DTMF Frequency vs. DTMF Codes Explained

This page explains DTMF (Dual Tone Multi Frequency) signal frequencies and DTMF signal codes. DTMF signaling is commonly used in local access networks where the transmission path between the transmitter and receiver is a 2-wire analog subscriber line. This signaling method is employed in telecommunication networks from one end to the other.

The figure above illustrates standard touch-tone frequencies and their corresponding keys/codes. Each key press generates two frequency tones that are transmitted on the transmission line. This dual-tone generation is represented by rows and columns. For example, when the ”*” key is pressed, it generates frequencies of 941 Hz and 1209 Hz simultaneously.

The table below lists the DTMF frequencies, categorized as “low group frequencies” and “high group frequencies,” for each DTMF code.

Refer to Pulse Dialing vs Tone Dialing for more information.