| Dear all ALSA Users, Recently my team and I are making an attempt to record audio signals from an open source sound card called 8 Sounds USB (http://sourceforge.net/p/eightsoundsusb/wiki/Main_Page/) and were facing great difficulty in the most fundamental of issues, being unable to get any signals recorded from the sound card/mic array system for months until we found out that the issue could be solved by enabling audio capture on the sound card in Alsamixer as shown on the page: (http://alsa.opensrc.org/Record_from_mic) . With the capture enabled, we were able to actually record down signals from all the microphones in the array with the Audacity application, and play them back without a glitch. However, we are really puzzled as to why enabling capture in Alsamixer solved the problem, so this comes to our first question of: 1. How does enabling capture in alsamixer actually allow for a device to be able to start recording signals when previously, without capture enabled, although we could detect the device on our system (but that too is quite fuzzy, with certain commands, we were able to detect the device, while with other means we did not detect the device on Ubuntu) in audacity at least, we could not get any recorded signals (we can initiate the recording but get zero inputs, no spikes whatsoever) ? what changes did alsamixer actually make to ALSA (its drivers etc) that would have miraculously enabled the signals to be recorded? Also, we made an observation that might be interesting and we are not sure if it has anything to do with the alsamixer enabling capture issue. Basically on the Ubuntu laptop that we have, we identified our sound card to be numbered as device 1. So when we do a listing of the /proc directory tree for this sound card, we get: augustine@augustine-ubuntu:~$ tree /proc/asound/card1 /proc/asound/card1 ├── id ├── pcm0c │ ├── info │ ├── sub0 │ │ ├── hw_params │ │ ├── info │ │ ├── status │ │ └── sw_params │ └── xrun_debug ├── pcm0p │ ├── info │ ├── sub0 │ │ ├── hw_params │ │ ├── info │ │ ├── status │ │ └── sw_params │ └── xrun_debug ├── stream0 ├── usbbus ├── usbid └── usbmixer 4 directories, 17 files And when we do a cat of the following directory when we are no doing any recording with Audacity, we get: augustine@augustine-ubuntu:~$ cat /proc/asound/card1/pcm0c/sub0/status state: RUNNING owner_pid : 4614 trigger_time: 26673.762479721 tstamp : 28544.782938570 delay : 926 avail : 926 avail_max : 926 ----- hw_ptr : 82477944 appl_ptr : 82477018 And this is the case all the time we are doing a recording, regardless of whether we have enabled or have not enabled Alsamixer capture for our sound card device numbered 1 on our machine. The only difference it seems, when we enable capture, is that we actually get a audio recording, as opposed to not getting anything when we don’t. Lastly, to complete the observation, we found that when we stop the recording in Audacity and do the same cat command, we get: augustine@augustine-ubuntu:~$ cat /proc/asound/card1/pcm0c/sub0/status closed So our second question would be: 2. What exactly does the /proc/asound/card1/pcm0c/sub0/status file tell us, and if we see a “RUNNING” state regardless of whether we have enabled alsamixer capture or not (as implied by what we observed), then does this suggest that alsamixer is independent from the /proc/asound/card1 directory? We really appreciate all your help and thank you all in advance! We have always been struggling to wrap our heads around ALSA and issues arising from getting our mic array + sound card system to work with our Ubuntu 14.04 machine, and any help here will be appreciated! Please feel free to chip in with comments even if they do not answer our questions too. PS: I’m not too sure if my mail should go to the developers mailing list too. If it should, please let me know and I’ll post it up there too. Best regards, Augustine Koh
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