Never convert a random YouTube video to MP3 and use it for e-stim. YouTube’s compression adds artifacts, and the audio may have near-DC offset or clipping designed for speakers, not sensitive nerves. Only use files labeled specifically as files.

A low-frequency thrum that felt like a steady heartbeat.

To use these files, you generally need a specific bridge between your digital device and your body: A phone or PC playing the MP3 file. Stereo Cable: A standard 3.5mm auxiliary cable.