benchmarked head-to-head on real data and ready to lower onto esp32-class edge hardware. Built with an emphasis on honest evaluation: leakage-proof, cross-dataset, and hard-negative tests over the optimistic in-distribution numbers most of the field reports.

Acoustic drone detection - signal chain & physics

The full signal chain, with this project's real parameters: rotor acoustics → pressure wave → sampling (Nyquist) → ADC quantization → STFT blade-pass comb → detection pipeline → hardware tiers. Regenerate with docker compose run --rm --entrypoint python plot scripts/infographic.py (scripts/infographic.py).

State of the project: detection works. We benchmarked a range of detection algorithms and models across hardware tiers and bundled everything into an extensible Rust crate toolbox, driven from a CLI and lowerable onto esp32-S3 or other edge hardware. Heads for drone situational attributes (distance, elevation, speed) and hardware attributes (type, vendor, rotor_count, drone_health, drone_weight) are wired in and ready to be performance-tuned and extended.

Notable mention worth checking out: batear-io/batear for simple drone detection on esp32-S3+mic.

TOC

  1. Scope
  2. On Audio and Sound (human reasoning)
  3. Problem Layers (human reasoning)
  4. Possible Approaches (human reasoning)
  5. Constraints of v0.1.0 (human reasoning)
  6. Implementation
  7. Contributing
  8. License

1. Scope

Design an acoustic drone detection pipeline, and validate the ideas in simulation. The questions this project answers:

  • Detection. What makes a drone signature distinguishable from background sound? What features or representations would you feed a model, and how would you know it's actually working?
  • Direction of Arrival. If you used multiple microphones, how would you estimate where the drone is? What does array geometry buy you, and what are the trade-offs?
  • Robustness. Real deployments are noisy - literally. Wind, rain, overlapping sources, varying drone types. How would you stress-test your approach? This is where simulation earns its keep: you control what you throw at it.
  • System Design. What would a real deployment look like? How many microphones, in what configuration, at what sample rate? What detection range would you expect and why? What are the fundamental physical limits?

2. On Audio and Sound (Human reasoning)

Sound is the pressure of a material (mostly air) fluctuating over time. Sound travels at 355 m/s in air at 40 degrees Celsius and 343 m/s in air at 20 degrees Celsius, so environmental conditions are relevant to detection.

Microphones come in different types, based on the physical quantity that changes with pressure:

  • magnetic (dynamic) microphones measure the vibration of air as it moves the microphone head up and down; they are omnidirectional
  • laser microphones measure the vibration (pressure) of an object the laser points at, interferometrically; they are unidirectional
  • other types exist: the gyroscopes in phones can sample audio at a low rate, and smart materials like piezo crystals turn pressure on a surface into electrical impulses

Sample frequency is how many times per second a microphone measures this pressure at one point.

  • old phones like a Nokia sampled around 8k measurements per second
  • a common rate today is 44.1 kHz, which most microphones and hardware support
  • higher rates exist for studio or specialised equipment

Audio is how the sound is stored by digital devices:

  • an ADC (Analog-Digital-Converter) converts electrical pulses from a microphone to a binary signal / value
  • the resolution of this conversion depends on the ADC: older ones gave 8 bit, newer ones 24 bit, 32 bit, or better
  • audio is usually stored compressed, since a raw .wav file (a pickled array of samples) takes a lot of storage
  • audio compression is lossy: humans do not need the whole spectrum to, for example, recognize a voice. Many codecs exist (e.g. those implemented in the ffmpeg project); modern ones include .mp3, .m4a, and .opus (used by WhatsApp). These differences matter for data quality: a lossy codec can erase the cues needed to predict finer properties of a drone or the situation.

3. Problem Layers (Human reasoning)

Acoustic drone detection is not one algorithm; it is a stack of engineering problems, each constraining the ones around it. Detection, localization, tracking, and type-ID are not separate layers - they are different outputs of one inference layer asked of the same signal.

