Soundcard 'monitor' stream doesn't arrive with Spectrum plugin

[Stefan Sauer]

On 06/12/2012 04:25 PM, Cefn Hoile wrote:
> On 12 June 2012 14:40, Stefan Sauer <ensonic at hora-obscura.de> wrote:
>> On 06/12/2012 04:13 AM, Cefn Hoile wrote:
>>> I'm hoping to base a tutorial demo on the first python example linked
>>> below, and I attempted to test its logic by playing music from
>>> Rhythmbox through my (Ubuntu Oneiric) soundcard while visualising the
>>> result of the 'spectrum' FFT as changing numbers streaming on the
>>> console. Sadly this first debugging step was a failure.
>>>
>>> http://pzwart3.wdka.hro.nl/wiki/Spectrum.py
>>>
>>> The spectrum plugin loaded by this python script only ever reports -60
>>> decibels for every frequency band in the spectrum, regardless how loud
>>> I turn up the music!
>> You can change that:
>> spectrum threshold=-96
>>
>> Stefan
>>> I have tried both alsasrc and pulsesrc with various device names
>>> (default, pulse, the introspected alsa monitor device name from pactl)
>>> at the beginning of the listener_desc pipeline (declared in the linked
>>> code). In most of the cases I've tried (barring typos) the pipeline
>>> seems to be established and run perfectly fine (as far as I can tell)
>>> but somehow no sound frequencies show up in the frequency analysis
>>> from the spectrum plugin.
>>>
>>> Does this python code work for anyone else? How would I verify that
>>> the pipeline is correct, or narrow down the problem? Any suggestions
>>> what the initial source plugin or entire pipeline should in fact be on
>>> an Ubuntu system to get loudnesses per frequency range streaming out
>>> of the spectrum plugin to the console using this code as a reference?
>>>
>>> Thanks for any help.
>>>
>>> Cefn
>>> http://cefn.com
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>>> gstreamer-devel at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
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> Thanks for the suggestion, Stefan. You're right you can change it :)
> Now I get regular lines which report -96 instead of -60 ...
>
> data: -96.0 -96.0 -96.0 -96.0 -96.0 -96.0 -96.0 -96.0
>
> My current pipeline looks like this...
>
> pulsesrc device="alsa_output.pci-0000_00_1b.0.analog-stereo.monitor" !
> spectrum threshold=-96 interval=1000000000 bands=8 ! fakesink
>
> ...and still the DB levels never vary depending on output from the soundcard.
Then I'd say there is a different problem. Are you sure you are
monitoring the right monitor-port?
Try gst-launch -e pulsesrc
device="alsa_output.pci-0000_00_1b.0.analog-stereo.monitor" ! wavenc !
filesink location=monitor.wav
and check the resulting wav file.

Stefan
>
> Cefn
> http://cefn.com
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