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Comment by antiterra | Hacker News Reader

I really like how you can figure out the phone number dialed with the representation of the DTMF tones. This was basically an audio coordinate system (or just a 2D array): an X tone and a Y tone played at the same time.

The upper component has three positions representing the columns on a phone keypad.

The lower four positions represent the rows.

For example, zeros are represented by upper tone 2 for the middle column (2,5,8,0) and lower tone 4 for the bottom row (*,0,#).

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https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_sign...

There was a fourth column (A,B,C,D) meant for menu selection, and for the US military to indicate call precedence. Also used for various kinds of system automation and signaling but not accessible directly.

Generate them all with:

      sox -n dtmf-1.wav synth 0.1 sine 697 sine 1209 channels 1
      sox -n dtmf-2.wav synth 0.1 sine 697 sine 1336 channels 1
      sox -n dtmf-3.wav synth 0.1 sine 697 sine 1477 channels 1
      sox -n dtmf-4.wav synth 0.1 sine 770 sine 1209 channels 1
      sox -n dtmf-5.wav synth 0.1 sine 770 sine 1336 channels 1
      sox -n dtmf-6.wav synth 0.1 sine 770 sine 1477 channels 1
      sox -n dtmf-7.wav synth 0.1 sine 852 sine 1209 channels 1
      sox -n dtmf-8.wav synth 0.1 sine 852 sine 1336 channels 1
      sox -n dtmf-9.wav synth 0.1 sine 852 sine 1477 channels 1
      sox -n dtmf-0.wav synth 0.1 sine 941 sine 1209 channels 1
      sox -n dtmf-star.wav synth 0.1 sine 941 sine 1336 channels 1
      sox -n dtmf-pound.wav synth 0.1 sine 941 sine 1477 channels 1
      sox -n dtmf-A.wav synth 0.1 sine 697 sine 1633 channels 1
      sox -n dtmf-B.wav synth 0.1 sine 770 sine 1633 channels 1
      sox -n dtmf-C.wav synth 0.1 sine 852 sine 1633 channels 1
      sox -n dtmf-D.wav synth 0.1 sine 941 sine 1633 channels 1

      sox -n dtmf-us-busy.wav synth 10 sine 480 sine 620 channels 1
      sox -n dtmf-rbt-US.wav synth 10 sine 440 sine 480 channels 1
      sox -n dtmf-uk-us-dialtone.wav synth 11 sine 350 sine 440 channels 1
      sox -n dtmf-uk-busy.wav synth 10 sine 400 channels 1 # needs cadence
      sox -n dtmf-uk-ringback synth 10 sine 400 sine 450 channels 1
      sox -n dtmf-eur-dialtone.wav synth 10 sine 425 channels 1
      sox -n dtmf-eur-busy.wav synth 10 sine 425 channels 1 # needs cadence
      sox -n dtmf-eur-ringback.wav synth 10 sine 425 channels 1 # needs cadence

I had forgotten about those! I had a phreaking program[1] with those on the C-64. They called the DTMF utility 'Silver Box.'

Turns out: https://en.wikipedia.org/wiki/Silver_box

[1] It was this one: https://commodore.software/images/jdownloads/screenshots/tel...

And they sounded _weird_. Almost spacey.

You have also just described how the old analog touch tone phones actually generated the tones. Each column of buttons generated a different tone per column, and each row also generated another tone per row. A given button when pressed activated a column and a row to generate the two tones associated with that button.

Yes, that's what my intent was.

Where I'm from we used pulse dialing. I remember being so proud of myself for figuring out that the number of pulses the phone sent represented the digit you're dialing.

This was basically an audio coordinate system (or just a 2D array): an X tone and a Y tone played at the same time.

Auditory....Vectors? (Thinking aloud)

The Quadrature Amplitude Modulation used by the modem (the last part of the sequence, which sounds like white noise) really is a sequence of auditory vectors.

Humans can't hear a phase difference.

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