Hedrot (for "head rotation tracker") is a low-cost (less than 40 euros) and efficient open-source hardware/software solution for head tracking. Hedrot is especially suitable for binaural rendering (3D-Audio on headphones), and has been initially designed for use with the binaural renderer Bipan as part of the Bili Project http://www.bili-project.org/.

Hedrot provides an estimation of the rotation of the sensor (thus of the head if the sensor is attached to headphones) for the most usual x-y-z coordinate systems, either as a quaternion, or as a set of 3 orientation angles yaw, pitch and roll with two different orders (yaw-pitch-roll or roll-pitch-yaw). The main application provided with the distribution, hedrotReceiver, sends this information as OSC streams, with the extra possibility to scale each stream independently.

Contrary to several generic open-source head tracking solutions, hedrot relies on and has been optimized for specific widely spread and efficient hardware parts, i.e. a Teensy 3 board (optimized Arduino-like board) combined to a IMU/MARG daughter board with 3 common sensors (Analog Devices ADXL345 accelerometer, Honeywell HMC5883L magnetometer and Invensense ITG-3200 gyroscope).

The estimation algorithm is based on a modified version of the precise and efficient open-source gradient descent algorithm from Sebastian Madgwick. The technology was dramatically optimized for speed: the head tracker can deliver data at rates up to 2 kHz. The hardware latency of the Teensy board and USB communication relies below 2 ms. The overall latency (including sensor latency and time constant of the algorithm) is being currently measured.

The first development phase of Hedrot has achieved in collaboration with the Conservatoire National Supérieur de Musique et de Danse de Paris (http://www.conservatoiredeparis.fr/) as part of the "Bili" project (http://www.bili-project.org/).

Matthieu Aussal (CMAP - Ecole Polytechnique / CNRS) contributed to new calibration routines (version > 1.2)

Hedrot is licensed under the terms of the GNU General Public License (version 3) as published by the Free Software Foundation.

Part of code is derived from Sebastian Madgwick's open-source gradient descent angle estimation algorithm (http://x-io.co.uk/open-source-imu-and-ahrs-algorithms/)

• Alexis Baskind (sound engineer, main developer)
• Jean-Christophe Messonnier (sound engineer)
• Jean-Marc Lyzwa (sound engineer)
• Matthieu Aussal, CMAP - Ecole Polytechnique / CNRS (calibration routines)

• Head tracker parts:
  • 1 Teensy 3 board (tested with versions 3.1 and 3.2)
  • 1 USB to Micro-USB 2.0 cable, minimum length 1.5 m
  • 1 gy85 IMU daughter board with the following sensors:
    • 1 Analog Devices ADXL345 accelerometer
    • 1 Honeywell HMC5883L compass (magnetometer)
    • 1 Invensense ITG3200 gyroscope

• Mac OS 10.9.5 or later
• Windows: Windows 7 or later
• the teensy.app firmware flash loader
• Windows: Microsoft Visual C++ 2012 Redistributable package (x86 or x64 version, depending on if a 32 or 64 bit version of the hedrot is being used)
• Windows: Teensy serial driver (called "Windows Serial Installer" on https://www.pjrc.com)

• Xcode version 6.2 or later (for Mac), or Visual Studio 2012 (for Windows)
• Windows: a windows version of awk (like gawk) and the program 7-zip to make the package
• Max version 6 at least
• Arduino IDE 1.8.1
• Teensyduino 1.35 (teensy support for the Arduino IDE and the teensy USB serial driver on Windows), with at least the i2c_t3 library. Note: Teensyduino already includes the Teensy serial driver on Windows

• the empty folder "build" is where the distribution will be built
• the folder "command-line-demo" contains the sources of the command-line demonstration
• the folder "doc" contains the documentation
• the folder "examples" contains application examples
• the folder "firmware" contains the sources of the firmware to be uploaded in the teensy board
• the folder "libhedrot" contains the sources of the receiver library
• the folder "matlab" contains programs for matlab and octave
• the folder "Max" contains the sources of the main receiver application, written in Max
• the folder "scripts" contains the scripts for building binaries and the distribution