Any audio file, or specifically analyzed audio files, can be used, with most systems working best with 1 or 2 channels. ElectraStim
Some creators post "stealth" estim tracks. Use caution; ensure the file is downloadable and labeled specifically for TENS/stereostim use. E-stim Audio Files Download
, can translate stereo audio signals into complex electrical patterns, allowing users to "feel" sound. The Evolution of E-Stim Audio Any audio file, or specifically analyzed audio files,