Method and apparatus for decoding DTMF tones

Abstract

A method for decoding a DTMF tone which includes collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; counting within the predetermined time the number of signal zero-crossing points; performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; identifying a first frequency that has the strongest magnitude from the resulting data; and calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal. The invention also includes apparatus that utilizes a zero-crossing detector for receiving a DTMF tone to be decoded and producing a digitized output; apparatus for collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; apparatus for counting within the predetermined time the number of signal zero-crossing points; apparatus for performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; apparatus for identifying a first frequency that has the strongest magnitude from the resulting data; and apparatus for calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal.

Dependencies are inferred from the claim text.