Type in your phone number 1234567890*# or an 'alphabetized' number
1800nyquist. You can also enter the military's A, B, C and D.
Characters other than these produce a length of silence.
Volume indicates the linear level for each tone (there are two
tones in each DTMF signal). There is also tone length (duration),
high to low tone ratio ('twist' in telephone jargon), and post tone
silence length (duration of silence after each DTMF signal).