[Openal] Filter problems

[Daniel PEACOCK]

Hi Luis,

> thanks a lot for the info. I've never looked into EAX before, so I
> don't know about its limitations and stuff. When you say that you
> don't think it would be impossible for a EAX 3 or lower card, what
> do you mean exactly?

There have been 5 different versions of EAX so far.  EAX 1 & 2 were made
public so they are supported on practically every soundcard and motherboard
audio device that supports 3D Audio (via DirectSound3D).   EAX 3, 4 and 5
are private specifications that are exclusive to Creative hardware (Audigy
and X-Fi products).  Before OpenAL, EAX was only available as PropertySet
extensions to DirectSound3D.

Roughly speaking these are the main features that were added to each EAX
version: -

EAX 1.0 Global Reverb with limited control over reverb parameters
EAX 2.0 Global Reverb with improved control over the parameters, and
per-Source low-pass filtering
EAX 3.0 Global Reverb with complete control over the parameters, and more
per-Source controls (e.g rolloff factor)
EAX 4.0 Multiple Global Effects
EAX 5.0 Multiple Global Effects, Global Effect filtering, per-Source
panning and Macro FX

EAX 4.0 and 5.0 implementations on Creative cards enabled stereo effect
sends and filtering.  On previous versions of EAX the features were assumed
to be applied to mono 3D Buffers only.  IIRC DirectSound originally did not
allow PropertySets to be querried from 2D DS Buffers - meaning that there
was no way to control EAX effects on anything except 3D Mono Buffers.

> On another hand, by looking into the EFX docs,
> there are things like the high pass and band pass filters, which are
> stated to be not implemented at the moment. Are there any pending
> revisions to the current EFX version?

There are plans for an EFX 2.0 that will add many new features including
the ability to write your own per-Source DSP effects (which will be the way
to implement other filter types).

The goal for EFX 1.0 was to make it much easier for developers to write
cross-platform (currently PC and Xbox 360) scalable effect code that could
take advantage of hardware when available and fallback to a software mixer
otherwise.

Dan