I am unable to record digital audio (e.g. from a computer or another phone) with my Android device. I have plugged in a TRRS audio and mic splitter and plugged that into my phone, and used a male-to-male cable to connect my source device to the mic input. It can be seen that the built-in mic is not recording, but all it records is static, no matter the gain level. How can I get this to work?
Microphone and Audio Input are separate inputs.
I can see the confusion as they both use 3.5mm Jacks, however Audio Lines require a pre-amp prior to the output side, the pre-amp amps up the raw line to give it volume and this outputs digitally formatted data rather than Analog data.
The Microphone on your Android is supposed to be connected directly to a small microphone inside the Headphones, this headphone Microphone is NOT pre-amped and therefore you get a raw analog output from that microphone.
The problem is because you are putting a pre-amped digital data into an analog raw line.
You can use a small microphone like the one in your headphones to test the cable is actually working.
To input Audio data into an Android device, you have many methods that do not require any cables like WiFi Media Servers or even USB OTG Microphone pre-amps .