I’ve been an Audacity user for quite a while now, and I’ve used it for a multitude of projects. Lovely program it is.
Of late, I’ve come into a project when I need to use the old Bell System MF tones. I have the barest idea of how to use the Nyquist language, so I have no idea how to write the plugin myself. I had the idea of modifying the DTMF generator, but I have no idea how to go about doing it (also, there’s the fact that the DTMF system doesn’t generate in the same manner as the Bell (R1) MF system).
For anyone who is interested in helping out by writing this generator, here’s the pertinent information regarding the Bell MF signalling system (which is the same as the ITU “R1” signalling scheme).
The tones used by the system are:
- KP 1100 Hz + 1700 Hz
- ST 1500 Hz + 1700 Hz
- 1 700 Hz + 900 Hz
- 2 700 Hz + 1100 Hz
- 3 900 Hz + 1100 Hz
- 4 700 Hz + 1300 Hz
- 5 900 Hz + 1300 Hz
- 6 1100 Hz + 1300 Hz
- 7 700 Hz + 1500 Hz
- 8 900 Hz + 1500 Hz
- 9 1100 Hz + 1500 Hz
- 0 1300 Hz + 1500 Hz
(If you’ll notice, the digit tones of the MF system follow a two of five code, with the 700, 900, 1100, 1300 and 1500 values corresponding to 0, 1, 2, 4, 7; the KP (start of pulsing) tone and ST (end of pulsing) tone use the 1700 tone plus 2 and 7, respectively. The European R2 MF signalling system uses the other combinations of 1700 with 0, 1, and 4 for more tones, but nevermind the R2 system.)
The KP tone must being 100 ms long, plus or minus 10 ms; and the digit and ST tones must be 68 ms long, plus or minus 7 ms. There must be 68 ms of silence between each signal, plus or minus 7 ms. Transmissions start with KP, and end with ST, tones are sent “en bloc”, so no pauses.
I.e. a number dialed as “1 (pause) 800 (pause) 555 (pause) 1212”, would be sent as “KP 18005551212 ST” (where the spaces are only inserted for clarity).
In terms of input to the generator, all that is really needed is the input of the number to be generated (with KP and ST generated automatically), and the volume.
Thanks to any one who is willing to take on this task, I wish I could be of more help.