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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. [ 2 ]
Digits are usually sent at a minimum of 55 milliseconds (ms) in length with at least 55 ms of silence between each digit. Some decoders may require much longer-duration digits. DTMF digits consist of paired tones: a row tone and a column tone. The levels of row and column tones must be similar in order for a decoder to interpret them reliably.
Multifrequency signaling is a technological precursor of dual-tone multi-frequency signaling (DTMF, Touch-Tone), which uses the same fundamental principle, but was used primarily for signaling address information and control signals from a user's telephone to the wire-center's Class-5 switch. DTMF uses a total of eight frequencies.
The Goertzel algorithm is a technique in digital signal processing (DSP) for efficient evaluation of the individual terms of the discrete Fourier transform (DFT). It is useful in certain practical applications, such as recognition of dual-tone multi-frequency signaling (DTMF) tones produced by the push buttons of the keypad of a traditional analog telephone.
A cue tone is a message consisting of audio tones, used to prompt an action.. In broadcast networks, a DTMF cue tone or subaudible tone was traditionally used to prompt insertion of a local TV commercial or radio advertisement by the broadcast automation equipment at the broadcast station or cable headend.
The use of digital squelch on a channel that has existing tone squelch users precludes the use of the 131.8 and 136.5 Hz tones as the digital bit rate is 134.4 bits per second and the decoders set to those two tones will sense an intermittent signal (referred to in the two-way radio field as "falsing" the decoder).
Pressing a single key of a traditional analog telephone keypad produces a telephony signaling event to the remote switching system. For touchtone service, the signal is a dual-tone multi-frequency signaling tone consisting of two simultaneous pure tone sinusoidal frequencies. The row in which the key appears determines the low-frequency ...
In the case of Quik Call I or a string of DTMF digits, the falsing would have to occur in the exact order required to actuate the decoder. This is much more improbable than falsing in a single tone decoder. In two-tone sequential, tone and voice radio paging, decoders are actuated by decoding one tone and then a second in the proper sequence.
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