OpenAudioTools Ecosystem Notes¶

Working document cataloging the open-source ecosystem used across the OpenAudioTools project.

1. Hardware & Design Tools¶

KiCad (v9.0+)¶

What: Open-source EDA suite for schematic capture, PCB layout, and routing.
Where used: All PCB design — schematics, placement, routing, DRC, Gerber export.
Link: https://kicad.org

FreeRouting¶

What: Standalone autorouter using Specctra DSN/SES interchange format.
Where used: Complex multi-layer trace routing — export DSN from KiCad, autoroute in FreeRouting, import SES back.
Link: https://github.com/freerouting/freerouting

SKiDL¶

What: Python library for creating KiCad netlists programmatically.
Where used: Text-native netlist definition for each PCB board module before layout in KiCad.
Link: https://github.com/devbisme/skidl

KiCad MCP Servers (AI-assisted PCB workflow)¶

kicadmixelpixx/KiCAD-MCP-Server — Component placement, DRC validation, zone operations, Gerber export (52 tools). https://github.com/mixelpixx/KiCAD-MCP-Server
Seeed-Studio/kicad-mcp-server — Schematic analysis, netlist reading, pin tracing, design review. https://github.com/Seeed-Studio/kicad-mcp-server

kicad-cli & pcbnew Python API¶

What: KiCad command-line interface and Python scripting API.
Where used: DRC validation, Gerber/drill export, programmatic placement scripts, DSN/SES import-export.

2. Firmware Platform¶

Teensy 4.1 / Teensyduino / Arduino¶

What: ARM Cortex-M7 @ 600 MHz microcontroller (PJRC) with Arduino-compatible framework.
Where used: Main processor for all firmware — audio DSP, mixer control, SD recording, USB host, Ethernet, I2C codec control.
Link: https://www.pjrc.com/store/teensy41.html

DESPEE (ESP32-S3 Display Module)¶

What: Standard display module for all Open Audio Tools devices. Custom PCB with ESP32-S3-WROOM-1-N16R8 + bare 4.3" 800×480 LCD. Runs a device-agnostic LVGL display engine — no device-specific knowledge on the module itself.
Where used: Touchscreen UI across all devices. Teensy streams binary widget commands (COBS-encoded, CRC16) over UART. Touch events forwarded as coordinates.
Link: https://github.com/openaudiotools/despee

XMOS XU216-256-TQ128-C20¶

What: Multi-core xCore processor for real-time USB audio.
Where used: USB Audio Class 2 bridge on the Main Board — 24-in/8-out UAC2 + USB MIDI composite device.
Link: https://www.xmos.com

3. Audio Libraries¶

PJRC Audio Library¶

What: Block-based audio DSP framework for Teensy (128 samples @ 48 kHz = 2.67 ms latency).
Where used: Core audio processing — AudioInputTDM, AudioOutputTDM, AudioMixer4, and custom objects. Multi-data-line TDM receive requires SAI_RCR3 register modification.
Link: https://www.pjrc.com/teensy/td_libs_Audio.html

XMOS sw_usb_audio¶

What: Open-source USB Audio Class 2 reference firmware for XMOS processors.
Where used: XU216 firmware providing 24-in/8-out multichannel audio + MIDI forwarding. Includes Thesycon ASIO driver for Windows.
Link: https://github.com/xmos/sw_usb_audio

alex6679/teensy-4-usbAudio¶

What: Community UAC2 implementation for Teensy 4.x.
Where used: Legacy/fallback alternative to the XMOS bridge for cost-reduced builds. Up to 8 channels on macOS/Linux; Windows limited without a commercial driver.
Link: https://github.com/alex6679/teensy-4-usbAudio

4. UI & Input Libraries¶

LVGL (Light and Versatile Graphics Library)¶

What: Embedded graphics library with widget toolkit and touch support.
Where used: Display rendering on the DESPEE display module (ESP32-S3) — meters, channel strips, navigation.
Link: https://lvgl.io

Adafruit NeoPixel / FastLED¶

What: Libraries for driving WS2812B addressable RGB LEDs.
Where used: 16× NeoPixel LEDs (one per key switch), daisy-chained on a single data pin. Firmware defaults to 30 % brightness cap for noise/power mitigation.
Links: https://github.com/adafruit/Adafruit_NeoPixel · https://github.com/FastLED/FastLED

PJRC Encoder¶

What: Quadrature decoding library for rotary encoders.
Where used: 3× rotary encoders (NavX, NavY, Edit).
Link: https://www.pjrc.com/teensy/td_libs_Encoder.html

