"Telephone Call Progress Detection Method" published in IBM Technical Disclosure Bulletin, vol. 28, No. 5, Oct., 1985. |
"Voice Detection and Discrimination" published in IBM Technical Disclosure Bulletin, vol. 27, No. 11, Apr., 1985. |
"Automatic Ringback Detector" by E. Federman and A. Ruiz, published in IBM Technical Disclosure Bulletin, vol. 24, No. 1B, Jun. 1984. |
"Detection Of Telephone Line Control Signals" by T. M. Campbell, published in IBM Technical Disclosure Bulletin, vol. 24, No. 1B, Jun. 1981. |
"Ring-Back Procedure For An FDM Telephone System" by D. R. Irvin, published in IBM Technical Disclosure Bulletin, vol. 22, No. 4, Sep. 1979. |
"Error Reduction Method For A Digital Signal Processing Voice And Audible Telephone Ring Tone Detection Algorithm" published in IBM Technical Disclosure Bulletin, vol. 28, No. 9, Feb. 1986. |