At Thu, 28 Sep 2006 01:54:47 -0700, Daniel Yek wrote: > > Hi, > > I have a lot of questions here; please feel free to pick and choose while answering > them. I hope all questions will eventually be answered. > > (A) Test Channels: > > I have the following sound card. > Card: Intel ICH7 > Chip: Analog Devices AD1981B > (AD1981B is AC '97 2.3 Compliant CODEC, 2 Channels of Audio with SPDIF) > > Why the following code reports that the system supports 6 channels audio > when the "default" device is used? > channels = 6; > snd_pcm_hw_params_test_channels( PCMHandle, hwparams, channels); > > As a result, many channels were simply lost, not being heard. The same happens even on > a 5.1 system if "default" device is used. This function returns whether the sound system _accepts_ the given number of channels. It doesn't care whether it's really played or not. Since "default" PCM uses plug layer, it accepts any number of channels. > (B) > > Plug: > > If opening "surround51" device failed, does it make sense for a > media application to try to open "plug:surround51"? > > Would "plug" play 5.1 channels content without losing any > channel? If _opening_ surround51 fails, it's usually a problem of device assignment (e.g. the device is already in use). The surround51 usually doesn't do softmixing unlike "default" PCM. The plug layer would be useful if you play sample formats that the hardware doesn't support, for example, playing 16bit format on ICE1712 boards. Basically, it's safe to use "plug:surround51" when you know you are going to play 5.1 sound. But, this doesn't guarantee that the device can be opened (because of non-dmix nature). > Or would it make more sense for the application to mix the channels into > a 2 channels output (in software)? No. > (C) > > dmix: > > Does ALSA use dmix if the sound card supports hardware mixing? No (usually). The configuration file for each driver is written to use the appropriate hw or plughw for such a hardware (e.g. emu10k1). > Are there different levels of hardware mixing supports? That is, if a > sound card has hardware mixing support, does it always has 5.1 channel > hardware mixing support? Not really. Currently, surround* and iec958 (spdif) are supposed to be non-mixing devices unless the hardware supports. The setup of 5.1-dmix isn't provided in the standard configuration yet. > ALSA library version 1.0.9rc2 and later is using dmix by default. > In the case of the sound card supporting hardware mixing, should a > demanding media application prefers another device name because > "default" is now configured with dmix? Yes. > If an application opens "surround51" device, would it hold the > device exclusively and preventing other media application from using it? Yes (in most cases). > If so, are they any standard dmix device name for surround51? Not yet. It's one of TODOs. > (D) > > Sampling Rate: > > What is the best Sampling Rate to be produced by a media application for > ALSA and ALSA dmix device? 48000. In the recent version, it can be changed via a system-wide setup (defaults.pcm.dmix_rate), though. > The following page claimed that dmix write directly to the soundcard's > DMA buffer. > Does that implicitly referring to sound card with hardware mixer? > > http://www.alsa-project.org/alsa-doc/doc-php/asoundrc.php No. > The same page says that ALSA dmix device is default to RATE=48000. > With sound quality in mind, should a media application with resampling > capability tries to resample to 48000Hz in software or should it let dmix > or the hardware handle resampling? The dmix cannot use the hardware resampling because the hardware _is_ running on 48kHz. Once ago I made an experimental patch to change dmix code to accept both 44.1 and 48kHz depending on the first application. But it's racy, so isn't a good solution yet... > (E) > > Volume Control: > > How can I use ALSA's Playback controls volume level interface? > Is it for the application to use or more for alsa-lib? > Refer to > > http://www.sabi.co.uk/Notes/linuxSoundALSA.html Every ALSA-native mixer app uses the mixer API. Also, some media players use it, too. > Are there any per-process Volume Control interface available? Not yet. It's on my TODO list. Currently, a player needs to pick up either "Master", "PCM" or whatever existing volume element. Takashi ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
