[Openal] EFX Clarifications

[Christopher Fitzgerald]

Greetings,

> Hi,
> 
> Yes, GainHF is one of the parameters used to computer a filter coefficient.
> 
> for example from the I3DL2 spec, g would be ...
> 
> g = 10^(gainHFdB / 10)
> 
> where gainHFdb = 20 * log10(gainHF)

That's making more sense to me now.  So that basically replaces the usual coefficient(s) derived from a cut-off parameter.
 
> Well the problem is that the direct gain can be completely different when switching from one distance model to another.   In the simple case, of no distance model (AL_NONE) you would expect no air absorption either.

So for no distance model, no air absorption is used.  That makes sense.

What about for the linear and exponent models?

I would have assumed they'd still use (distance - reference_distance), maybe clamped if the model requires it (this would include the inverse model too).

> The SBLive! supports EAX 2.0 so does explain why certain features are unavailable.

Makes sense.
 
> Yes that could be a driver bug.

Yay for driver bugs. :P  At least it's not a common platform anymore.
 
> It is working on Audigy and X-Fi cards as far as I'm aware.

Sounds good.
 
> Dan

Thank you for your time and help. :)

Regards,
 - Christopher
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