page_title: Dual-tone multi-frequency signaling
section_title: Decoding
hierarchical_section_title: Dual-tone multi-frequency signaling / Decoding
caption_attribution_description: English: 1&amp;1 NetXXL powered by FRITZ! - CMD CM8870CSI (CMOS Integrated DTMF Receiver) on mainboard
context_page_description: Dual-tone multi-frequency signaling is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized as ITU-T Recommendation Q.23. It is also known in the UK as MF4.
  The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service. Other multi-frequency systems are used for internal signaling within the telephone network.
context_section_description: DTMF was originally decoded by tuned filter banks. By the end of the 20th century, digital signal processing became the predominant technology for decoding. DTMF decoding algorithms typically use the Goertzel algorithm. As DTMF signaling is often transmitted in-band with voice or other audio signals present simultaneously, the DTMF signal definition includes strict limits for timing (minimum duration and interdigit spacing), frequency deviations, harmonics, and amplitude relation of the two components with respect to each other (twist).
caption: Two CMD CM8870CSI DTMF Receivers
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