There’s actually no digital audio involved anywhere in this process. It’s all analog.

A magnetic tape cassette holds raw wave data of the sounds it records. Just like a vinyl record, except the groove is in the magnetic field instead of physically etched into the surface of the tape, and the needle is an electromagnet instead of, well, a needle.

An audio cable using a standard 3.5mm jack also transmits raw wave data. It has to, because the electromagnetic pulses in the cable are what directly drive the electromagnets in whatever speakers they’re hooked up to. If it’s coming out of a digital player, the player has to convert the signal on its own using an onboard digital-to-analog converter (a DAC).

The neat part is that since a tape deck read head is looking for an analog wave signal, and an analog wave signal is what an aux cable carries, the two are directly compatible with one another. If you actually crack one of these tape deck hacks open, you’ll find the whole thing is completely empty, save for the audio cable wires going directly to the write head that mimics the tape. Beyond that, there’s no conversion equipment, no circuit board, nothing. It’s a direct pass-through.

The body of the thing is nothing more than an elaborate way to trip all the mechanisms in the tape deck to trick it into thinking it’s holding a valid cassette, while simply holding the write head fixed in the proper spot.

I’m sure you already know all of this. I just think it’s really cool and I enjoy talking about it. Analog tech is amazing.