Am Donnerstag, den 28.01.2016, 14:00 +0100 schrieb Pander:
> On 01/28/2016 01:51 PM, Markus Glugla wrote:
> > 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
>
> Make sure to validate what the impact is of including or omitting the
> last sample as it often is not complete and distorts the spectrum, see
> my earlier analysis with graphs illustrating that.
>
I read your hints, thank you very much.
I think, it is typical of FFT which needs a even number of samples (2n).
On short sequences, the 2n FFT array is longer than the sequence you get
also porblems. A FFT with a number of less than 2n will be incorrect. I
think it's better to cut the sequence on right position to 2n before
FFT, is'nt? What is with windowing?
Thank you for your hint,
Markus
> >
> >
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