[Openal] Use of ALC_FREQUENCY property

[Chris Robinson]

On Tuesday 19 May 2009 1:20:05 pm Jim B. wrote:
> The existing program allows menu selection of sound quality by setting the
> maximum sampling rate. As near as I can tell, this is not useful in OpenAL.
> Is it true that the ALC_FREQUENCY property is not settable in current
> OpenAL implementations?

It's not settable in OpenAL Soft, currently. I'm not sure if it has an effect 
on the Windows implementation or not, though.. it may work there. I do have 
plans for implementing it in OpenAL Soft, when I find a safe way to do it.

> Also, in the current versions, is it possible for
> ALC_FREQUENCY to be anything other than 44100 KHz?

Yes. OpenAL Soft allows the user to set a default frequency for playback via a 
couple config files (eg. I use 48khz output), and it may also be modified 
according to the hardware's needs. Calling alcGetIntegerv with ALC_FREQUENCY 
should show these changes.

> It looks like OpenAL
> will resample any file that is not at ALC_FREQUENCY when the Buffer is
> loaded. So, there is no point in resampling before loading the Buffer --
> correct? Also. I am trying to decide if it would be worthwhile to check for
> ALC_FREQUENCY at 22050 KHz (or less) and low pass filter our 44100 KHz
> sound files.

There's no need to filter sounds before loading. Just load the sound with its 
original sample rate, and OpenAL will take care of resampling and everything 
for you.