When a tone is detected, it will generate an out of band DTMF event which will be sent to the PBX. With DTMF Detection enabled, the Sangoma card will use the echo canceler chip to listen for incoming tones.

There are two configuration options available for the Wanpipe driver that relate to DTMF. If your Sangoma card is equipped with a hardware echo canceler, you can use it to detect DTMF tones which come through the card. For DTMF to work reliably, the audio on the line must be clear and of high quality. It is important to bear this in mind when troubleshooting problems with DTMF. Due to the nature of DTMF and inband signaling in general, any noise or distorting of audio on the line will in turn distort the tone, making detection by a remote system impossible. This is referred to as in-band signaling because we are using the same channel as the voice conversation to send the signaling tones. Because DTMF tones are simply audio on the line, they can be heard in any conversation or audio recording on the line. These frequencies are described in standards which ensure compatibility between different systems. The combination of two tones of certain frequencies will signify a digit being pressed on the keypad.

For more information, see the wikipedia article on DTMF ( ).ĭTMF tones are generated by combining two tones of different frequency. There are many other applications for this signaling.

It features audible tones in the frequency range of the human voice which are typically used when dialing a call (on analog lines) or when operating an IVR menu. DTMF (Dual Tone Multi Frequency) is a type of signaling used primarily in voice telephony systems.

Dtmf frequency