[openal] HRTF sound coloring

[Ian Reed]

Ahem, those links again with %20's so you can just click them in your 
mail client:
https://BlindGamers.com/downloads/HRTF%20mono%20coloring.flac
https://BlindGamers.com/downloads/HRTF%20stereo%20coloring.flac

On 2/4/2017 9:45 AM, Ian Reed wrote:
> Hi Chris,
>
> We are using OpenAL Soft 1.17.2.
> Our sound designer noticed some coloring of sounds when playing them 
> with HRTF enabled and source relative set to true.
> Is having HRTF enabled supposed to affect sounds played with source 
> relative set to true and no panning applied?
> We don't mind some coloring when the sounds are positioned in 3D, 
> obviously HRTF is supposed to change how they sound.
> But we want to play some sounds exactly as they were recorded, without 
> any coloring.
> Is setting source relative to true the right way to play unpanned mono 
> and stereo sounds?
>
> I made a test program to demonstrate the issue.
> It plays a sound with HRTF, then without, then with, then without, so 
> you can hear them side by side.
> That is, first and third plays are with HRTF, second and fourth are 
> without HRTF.
> I'm using your updated API for resetting the device while the program 
> runs in order to change the HRTF setting.
> I played a mono sound in the first example, then a stereo sound in the 
> second.
> Both have coloring, but the stereo sound also sounds "wider" when HRTF 
> is off.
> I recorded them in Audacity and exported as flac:
> https://BlindGamers.com/downloads/HRTF mono coloring.flac
> https://BlindGamers.com/downloads/HRTF stereo coloring.flac
>
> Here is a snippet of my C# code that uses the OpenTK wrapper around 
> OpenAL to create the source:
> var s = new Source();
> s.SourceID = AL.GenSource();
> ALAnnounceError("AL.GenSource");
>
> s.BufferID = CreateAndFillBuffer(path, false);
> AL.Source(s.SourceID, ALSourcei.Buffer, s.BufferID);
> ALAnnounceError("setting buffer on source");
>
> AL.Source(s.SourceID, ALSourceb.SourceRelative, true);
> ALAnnounceError("setting source relative to true");
>
> No errors are reported, and I am happy to provide the full source of 
> the test program if you would like.
>
> Thanks,
> Ian Reed
>