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audacity under jack records system capture and not output

Posted: Sat Oct 30, 2010 3:54 pm
by nickleus
i looked at the thread about audacity and jack and made a patchbay thing for it, but audacity still records the system capture (mic) and NOT the system output, with or without using patchbay.
i'm using 1.3.12-beta on ubuntu 10.10.

in the properties recording dropdown box there are the following:
system
hydrogen
zynaddsubfx

i want system, but when i choose it it records the system capture (mic) and not the system output

Re: audacity under jack records system capture and not outpu

Posted: Sun Oct 31, 2010 8:41 am
by bgravato
What host have you selected? If it's ALSA change to JACK. You should get more options in the recording device dropdown menu. If you don't have JACK as an option in host, maybe that version of the package in ubuntu wasn't compiled with proper jack support... (it happened on Debian and it was recently upgraded).

Re: audacity under jack records system capture and not outpu

Posted: Sun Oct 31, 2010 10:33 am
by nickleus
yes, jack is selected. and "Recording > system" records the mic, not the system output. seems like a bug to me.

Re: audacity under jack records system capture and not outpu

Posted: Sun Oct 31, 2010 5:17 pm
by bgravato
nickleus wrote:yes, jack is selected. and "Recording > system" records the mic, not the system output. seems like a bug to me.
That is the expected behaviour in a normal system...

Do you have qjackctl installed on your system? If not install it and open it, it will help you to see the architecture of jackd's inputs and outputs...

Once you open qjackctl click on the "Connect" button. You'll see a list of active inputs and outputs. On the left pane you have the Outputs and on the right pane you'll have the Inputs.

If you expand "System" on the left pane you'll probably see listed "capture_1" and "capture_2", this probably captures and outputs what is coming from the mic. This is what will be outputted by the system.

If you expand "System" on the right pane you'll probably see listed "playback_1" and "playback_2". This is system's inputs. So if you send something to the system it will send it to playback, which probably means sending the sound to the speakers.

When you make a connection on JACK you have to connect an output to an input and the sound will flow from the output to the input. You can't connect an output to another output, or an input to another input. Must always be output -> input.

Applying this to Audacity... Well audacity's recording is an input (in gets sound in it), so you'll have to connect an output to it). If you connect system to it, then it will be system output -> audacity input. As you can see in jack connections system output is capture_1 and capture_2.

I hope this explains it clearly :)

Re: audacity under jack records system capture and not outpu

Posted: Sun Oct 31, 2010 9:31 pm
by nickleus
bgravato wrote:
nickleus wrote:yes, jack is selected. and "Recording > system" records the mic, not the system output. seems like a bug to me.
That is the expected behaviour in a normal system...

Do you have qjackctl installed on your system? If not install it and open it, it will help you to see the architecture of jackd's inputs and outputs...

Once you open qjackctl click on the "Connect" button. You'll see a list of active inputs and outputs. On the left pane you have the Outputs and on the right pane you'll have the Inputs.

If you expand "System" on the left pane you'll probably see listed "capture_1" and "capture_2", this probably captures and outputs what is coming from the mic. This is what will be outputted by the system.

If you expand "System" on the right pane you'll probably see listed "playback_1" and "playback_2". This is system's inputs. So if you send something to the system it will send it to playback, which probably means sending the sound to the speakers.

When you make a connection on JACK you have to connect an output to an input and the sound will flow from the output to the input. You can't connect an output to another output, or an input to another input. Must always be output -> input.

Applying this to Audacity... Well audacity's recording is an input (in gets sound in it), so you'll have to connect an output to it). If you connect system to it, then it will be system output -> audacity input. As you can see in jack connections system output is capture_1 and capture_2.

I hope this explains it clearly :)
that's a great explanation, thanks =) it just seems backwards =) when you think of speakers you think of output and mic you think of input, not the other way around, but i'll trust you on this one =) i guess i've never noticed this in qjackctl before...

Re: audacity under jack records system capture and not outpu

Posted: Sun Oct 31, 2010 9:46 pm
by bgravato
nickleus wrote:that's a great explanation, thanks =) it just seems backwards =) when you think of speakers you think of output and mic you think of input, not the other way around, but i'll trust you on this one =) i guess i've never noticed this in qjackctl before...
Imagine a traditional analogic hifi system where you have a mixer, a mic and a tape recorder. You want to record the sound from the mic to a tape, going through the mixer. What do you do?
1) connect the mic to an input connector on the mixer
2) connect the mixer's output to the tape recorder's input
3) start recording

Now imagine JACK is the mixer and Audacity is the Tape recorder.

The mic is an input to the mixer, but it will then become an output from the mixer to the tape recorder. Here with JACK and Audacity the same thing happens! ;)

Re: audacity under jack records system capture and not outpu

Posted: Mon Nov 01, 2010 2:56 am
by bgravato
You might be interested in jack_capture.

Description take from Debian's package jack-capture (at the moment only available in sid/unstable):
Description: program for recording soundfiles with jack
With this program you can record any sound which is
played via jack.
.
jack_capture allow you record to all formats supported by sndfile.
(wav, aiff, ogg, flac, wavex, au, etc.)

Re: audacity under jack records system capture and not outpu

Posted: Mon Nov 01, 2010 9:04 am
by nickleus
bgravato wrote:You might be interested in jack_capture.
that's exactly what i did, i installed jack_capture and it works magnificently =)

fyi, for ubuntu 10.10, you have to download the source and build it yourself:
http://archive.notam02.no/arkiv/src/

and make sure to install this package before you try to build it: libjack-jackd2-dev