Dtmf

Hi,

DTMF is dual tone multi-frequency.
There is a row tone and a column tone.
These tones identify which key is pressed.

Question: Where did these tone values originated?

Were they assigned or there were some calculations to get them.

meowth08 said:

Hi,

DTMF is dual tone multi-frequency.
There is a row tone and a column tone.
These tones identify which key is pressed.

Question: Where did these tone values originated?

Were they assigned or there were some calculations to get them.

Click to expand...

Hi meowth08

Google and Wiki are wonderful sources of info you should try them one day

DTMF Tones

cheers
Dave

"The tone frequencies, as defined by the Precise Tone Plan, are selected such that harmonics and intermodulation products will not cause an unreliable signal. No frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies."

In addition, DTMF was designed in the days of analog filters so there was consideration in ability to select out given tone frequencies with reasonable Q tank circuits.

I began to work with telephone systems in 1980. The DTMF decoder ICs in those days made errors. A spec for a decoder was how many "talk-off" errors occured during one minute of normal speech where the DTMF decoder gave a false output.
Decoders are better today.