Recently I needed to build an audio breakout cable to connect an iPhone to an iPad. The idea was to run a noise/tone generator on one and run a spectrum analyzer on the other. I had a really hard time finding a straightforward solution online so I’m posting a very simple schematic here.
Technically you don’t need a TRRS (4-pole)connector for the receiving end. If you decide to use a TRS connector there then you’d just connect the resistor to the single “ring” pole.
If you don’t need to put any circuitry between the devices then you should just buy two TRRS pigtails and wire them together for a simpler connection.