A bit of a warning... Richard Furse's Ambisonic Decoding Equations page is a useful resource, but is a bit vague on how the different matrices should be used (or adapted).
Specifically, the coefficients listed as "Rig Decode Matrix to Reproduce Spherical Harmonics" (which have also been called "matching", "system", "basic", ....) should not be used above roughly 400Hz. (See BLaH3 for a discussion of this). Also, the "controlled opposites" matrices given are useful for large areas, but are not optimal for smaller setups, for listening by one or two people. These matrices minimize opposite polarity signals. Decode matrices that maximize the "energy localization vector" (rE_max) lie between these two. My understanding is that Richard's Blue Ripple uses rE_max decoders. Appropriate gain adjustments for 1 to 5th order are in Tables 1 and 2 in BLaH6. Formulas are in given in Appendix A. Some of the difficulties and tradeoffs in designing a first-order decoder for irregular layouts like ITU5.1 layout are discussed in BLaH4. The BLaH papers can be downloaded at http://www.ai.sri.com/ajh/ambisonics/ Also, as discussed in BLaH3, we've found that the quality of software ambisonic decoders varies widely. I urge thorough testing before using any of them for research work, and when writing up the work, please specify precisely how the decoding was done. -- Aaron (hel...@ai.sri.com) Menlo Park, CA US On Thu, Oct 4, 2012 at 11:20 AM, Michael Chapman <s...@mchapman.com> wrote: > Martin Leese wrote : >> The Ambi-5 Auditorium Decoder. I have a >> PDF of an Audio + Design leaflet which >> somebody sent me. If people want it I can >> place it on my Google Site for download. >> However, it just says: >> >> "The Ambi-5 produces five loudspeaker feeds >> arranged as a regular pentagon with > > See also > > "Pentagon [ . . . ] This rig configuration produces a strict idealised > response that satisfies the Ambisonic matching equations. Generally this > type of configuration produces a relatively small stable listening area. > (See controlled opposites below.)" > <http://www.muse.demon.co.uk/ref/speakers.html> ( Richard Furse) > > Michael > > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
