Ask HN: How did/does the "dial tone" work?
I haven't heard it in a while, but IIRC it's two synthesized tones roughly a "major third" apart (https://en.wikipedia.org/wiki/Major_third), slightly buzzy-sounding, which means they probably weren't a "just" major third (https://en.wikipedia.org/wiki/Just_intonation).
Once you started dialing, the dial tone would go silent. I think the dial tone would remain in place if you spoke, but I don't remember for certain.
Does anyone know how this worked? What generated the dial tone? Presumably there must have been a network of machines responsible for processing people's dialing and routing calls appropriately; did these machines also generate the dial tone? If so, were they all made by the same company, Bell-something-something? The dial tone was/is so consistent in its sound and behavior that it seems likely.
Just curious if anyone knows or has links!
https://de.wikipedia.org/wiki/Ruf-_und_Signalmaschine
Dialing a number was done by DTMF dual-tone, multi-frequency tones or by pulses (interruptions of the circuit).
And to answer your likely next question: No. The ringing tone was not synchronized with the bell on the target telephone.
There is actually a picture of the dial tone generator in Flickr. Motor was moving generators on various speeds. https://www.flickr.com/photos/9479603@N02/1814546737/in/phot...
As regards to logistics of tones and stuff. You dont want to know. It involved multi-level signalling of currents and voltages.