  1. Requirements & metrics - defines what "good" means: required outputs, detection range, environments, threat model, and the error-cost asymmetry. A missed drone usually costs more than a false alarm, so detection leans toward recall - but the operational metric is false-alarms-per-hour at a required recall, not raw false-positive rate (drones are rare, so base rate makes a flat FPR misleading).
  2. Sensors - mic technology (MEMS, condenser, piezoelectric, fiber-optic), count, geometry, directionality, frequency/dynamic range, weatherproofing. Sets what is physically observable.
  3. Signal acquisition (front-end) - what the hardware already did to the signal before you see it: ADC characteristics, automatic gain control, on-device denoise, beamforming, codec, sample rate / bit depth. Commercial mics and phones alter the signal in ways that can erase drone cues.
  4. Compute - where inference runs (MCU, edge node, server, cloud), with its latency, power, and memory budgets. Directly limits algorithm complexity.
  5. Data - datasets and their diversity (drones, distances, weather, terrain), labeling, augmentation, synthetic data, and field/continual collection. Usually the dominant uncertainty; cross-environment generalization is the hard part.
  6. Signal processing / representation - denoise, framing/windowing, and the representation itself: FFT/STFT, mel, MFCC, cepstral, harmonic features. Blind source separation (ICA/IVA) lives here when several drones or strong interferers must be separated.
  7. Inference - one chain, several outputs: detection, type, direction-of- arrival, tracking, RPM / distance / health. The design choice is which outputs are realistically achievable from the available signal.
  8. System architecture - beyond a single node: multi-node ("swarm") cooperation and synchronization, plus cross-modal fusion (RF, radar, EO/IR, lidar). Acoustic often serves as the cheap, non-line-of-sight gate that cues heavier sensors.
  9. Validation & robustness - performance vs SNR, weather, unseen drones, and hard negatives; the dominant failure modes; and honest cross-dataset evaluation.
  10. Deployment & operations - power, enclosure, networking/outages, monitoring, and lifecycle (drift detection, field-data pipeline, retraining), plus security (evasion, spoofing, jamming, decoys) and cost/scalability per node.

This repo currently lives mostly in layers 6-9 (signal processing through validation), with drone-edge / drone-live reaching into 3-4 (acquisition and edge compute). Real sensor front-ends and full deployment/operations are the open ends.

4. Possible Approaches (Human reasoning)

There is no single "drone-detection algorithm". We benchmark several methods against the same data and compare accuracy, robustness, compute, and deployability - the goal is the simplest approach that stays reliable under realistic conditions, not the most complex model.

  • Detection from frequency structure - propellers produce harmonic peaks. audio -> FFT/STFT -> representation -> detector. Detectors range from band energy, harmonic-product-spectrum, cepstrum, and spectrogram templates to MFCC + classifier (logistic / random forest / SVM), CNNs on spectrograms, and audio foundation models (e.g. YAMNet). Open question: do cheap DSP methods suffice before reaching for ML? (drone-bench benchmarks 12 such approaches.)
  • Detection from periodicity - rotor rotation makes drone audio strongly periodic, so autocorrelation, cepstrum, amplitude-modulation, and blade-pass estimation can detect even when individual frequency peaks are buried in noise. (drone-freq, envelope_periodicity.)
  • Drone attribute estimation - beyond yes/no: type, rotor_count, rpm, direction, elevation_angle, distance, speed, motor_health, rotor_damage. Some are correlated and estimable jointly; distance-range classification is shown feasible in the literature. (drone-id, drone-freq.)
  • Direction of arrival & localization - multiple synchronized mics enable TDOA (GCC-PHAT), beamforming, and super-resolution (MUSIC / ESPRIT) plus triangulation. Questions: mic count, spacing (d < c / 2*f_max to avoid spatial aliasing), achievable angular accuracy, and degradation with noise. (drone-doa, simulated; real-world DoA is ~6-42 deg, not sub-degree.)
  • Robustness - wind, rain, traffic, construction, aircraft, birds, multiple drones, unseen models. drone + background + synthetic noise = test scenario, scored as a function of SNR. The real confusers are other rotary/harmonic machines (chainsaw, engine, helicopter). (drone-bench --snr, xeval, plus a hard-negative suite.) Software noise-cancellation can help where the noise is periodic or white (subtract the predictable part, "rausrechnen"); and it is worth talking to people who detect unique events in noisy real-time data (e.g. hydrop-systems, kinemic).
  • Sensor design - single mic (cheap, detection only) vs array (direction, beamforming, better SNR) vs directional / fiber-optic / laser mics (higher SNR, smaller search space). Mixed setups are future work.
  • Hardware exploration - ESP32-S3 / -P4, Arduino / AVR8-class, embedded Linux, Jetson, and FPGA (we have one, ~45k LUTs). Map the accuracy / latency / power / cost tradeoff, and the field enclosure (weatherproofing, and depending on the threat, EMP/laser hardening). (drone-edge is a no_std cross-build proof.)
  • Data strategy - public sets (DADS, Al-Emadi, Kaggle, HuggingFace; e.g. saraalemadi/DroneAudioDataset and the Drone Sound Detection set), self-recorded flights, and augmentation (added noise, SNR levels, codec degradation, sample-rate reduction, reverberation). The key uncertainty is how well a model trained on one dataset transfers to entirely different environments and drones.
  • Multi-sensor fusion - acoustic + RF + radar + EO/IR + thermal. Acoustic is the low-power, non-line-of-sight modality that cues the others (fielded by Fraunhofer IDMT; RF-assisted variants by Toma et al.).
  • Validation - the same metrics for every approach: precision, recall, F1, ROC-AUC, PR-AUC, false-alarm rate (detection); angular and position error (localization); latency, power, memory, range (deployment).

