[Alsa-user] Screwy full duplex audio with SB Vibra16C.

[Jeff Pierce]

I am really getting frustrated.

I am writting a VOIP app for amateur radio which has been half duplex sound, but now needs to go to FULL duplex.
My app uses OSS type access, ioctl calls, as many using it only have OSS free from teh kernel distrobutions.

Ok, I get alsa 0.9.0rc6 and compile and install it for via82c686, which I get running with the half duplex code. No problem. I then write a super simple app using OSS ioctl to test if full duplex will work that way, not using alsa api. It simply reads the /dev/dsp and just writes the buffer right back to /dev/dsp. Run it on and it works no problem. Using alsamixer to change the line out audio on the pcm control, etc.

Ok I have another Linux box with a SB Vibra16C to do testing between the two boxes. I install alsa 0.9.0rc6 on it and install for sb16. I try running my full duplex app on it. What an abortion!!!

First, in alsamixer, where is the "mixer" control to keep mic from going directly to output. I find "auto mic", UNMUTING it stops mic from output with no app working.

Then the really big problem. When running my fullduplex app, the mic audio is once again at the output, albeit at a lower volume and the pcm control HAS NO EFFECT on it, and the actual audio read from and written to /dev/dsp is 5 seconds behind my speaking it, if it makes it at all. This is the audio that the pcm control will vary.

It seems to me the snd-sb16 has a whole lot of problems, beacause code that works perfectly on a via82c686 alsa driver screws up on a sb16 alsa driver.

Even my half duplex VOIP code that runs perfectly on oss SB16 and alsa via82c686 has problems running with alsa sb16. Run the sb16 oss drivers and audio is IMMEADIATLY sent to the receiving machine. Run it using alsa sb16 and sometimes it has a 5-7 second delay BEFORE it is sent. Stop the app and restart it,nothing done to alsa drivers, and you do not have the delay.

What's wrong with the alsa sb16 driver?

Both Linux systems running 2.4.16 kernel.

I want to tell users of my app to use ALSA drivers instead of OSS to get ready for full duplex. But, no way I can do that when one of the most popular sound cards, SB16 isa, driver doesn't work.

--
Jeff, wd4nmq
[EMAIL PROTECTED]
http://mywebpages.comcast.net/wd4nmq



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