How were DTMF frequencies selected?

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sameerbabu

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On what basis DTMF frequencies were selected? ANy body is having any idea? CAn we choose diffrent frequencies?
 

Re: DTMF frequencies?

DTMF = Dual Tone Multiple Frequencies. It uses selected audio frequencies for row and column of a number pad of an analog telephony system.

The selection basis is such that none of the frequency is a harmonic or a multiple of one another. Therefore there is no aliasing.

When a number is pressed, two frequencies (one from the row and the other from the column) are sent to the public switched telephone network (PSTN). These tones are used to differentiate which number is pressed by the calling party.
 

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