OK, from what I understand, dial tones replaces manual telephone office operators. Instead of having them connect you to your number, the numbers you press correspond to particular frequency which get recognized automatically by a computer and automatically connects you to that number
Except, how do the tones even get recognized? I use audacity for instance which has a pitch recognition feature. It’s… Not the best and can and will get things wrong on crystal clear audio
Phone audio on the other hand? The connection would be weak, someone playing or shouting something in the background could mess with the dial tone data sent to the office (of which I am aware phreaking exploited)
It’s the late 70’s. How did the telephone office computers recognize the tones perfectly and without error? All it takes is someone shouting or playing something in the background or a telephone microphone with terrible frequency response, or electromagnetic interference to mess with the dial tone data sent to the office and confuse it
This could cause everything from numbers never going through, to connecting one to the wrong number, yet this never happened, on 70’s tech no less
What did they do for crystal clear tone recognition in the 70s that my audio software on my 2019 laptop can’t?
In: Technology
Because when you pressed the button, it cut off the microphone so there was no background noise getting through. Also a single tone could easily accidently be sent, but in a DTMF system (Dual Tone Multi Frequency) it is two tones in a 3 x 4 matrix, one tone for each row, one for each column. And to not trigger on transients, both tones had to be present for over 40ms. I worked in a telephone exchange for many years and never had anything like a whistle dial a digit.
yo that’s a good question man. they used something called dual-tone multi-frequency signaling. two tones at once made it easier to tell the number. kinda genius right? plus their tech was built for that kinda clarity. makes our stuff look lame. guess they had no background noise drama back then too
To add to what others have said, there is the older technology of pulse dialling that was developed in the 1890s the was standard until tone dialling was developed in the 1960s. In a pulse dial phone you would put your finger in the hole on the dial corresponding to the digit to dial, rotate it to the stop position and release it. As the dial rotated back to its rest position, it generated a series of electrical pulses. The higher the number the further dial rotates, so the more pulses get generated. At the exchange, a machine counts the pulses and rotates an electrical switching device by the number of pulses, stopping once the pulses end, making the connection for that digit. While tone dialling was invented in the 1960s, it took time for exchanges to be updated, and more modern exchanges could cope with both pulse and tone dialling.
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