How were DTMF frequencies determined exactly and how can I extend them?

1. How are DTMF tones generated?
2. What method can be used to send DTMF tones?
3. What are the frequencies used in the DTMF phone?
4. What is DTMF duration?

How are DTMF tones generated?

As mentioned above, DTMF tones are created by the synchronized combination of the high- and low-frequency signal. The high-frequency signal of a key is determined by the column that the key is in, and the low-frequency signal is determined from the row that the key is in.

What method can be used to send DTMF tones?

You can use the vgwActSendDTMF action to send dual-tone multi-frequency (DTMF) tones to a caller as described in RFC 4733, section 3.2. IBM® Voice Gateway supports RFC 4733, RTP Payload for DTMF Digits, SIP Info, Telephony Tones, and Telephony Signals.

What are the frequencies used in the DTMF phone?

The DTMF keypad for consumer use is designed in a four-row by three-column matrix. Each dial row is represented by a low tone frequency and each column by a high tone frequency. The frequencies used are 697 Hz, 770 Hz, 852 Hz, 941 Hz, 1209 Hz, 1336 Hz, 1477Hz, and 1633 Hz.

What is DTMF duration?

Default. The duration of DTMF tones and the interval between DTMF tones are both 120 milliseconds.