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how to capture line in

 
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Frank Cox



Joined: 13 Jun 2009
Posts: 17

PostPosted: Mon Jan 18, 2010 9:40 pm    Post subject: how to capture line in Reply with quote

I can't capture line in. I plugged speakers into the server computer and I can play a wav file on the speakers with "aplay test.wav"; that works fine.

I can stream audio from ogg files that I have on the server; that also works fine.

But I'm stumped as to how to capture line in to stream (or even play) that.

I have a FM receiver that I attached to the Line In plug and I have also tried it with a CD player that has a Line Out on it to be sure that I actually have sound input. No matter which player I use I apparently have no sound.

I have used alsamixer to set "capture" on Line In Mixer, Capture, and Capture 1. I have been using "aplay /dev/dsp" to test this, thinking that I should hear the audio (or something) on the local speakers, but all I get is silence. I tried other settings with alsamixer but the only one that seemed to make a difference was "DAC Mixer"; when I set "capture" on that I got a bunch of static on the speakers with "aplay /dev/dsp"

I have posted screenshots of my alsamixer settings here:

http://www.melvilletheatre.com/alsamixer-capture.png
http://www.melvilletheatre.com/alsamixer-playback.png

Can anyone tell me what I'm doing wrong or missing? Or give me suggestions as to something else to try?
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karlH
Code Warrior
Code Warrior


Joined: 13 Jun 2005
Posts: 5476
Location: UK

PostPosted: Mon Jan 18, 2010 10:10 pm    Post subject: Reply with quote

aplay /dev/dsp would be wrong, aplay is an alsa util, /dev/dsp is a oss reference. try arecord -f cd sample.wav (ctrl-C after a few seconds) then aplay sample.wav. That input source shows Mic

karl.
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Frank Cox



Joined: 13 Jun 2009
Posts: 17

PostPosted: Mon Jan 18, 2010 10:27 pm    Post subject: Reply with quote

> try arecord -f cd sample.wav (ctrl-C after a few seconds) then aplay sample.wav.

Dead silence

> That input source shows Mic

If you're referring to the last two settings on the right of the alsamixer screenshot I posted, their full names are apparently "Input Source" and "Input Source 1". Moving up and down with the cursor keys on those setting shows that my choices there are "Mic" and "Front Mic", and nothing else. Perhaps, based on that, Line In is not available as an input source, somehow? I thought that was what the "Capture" toggle meant; I suspect my understanding is wrong.

Can (should?) I use Mic instead of Line In? Would I be better off if I did so? My reading indicates that Mic takes a much lower input signal than Line In; does that need to be compensated for?
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Frank Cox



Joined: 13 Jun 2009
Posts: 17

PostPosted: Tue Jan 19, 2010 3:42 am    Post subject: Reply with quote

I think I have found the problem, though I don't know how to fix it.

"amixer" shows me this:

Simple mixer control 'Line In Mixer',0
Capabilities: cvolume cswitch
Capture channels: Front Left - Front Right
Limits: Capture 0 - 31
Front Left: Capture 24 [77%] [1.50dB] [on]
Front Right: Capture 24 [77%] [1.50dB] [on]

and

Simple mixer control 'Amp Selector',0
Capabilities: cenum
Items: 'Front Microphone' 'Microphone' 'Line In'
Item0: 'Line In'

and

Simple mixer control 'Input Source',0
Capabilities: cenum
Items: 'Mic' 'Front Mic'
Item0: 'Mic'
Simple mixer control 'Input Source',1
Capabilities: cenum
Items: 'Mic' 'Front Mic'
Item0: 'Mic'

As you can see, "Line" is missing as an option under Input Source.

Does anyone know how I can add it?
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karlH
Code Warrior
Code Warrior


Joined: 13 Jun 2005
Posts: 5476
Location: UK

PostPosted: Tue Jan 19, 2010 4:23 am    Post subject: Reply with quote

check the version of alsa you have /proc/asound/version and see if you need to update your drivers. A search on google for your chipset did highlight an interesting entry at
http://alsa-project.org/main/index.php/Changes_v1.0.21_v1.0.22

ALSA: hda - Fix input source selection of IDT92HD73xx

karl.
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Frank Cox



Joined: 13 Jun 2009
Posts: 17

PostPosted: Tue Jan 19, 2010 5:50 am    Post subject: Reply with quote

I took the path of least resistance. I put a microphone in front of a set of speakers and tried capturing the mic input. Which works fine. I am listening to my audio stream right now, in fact.

So I shall get an attenuator to drop the input signal from line level to mic level and hook up the tuner through the mic input, as that works.

In view of the bug fix that you found, I suspect that if I had installed the latest version of Fedora Linux on the streaming server this issue would not have come up. However, I got tired of the Fedora upgrade treadmill quite some time ago and am using Centos for all of my projects now. And now it's working. (Yippee, hooray, yahoo, and all that.)

Thanks loads for all of your assistance with this; I have learned a huge amount about streaming audio using your comments (both in this thread and in your replies to others on this message board) as a guide to what I should be researching through Google.

I am truly grateful to you. You're doing a really great thing here. Really.
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