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.
(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? Or would it make more sense for the application to mix the channels into a 2 channels output (in software)?(C)
dmix: Does ALSA use dmix if the sound card supports hardware mixing? 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? 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? If an application opens "surround51" device, would it hold the device exclusively and preventing other media application from using it? If so, are they any standard dmix device name for surround51?(D)
Sampling Rate: What is the best Sampling Rate to be produced by a media application for ALSA and ALSA dmix device? 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 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?(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.htmlAre there any per-process Volume Control interface available?
Thanks very much.
Daniel
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