Re: Units for position?

On 12/29/2012 04:12 PM, [email protected] wrote:
> Hey all!
>
> I hope you are in the midst of having a great holiday season!

Hi! :)

> I've been working on a demo, and it occurs to me that I have no idea what
> units are used in the position coordinates, nor how to set or change them
> if I need to use something different.

In practical terms, unextended OpenAL uses scale-invariant units. That 
is to say, it doesn't matter whether you're using meters, feet, 
centimeters, inches, etc... as long as /all/ distance values use the 
same scale, you'll get the same output.

A common pitfall, however, is to ignore or set an improper value for 
AL_REFERENCE_DISTANCE on sources. This is essentially the distance from 
the sound that the audio was originally recorded at, or more basically, 
the in-game distance where the source should not be attenuated. So for 
example, if you had this set to 1 when using a scale of 1 unit = 1 
meter, you'd want to set it to 100 if using 1 unit = 1 centimeter to 
keep the scale correct.


When using EFX, there is a setting to specify the unit scale. This 
setting applies to certain effects, like the air absorption effect which 
defines high-frequency attenuation in meters rather than units. This 
scale can be set using the listener's AL_METERS_PER_UNIT property, and 
it defaults to 1.

> So what surprised me is that these distances seem to be "too far away" -
> the volume attenuation basically shuts the sounds off.  If I use arbitrary
> but small numbers FC=(0, 0, 1) BC=(0,0,3), LT=(-1,0,2), RT=(1,0,2) it
> seems to work OK.

Then you'll want to increase the source's AL_REFERENCE_DISTANCE until 
you get good attenuation levels. Every doubling of the distance from the 
reference distance halves the gain, so at a distance of 10 with a ref 
distance of 1, you'll basically have an attenuation of 1/10, or 0.1. 
Increase the ref distance to 5 and you'll get an attenuation of 5/10, or 
0.5, at the same distance.
_______________________________________________
Openal mailing list
[email protected]
http://opensource.creative.com/mailman/listinfo/openal