DTMF detector system and method which performs improved twist computation and thresholding

A method for detecting dual tone multifrequency (DTMF) signals with improved twist computation and thresholding, comprising:

• receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups;
• determining energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame;
• determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame;
• comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame;
• determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame;
• and
• setting said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.

A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising:

• means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups;
• a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame;
• wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame;
• wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame;
• wherein said digital signal processor calculates a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.

A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising:

• means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups;
• a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame;
• wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame;
• wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame;
• wherein said digital signal processor sets said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.

A method for detecting multi tone multifrequency (MTMF) signals, comprising:

• receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups;
• determining energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups for a first frame;
• determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said one or more frequency groups for said first frame;
• comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame;
• determining if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame;
• and
• calculating a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.

A multi tone multifrequency detector for detecting multi tone multifrequency (MTMF) signals, comprising:

• means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups;
• a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups;
• wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said one or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame;
• wherein said digital signal processor determines if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame;
• wherein said digital signal processor calculates a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.