How to hardware unite several audio outputs into one (by priority)?

Question

Iron

There are several devices with an audio output for connecting a headset (headphones). Either radios or phones.
In the case of three or more devices (a person has 2 ears), it is impossible to listen to everything at the same time, therefore, the task is to drive the sound from several devices into one headset.
In the case of walkie-talkies, the sound does not go constantly. Therefore, ideally, give sound to the headset by priority.
For example, 3 devices - A, B, C. with the help of jacks, dad-dad is connected to device D. From device D, the headset goes into the ear.
The task of two levels of difficulty, 1) to drive from A, B, C all at once into the ear.
2) device D has the ability to set priorities. A is the first, B is the second, C is the third. And if there is silence in A, C, then the sound comes from B to the ear; if there is silence only in B, then the sound comes from A, because it has a higher priority than C.
To solve problem 1, I'm thinking about just soldering. I know there are adapters for separation (you insert an adapter into the socket - a double and you can already insert 2 jacks into it). Is it possible to solder 3 jacks into one, so that from three sources everything goes into one?
2) Small hardware solution. The question is, does it exist? What would be easier to build on? I thought about arduino + jack modules + google_code_for_analysis_aduio_flow_to_implement_priority_system

Answer 1

3 solid-state relays (so as not to distort the sound) controlled by a microcontroller (STM, Atmega or someone else),
a signal level goes from each input to the ADC of the microcontroller (you can google what the connection will look like)
MK decides which of the 3 relays to connect to one or another moment of time, while the rest are turned off. It is possible, but why it is needed is not clear.

Answer 2

1 is not just soldered, but soldered through resistors.
2 from the output through the diode to the RC circuit, calculate the circuit for the target response time, from it either a comparator and further from the logic elements to taste, or, if the signal level allows, immediately logic elements with a Schmidt trigger at the input. Or a small controller with analog inputs (comparators or ADCs). Well, this economy manages even the simplest keys, even iron relays.