Hi there! I keep meaning to take that ancient decoding equation page down, but never quite seem to get around to it! The old code could cope with some rigs (well, for a rather basic decode) but really struggled with others; for instance, doing a matching solve for second order on an irregular five speaker layout just isn't clever. At least it more-or-less knew when it hadn't done a good job, hence the warnings on some of the decoders. Stay well clear of those!
I put some "reference" decoders at http://www.blueripplesound.com/decoding a while ago in anticipation of taking down the old site, some of which some of you will recognise. These are all single-band optimised, and mostly "in-phase" - not beautiful, but simple, and intuitive for new users. Rapture3D doesn't use these reference decoders; Blue Ripple Sound decoders are generally single-band at low order but become quite frequency-dependent as the order is increased, particularly if the decoder knows the speaker distances. The decoder generator also handles irregular rigs *much* more gracefully than the old stuff... Best wishes, --Richard -----Original Message----- From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On Behalf Of Aaron Heller Sent: 05 October 2012 19:03 To: s...@mchapman.com; Surround Sound discussion group Subject: Re: [Sursound] Hybrid Hi-Fi (HyFi?), IRs, etc. 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 _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