5. Constraints of this projects first iteration (v0.1.0)

  • Only one real drone available for testing.
  • Limited hardware: esp32-S3, -C6, and -P4 modules, plus a few Arduino boards (notably the 4 GB-RAM one).
  • Hardly any specialised microphones on hand (one camera mic, otherwise phone and laptop mics).
  • Limited AI budget of 50 EUR (the Claude weekly limit).
  • Limited dev time: a single afternoon for v0.1.0.

6. Implementation (v0.1.0)

Built in Rust for fast, typed iteration on real DSP - and so the core can later be lowered onto edge hardware (esp32 xtensa / riscv). It's structured as a multi-task suite (insightface-style: one shared DSP backbone + a common eval harness + many task "heads"). Crates live under crates/ (no workspace yet, by design):

  • drone-dsp - no_std DSP backbone reused by every head: Hann windowing, real FFT (microfft), magnitude spectrum, spectral features. Math via libm, so it builds bare-metal.
  • drone-detect - no_std heuristic detector (energy-in-band + dominant tone). The transparent baseline.
  • drone-cli - host binary drone: synth a test signal, analyze WAVs.
  • drone-bench - shared eval harness: pluggable Approach trait, dataset loader (CSV/synth, stratified split, k-fold, SNR augmentation), metrics (F1, calibrated-F1, ROC-AUC, PR-AUC, Brier, real-time factor), JSON output. Hosts 12 detection approaches.
  • drone-doa - direction-of-arrival: GCC-PHAT TDOA + ULA geometry → azimuth, with a propagation simulator and an angular-error benchmark (no_std core).
  • drone-id - multiclass drone-type recognition (MFCC + multinomial logistic) with per-class F1 + confusion matrix.
  • drone-freq - blade-pass-frequency / RPM estimation (HPS + cepstrum + autocorrelation fusion) - an inferrable drone property.

Capabilities at a glance (real-data results)

task crate headline result notes
Detection (drone vs not) drone-bench best F1 1.000 / ROC-AUC 1.000 (feature_fusion); 8/12 beat CNN baselines all run 90-2400× real-time
Direction of arrival drone-doa RMSE 0.88° @20 dB (±60°), 2.8° @10 dB 4-mic ULA, simulated
Type ID (bebop/membo/unknown) drone-id macro-F1 0.86 on Al-Emadi multiclass linear softmax; honest
Blade-pass freq / RPM drone-freq synth f0 MAE ~1 Hz, 0% octave error real DADS drones cluster ~230 Hz
Robustness drone-bench --snr learned methods hold ROC-AUC >0.95 to −10 dB; naive baselines collapse see benchmarks/plots/robustness_*.png

Detection approaches & benchmark

Twelve approaches are implemented and benchmarked head-to-head (each emits a confidence in [0,1], so they're comparable via ROC/PR). On a real DADS subset (300 + 300 clips, 50/50 split); F1* = best-threshold (calibrated) F1, ×RT = times faster than real time:

