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.

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.

developers and contributors

  • alexis baskind (sound engineer, main developer)
  • jean-christophe messonnier (sound engineer)
  • jean-marc lyzwa (sound engineer)
  • matthieu aussal, cmap – ecole polytechnique / cnrs (calibration routines)