Why are these details needed here?

Question

Electronics

Diagram for connecting audio output to audio input.


1. Why do we need resistors for the first circuit and will it work without them?
2. Why is ground connected to the microphone wire?
3. Please explain the principle of operation of 2 circuits.

Answer 1

The picture is not a diagram. The picture is some kind of artistic abstraction.
It seems like they tried to depict on it how the existing audio signal can be brought into the audio input, for example, on a home-made device, and these are two connection options.
If you make a homemade amp or something like that, then there may be a problem of hum from interference when connecting a source, so to solve this problem, they put resistors that will reduce the rumble from interference to a minimum.
Exactly, I read the comments. There would be no need to immediately write what it was about, arranged a guessing game.
This design is needed in order to direct the sound that goes to the headphones to the microphone input, in the second circuit they make mono from the stereo signal (the microphone is mono), plus lower the signal level so as not to "yell" into the receiver too loudly, the output signal level to the headphones is too powerful for the microphone input .
Without resistors it will be too loud, plus there is a chance to burn the microphone input, try only at your own peril and risk.

Answer 2

Signal level matching and transient current limiting