Master clocks have their place.
These were far more expensive.
I worked on Central Office Phone Switches 1983-1995 or so. A big one would cover a basketball court. A bigger one would occupy several floors of a downtown building.
It had a Master Clock module, providing clock (probably) to (eventually, including repeaters/distributors) every card in the local system.
Each analog phone line would be digitized (ADC) at an 8kHz sample rate. The active lines in a Line Frame would be multiplexed (time slots) on to a cable going to one of the Switching Frames.
The time-multiplexed samples were then space-multiplexed by switch (changing their time slot assignments) and sent out on different cables, again time multiplexed and sent to another Line Frame to be demultiplexed to the Line Card handling the other phone in the conversation, or, if the call was to terminate externally to the office, to a time slot on a Trunk going down the road.
A small office would be TST - time space time, a larger facility would be TSST adding another space switching step.
The voice calls were - regardless of the distance, synchronous - one sample in, one sample switched, one sample delivered to the destination line card's DAC and cable to the phone.
Since the base 8kHz rate had to match among different Offices, that Master Clock was really a slave to the clock rate on a selected Trunk line from another office. Ever make a call and hear tick-tick-tick as the time slots slipped due to missing sync somewhere?
It could free-run if the distant clock disappeared, so it had to be stable to maintain reasonable sync with other offices during such an outage.
Later, Sonet (Synchronous Optical Network) came into being, along with the need for the whole network of machines to be synced for the signalling (SS7) and time multiplexed voice samples got to the destination on time and in order.
Then that all blew up and is likely replaced with VOIP, voice mingled with Internet Traffic, no longer single synchronous voice samples delivered to a destination, but bundles of your voice samples delivered to a destination to be resampled and ASRC'd at the endpoint.
At home, I don't think about it. Stuff works and doesn't squeal or tick so it must be working just fine.
The
Ceiling Fan, somebody moving in the room, even just waving your hand creates more disturbance in the Audio delivered to your ears than what is seen from any imperfections in the electronic's clock, in my view
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