[Openal] Effects/filter chain lacking

[Tim Sorrells]

I'm looking through the Effects Extension documentation and there's a
lot of discussion which seems to ultimately boil down to one parameter
which is AL_AUXILIARY_SEND_FILTER which allows you to specify the effect
and filter applied to a source.  Perhaps I'm missing something but this
only allows the sound designer to specify at most one effect and one
filter.  But what happens when you want to apply 2 effects and a filter
to a source?

 

I really want to be able to construct a chain so that I can specify
something like this: Source->Filter->Effect1->Effect2->Output.  I'd also
like to attach an effect to the master so that every source is affected
by that without me manually telling it so.

 

Even using the AL_AUXILIARY_SEND_FILTER with a reverb and a low pass
filter it's obvious the reverb effect is bypassing the low-pass filter.
It sounds to me like the dry sound is fed to the filter and the effect
in parallel and then both are getting recombined before output.  This
means the reverb adds back everything filtered by the low-pass filter.
This differs from the graph on page 16 in the Effects Extension
documentation which puts the filter first, and then the effect.
Assuming this problem isn't specific to my platform, you can hear this
yourself by using the EFXFilter sample.  A better sample sound (I'm
using an explosion) and a more exclusive low-pass filter setting will
make this more clear.

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