In the case of DTMF, 12 segments are stored and recalled for use in subsequent tests. Storage of Segments. The waveform generator should offer memory management technology that supports the storage of the waveforms created. In the case of the “1” key, 15 cycles at 697 Hz and 26 cycles at 1209 Hz yield a differential of 3 degrees only. In order to solve the problem, we must define the number of cycles for each frequency that will result in a zero (or close to zero) degree phase differential. Because the two waves are not harmoni¬cally related, a problem arises with the phase relationship of the two signals when created over a single cycle, as shown in Figure 1 below. Take, for example, the encoding of the “1” key, which uses the 697 Hz and 1209 Hz frequencies. Sine wave addition and cycle adjustment. The two sine waves must be summed and programmed to complete their cycles at or near the same phase. The generator must be capable of performing the following functions: In testing these systems, it is necessary to add noise to simulate the worst-case signal quality that the systems are required to support.Ī sophisticated waveform generator is required to test DTMF systems. A table of frequencies and encoding combinations appears in Table 1 below.ĭTMF-based systems must be able to function reliably over noisy transmission lines. DTMF signaling is widely used in telephony and IVR (interactive voice response) applications. Using DTMF, a key press results in the generation of 2 tones using distinct frequencies, with a different combination representing each key. DTMF (Dual-Tone Multi Frequency), or “touch-tone” signaling, was developed as a handset-to-switchboard signaling system for use over analog telephone lines.

Dtmf ivr