Like the birth of a child, some experiences are so profound that words only cheapen them. One such experience is Blue, Joni Mitchell’s 1971 classic — an album as essential to the lexicon of rock and roll as Sgt. Pepper and Blonde on Blonde. Along with the Beatles and Bob Dylan, Joni Mitchell is a 20th century musical icon, one whose style is uniquely her own, and whose brilliance eludes understanding. The unconventional tunings; the soaring vibrato; the see-sawing lyrics — Mitchell’s music is so visceral, so free, so untamed, that pinning it down diminishes it, like putting a wild animal into captivity.