Re: [Discuss-gnuradio] Resampling audio using rational resampler doesn't work for multimon-ng

[Marcus Müller]

Hum, this is a wild guess, but the sox aspect reinforced it:

somewhere, there's a network buffer overflowing. If that interpretation
is right, sox just adds a quickly-absorbing buffering layer to the
processing chain.

In any case, would sound like the pipe approach would be best. Is there
a reason not to use it? Maybe we can come up with a way to make
whatever it is work :)

Best regards,
Marcus

On Fri, 2019-05-24 at 13:29 +1000, Ignatius Rivaldi wrote:
> sox is the magic thing that makes netcat and multimon-ng works. Even
> if I don't do any resampling, ie sox -t raw -esigned-integer -b 16 -r
> 22050 - -esigned-integer -b 16 -r 22050 -t raw - and use the UDP
> channel from the resampled audio it works, while if I  in I pipe
> netcat directly into multimon-ng it doesn't work
> 
> On Fri, May 24, 2019 at 1:24 PM Ignatius Rivaldi
> <address@hidden> wrote:
> > Its the UDP sink. If I use File Sink to a named pipe file multimon-
> > ng
> > can decode it by using cat pipe | multimon-ng -Aq - but if I use
> > the
> > UDP port and netcat -ulk localhost 8000 | multimon-ng -Aq - it
> > doesn't
> > decode, so the resampler does work but somewhere in the UDP channel
> > something corrupts the data
> > 
> > On Sun, May 19, 2019 at 1:50 AM Kevin Reid <address@hidden>
> > wrote:
> > > On Sat, May 18, 2019 at 12:07 AM Albin Stigö <
> > > address@hidden> wrote:
> > > > You need to use a low pass filter (taps) in you resampler. Look
> > > > at the spectrum after the resampler and this will be obvious to
> > > > you. A lowpass filter with a cutt off at 3-4kHz or so should do
> > > > it.
> > > 
> > > This cannot be the problem, because rational_resampler
> > > automatically calculates a filter if taps are not specified:
> > > https://github.com/gnuradio/gnuradio/blob/4e4f44c726556496c420bceb87ccafe6843916f7/gr-filter/python/filter/rational_resampler.py#L107
> > > 
> > > (I also checked the GRC file, and the fractional bandwidth is
> > > also None (auto-set) despite appearing as "0" in the screenshot.)
> > > 
> > > Unfortunately, I don't have any ideas what the problem is. For
> > > what it's worth, I have successfully integrated multimon-ng into
> > > a flow graph (
> > > https://github.com/kpreid/shinysdr/blob/master/shinysdr/plugins/multimon.py
> > > ) but the code is very differently structured so it would be hard
> > > to transfer the knowledge into GRC.
> > > 
> > > As a next troubleshooting step I would recommend adding GUI sinks
> > > at various parts of the flow graph so that you can check the
> > > signal integrity. (For an example, consider adding after the
> > > float-to-short a short-to-float and QT GUI Sink — to ensure the
> > > signal hasn't gotten lost in quantization noise and just needs to
> > > be amplified before converting to short, as well as checking that
> > > the bandwidth/resampling is good.)
> 
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