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Binaural panning and HRTF

December 28, 2004

One day of browsing/searching for theory on binaural spatialisation and ambisonics and technical ways of doing it mainly on the Mac OS X platform.

  • Tom Erbe has made Spectral Shapers a set of 4 real-time plugins from of some of the Soundhack functionalities. One of them is binaural a binaural panner. There’s a very positive review of the plugins at OS X Audio. An important limitation of binaural is that it is not able to work on vertical movements only 0 degree elevation at a 44100 sample rate. According to the manual future versions of binaural will contain multiple elevations and sample rates. binaural allow you to
    select between two binaural filter sets. filter one is
    derived from Bill Gardner and Keith Martin’s measurements
    of the KEMAR dummy head microphone at the MIT Media Lab. The diffuse- field equalized HRTFs are used in this plugin. Filter two is the original SoundHack binaural filter developed by Dr. Durand Begault.
  • Aristotel Digenis has made a number of plug-ins for ambisonic decoding. Most of them are Audio Unit plugins which make them impossible to use at current in MaxMSP. The VST version of the Binaural decoding is Windows XP only. Anyway these plug-ins are for decoding of ambisonic recordings and as such not relevant for what I’m going to work at right now. I’d like to get back to them later on though.
  • Along a similar line SoundField has released Surround Zone plug-in for Nuendo.
  • WaveSurround is a Mac/PC VST/MAS/AU/RTAS/DirectX plugin by Wave Arts using HRTF binaural processing.
  • SpinAudio has a number of products (mainly for Windows) using HRTF.
  • also offers a range of VST plug-ins (Mac and Win) for ambisonics. Some of them are freeware. bPanX is a port to OSX of Dave Malhams open source bPan plug-in. The sources for Malhams plug-ins are available as GNU Open Source here. Malham has also written an introduction to spatial hearing mechanisms and sound reproduction including basic equations for ambisonic encoding and decoding.
  • Speaking of Malham The Music Technology Group at The University of York has a home page for Ambisonics and related 3-D audio research.
  • spat part of the Ircam forum real-time composition group is an obvious candidate to check out. This seems to be the only native Max solution available at the moment. Spat binaural panning is based on the MIT KEMAR measurments.
  • Another possibility would be to use the csound~ object to access the Csound hrtfer opcode. Chapter 25 of the Csound book seems to cover auditory localization in depth and give an example of the use of the hrtfer opcode.
  • According to these posts on the Music-DSP mailing list phase offsets are more important than amplitude differences for determining spatial localisation and hence all-pass-filters can be used quite effectively instead of FIR filters.
  • Angelo Farino has done a lot of work on acoustics in closed space. Ramsete is a computer program (Windows only) for the simulation of the acoustics of closed spaces which can be used also outdoors. Aurora is a software tool (Windows freeware) for measuring filtering and convolving the Impulse Responses of theatres and other spaces. A large waveform collection is supplied to Aurora users including anechoic samples of music and speech experimental binaural impulse responses of more than 20 theatres and concert halls some B-format 4-channels impulse responses the complete set of binaural Head Related Transfer Functions of the Kemar dummy head as measured at MIT Medialab the HRTFs in the horizontal plane of the Sennheiser MKE2002set dummy head the HRTFs in the horizontal plane of the Bruel &amp Kjaer types 4100 and 4128 the HRTFs in the horizontal plane of the Ambassador dummy head and the HRTFs at various elevations of the Bruel &amp Kjaer type 4100D.

That’s it for now. Enough to start digging into…