approach F1 F1* ROC-AUC ×RT
feature_fusion - fused MFCC+spectral+harmonic+cepstral + logistic 1.000 1.000 1.000 1300×
mfcc_lr - MFCC + logistic regression 0.997 0.997 1.000 2300×
fusion - logistic stack (ensemble) over the classics 0.997 1.000 1.000 90×
mfcc_mlp - MFCC + small MLP 0.987 0.993 1.000 2400×
gtcc_lr - gammatone cepstral coeffs + logistic 0.987 0.990 1.000 1900×
spectral_gate - flatness/entropy/band-ratio + logistic 0.977 0.986 0.998 1900×
cepstrum - cepstral / autocorrelation periodicity 0.967 0.977 0.990 110×
envelope_periodicity - AM modulation spectrum 0.966 0.987 0.991 95×
hps - harmonic-product-spectrum / comb 0.949 0.967 0.987 2150×
spectrogram_template - 2D spectro-temporal template 0.925 0.974 0.980 2300×
band_ratio - baseline heuristic 0.766 0.921 0.915 2450×
template - cosine vs. averaged drone spectrum 0.706 0.986 0.995 2370×

Cheap classical/light methods score very high here - no GPU, all real-time on a desktop. ⚠ Honesty caveat: these are in-distribution numbers on a random clip-level split of one dataset (DADS), which very likely has recording-level leakage (short clips from shared source recordings landing in both train and test), so they are optimistic and not an apples-to-apples win over published CNN baselines. The trustworthy tests - cross-dataset and hard-negative (aircraft / car / wind) evaluation - are the current priority; see agent-memory/notes/honest-limitations.md. Plots (ROC, PR, cost-vs-quality, robustness) live in benchmarks/plots/; methodology in benchmarks/README.md.

Benchmark plots

ROC curves for all approaches
ROC · in-distribution, all 12 approaches (labelled with ROC-AUC)		 ROC-AUC vs SNR
Robustness · ROC-AUC vs SNR; learned methods hold above 0.95 to -10 dB
Inference cost vs F1
Cost vs quality · inference ms/clip (log x) vs F1		 Sample-rate and bit-depth sweep
Rate / bit-depth · detection flat from 8 kHz up, robust to 4-bit

Regenerate any of these with docker compose run --rm plot (see benchmarks/README.md); the physics + signal-chain poster above is scripts/infographic.py.

Quick start (Docker-first)

# Generate a synthetic drone signal and analyze it (writes into ./data)
docker compose run --rm detector synth   --out /data/test.wav --fundamental 120
docker compose run --rm detector analyze --input /data/test.wav

# Fetch a real dataset subset, benchmark all 12 detectors, and plot
docker compose run --rm data --per-class 300
docker compose run --rm bench --data /work/data/dads      # add --kfold 5 or --snr 0
docker compose run --rm plot

# Other task heads (run inside the dev toolchain container)
docker compose run --rm --entrypoint bash dev -c \
  "cargo run -r --manifest-path crates/drone-doa/Cargo.toml --bin doa-bench"   # direction of arrival
docker compose run --rm --entrypoint bash dev -c \
  "cargo run -r --manifest-path crates/drone-id/Cargo.toml -- --synth"          # drone-type ID
docker compose run --rm --entrypoint bash dev -c \
  "cargo run -r --manifest-path crates/drone-freq/Cargo.toml -- --data /work/data/dads"  # blade-pass freq

# Run the full check suite: folderinfo lint, fmt, clippy -D warnings, tests, no_std builds
docker compose run --rm dev

On Git Bash (Windows) prefix docker commands with MSYS_NO_PATHCONV=1, or use PowerShell - otherwise /data/... args get rewritten. See CLAUDE.md.

Agent working memory - decisions, insights, domain notes, and session handoffs - is tracked in agent-memory/.

7. Contributing

Contributions are welcome. The workflow is:

fork -> branch [name]/feat|fix-[short-name] -> PR -> address feedback -> merge

Everything builds and tests in Docker (no host Rust toolchain needed); run the full correctness oracle with docker compose run --rm dev before opening a PR. See CONTRIBUTING.md for setup, conventions (no em-dashes, no_std-clean core, a .folderinfo per directory), and how the check suite runs in CI.

8. License

This project is licensed under the GNU Affero General Public License v3.0 (AGPL-3.0-or-later) - strong copyleft with a network-use clause, so anyone who runs a modified version, including over a network, must share their source.

Acoustic Drone Detection
Copyright (C) 2026 Julia Yukovich

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Affero General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version. See the LICENSE file for the full text.

Datasets retain their original upstream licenses and are not redistributed here; see DATA_SOURCES.md. If you use this work, citation metadata is in CITATION.cff.