[Openal] OpenAL/DirectSound3D issue on Realtek/Intel HD

[Garin Hiebert]

> I've encountered an issue which appears to show up on Intel/Realtek HD 
> Audio
> Boards when using "DirectSound3D" as the OpenAL "Device". If we exceed 
> a set
> threshold (I narrowed it down to 15) of buffers then any of those 
> buffers over
> that limit seem to have a different volume calculation to those under 
> this
> threshold. When I say different volume calc, I mean that the final 
> output vol
> is considerably louder on these buffers over this threshold than those 
> below.
>
> I'm not sure whether this is a driver issue for these cards or a 
> possible
> problem with how OpenAL allocates buffers, The hope is that someone 
> will
> provide some explanation.

This pretty much _has_ to be a driver issue, since AL creates and makes 
use of DS3D buffers in a consistent way -- there is no special handling 
of a subset of the DS3D buffers.  The only magic number used when 
running the DS3D backend is a check to make sure that DS3D can provide 
at least 16 DS3D buffers -- if not the implementation falls back to DS.

Hopefully when you are referring to a "set threshold of buffers" you 
actually mean OpenAL sources -- because if the behavior is changing 
based on how many OpenAL buffers are being created, then all bets are 
off...  (That certainly shouldn't happen -- you can have up to 65535 AL 
buffers, and your system should be getting awfully slow before you hit 
that limit.)

> It would be helpful to identify the underlying device being used by
> DirectSound3D. Is that possible with the OpenAL API?

Not within the API -- you'll have to build a debug version of AL and 
track this down.  The code you want is in alcOpenDevice -- 
openal/win/Alc/ALc.c.  The device being opened is the default device 
(whatever is the preferred audio device on the system's audio control 
panel).

> It also would be helpful to know what this threshold is, a guestimate
> would be the number of hardware channels. If that is correct, is it 
> possible to
> get the number of hardware channels using the OpenAL API?

Sort of -- you just create sources until AL stops giving you sources.  
With the DS3D implementation, that number will be the same as DS3D's 
GetMaxNum3DMonoBuffers.


Garin