Voice API Programming Guide — June 2005 77
Call Progress Analysis
7.15.6 Setting Single Tone Frequency Detection Parameters
The information in this section does not apply to DM3 boards, as the DX_CAP fields mentioned in
this section are not supported on DM3 boards.
The following paragraphs describe how to set single tone frequency detection on Springware
boards.
Setting single tone frequency detection parameters allows you to identify that a SIT sequence was
encountered because one of the tri-tones in the SIT sequence was detected. But frequency detection
cannot determine exactly which SIT sequence was encountered, because it is necessary to identify
two tones in the SIT sequence to distinguish among the four possible SIT sequences.
The default frequency detection range is 900-1000 Hz, which is set to detect the first tone in any
SIT sequence. Because the first tone is often truncated, you may want to increase ca_upperfrq to
1800 Hz so that it includes the third tone. If this results in too many false detections, you can set
frequency detection to detect only the third tone by setting ca_lowerfrq to 1750 and ca_upperfrq to
1800.
The following fields in the DX_CAP are used for frequency detection. Frequencies are specified in
Hertz, and time is specified in 10 msec units.
ca_stdely
Start Delay: the delay after dialing has been completed and before starting frequency
detection. This parameter also determines the start of cadence detection. Default: 25 (10 msec
units).
ca_lowerfrq
lower bound for tone in Hz. Default: 900.
ca_upperfrq
upper bound for tone in Hz. Default: 1000.
ca_timefrq
time frequency. Minimum time for 1st tone in an SIT to remain in bounds. The minimum
amount of time required for the audio signal to remain within the frequency detection range
specified by ca_upperfrq and ca_lowerfrq for it to be considered valid. Default: 5 (10 msec
units)
7.15.7 Obtaining Single Tone Frequency Information
The information in this section does not apply to DM3 boards, as the DX_CAP fields mentioned in
this section are not supported on DM3 boards.
Upon detection of a frequency in the specified range, you can use the ATDX_FRQHZ( ) extended
attribute function to return the frequency in Hz of the tone detected in the range specified by the
DX_CAP ca_lowerfrq and ca_upperfrq parameters. The frequency returned is usually the first tone
of an SIT sequence.