HI Bo-Erik, Sorry I wasn’t very clear on my comments about the HRTF order, Jörn covered it much better!
You need very high orders if you want to preserve HRTFs as they are when you measure them, and the order that you can expand them depends on how many points you measure them around the head. For a typical measurement setup this days with a resolution of ~5deg elevation and azimuth, that corresponds to an effective ambisonic order of ~15, which is enough. If you want to play a virtual source at a direction of some HRTF, you just need to convolve them with the respective ones, and you can do that either by using directly the measured (or modelled one) or do it in the ambisonic domain; this is not a heavy operation, it’s just a few tens to a few hundreds multiplications and additions per frequency band for all these orders. In any case, for binaural panning and spatialisation, no need to discard any of that information and lose accuracy. And I don’t think it’s just strictly about distinguishing the direction between two closely spaced sounds, it’s about delivering correct binaural cues in general, correct fluctuations of ITDs and ILDs in complex sound scenes with many sounds including early reflections and late reverberation, which are important for reverberation perception, apparent source width and externalization. When however you want to reproduce or binauralize a recorded sound scene, the available orders are limited by the (physics of) the microphone array. In this case no matter your HRTF resolution, it’s always going to be limited by the order of the recording, blurring the binaural cues gradually at higher frequencies. That may or may not be a problem depending on the application. One kind of solution is given by parametric processing of the FOA/HOA signals (such as HARPEX or DirAC), which restore somewhat the correct cues, by “de-blurring” the directional components in the recording. That’s the field I am working on too, and even though I think they are impressively effective, they need a lot of care in implementation, and they have their own issues to address (that’s why it’s a field of current research). But regarding VR or AR applications or virtual monitoring of other multichannel setups, where you want maximum sharpness (and where you can employ the full HRTFs), I don’t think going through a FOA representation is a good solution, as I find the blurring of the virtual sources to be very high compared to when using directly the HRTFs (basically a point source is spread in space around you with an almost cardioid or supercardioid shape). Another factor that is overlooked sometimes is that the same blurring affects the sense of reverberation and externalisation, as it “correlates” more than necessary the reverberant sound at the two ears.. Best regards, Archontis Politis On 28 Jan 2016, at 23:12, Bo-Erik Sandholm <bosses...@gmail.com<mailto:bosses...@gmail.com>> wrote: I do understand that HOA can represent resolution of directivity in the mathematic domain better than FOA. But I am starting to suspect we are overworking something when we are talking of order 8 to 15? Is it realistic to even think of measuring individual HRTF response with that angle resolution? And is it even neccessary when we know the adaptability of the auditory system? As stereo works good enough over 45 degrees with 2 speakers and correct psycho acoustic setup and a good recording are we not aiming for a overkill system? As a normal guy without training in listening for direction of sound sources I suspect I cannot really pinpoint many things in more than +-10 degrees without visual cues. I remember old discussion results about ideal number of loudspeakers for horizontal FOA replay being 6 speakers. My goal is to have a device that can play through headphones a stereo or FOA recording and give me a minimum experience of listening to a stereo system or FOA setup with out of head sound and a stable position of the soundstage. I am not certain this is relevant in this discussion thread as we probably have different views of the goals and the path to the goals. Bo-Erik -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20160129/8a66d611/attachment.html> _______________________________________________ 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.
