[openal] Preparing for 1.18

Christian Hoene christian.hoene at symonics.com
Sun May 28 13:24:16 EDT 2017

Hi Chris,

in respect to regular layouts, I thought about a solution for OpenAL. OpenAL likes to have a regular layout and has restrictions on the maximal size of this layout. It does not work well with all Sofa files.

Instead of using the original layout of a Sofa file, especially if it is not suitable for OpenAL, one could resample/interpolate the HRTF using a layout that works well with OpenAL.

Libmysofa (see https://www.hdfgroup.org/2017/04/hdf5-under-the-sofa-hdf5-on-embedded-and-mobile-devices/) has an interpolation unit. Thus, it would be straight forward to change makehrtf to support irregular HRTFs by simply resampling the HRTF for a given, fixed layout.

The only thing which needs to be changed in the OpenAL core is the mirroring of HRTFs. Mirroring HRTFs can be imprecise, see: http://www.aes.org/e-lib/online/browse.cfm?elib=18590

With best regards,

 Christian Hoene

> Chris Robinson <chris.kcat at gmail.com> hat am 28. Mai 2017 um 18:09 geschrieben:
> On 05/28/2017 07:32 AM, Christian Hoene wrote:
> > Hi Chris,
> >
> > sadly enough, support for SOFA files has not yet been added:
> > https://github.com/kcat/openal-soft/pull/80
> >
> > Any changes that this extension (or a similar) to support powerful HRTFs will be considered at some times?
> Supporting SOFA files is something I'm going to look into after 1.18 is 
> released. In regards to that PR in particular, it seems quite a bit more 
> complex than should be necessary given this loading function by 
> comparison 
> <https://github.com/sofacoustics/SOFAlizer/blob/master/modules/audio_filter/sofalizer/sofalizer.c#L286>. 
> It should only need a relatively minor change to makehrtf.c to use an 
> alternate loading function to prepare the HrirDataT structure from a 
> SOFA file.
> I've done tests to successfully load a .sofa file in an independent app, 
> but there's some things to work out before being able to make mhr files 
> out of them (such as checking for and dealing with irregular layouts, 
> where a ring of measurements are not equally spaced; and it would 
> greatly benefit from stereo/dual-ear measurements). And considering how 
> long it's been since the last release and not knowing how long it would 
> take to work the issues out, it's on hold until after the release.

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