+VSD Silence Detection command not working on Conextant-based modems

[emxsys]

Problem: The modem, after answering a call, does not detect/report the silence after the caller hangs up. Upon investigation, I note the modem accepts, but does not apply, the provided silence detection settings.

Test details: I opened up a terminal session with the modem (using minicom on Linux) and attempted to set a silence detection of 5 seconds in voice mode. The modem accepts the +VSD=128,50 command, but the silence detection remains disabled (0 seconds), as reported by the modem. This can be seen in the following minicom log, annotated with my comments.

---

Welcome to minicom 2.7.1

OPTIONS: I18n
Compiled on Aug 13 2017, 15:25:34.
Port /dev/ttyACM0, 13:33:04

Press CTRL-A Z for help on special keys

I entered atz to reset the modem
OK

I entered ate1 to echo my commands to the screen
OK

at
OK

at+vsd? # query silence detection settings before entering voice mode
ERROR # returned expected error: not in voice mode

at+fclass=8 # enter voice mode
OK

at+vsd? # query silence detection settings
128,0 # returned silence detection disabled: 0 secs
OK

at+vsd=? # query silence detection accepted parameter values
(0-255),(0-255)
OK

at+vsd=128,50 # set silence detection to 5 seconds
OK

at+vsd # query silence detection settings
128,0 # silence detection is still disabled. Expected 128,50
OK

[J0hnMatrix]

Hello,
Same result here:

Welcome to minicom 2.7.1

OPTIONS: I18n
Compiled on Aug 13 2017, 15:25:34.
Port /dev/ttyACM0, 14:56:17

Press CTRL-A Z for help on special keys

atz
OK
ate1
OK
at
OK
at+vsd?
ERROR
at+fclass=8
OK
at+vsd?
128,0
OK
at+vsd=?
(0-255),(0-255)

OK
at+vsd128,50
ERROR
at+vsd=128,50
OK
at+vsd?
128,0
OK

Event if you try another numbers, the result is the same:

at+vsd=127,70
OK
at+vsd?
128,0
OK

Maybe a kind of "commit" command needs to be type after the "at+vsd=xxx,xxx" or maybe this command is unsupported as the returned values are 0-255,0-255 for both sds and sdi?

[emxsys]

@J0hnMatrix I'm testing the following block of code in Modem.record_audio. Seems to work in bench tests. Will test and refine on a live phone system.

 # Test for silence on Zoom modems (Conextant). The +VSD doesnt work on these modems.
 if self.model == "ZOOM":
     # Silent frames are made of a mix of \x80 and \x79 bytes, with 90% or more == \x80.
     count = audio_data.count(b'\x80')
     if count >= (CHUNK * 0.90):
         silent_frame_count += 1
     else:
         silent_frame_count = 0
     if silent_frame_count > 40: # 40 frames is ~5 secs
         print(">> Silent frames detected... Stop recording.")
         break