Alc_ext_efx

Java Sound & OpenAL
#1

This is a crosspost from the LWJGL forums but then I thought… maybe it belongs here too.

Is there any documentation anywhere for the ALC_EXT_EFX extension? I’m about to implement sound effects in my new 3D game and I was rather hoping AL would be able to do all of the hard work for me like muffling distant sounds (not just attenuating but actually applying a low-pass filter and stuff like that).

Cas :slight_smile:

#2

See “Effects Extension Guide.pdf” in the OpenAL SDK. Found a random copy here.

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#3

That would be the easiest, if the code has already been written. If there are hitches and you decide to use SourceDataLine (or AudioCue), I might have sufficient code to help out. I have dynamic volume, panning and pitch working, but haven’t done the specifics for coding doppler using the pitch. I have coded a filter or two now. I was just working on simple delay-based panner today, as well (sound hits one ear before the other, but works best with headphones). Haven’t mapped values to locations and angles yet, though.

#4

Thanks ever so much! Seems there’s a lot to read in that pdf.

@philfrei I’ve not actually written any code yet to do anything fancy, what I currently have is just what I’ve been using for the last 20 years - basic buffers, sources, and a listener. I’ll have an experiment or two with the basics first to see if it sort of works and then maybe play with some effects. I will probably have questions :stuck_out_tongue:

#5

In other words, same as you were doing with “Revenge of the Titans”?

#6

Well… sort of. In RotT I did everything manually, the hard way: I used mono sound only, and panned sounds according to their X coordinate on the screen. I mixed a muffled version of samples with a crisp version (simply played both together) according to distance from the centre of the screen. It was all a bit daft.

Now I’ve just literally done

alSourcei(source, AL10.AL_DISTANCE_MODEL, AL11.AL_EXPONENT_DISTANCE);
alSourcef(source, AL10.AL_REFERENCE_DISTANCE, loudness);
alSourcef(source, EXTEfx.AL_AIR_ABSORPTION_FACTOR, absorption);
alSource3f(source, AL_POSITION, x, y, z);

… and it all just … worked (when I set the listener position to the camera location). I was amazed. Haven’t started on reverb and echo stuff yet though.

Cas :slight_smile:

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