qa40x-rs Audio Analyzer

A desktop app for controlling and measuring with the QuantAsylum QA402 / QA403 audio analyzers — written in Rust.

More screenshots (sources, scripting, live spectrum) in doc/screenshots/.

This is a personal project. It is not meant to replace the official QuantAsylum application, which remains the reference in any case — please use it. The main goals here were:

• a native macOS app, simple to install and to use — and cross-platform where possible;
• learning about audio analysis and measurement along the way.

Feature-wise, the app currently sits somewhere between the official application v1 and the upcoming v2 expected in 2026.

Unofficial project. Not affiliated with, authorized, or endorsed by QuantAsylum. "QA402", "QA403" and "QuantAsylum" are trademarks of their respective owners. This is an implementation of the device protocol and measurement UI, named qa40x-rs to avoid any confusion with the official software.

Developed with AI assistance. This software was written almost entirely with the help of AI coding tools. It has been reviewed and tested as carefully as I could manage, but despite that effort some mistakes may well have slipped through — in the code, the measurements, or the documentation. Treat the numbers critically, cross-check anything that matters against the official application, and please report anything that looks wrong. The software comes with no warranty (see the license).

That cross-check is itself automated: an A/B loopback bench runs the same measurement battery against this app and the official one on the same QA402, with the same analysis window forced on both. All 24 compared metrics currently agree within tolerance under both flat-top and Hann (absolute level to 0.014 dB, every FR point to ≤ 0.001 dB, THD @ 100 Hz to 0.9 dB); methodology and baseline in doc/bench-ab.md.

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Features

• Live views — spectrum, oscilloscope and swept measurements in a configurable multi-tile grid; any trace can be frozen and kept as a reference for comparison.
• Scope trigger — Auto/Normal/Single edge trigger per input or output channel, with draggable level/position markers on the oscilloscope and sub-sample alignment; it only picks which slice the scope displays and never affects spectra or measurements.
• Measurements — THD, THD+N, SNR, RMS and peak levels (dBV), crest factor; input-attenuator status surfaced in the UI.
• Frequency response — swept (log-chirp) measurement with fractional-octave smoothing.
• Signal generation — backend-mixed multi-source generator: sine, square, multitone mixes, script-defined sources; output-only mode for driving external gear.
• Weighting — A/C curves, inverse RIAA for phono work, user-loadable custom curves.
• Workspaces — the whole session (layout, sources, traces, settings) can be saved and restored as named workspaces.
• Automation — a QA40x-compatible REST API (localhost by default, bearer-token protected when exposed to the network) and in-app scripting (Rhai) for measurement sequences. An A/B loopback bench diffs the whole measurement chain against the official app on the same hardware (see doc/bench-ab.md).
• Device panel — live telemetry (USB voltage/current, temperature), firmware version and serial at connect.
• Demo mode — a Demo button next to Connect attaches a built-in virtual QA403 (the virtual-qa40x-rs device model, embedded in-process): no hardware, nothing extra to download. The whole app runs on it — simulated DAC→ADC loopback with a realistic noise floor and mild harmonic distortion, a real factory calibration page, live telemetry, REST and scripting included. Sessions are badged DEMO so a demo screen can never pass for a measurement, and plugging a real unit in mid-demo hands the session over to it automatically.
• Firmware tools (advanced, opt-in — see the warning below) — extract official firmware from a QuantAsylum installer you already own, verify it against a known-hash registry and its cryptographic signature, and flash it.

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Install

No QA40x at hand? You can still try everything: click Demo (next to Connect) and the app attaches a built-in virtual QA403 — spectrum, THD, sweeps, generator, REST and scripting all work against a simulated, calibrated loopback. Nothing extra to download. The session is badged DEMO, and the moment you plug a real unit in, the app switches over to it automatically.

Prebuilt apps

Latest release (all platforms and older versions) on the Releases page. Direct downloads for the current version:

• macOS (Apple Silicon) — qa40x-rs Audio Analyzer_0.4.0_aarch64.dmg: drag the app onto Applications. Release builds are signed with a Developer ID and notarized by Apple, so they open with no Gatekeeper warning.
• macOS (Intel, legacy) — qa40x-rs Audio Analyzer_0.4.0_x86_64-legacy.dmg: same signed + notarized build for older Intel Macs. Provided for the shrinking Intel-Mac base and expected to be retired within a year or two.
• Linux — .deb / .rpm (both install the USB udev rule and reload udev automatically) or AppImage (needs the manual udev rule below).
• Windows — installer built per release.

Build from source

Prerequisites: Rust (stable) and Node.js 18+.

Platform system dependencies:

• macOS — none beyond Xcode command-line tools.
• Linux (Debian/Ubuntu)

  sudo apt-get update && sudo apt-get install -y \
    libwebkit2gtk-4.1-dev libappindicator3-dev librsvg2-dev \
    libgtk-3-dev libssl-dev libudev-dev patchelf

  USB access (udev rule) — the .deb / .rpm packages install /usr/lib/udev/rules.d/99-qa40x.rules and reload udev automatically. Only for the AppImage or a from-source build, create /etc/udev/rules.d/99-qa40x.rules yourself:

  SUBSYSTEM=="usb", ATTR{idVendor}=="16c0", ATTR{idProduct}=="4e37", MODE="0666"
  SUBSYSTEM=="usb", ATTR{idVendor}=="16c0", ATTR{idProduct}=="4e39", MODE="0666"
  # NXP bootloader (firmware flashing)
  SUBSYSTEM=="usb", ATTR{idVendor}=="1fc9", ATTR{idProduct}=="0022", MODE="0666"
  KERNEL=="hidraw*", ATTRS{idVendor}=="1fc9", ATTRS{idProduct}=="0022", MODE="0666"
  

  then sudo udevadm control --reload-rules && sudo udevadm trigger. Inside a VM (Parallels, UTM, VirtualBox…), also make sure USB auto-attach covers the NXP bootloader (1fc9:0022) — during flashing the analyzer re-enumerates as a different USB device, which some hypervisors do not reconnect to the guest automatically.
• Windows — Visual Studio C++ Build Tools.

Then:

npm install
npm run tauri dev      # run in development
npm run tauri build    # produce a release bundle in src-tauri/target/release/bundle/

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Firmware flashing — read this first

The firmware feature is advanced and optional. It:

• never bundles QuantAsylum firmware — you point it at an installer you legally obtained;
• verifies provenance (known-hash registry) and authenticity (RSA signature) before offering to flash;
• only enables the flash button for the model actually connected, and always asks for explicit confirmation — it is never triggered automatically.

⚠️ Flashing firmware can brick a device. Use at your own risk. The safest first test is re-flashing the same version your unit already runs. There is no warranty (see license).

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License

Licensed under either of

• MIT license (LICENSE-MIT), or
• Apache License, Version 2.0 (LICENSE-APACHE)

at your option. Unless you explicitly state otherwise, any contribution you submit shall be dual-licensed as above, without additional terms.

Third-party dependencies and their licenses: THIRD_PARTY.md.

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Related

• virtual-qa40x-rs — a virtual QA402/QA403 over USB/IP, built alongside this project to develop and test without hardware attached. Its transport-agnostic device model (vqa40x-core) is also embedded in this app as the Demo mode device. It may be useful to anyone else building around these devices.
• doc/device-notes.md — notes on the device's control protocol, timing, and measurement-level handling.

Acknowledgments & references

• QuantAsylum for the QA402/QA403 hardware and their public reference material: QA40x, PyQa40x, QA40x_BareMetal.
• The Tauri, Rust, and Rust-audio communities.