Curtis L. Olson wrote:
3. The maximum pitch factor that OpenAL allows is 2.0 ... we blow
by that with some of our sound configs ... that's another
thing that will need to be tweaked and looked at.
We can do the down-sampling manually and choose the right one at runtime; basically mipmapping the audio data. This wouldn't be too hard.
Then again, do we really need more than two octaves of pitch shift or
is this just an artifact of poor frequency choice in the original
sample?
Looking at the default c172 engine sound. It is a 22000 hz sample. However, plib was playing this at 8000 hz. So we had to specify a pitch of 2.75 just to get it back up to "normal" speed. This stuff is built into the sound config.xml, but when we use the same config file with openal, the pitch comes out 2.75x too high so we will need to track down these situations and fix them in the config file. That should get us back within reasonable range. I doubt we would need more than 2 octaves, although we can go significantly less than 1.0 so that gives us quite a bit of range.
One thing that I've always wanted to do is set things up so we can sample then engine at different rpm's and then have the system transition between them (with appropriate blending) as the engine speed changes. We didn't push this originally, because in the early days, plib only supported 3 concurrent sounds and we had other things to spend our 3 sample budget on.
Regards,
Curt.
--
Curtis Olson http://www.flightgear.org/~curt HumanFIRST Program http://www.humanfirst.umn.edu/
FlightGear Project http://www.flightgear.org
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