DTMF
DTMF (dual-tone multi-frequency) is the pair of tones a phone sends when a key is pressed, used by IVRs and voice agents to read keypad input.
Each key on a phone keypad produces two tones at once, one from a low-frequency group and one from a high-frequency group, which a receiving system decodes into the digit. That is how “press 1 for sales” menus and PIN entry work.
Voice agents still use DTMF alongside speech for things callers would rather type than say out loud, such as account numbers, PINs or card details, and for callers in noisy places. VocalStack Voice supports DTMF alongside speech.
