540 Voice API for Windows Operating Systems Library Reference — November 2003
Supplementary Reference Information
6.2 DTMF and MF Detection Errors
Some MF digits use approximately the same frequencies as DTMF digits (see Table 27 and
Table 28). Because there is a frequency overlap, if you have the incorrect kind of detection enabled,
MF digits may be mistaken for DTMF digits, and vice versa. To ensure that digits are correctly
detected, only one kind of detection should be enabled at any time. See the dx_setdigtyp( )
function description for information on setting the type of digit detection.
Digit detection accuracy depends on two things:
•the digit sent
•the kind of detection enabled when the digit is detected
Table 29 and Table 30 show the digits that are detected when each type of detection is enabled.
Table 29 shows which digits are detected when MF digits are sent. Table 30 shows which digits are
detected when DTMF digits are sent.
Table 28. MF Tone Specifications (CCITT R1 Tone Plan)
Code Tone Pair
Frequencies (Hz)
Default Length
(msec) Name
1 700, 900 60 1
2 700, 1100 60 2
3 900, 1100 60 3
4 700, 1300 60 4
5 900, 1300 60 5
6 1100, 1300 60 6
7 700, 1500 60 7
8 900, 1500 60 8
9 1100, 1500 60 9
0 1300, 1500 60 0
* 1100, 1700 60 KP
# 1500, 1700 60 ST
a 900, 1700 60 ST1
b 1300, 1700 60 ST2
c 700, 1700 60 ST3
* The standard length of a KP tone is 100 msec