I've never been able to find any figures for the operating voltages typical of analog audio circuits. Everything is always expressed in terms of impedance, which isn't really helpful to me. How does one determine the correct full-scale voltage for a given audio input jack?

 

Hello,

Do you mean line-in and line-out?
https://en.wikipedia.org/wiki/Line_level

Bertus

 

There are specifications for "Line In" and "Line Out" voltages. An unmarked audio jack may or may not comply with those requirements. For example it might be designed for a particular type of microphone of which there are mote than a few different types. It might also be designed for either high or low impedance headphones. In short, you just can't say with certainty by looking at it. You must depend on the manufacturer of the equipment to tell you what the intended use should be.

https://en.wikipedia.org/wiki/Line_level#:~:text=The line in/out connections on consumer-oriented audio equipment,channel, and right channel, or stereo RCA jacks.