What is hedrot?
Hedrot (for "head rotation tracker") is a low-cost (around 25 euros with a teensy LC) 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.
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 a 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) relies between 25 and 45 ms.
How to use hedrot?
Hedrot can be used with any renderer or plugin that accepts OSC input for the rotation information (either yaw/pitch/roll or quaternion).
The free binaural VST plugin Mybino, developed by the Ecole Polytechnique's Center for Applied Mathematics (CMAP), is strongly recommended (for Mac and PC). It offers an efficient and precise binaural rendering and works perfectly with hedrot. The user manual from hedrot explains how to connect it to mybino, and a corresponding preset is provided.
hedrot has been also succesfully tested with:
- the free Ambix plugin suite from Matthias Kronlachner for High-Order Ambisonics
- the Spat library for Max> from IRCAM (an example patch is provided with the distribution of hedrot)
Current version: 1.2.2 Download hedrot distribution
Previous versionsSee here to access all versions of hedrot
The next developments and research include among others: Further Developments
- Measurements of the overall (software+hardware) latency
- A 3D-printable enclosure
- Calibration enhancements
Licensing and Credits
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/).
Hedrot is licensed under the terms of the GNU General Public License (version 3) as published by the Free Software Foundation.
Matthieu Aussal (CMAP - Ecole Polytechnique / CNRS) contributed to new calibration routines (version > 1.2)
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/)
Developers and Contributors
- Alexis Baskind (sound engineer, main developer) (webpage: http://www.alexisbaskind.net)
- Jean-Christophe Messonnier (sound engineer)
- Jean-Marc Lyzwa (sound engineer)
- Matthieu Aussal, CMAP - Ecole Polytechnique / CNRS (calibration routines)
Head tracker parts: Hardware Requirements
- 1 Teensy 3 board (tested with versions 3.1, 3.2 and LC), can be found for example by the following vendors:
- 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: 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 8.2 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 1.8.3
- Teensyduino 1.37 (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
- Windows: a distribution of BLAS, Lapack and LAPACKE. See README-BUILD.txt for more information about how to build it