More sources then the apps limit? Was: Re: [Openal] simultaneous
source limit on osx
Ryan C. Gordon
icculus at clutteredmind.org
Fri Oct 21 08:00:01 PDT 2005
(I'm discussing Unreal, but this really applies to anything that uses
> The question is how this high number of active audio sources is handled
> by OpenAL when the client (2k4) itself have a preference setting of
> something much lower like 8, 16 or 32 channels for example.
Unreal doesn't (at this time) use Apple's ALC_MIXER_MAXIMUM_BUSSES
property...we generate [ALAudio.ALAudioSubsystem].Channels+1 AL sources
at startup, and if the AL won't give it that many, Unreal uses as many
as it can get (so if you ask for 64, and get 32, it'll make do with 32).
...I can't see any practical use for more than 64 sources...in ut2003,
we dropped the default on the Mac to _8_, since the original
SoundManager implementation was so expensive, and no one really noticed
the difference in output, but...
> How do OpenAL handle this?
> What are the implication for those with a low amount of channels/sources
...as ArmyOps users found on some noisy maps when some of their gunshots
didn't make any sound, if you have less channels in the .ini, the engine
will just not play some audio. Well designed maps, mods, and entire
licensee games will be conservative in their sound usage, and will be
careful to prioritize the important sounds, so if Unreal needs to stop a
playing sound to reuse its AL source, it'll throw away some ambient
noise three streets away instead of, say, the conversation dialog with
the NPC in front of you.
> Would it be any negative issues with allowing 64 sources per default in
> the 2k4 OpenAL ini file?
Framerate. Remember that most of those 64 sounds are being mixed on the
CPU but aren't really distinguishable. Less is more...don't play
anything that you can get away with avoiding!
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