The LINEMONITORTONE structure describes a tone to be monitored. This is used as an entry in an array.

typedef struct linemonitortone_tag {

DWORD dwAppSpecific;

DWORD dwDuration;

DWORD dwFrequency1;

DWORD dwFrequency2;

DWORD dwFrequency3;




This field is used by the application for tagging the tone. When this tone is detected, the value of the dwAppSpecific field is passed back to the application.


The duration in milliseconds during which the tone should be present before a detection is made.




The frequency in Hertz of a component of the tone. If fewer than three frequencies are needed in the tone, a value of zero should be used for the unused frequencies. A tone with all three frequencies set to zero is interpreted as silence and can be used for silence detection.


No extensions.

The LINEMONITORTONE structure defines a tone for the purpose of detection. An array of tones is passed to the lineMonitorTones function which monitors these tones and sends a LINE_MONITORTONE message to the application when a detection is made.

A tone with all frequencies set to zero corresponds to silence. An application can thus monitor the call's information stream for silence.

See Also

LINE_MONITORTONE, lineMonitorTones

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