Ok so I have tried something else.
In the console, I am executing the below comand:
pi@raspberrypi:~ $ pactl load-module module-loopback latency_msec=1 source=1 sink=0 | multimon-ng -a DTMF /dev/stdin
It is successfully working:
multimon-ng 1.1.8
(C) 1996/1997 by Tom Sailer HB9JNX/AE4WA
(C) 2012-2019 by Elias Oenal
Available demodulators: POCSAG512 POCSAG1200 POCSAG2400 FLEX EAS UFSK1200 CLIPFSK FMSFSK AFSK1200 AFSK2400 AFSK2400_2 AFSK2400_3 HAPN4800 FSK9600 DTMF ZVEI1 ZVEI2 ZVEI3 DZVEI PZVEI EEA EIA CCIR MORSE_CW DUMPCSV X10 SCOPE
Enabled demodulators: DTMF
If I try to launch the very same command using Node-RED and having a look at the logs, I am getting the below error message:
Failed to parse module arguments
Failed to load module "module-loopback" (argument: "latency_msec=1 source=1 sink=0 | multimon-ng -a DTMF /dev/stdin"): initialization failed.
^C
I also found a similar thread here: Exec Node and Terminal Problem ( Alsa)
Not sure it is related to the same issue...
I am really clueless... Why would it work with the console, and not node-Red ?