On Thu, Jun 4, 2009 at 1:28 PM, Lex Wassenberg<lex.wassenberg@xxxxxxxxx> wrote: > Hi all, > > I'm completely new to ALSA, so forgive me if these are newby questions. > > I'm working on an application which receives sound chunks via an IP > connection, and it should use the local sound card to make this sound > audible. Up to now it used OSS, but there were some problems with > that, so I'm busy with rewriting the application to ALSA. The sound is > 16-bit stereo, sampled at 8000 Hz, and it comes in chunks of 1024 > frames. I managed to get things more or less working, but there are > still some things unclear to me. > > 1. If I open the soundcard with device "default" or device "plughw" I > get good sound, but the device "default" only accepts 1020 frames of > every 1024 that I offer it (as can be seen from the return value of > snd_pcm_writei() ). The device "plughw" nicely accepts all 1024 > frames. Why is this? In both cases I have set the sample rate to 8000 > via a call to snd_pcm_hw_params_set_rate_near() and the buffer size to > 2048 frames via snd_pcm_hw_params_set_buffer_size_near(). > > 2. If I use device "default", there seems to be no obligation to set > the buffer size nor the period size, I still get good sound at the > output. If I use "plughw", I have to set either the buffer size (2048 > frames) or the period size (1024 frames), otherwise I get distorted > sound. If I set both (the buffer size being 2048 and the period size > being 1024) I also get distorted sound. Why? > > 3. If I set the buffer size twice the period size (as above), and ask > the sizes back, ALSA nicely reports the buffer size as being twice the > period size. But if I ask the buffer and period TIMES, they are > reported as being the same: 128000 us! Huh???? > > 4. The return value of snd_pcm_hw_params_set_rate_near() is sometimes > 8000, sometimes 7999, from the very same program. I would expect ALSA > to always return the same value, be it what I request or not, but at > least being deterministic. How can this be? > > 5. There is another application running on the same target system, > which will sometimes produce audible alarms. However, if my > application is running that other application cannot generate the > alarms, it produces a "resource busy" error. It is clear to me that my > application is using the sound card exclusively, but how can I get it > to allow other applications access to it too? I tried using the device > "dmix", but then my sound is again very distorted. > > Hope that somebody can help me out. > Thanks in advance. > > Lex > Is there nobody that can help me out on the questions above? I figured the answer to question 4 (passing a pointer to an uninitialized integer; I thought the integer was only used for reporting back, which is not true), but all other questions still stand. Nobody?? Lex _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
