: Most e-stim .wav files use the Left and Right channels to control two separate electrodes.
: .wav is preferred over .mp3 because it is lossless; compression in MP3s can sometimes clip the waveforms, leading to a "scratchy" or inconsistent sensation. Community Recommendations Estim Wav Files
For the highest quality, look for professional sound designers. They use oscilloscopes to ensure no DC offset (which can sting) and balanced asymmetry. : Most e-stim