DTMF Recognition


This article helps to understand whats is DTMF Signal and to check your sound card if it can recognize DTMF signals. Possibility to recognize DTMF signals is needed when radio subscriber initiate call to telephone subscriber and don't use text message (Control Station and Capacity Plus configurations). 

A DTMF signal consists of the sum of two sinusoidal waves, frequencies of which correspond to the numerals of dialed number. In case of Control Station usage, possibility to recognize DTMF tones depends on quality of the audio channel and quality of the sound card.

Verification of DTMF recognition:

1.     Audio file recording (with DTMF tones)

1.1.   Make sure that SmartPTT Radioserver is started

1.2.   Launch Sound Recorder program on the PC where SmartPTT Radioserver is started (Start/Programs/Accessories/Entertainment/Sound Recorder)

1.3.   Push the button Record 

1.4.    Make a private call to the Control Station

1.5.    Sequentially push 1,2,3,4,5,6,7,8,9,0 buttons on the radio’s keypad

1.6.   Then release PTT button of the radio

1.7.   Push the button Stop 

2.     Launch Cool Edit Pro or Adobe Audition program

2.1.    Open recorded audio file (menu File/Open)

2.2.   Choose View/Spectral View

2.3.    Assess spectral view of the audio file


Spectral view of DTMF tones of high quality:

Spectral view of DTMF tones of low-quality:

Signal with such spectral view cannot be processed by SmartPTT Radioserver.

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