Question: how many dtmf tones are there?
Answer: There are twelve DTMF signals, each of which is made up of two tones from the following selection: 697 Hz, 770 Hz, 852 Hz, 941 Hz, 1209 Hz, 1336 Hz, 1477Hz. The tones are divided into two groups (low and high), and each DTMF signal uses one from each group.