[linux-audio-dev] surround sound project. looking for suggestions

[Dennis Thompson]

Hi,
I am working on a surround sound project.  When finished this code will update a virtual acoustic environment based on a persons head motion.  I am hoping for some hints on solving a problem I have.  Note!  My background is in signal processing, not software/hardware interfacing. So I am still clueless on the process of moving data between user memory and the sound card.  Current development is done using ALSA.

My problem:

The current code can process the audio far faster then the sound card can except/output it. Therefore, to reduce the latency between head motion and changes in the sound output, I will need to keep the amount of data in the output buffer to a minimum.  For the sake of discussion say about a 1024 frames (the exact amount is flexible)  Currently I try to control the flow by pausing the output loop. My problem is that I keep getting buffer underruns, even when I am writing another 1024 frames of data to the sound card before 1024 frames have had time to play (which does not make any sense to me). 

What I want to do is poll the data buffer so that I can determine the amount of data remaining in the buffer.  So far I have only been able to determine (by polling) that the buffer is willing to accept new data.  

So my question. Does anyone have a idea on how I can determine the percentage of fill in the output buffer?  

I am also open to any ideas on keeping the amount of data queued for output to a minimum, in a controlled fashion.


Thank You 

  Dennis Thompson

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  Center for Image Processing and Integrated Computing (CIPIC) 
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