In our younger days (think cassette tapes) bootleg tapes of Grateful Dead live concerts were precious to fans of the band. This band actually encouraged anyone to record their shows/concerts and share them as long as these were not sold for profit. Many concert goers used small cassette players to record their concerts. As you can imagine the quality of these were as @keith_correa puts it “Truly horrible”These are mastered. If one wants "true" live sound, listen to some of the bootleg live recordings. Truly horrible!
But then there were others that sounded … pretty good (Europe 72’), as also other bands’ recordings from that era that sounded pretty good. “Peter Frampton comes alive” sounds lovely even today.