I'm not sure whether I should put this or in multimon-ng github page. multimon-ng wants 22050 Hz sample rate, and to feed this I use this flow:
To generate the APRS RF signal I used USRP B210 and another gnuradio flowgraph.
If I use sox to resample the 48 kHz audio into 22050 Hz, using this command: netcat -ulk ::1 8001 | sox -t raw -esigned-integer -b 16 -r 48000 - -esigned-integer -b 16 -r 22050 -t raw - | multimon-ng -Aq - , multimon-ng decodes the APRS signal normally. If I use rational resampler to resample it inside Gnuradio from 48k to 22050, and run multimon-ng with this command: netcat -ulk ::1 8000 | multimon-ng -A - it doesn't decode the APRS signal at all.
The thing is that if I generate the signal from inside the flowgraph, by using NBFM transmit, and resample it then connect it into frequency xlating filter instead of the RTL-SDR source, both sox resampler and rational resampler works, same if I use audio source instead of RTL-SDR.
I have the flowchart attached