On Fri, Nov 7, 2008 at 2:55 PM, Curtis Olson wrote:
> Question: has anyone noticed anything odd with the stall horn sound in the
> default c172p in the current cvs (although it's likely been an issue since
> we migrated to openal?)
>
> When the stall horn goes off, it used to be a clean/constant tone, however
> in openal it's warbly disjointed crackly sort of sound. It's enough to be
> very aurally annoying.
>
> I almost wonder if this issue affects all our sounds, but because the stall
> horn audio is such a clean sine wave with no extra noise or "character", any
> little imperfection in the audio system really jumps out when the sound is
> played. This really seems like it could be related to inconsistent
> positioning of the listener versus the sound source?
>
> The audio imperfections seem to be correlated with frame rate changes.
>
> Anyone have any ideas on this?
Replying to my own message here ...
In src/Main/main.cxx the sound positions and velocities are updated. I
observe that the velocity is computed as (current position - last position)
/ dt. However, this approach leads to inconsistent velocities because of
some very subtle issues related to the flight dynamics update loop.
If I force the velocities to be zero, the sound quality *greatly* improves,
and not just with the stall horn. The overall sound is much more "rich" and
vibrant (at least to my ears.)
I'm not sure the best solution here since I'm sure we need correct
velocities to get correct doppler effects.
I am trying to understand the code a bit more and I see that both the
listener and the sound velocities are rotated into a new coordinate space.
Is this necessary? It seems like the important thing is the relative
velocity of the sounds, not what coordinate system they are transformed
into?
Is it worth giving up on doppler effect to get reasonable cockpit sounds, or
is doppler a big enough win to put up with really crappy cockpit sound with
lots of artifacts?
It wouldn't be hard to add an --enable/disable-doppler configuration option?
Thought/comments?
Regards,
Curt.
--
Curtis Olson: http://baron.flightgear.org/~curt/
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