I just want to say that when I read Joseph's mail I feel like christmas has come early this year :-)
I have been thinking about headtracked binaural listening for a couple of years and discussing it here and in other forums. The goal is to make it possible to listen to ambisonics first order with earphones with head tracking usen open source programs and procedures. I do not think we should wait until it is possible to create a individual HRTF for a everey day nontechnical person. This is avaliable: Software and hardware to do it with software written by http://www.matthiaskronlachner.com/?p=2015 or the Ambiexplorer on the phone with the same effort to build the head tracker bu also t adding a blutooth transmitterand and using another firmware. I have been thinking of taking another way to the goal. What I have been thinking of is a tinted head tracking binaural decoder (I did not know the principle had a name) My take on the decoder is that it - below ~ 4kHz it should use standard HRTF decoding and have a few profiles selectable on the width of the head, ignoring individual ear shape effects above 4kHz. - tinting used to improve the height perception in binaural decoding, tinting subsituting for HRTF above 4kHz for height. tinting has shown it is possible to add height information to Stereo, This has been demonstrated. - I want the shoulder reflections to be taken in to account, I belive the varying impact of a comb filter effect of the shoulder reflection is VERY important. - the software should be controlled by parameters for head tilt related to shoulders and head versus body turning - maybe also the normal distance from the ears to the shoulders, but I do not think this is very important as we adjust to clothes on shoulders very easily. I belive we should take inspiration from UNIX principles when creating the software, that is to use a chain of software that each does one thing well and do not have to be rewritten all the time, A number of VST modules that can be chained for could be the solution. We already have a number of the needed modules, the advantage of modules is that they can be replaced or switched between. - Ambisonic rotation and tilt controlled by OSC in VST - ambix_rotator for example - Binaural decoder, Ambix_binaural, Tinted binaural decoder - not available - Shoulder reflections - I believe the shoulders are in many cases left out of the HRTF sets. If not we work with the difference intoduced when turning the head in relations to the fixed shoulders. Reaper DAW that I use is not free (shareware) but very low cost, Head tracking module, http://www.rcgroups.com/forums/showthread.php?t=1677559 - I hope to get assistance to make two modifications to the firmware and hardware, the first is to change the output syntax of the data stream to OSC. The second is to add a second 9DOF sensor on a cable and use this to track shoulder movement. Best Regards Bo-Erik Sandholm Stockholm Amateur ambisonic recordist Interest in sound reproduction since beginning of 1960's. Ex Network Engineer and unix system manager Not a Programmer now for 35 years :-) 2015-12-10 21:05 GMT+01:00 Joseph Anderson <j.ander...@ambisonictoolkit.net> : > I'd just add here that a sensible approach would be to use (or design) a > 'tinted' decoder. That is, a decoder that includes frequency (& or time) > domain filtering to color the soundfield on playback. > > Blue Ripple Sound <http://www.blueripplesound.com/> includes tinted > decoders > <http://www.blueripplesound.com/products/poa-decoding-vst> in their > technology portfolio. (Furse describes this in a patent > <http://www.google.com/patents/US20120014527>.) For the ATK > <http://www.ambisonictoolkit.net/wiki/tiki-index.php>, I've thought about > including a help page in the SuperCollider documentation > <http://doc.sccode.org/Browse.html#Libraries%3EAmbisonic%20Toolkit> on how > to go about implementing a tinted decoder, but haven't done so at this > time. > > The basic idea of 'tinting' is very simple: process the reproduced > soundfield in a way that 'enhances' or further achieves some effect you'd > like. To enhance elevation, we may choose to color the soundfield in a way > that exaggerates this sense. We have two choices in the processing: > > 1. process the soundfield before decoding > 2. process the soundfield after decoding > > A combination of both gives the most flexible results, and the best choice > really depends on what kind of decoding array you're working with. If you > have a full 3D array, choice 2 makes sense. Whereas, with a 2D layout, > processing the soundfield before decoding (option 1) is probably the best > idea. > > Option 1 is implemented like this: > > - decode soundfield to array of equally distributed 'virtual > loudspeakers' > - filter 'virtual loudspeakers', depending on direction > - re-encode soundfield > > Option 2 is this: > > - decode soundfield to array of real loudspeakers > - filter these, depending on direction > > Choosing the correct filtering to enhance elevation is the tricky part. > You'll want these to be phase matched. (Linear FIR, is an easy choice. > Phase matched 2nd-order IIR shelfs also work well.) There are many papers > about modeling HRTFs, a simple choice is to just review the suggested > filtering for simple spherical head modeling. A very quick search turns up > a paper from Duda and Brown > <http://www.ece.ucdavis.edu/cipic/files/2015/04/cipic_Brown_Duda98.pdf>. > With listening in an Ambisonic soundfield, you need to remember that the > listener's head already applies the listener's own HRTF. The trick will be > to enhance without unduly distorting. > > Something also useful to note: if you're a creative artist, you can 'tint' > the soundfield for creative purposes. A simple example is what might be > what we call 'soundfield highlight'. The idea here is that we'd low-pass > all of the soundfield, except our 'highlight'. And notably, we can steer > where the 'highlight' is located. (E.g., highlight different parts of the > soundfield.) We can think of this as 'directional masking', but with a > frequency dependence. I won't go into the exact details of implementing a > signal flow to generate this effect, but the ATK > <http://www.ambisonictoolkit.net/wiki/tiki-index.php> includes all the > parts needed to do so. > > > My kind regards, > > > *Joseph Anderson* > > > > *http://www.ambisonictoolkit.net/ <http://www.ambisonictoolkit.net/>* > > > On Thu, Dec 10, 2015 at 9:29 AM, Jörn Nettingsmeier < > netti...@stackingdwarves.net> wrote: > > > On 12/10/2015 04:59 PM, Peter Lennox wrote: > > > >> It does imply that an ambisonic panner plugin that incorporates spectral > >> manipulation would be more efficacious > >> > > > > noooooo! > > > > if it's an ambisonic panner, it doesn't change the spectrum. if it > changes > > the spectrum, it's not an ambisonic panner :) > > > > > > > > -- > > Jörn Nettingsmeier > > Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 > > > > Meister für Veranstaltungstechnik (Bühne/Studio) > > Tonmeister VDT > > > > http://stackingdwarves.net > > > > _______________________________________________ > > 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. > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > https://mail.music.vt.edu/mailman/private/sursound/attachments/20151210/d099a481/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. > -------------- next part -------------- An HTML attachment was scrubbed... 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