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Re: [Discuss-gnuradio] Resampling audio using rational resampler doesn't


From: Ignatius Rivaldi
Subject: Re: [Discuss-gnuradio] Resampling audio using rational resampler doesn't work for multimon-ng
Date: Fri, 24 May 2019 13:24:33 +1000

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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