I will chime in here on this discussion again. While HRTF selection/individualization is a work in progress, the use of selection combined with ITD individualization and better yet with headtracking tackles many of the issues. I do not think personal ear molds and the like are required, though they are a nice way to get individual HRTFs via gestalt measurements (either on a dummy head or numerical simulation).
Head dimensions provide a very good indication of ITD variations, and can be used to individualize HRTF data on that front. I know of no studies that should there are significant individual HRTF differences resulting from fat content or torso shape. These elements can likely be assumed common across people, at least as a first or second approximation. Hair/head covering is a different factor, and has been shown to be audible. However, the effect would not be expected to beyond understanding, and one could imagine spatial correction filters to modify the HRTF relative to such absorption characteristics. It all remains a linear system and such layers could be separately processed, as with ITD processing. It must be repeated that our auditory system adapts to our own local changes, in clothing, hair style, etc. and we are not significantly thrown off by such things (at least after adaptive listening for a bit). So, such changes can be feasibly incorporated, with the inclusion adaptation. As for the multichannel headphone proposal, this does not alleviate all the above non-pinna variations mentioned. However, it is an interesting notion to provide wavefronts tot the indvidual's actual pinnae (requiring only multichannel head/torso related intensity vector transfer functions) that has been developed on and off over the years. See, for example: - D. Sastrapradja, Sound Localization Simulation via Wavefront Recreation, Masters of Science, The Pennsylvania State University, 1997 - R. Greff, Binaural holophony - Sound spatialization over circumaural transducer arrays, PhD Thesis, Paris VI, 2008 (https://hal.archives-ouvertes.fr/tel-00619404) - J. Wang, P. Samarasinghe, T. Abhayapala and J. A. Zhang, "Binaural Reproduction Using Multi-Driver Headphones," 2022 International Workshop on Acoustic Signal Enhancement (IWAENC), 2022, pp. 1-5, doi: 10.1109/IWAENC53105.2022.9914750 There are also on-going projects in this area with the team of Piotr Majdak at the Austrian Academy of Sciences. The main issue in my experience has been the acoustics within any type of headphone cavity which make creating directional wavefronts almost impossible. For example, the prototype of Greff used an open grid with speakers, providing interesting results, but once enclosed for better frequency bandwidth and a commercial device the same results were not achieved. > Date: Fri, 30 Dec 2022 04:38:13 +0200 (EET) > On 2022-12-26, Bo-Erik Sandholm wrote: > > As a amateur I had a idea that I could use a CIPIC HRTF but I did not > > find an easy way to select one that had any chance to be a a good fit > > for me. > This has always been a problem with in-ear measurements and HRTF/HRIR > processing reliant on them. While in theory that's the ultimate way to > deliver binaural sound to our two ears, fitting the transfer functions has > always been a pain, and rarely doable right without going with personalised > ear molds and the like. > > In my naivity I hoped for at least skull diameter and som pictures of > > ear shape. > Not going to happen, because skull, upper torso shape, and e.g. > subcutaneous fat content in the face and upper torso areas influence the near > field reaching the ears quite a lot, especially at the lower frequencies. > Even the uneven cartilage development of the pinnae, and the hairstyle worn, > appear to heavily influence the field impinging on your ear canals. So does > clothing and apparel, as does instantaneous posture. > So, at least to my amateur's eye (ear) it seems almost impossible to average > over all of those separate and temporally variable locational cues so that we > could somehow find a way to calibrate binaural in-ear phones to work truly > well. When headtracked, they sort of work, but even then I know from a couple > of tests they aren't perfect. The two friends I have who've actually had > their ear canals molded and have taken a KEMAR-like test set on theirselves, > aren't too impressed by the results. > So how about going about it a different way for a change? Would it be > possible to design a set of headphones which actually locally reproduced a > high order soundfield, for any set of pinnae to utilize? As they naturally > do? Kind of like do very high order ambisonics or WFS, but now right besides > the ear, and headtracked? I mean that ought to take the HRTF modelling aspect > fully out of the picture: the pinna would do what it does for each, and then > the upper torso reflections would also be much easier to simulate > numerically, since they are of lower order and at lower frequency. -- Brian FG Katz, Research Director, CNRS Groupe Lutheries - Acoustique – Musique Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂'Alembert http://www.dalembert.upmc.fr/home/katz _______________________________________________ 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.
