Detection of both voice and tones using Goertzel filters
Device for automatically identifying DTMF and FSK for caller ID
Device for detecting tones on telephone lines
Dial tone detector
Dial tone detector
Digital composite tone alerting
Digitally controlled ring signal generator
Digitally controlled ringer signal generation
Distinctive ringing and distinctive call-waiting tones in an ISD
Distinctive telephone annunciator
Dual signal triggered message waiting notification system for in