Hello everyone.
My scenario is the following:
I have two phones let's name them P1 and P2.
I need to get the sound from P1 Out and redirect it in P2 In (Mic).
I also need to do the same thing but reversed, to get the sound from P2 Out and redirect it in P1 In (Mic).
So basically when P1 will sing P2 will be able to record the sound and when P2 sing P1 will be able to record that sound.
What I tried:
Test 1:
I bought 2 jack splitters, I connected to the phones and after I connected 2 audio extender cables in reversed order: P1 out to P2 In (Mic) and P2 out to P1 In (Mic).
The behavior was very strange. It was like Volume down button was pressed. I recorded some sound with this method but it works just one way.
Test 2:
I tried to cut a 4 pin audio extender cable and just solder the wires in reverse order. P1 (left or right) out to P2 In (Mic), and P2 (left or right) out to P1 In (Mic) and Ground to Ground.
Of course, it didn't worked, it behaved just like in Test 1.
After that I found that documentation here
https://source.android.com/devices/accessories/headset/jack-headset-spec
It said that some impedance is required. (I mention that I have limited experience and knowledge in electronics.)
Applications for this project:
Recording, audio bridge for voip calls (whatsapp and skype, for example), avoid huge call taxes when you are in roaming by remote calling Voip to Regular Phone and so on.
Thank you in advice for any suggestion,
Cristian.