[Discuss] line in for Intel sound chipset apparently has quit working with Debian Jessie kernel upgrade

Alan W. Irwin irwin at beluga.phys.uvic.ca
Tue Jun 6 11:55:51 PDT 2017

On 2017-06-06 06:14-0700 pw wrote:

> Looks like all the drivers are loading.
> What does the '/dev' path have for hard links?
> is there '/dev/tvaudio' by any chance?
> That should be a PCM device that you can just cat to a file and then
> load with audacity.

Hi Peter:

There is nothing in the top-level of /dev that looks relevant
(i.e., no hits with pcm, audio, or sound in the name).

Here is everything in /dev/snd

irwin at raven> ls -l /dev/snd
total 0
drwxr-xr-x  2 root root       80 Jun  4 12:51 by-path/
crw-rw----+ 1 root audio 116,  5 Jun  4 12:51 controlC0
crw-rw----+ 1 root audio 116,  2 Jun  4 12:51 controlC1
crw-rw----+ 1 root audio 116, 10 Jun  4 12:51 hwC0D0
crw-rw----+ 1 root audio 116,  7 Jun  6 00:03 pcmC0D0c
crw-rw----+ 1 root audio 116,  6 Jun  6 09:40 pcmC0D0p
crw-rw----+ 1 root audio 116,  8 Jun  5 14:37 pcmC0D1p
crw-rw----+ 1 root audio 116,  9 Jun  4 12:51 pcmC0D2c
crw-rw----+ 1 root audio 116,  3 Jun  6 00:03 pcmC1D0c
crw-rw----+ 1 root audio 116,  4 Jun  4 12:51 pcmC1D1c
crw-rw----+ 1 root audio 116,  1 Jun  4 12:51 seq
crw-rw----+ 1 root audio 116, 33 Jun  4 12:51 timer

irwin at raven> ls -l /dev/snd/by-path/
total 0
lrwxrwxrwx 1 root root 12 Jun  4 12:51 pci-0000:00:1b.0 -> ../controlC0
lrwxrwxrwx 1 root root 12 Jun  4 12:51 pci-0000:04:00.1 -> ../controlC1

Recall these results:

irwin at raven> lspci |grep Bro
04:00.0 Multimedia video controller: Brooktree Corporation Bt878 Video Capture (rev 11)
04:00.1 Multimedia controller: Brooktree Corporation Bt878 Audio Capture (rev 11)

So from the 04:00.1 coincidence in the numbers it appears
/dev/snd/controlC1 is associated with the Bt878 audio capture (and 
/dev/snd/controlC0 associated with audio capture from the Intel sound

Also from the "C1" I assume /dev/snd/pcmC1D* are PCM devices associated
with the Bt878.  However,

irwin at raven> cat /dev/snd/pcmC1D0c >|test.wav
cat: /dev/snd/pcmC1D0c: File descriptor in bad state

Note, the "groups" command confirms the irwin account belongs to the audio group
so the above bad result is not due to some permissions problem.

Since cat doesn't work, I assume there must be some other means to get
access to Bt878 sound chip capture results.

Or better yet, why not start with attempting to capture sound from the
Intel sound chip (which I have never done before) since I am more
confident that chip should work compared to the uncertainties in the
Bt878 case.  Once I have a working method for the Intel sound chip,
then I should be able to infer what might work with the Bt878.

Here is what alsamixer says are the Intel (Card: HDA Intel, Chip:
Realtek ALC883) capture channels (using F6
to get to the intel chipset and F4 to look at just capture channels).

<Front Mic Boos>  Line Boost      Capture       Capture 1
Digital      Input Source  Input Source 1 Rear Mic Boost

I am going to ignore the Mic stuff because I don't have access to a
microphone.  Also, the Digital channel is simply a volume slider, I
don't have a clue what it refers to, but I think it is irrelevant
since I am not aware of any digital input channels available with my
Intel sound chipset. I do apparently have a means (through the PHONES
jack on my ghetto blaster) that is independent of my TV card of
transmitting analog audio signals to line-in on the Intel sound chip.
So for the line-in capture case can you help me interpret the non-mic
non-digital channels above?

Line Boost is a volume slider that starts at dB gain: 0.00, 0.00 so I
will probably leave that at the minimum level.  Capture and Capture 1
are volume sliders that start at dB gain: -12.00, -12.00 and end at dB
gain: 34.50, 34.50 so I will probably leave Capture (likely associated
with Input Source) near the top of its range and Capture 1 (likely
associated with Input Source 1) at the bottom of its range. Both Input
Source and Input Source1 provide a choice (which you can get to with
up and down arrow keys) between Line, Rear Mic, and Front Mic.  So to
capture from line-in I assume I would set Input Source to Line and the
volume of that would be controlled by the Capture slider, and I would
set Input Source 1 to one of the mic choices so it doesn't interfere
with Input Source. Do you confirm from your own experiments with
alsamixer that is likely the right alsamixer setup to capture line-in?

And once alsamixer is set up properly for capturing Intel sound chip
line-in, how can I play that captured sound (since your cat trick does
not appear to work with the above pcm* files)?

Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).

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