Stephan, hi The main mechanisms for disambiguating 'cones of confusion' (and this includes front-back reversals) are: pinnae effects (Batteau) and head-movements (Wallach) - so, without either of these mechanisms at play, one would expect directional ambiguity.
In respect of elevation cues - well, I've heard many, very expert listeners, swear that in some stereo recordings, listened to over speakers, they can hear 'height'. This could simply be a speaker artefact at Hf, but it could also be that elevation actually means 'up' - elevated sources have different relationships with items in the environment and ground effect (I loosely call this phenomenon ambience labelling) - so some elevation cues might not simply be pinnae effects. Cheers ppl Dr. Peter Lennox Senior Lecturer in Perception College of Arts University of Derby, UK e: p.len...@derby.ac.uk t: 01332 593155 https://derby.academia.edu/peterlennox https://www.researchgate.net/profile/Peter_Lennox -----Original Message----- From: Sursound [mailto:sursound-boun...@music.vt.edu] On Behalf Of Stefan Schreiber Sent: 13 June 2016 02:03 To: Surround Sound discussion group <sursound@music.vt.edu> Subject: Re: [Sursound] Using Ambisonic for a live streaming VR project Hi Archontis, sorry for the relatively late response. I was travelling and had some problems to post anything on sursound during my trip. (I finally know what went wrong...) Anyway, many thanks for the (as always) clear and well-informed answer you gave to my posting. It is quite remarkable that some "pinnae-less" (but multi-perspective) binaural format seems to work well for HT VR applications. This is just another proof that some perceptual cues can be omitted (here: pinnae cues) if other cues (ILD, ITD) are more or less intact. However, there seem to be a couple of limitations of the (propietary) MTB recording format. - I would expect some problems to distinguish between front and back. (Head movements will fix these, but what if you want to keep your head in some "listening position"?) - I would not expect that any or at least some significant height cues are captured. (?) More important: - It seems to be very difficult if not impossible to bring MTB recordings into some loudspeaker format. (Even to classical Stereo...) "Application case": Imagine you would like to present some VR/360ยบ movie in some ("plain old") cinema version, or just to broadcast it on TV. You would need some 2.0 or 5.1 (or Auro-3D/Dolby Atmos etc.) audio version to do so. How to derive this from any binaural recording, in some rational way? (Unless they would interpret the 8-mic= RondoMic sphere recording as some HOA source. Which brings us back to my 1st mail...) Last, but not least: Good MTB recordings require many capsules assembled in an SA mirophone, in my eyes not any less than for HOA. Sources: http://dysonics.com/rondo360/ http://dysonics.com/wp-content/uploads/2014/05/dysonics_immersive_spatial_sound_for_mobile.pdf "In practice, we find that this procedure produces high-quality results using 8 microphones for speech and < 16 microphones for music >." "Although MTB produces highly-realistic, well externalized spatial sound, the signals produced by this method only approximate the exact experience, and critical listening tests have revealed various audible defects [7]. We have developed methods to correct for these problem, if corrections are required, and refer the interested reader to [7] for an extended discussion of this topic." Chapter 4.1: "For the numerical values a = 0.0875 m, c = 343 m/s and fmax = 2.5 kHz, these formulas call for 55 microphones for omnidirectional and 16 microphones for panoramic sampling." 55 microphones is quite a lot, especially if you are restricted to binaural applications. <>Best regards Stefan ----------------------- Politis Archontis wrote: >Hi Stefan, > > >On 07 Jun 2016, at 04:35, Stefan Schreiber ><st...@mail.telepac.pt<mailto:st...@mail.telepac.pt>> wrote: > >Politis Archontis wrote: > >But instead of combining all microphones to generate the binaural >directivities (as in ambisonics), it interpolates only between the two >adjacent microphones that should be closest to the listener's ears. Otherwise, >it does not capture pinna cues or cues from a non-spherical/assymetrical head. >Any source for this explanation? > >I actually dare to question your view... How will you receive any binaural >cues via interpolation between two relatively closely spaced omni mikes (fixed >on a sphere)? > >As you even write, this doesn't seem to give any head and pinna cues. >(It's called MTB. So I guess they would aim to provide several binaural >perspectives, including head and pinna cues?) > >The source is the AES paper describing the method: > >Algazi, R. V., Duda, R. O., & Thompson, D. M. (2004). Motion-Tracked Binaural >Sound. In 116th AES Convention. Berlin, Germany. > >It does give head-related cues, that of a spherical head without pinna. If you >put an omni on a rigid sphere, it is not an omni anymore, it has a >frequency-dependent directionality, if you put two of them at opposite sides, >they have opposite directionalities and introduce inter-channel level >differences. Depending on the size of the sphere, the two signals have a >direction-dependent phase-difference too. If the size of the sphere is >approximately the size of a head, then you can assume that the level and time >differences are close to the binaural ones. This is the infamous spherical >head model, and its ITDs and ILDs are known analytically. It captures the cues >for lateralization, but not for a pinna (that it doesn't have) or for head >assymetries. > >If instead of two omnis, you put many of them on the horizontal plane, then >you can track the listener's head yaw rotation and use the two omnis that are >closer to their ears - or interpolate for a smoother transition. That's what >Algazi and Duda are doing in their paper, and they compare various >interpolation schemes. > >Regards, >Archontis > > _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on. 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