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+VSM
Select Voice Compression Method
Description:
Sets the modem to a specified voice compression method, silence compression
sensitivity, and voice sampling rate. The modem can maintain a different event
detection capability for each compression method. For example, you may want to
record your welcome message with the lowest amount of silence removal, with the
goal of reducing distortion. For other messages you may want a more assertive
silence removal, to limit disk space used for recording purposes.
Syntax:
AT+VSM=<cml>,<vsr>,<scs>,<sel>
Values:
<cml> A decimal number identifying the compression method. The valid values are
<vsr>
<scs> A <range of values> containing the supported range of sensitivity settings for
<sel>
Result Codes:
OK if the modem accepts the command.
ERROR if one or more of the following apply: 1) the any parameter entered is out of
range, or 2) any of the four parameters are missing from the command string. If an
error occurs, the modem retains the previous <sds> and <sdi> parameter values.
Reports:
+VSM?
+VSM=?
Multi-Tech Systems, Inc. AT Commands for the MultiModem & SocketModem MT9234 Series (S000434D)
1, 129, 130, 140, 141.
A <range of values> containing the supported range of for voice samples per
second of the analog signal (8000).
voice receives.
Has different meanings in voice transmit and voice receive modes.
In receive, the PC uses <scs> to select greater amounts of compression
activity; larger <scs> values mean that the PC wants the modem to treat
noisier conditions as silence. There is no unit of measure for this parameter;
it merely represents a number in a range.
In voice transmit mode, the PC signals the modem that the data stream was
recorded with silence compression by selecting a non-zero value from within
the valid range (the same value as receive).
Unpredictable results can occur if you 1) enable silence compression for
transmitting a voice data stream that was not recorded with silence
compression enabled, or 2) you disable silence compression for transmitting
a voice data stream that was recorded with silence compression enabled
A <range of values> containing the supported range of expansion values for
voice transmit. This parameter represents the minimum amount of silence
that the modem will expand a period of silence that was previously deleted
with a non-zero <sel> parameter. A setting of <sel>=0 means the modem
will not modify the silence expansion. The valid range of values is ____ -
____ in 0.1second increments. The modem ignores the <sel> parameter if
the <scs> parameter is 0 (silence compression disabled).
You can modify the silence expansion with the <sel> parameter. The range
of valid values is 0–255. The modem may limit silence compression
sensitivity to a narrower range (e.g., 120–128). A setting of <scs>=0
disables silence compression.
Displays current or selected values.
Reports <cml>,<vsr>,<sds>,<sel>
Example: 1,8000,0,0. This is the default.
The +VSM=? command reports several compression method identifiers
in one of two ways: either 1) a compression method (for PCM coding)
from the table below, or 2) a co-operative identifier (non-PCM coding)
used with other manufacturer's equipment.
Reports the following:
<cml> See above
<cmid> An alphanumeric string describing the compression method
(UNSIGNED PCM, IMA ADPCM, 2-Bit ADPCM, or 4-Bit
ADPCM)
Continued on next page.
Chapter 4 – Voice Commands
51
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