Search code examples
iphoneiosaudiocore-audioopenal

How to generate and play white noise on the fly with OpenAL?

I'm using OpenAL in my app to play sounds based on *.caf audio files.

There's a tutorial which describes how to generate white noise in OpenAL: 

amplitude - rand(2*amplitude)

But they're creating a buffer with 1000 samples and then just loop that buffer with 

alSourcei(source, AL_LOOPING, AL_TRUE);

The problem with this approach: Looping white noise just doesn't work like this because of DC offset. There will be a noticeable wobble in the sound. I know because I tried looping dozens of white noise regions generated in different applications and all of them had the same problem. Even after trying to crossfade and making sure the regions are cut to zero crossings.

Since (from my understanding) OpenAL is more low-level than Audio Units or Audio Queues, there must be a way to generate white noise on the fly in a continuous manner such that no looping is required.

Maybe someone can point out some helpful resources on that topic.

Solution

  • The solution with the least change might just be to create a much longer OpenAL noise buffer (several seconds) such that the wobble is at too low rate to easily hear. Any waveform hidden in a 44Hz repeat (1000 samples at 44.1k sample rate) is within normal human hearing range.