User's Manual

Chapter 4 – Voice Commands
Multi-Tech Systems, Inc. SocketModem MT5634SMIxx Reference Guide (S000263C) 113
Command: +VSD=<sds>,<sdi> Set Silence Detection Sensitivity
Values: 0–256 (in 0.1 second intervals)
Result Codes: OK if modem accepts the command; ERROR if one or more of the following apply: 1) the
<sds> or <sdi> parameter entered is out of range, or 2) either of the two parameters is
missing from the command string. If an error occurs, modem retains the previous <sds>
and <sdi> parameter values.
Description: The +VSD= command sets the silence detection sensitivity and the required period of
silence before the modem reports silence detected at the end of a voice receive, either
with the Presumed End of Message (Quiet) or Presumed Hang Up (Silence) event
reports. The table below outlines the possible combinations of the +VSD and +VSM
commands using the <sds> parameter. An <sdi> parameter value of 0 means that long-
term silence detection is disabled. (Note that long-term silence detection refers to the
use of this function to detect the end of a voice receive (i.e., the user stops talking).
+VS<sds> +VSM Silence Compression in Use +VSM Silence Compression Not Used
0 Use +VSM silence compression
setting and algorithm for long-term
silence detection.
Use default long-term setting silence
detection level and algorithm,
not 0 Sets long-term silence detection setting independent of presence or use of
silence detection, where:
<sds> = 128; nominal level of silence detection sensitivity
<sds> > 128; more aggressive level of silence detection sensitivity (less
sensitive, higher noise levels considered to be silence).
<sds> < 128; less aggressive level of silence detection sensitivity (more
sensitive, lower noise levels considered to be silence).
The parameter <sds> is used by the PC to select greater amounts of modem silence
detection activity; larger values imply that the PC wants the modem to treat noisier
conditions as silence. The value entered for <sds> has no actual unit of measure. The
modem may limit silence detection sensitivity to a more narrow range (e.g., from 120 to
136). A setting of 0 has no meaning.
The parameter <sdi> sets the required period of silence before the modem can report
silence detected either with the Presumed End of Message (Quiet) or Presumed Hang Up
(Silence) event reports. A value of 0 disables modem silence detection, in which case the
modem will not report the Presumed End of Message (Quiet) or Presumed Hang Up
(Silence) event reports.