Following the advice here I tried recording data to a cassette. I’m using maxwell tapes and a “tomashi” walkman with a mic input. The output is extremely noisy and I have very high data loss. I tried recording music and that’s very noisy too. I’m guessing I need a better recording device? Why does it matter though? Or am I missing another step?
First thing that comes to mind is making sure the line out gain matches the recorders input. Basically turn the volume down on the output- microphone signals are very weak, like 50 or 100 times weaker. Your recorder is amplifying that signal beyond what the circuit can handle and you’re getting distortion.
https://www.theengineeringknowledge.com/wp-content/uploads/2020/10/Amplitude-Distortion-due-to-Clipping.jpg
If there is a Line In jack use that instead. It may be a switch that says Mic/Line. If you only have Mic level input, turn the output down on the music until it sounds good on playback, and your data should flow.