On Monday 19 Oct 2009, Erik Hofman wrote:
[snip...]

> The odd part is, Doppler is working for the F-16 and Fokker-100
> for example. It's as if OpenAL is limiting the total pitch to 2.0
> which means that AL_PITCH and Doppler combined can not be higher
> than 2 times the normal playback frequency. Or something like
> that.
>
> Erik

I think the maximum drop of pitch is 0.5 of the emitted frequency, 
at least for a stationary receiver and a sub-sonic source.

If...

  Fo= emitted frequency
  V= velocity of waves in the medium
  Vs= velocity of the source relative to the medium
  Vr= velocity of the receiver relative to the medium
  Fr= frequency observed by the receiver

Then...

  Fr= Fo * ( (V + Vr) / (V + Vs) )

So when Vr= 0
and Vs= V (i.e. the speed of sound)

  V / (V + Vs) = 0.5

So Fr= Fo * 0.5 for something receding at V

which means that for sound, the pitch can only drop to half of its 
original pitch while the source remains in the sub-sonic regime.

This doesn't apply when the source is approaching though, and I 
wonder if the people writing the Open_AL code just thought the 
effect was symmetrical i.e. if the pitch halves for a retreating 
source then it should double for an approaching source.

LeeE

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