What are dual tone multi frequency tones?

Dual-tone multi-frequency dialing refers to the fact that when a non-rotary phone dials, it sends two tones at the same time. When these tones are put together, a distinct sound is created, which is...

It is a dial tone ( like Morse Code) and functions as the carrier wave for the phone call, once ( dialed up) the message traffic rides on the carrier. ( not necessarily Flat on top- pun intended with...

Sounds consist of fundemental tones and overtones. A single frequency is a fundemental tone.

Middle C is 261.626 Hz

"Tone-Tone"