I listened few HemiSync tapes from YouTube, until they were pulled off as property of Monroe Institute. Darn, should have downloaded them all.

Main idea is to send one frequency to left ear and bit different to right ear, brain will combine them to the final frequency which will trigger the brains.

It reminds closely this technique, which works longer distances. https://rumble.com/v4829bf-voice-to-skull-technology.html
 

 I thought they were still pretty widely available, I can publish them to a drive if anyone is interested