Command Reference Guide

144 ● dtmf threshold 3Com Router 5000 Family and Router 6000 Family
Command Reference
Example Set DTMF threshold 9 in voice subscriber-line view.
[Router-voice-line0/0/0] dtmf threshold analogue 9 30
Restore the default of DTMF threshold 9 in voice subscriber-line view.
[Router-voice-line0/0/0] undo dtmf threshold analog 9
View This command can be used in the following views:
■ Voice Subscriber-Line view
Description The dtmf threshold command issues the thresholds for DTMF dial tone detection
to the underlying layer DSP for the purpose of tuning detection sensitivity and
reliability of the device subtly. Inside the DSP, a set of generic default values have been
configured. They are 1400, 458, -9, -9, -9, -9, -3, -12, -12, 30, 300, 3200, 375, with
their index being 0 through 12. Professionals can use this command to adjust the
device when DTMF digit detection fails. In normal cases, the defaults are adequate.
When the value2 argument is set to 0 or DTMF digit detection to insensitivity, the
neglect probability is decreasing and the detection error probability is increasing as
the DTMF digit collection tolerance becomes larger.
DTMF digit detection is implemented by calculating the spectrum of the input voice
signal. Its spectrum shape is restricted to the configured thresholds. A DTMF dial tone
is regarded valid only when all the constraints are met. To understand this, you must
be aware of DTMF dial tone, as shown in the following figure:
12 The lower threshold of the amplitude of the input signal. The
average amplitude must be greater than this threshold for the input
signal to be recognized as a DTMF digit.
This threshold is an integer in the range 0 to 700 and defaults to
375. A greater value means increased detection reliability but
decreased sensitivity.
This parameter is a time domain threshold, which is specified to
prevent the noise with small amplitude from being detected.
Index numbers Indicates