You don't have to be a country fan to recognise Johnny Cash's weary, righteous baritone. On the mariachi-influenced "Ring of Fire", it describes a lover's descent into hell and dares the devil to turn up the flames. On "Folsom Prison Blues", after being introduced by a chain-gang guitar line, it gives you a taste of the miserable, nihilistic monotony of life behind bars. And though Cash was one of the most uncompromising artists of the 20th century, he saved one of his greatest performances for the 21st, when he let that voice wither away on the sparse, haunting "Hurt".