Hi Chuck, > I was talking to a telecom guy about this problem and he claims that 90% of > the signaling gear he encounters, generates the DTMF with a syntesizer chip. > This > means that the two tones are essentially equal in amplitude and their phase > relationship is constant. You can't design telco gear assuming this, but you > also can't design RS-232 interfaces with just a diode :-) The phase relationship is not constant so if the tones start in phase it is a bit of information of almost no value. Cheers -- Kalle Pihlajasaari kalle@data.co.za Interface Products Box 15775, Doornfontein, 2028, South Africa +27 (11) 402-7750 Fax: +27 (11) 402-7751