Insults couldn’t pierce the thick skin of musicians like Duke Ellington, Louis Armstrong or Count Basie, long accustomed to bigoted slurs and crude critique. But when reviewers blithely demeaned them as uncultured clowns, or savage beasts, something snapped Armstrong “might have come straight from some African jungle and then, after being taken to a slop tailor’s for a ready made dress-suit, been put straight on the stage and told to ‘sing,’” Hannen Swaffer, one of Britain’s best-known drama critics, wrote in the Daily Herald in 1932. A competing London rag,…