Interface, but I don't want to invest in one just yet. I realize the proper way of doing this would be to get an audio It never converted a signal to line level. The cable, was just a 'breakout' that separated the headphone (out) from the microphone (in) connectors. The thread you referenced is about the TRRS jack or Tip, Ring, Ring, Sleeve and these are typically used in telco, not pro audio (yes, you can get very good quality sound from them, but they’re never found in even the smallest recording studio).
Macs aren’t recording/pre-amp devices and do not contain the necessary components to raise the voltage to line level. Microphone voltage is extremely tiny (millivolts) where line level input is about 1 1/4 volts. The key differentiation between mic and line signals is the voltage. Your 2009 MacBook had only a microphone input and not a line input. The audio jacks on all Macs are microphone inputs and not line inputs. This was possible with my very old 2009 white MacBook.
I would like to plug in a 3.5 mm cable to the output jack of the electronic drumset and connect the other end to my computer to record the drumset's sound.
