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

[Ignatius Rivaldi]

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.)