Touch-Tones were analog.
That is very misleading. Rotary phones sent a sequence of electrical pulses to the CO switch either, crossbar or step-by-step. Both switching systems existed over a century ago, long before digital computers were created.
Touch Tones or DTMF (Dual Tone Multiple Frequency) telephone signaling was planned to be used on the old analog crossbar or step-by-step switches, but were used in the transition into digital frontend telephone switches like the 1ESS (Number One Electronic Switching System) and all the electronic switches that followed.
Each tone of a touch phone key was a combination of two frequencies together.
DTMF Frequencies | |||||||||||||||||||||||||
If you pressed the number one, the dual tone of 1209 Hz and 697 Hz was sent to the Central Office and is detected by the switch. Since analog switching goes back 125 years and rotary phones used electrical pulses like an old fashioned telegraph key, they are considered analog technology and the DTMF phones are considered digital because they more connected to the modern digital world. |
The dialing output of a rotary is digital. Just a bit more sophisticated than the wall switches installed in my house in the 50s.
The dialing output of a touchtone was analog.
We used to be able to “dial” a rotary with a lock on the dial by carefully tapping the switch under the handset.