SIGNAL GENERATION CIRCUITS Application Note 97: Jul 09, 1998 Telephone Tone Generator Requires No Trimming Many products that connect to phone lines (modems, for instance) incorporate a "callprogress monitoring" function known as CPM.
CPM circuits "listen" to the lines as a human would, and respond according to what they "hear.
" You shouldn't dial a number unless you first hear a dial tone, for example.
Neither should your computer.
Tone accuracy is not very important when people monitor the call-progress tones, but the use of computers for this purpose has produced a need for tone-accuracy specifications to prevent errors in interpretation.
Accordingly, CCITT has introduced the North Amer...

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