PJRC Bounce¶

What: Debouncing library for mechanical switches.
Where used: 16× CHOC key switches and other button inputs.
Link: https://www.pjrc.com/teensy/td_libs_Bounce.html

5. Connectivity Libraries¶

QNEthernet¶

What: TCP/IP stack for the Teensy 4.1 built-in Ethernet PHY (DP83825I).
Where used: Network audio streaming (RTP/AES67), mDNS/DNS-SD service discovery, PTP clock synchronization.
Link: https://github.com/ssilverman/QNEthernet

USBHost_t36¶

What: USB host library for Teensy.
Where used: MIDI controller connectivity via 2× USB-A host ports (through FE1.1s USB hub IC).
Link: https://github.com/PaulStoffregen/USBHost_t36

SdFat (Bill Greiman)¶

What: SD card file I/O library with SDIO DMA support.
Where used: 16-track interleaved WAV recording to SD card. Uses createContiguous() for pre-allocation to eliminate filesystem fragmentation. RF64 for files > 4 GB.
Link: https://github.com/greiman/SdFat

6. Standards & Protocols¶

USB Audio Class 2 (UAC2)¶

What: Standard USB device class for multichannel, high-resolution audio.
Where used: XMOS XU216 provides 24-in/8-out, 24-bit, 48 kHz, class-compliant audio. Native on macOS (Core Audio) and Linux (snd-usb-audio); Thesycon ASIO driver on Windows.

USB Power Delivery (USB PD)¶

What: USB PD 2.0/3.0 power negotiation standard.
Where used: STUSB4500 breakout module on the power USB-C port. Configured for 5 V @ 5 A; falls back to 5 V @ 3 A via 5.1 kΩ CC resistors when PD is unavailable.

TDM / I2S¶

What: Serial audio bus protocols (Time Division Multiplexing / Inter-IC Sound).
Where used: 2× SAI buses on Teensy 4.1 (SAI1 = TDM1, SAI2 = TDM2). 24.576 MHz BCLK, 48 kHz LRCLK, 24-bit, 16 slots per bus. Each bus connects 2× AK4619VN codecs via dual data lines (RX_DATA0 + RX_DATA1).

AES67 / RTP¶

What: Professional audio-over-IP standard; RTP carries audio payload over UDP.
Where used: Network audio streaming — 48 kHz 24-bit PCM, 1 ms packet time (48 samples). RTP timestamps derived from PTP clock.

PTP (IEEE 1588v2)¶

What: Precision Time Protocol for clock synchronization across a network.
Where used: Software-based implementation on Teensy's GPT timer (1 MHz). One mixer acts as PTP grandmaster; others as slaves. Accuracy: ~10–100 µs (sufficient for studio use with 1 ms packet times). Hardware PTP would require DP83640 PHY.

mDNS / DNS-SD¶

What: Zero-configuration networking for device discovery and service advertisement.
Where used: Advertises audio and MIDI services (_jfa-audio._udp.local, _jfa-midi2._udp.local). Hostname format: device-type-XXXX.local. TXT records carry role, direction, channel count, sample rate, format, packet time, stream ID.

MIDI 2.0 / UMP¶

What: Universal MIDI Packet protocol (successor to MIDI 1.0).
Where used: USB MIDI via XMOS composite device (forwarded to/from Teensy via SPI0). Physical 3.5 mm TRS Type A jacks for MIDI IN (optoisolated) and MIDI OUT (31.25 kbaud current-loop). Network MIDI 2.0 over UDP planned for future versions.

TRS Type A MIDI¶

What: Standard 3.5 mm TRS wiring convention for MIDI (tip = current source/sink, ring = current return, sleeve = shield).
Where used: MIDI IN and MIDI OUT jacks on the IO Board.

BWF / RF64¶

What: Broadcast Wave Format extension allowing WAV files > 4 GB.
Where used: SD card recording — SdFat handles RF64 transparently. iXML or cue chunks carry channel naming for DAW import.

7. Licenses¶

Scope	License	Notes
Firmware	MIT	Teensy/Arduino source code
Hardware	CERN-OHL-P v2	PCB designs and schematics; permissive variant allows commercial use without reciprocal disclosure. License text required on PCB silkscreen.
Documentation	CC BY 4.0	All markdown, diagrams, and specifications. Attribution to Juliusz Fedyk / openaudiotools required.

Last updated: 2026-03-08