Re: Eric's OpenAL presentation

On Sep 2, 2011, at 11:43 AM, Eric Wing wrote:

> On 9/1/11, [email protected] <[email protected]> wrote:
>>> My monster 2 hour presentation is finally posted on YouTube.
>>> http://www.youtube.com/watch?v=6QQAzhwalPI
>>> 
>> 
>> Thanks for posting that, I'm not a iOS user but it was a good
>> introduction/explanation of how the 3D modelling works.
>> 
>> Does anyone have examples/experience with listeners with more that 2 (L/R)
>> channels?
>> 
>> Simon.
>> 
> 
> I might be misunderstanding the question, but the question that is
> missing in the middle of the video seems similar. Canonical OpenAL
> only spatializes mono sounds. It is the responsibility of the
> application programmer to specify the 3D positions of sources. But it
> is the responsibility of the OpenAL implementation, driver, and
> hardware to play the sound in the correct way so it sounds like it
> comes out at the correct position.
> 
> So in a theoretical world where you had a speaker system that
> surrounded you in 360 degrees, the ideal OpenAL implementation would
> render sounds at the correct points in your speaker so you hear things
> as you would expect.
> 
> A little less theoretical, if you have 4 speakers: two front corners,
> two back corners, for a sound that is supposed to play directly behind
> you, the OpenAL implementation, driver, and hardware, might try to
> coordinate so that the sound plays equally in the two back speakers to
> make it seem like the sound is coming directly behind you.
> 
> I have seen some fancy sound card driver setups (on Windows) where you
> could specify the number of speakers you had connected, and I think
> you could also specify their positional arrangements, presumably so
> the driver could do the necessary balancing/offsets.

You can do this on the Mac as well

Audio MIDI Setup allows you to configure your system to tell the OS what kind of spkr system you have and how it is connected.

If you have a display port interface, that is already reported for you by the DP meta-data that is a part of the DP connection.

Then, when you use OpenAL, it will see that there is a multichannel interface available, it will see where the channels are located, etc, and it renders according to that. So, for the user, you have a "surround" or a "stereo" rendering completely based on their audio device configuration and there is no additional setup needed by the game.

Bill

> 
> But the ultimate point is that as an OpenAL programmer/user, you don't
> worry about channels yourself for 3D spatialization. That is the job
> of OpenAL.
> 
> -Eric
> -- 
> Beginning iPhone Games Development
> http://playcontrol.net/iphonegamebook/
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