Re: spectrogram values

[Markus Glugla <markus.glugla@physik.tu-berlin.de>]

Am Mittwoch, den 20.01.2016, 03:37 +0100 schrieb Thor Andreassen:
> On Fri, Jan 08, 2016 at 03:31:18PM +0100, Markus Glugla wrote:
> > Hi,
> 
> Hi Markus
>  
> > I read the spectrogram threads and affiliate a request. I'm using
> > sometimes sox spectrogram to get an spectral overview of various
> > measurement datas. But i want to plot the spectrogram with other tools
> > e.g. gnuplot.
> > 
> > I would be very grateful if it were possible to output the spectrogram
> > data as plotable values in a file or stream. Does anybody have the
> > same intention and more experience than me to produce a patch?
> 
> I have been planning to implement an amplitude and water-fall output,
> that can be sent to Gnuplot. I will need these in the coming months, so
> perhaps it will get done.
> 
> A crude way of getting the raw numbers could be to use the color values
> from the generated png file, e.g. with Imagemagick:
> 
>     sox -n -n synth 1 synth 1k:5k spectrogram -r -o - |
>     convert png:- txt:-                 |
>     
>     # translate into Gnuplot compatible input
>     awk -v FS='[,:() ]+' 'NR > 2               { print $1, $2, ($3+$4+$5)/3 }'  |
>     awk                  'NR > 2 && $2 != prev { printf "\n" } { prev = $2 } 1' \
>     > spectrogram.dat
> 
> Note the use of the `-r` option to sox, which omits all decorations. See
> `sox --help-effect spectrogram` for more.
> 
> Now plot the data file with Gnuplot:
> 
>     echo 'splot "spectrogram.dat" with pm3d' | gnuplot --persist
> 
> If you want to get at the raw spectrogram, you need to patch
> spectrogram.c. The attached patch works best with single channel files.
> Use the new `-O filename` switch to save the binary data.
> 
> The default output is a sequence of floats which are 4 bytes long. This
> is also Gnuplots default for binary input. This means you can plot the
> output like this:
> 
>     echo 'plot "<sox -n -n synth 1 sine 1k:5k spectrogram -O -" \
>             binary array=(513,800) flipy rotation=90d with image' |
>     gnuplot --persist
> 
> Note that if your output from sox is short, the spectrogram dimensions
> will be different from 800x513 and Gnuplot will barf.
> 
Hi Thor

Thank you for your source code and your patch. I enjoy about your idea
which increases the productivity. 

It is also in my opinion to use gnuplot as plotting tool to create
spectrogram in the same, my, style.

I also think about the grab the spectrogram datas via imagemagick. But
in this case it is easier to use GSL.

Thank you for your help. Your code snippets are very informative.

Markus


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