Evans had been the arranger for the orchestra of Claude Thornhill and it was the sound of this group , as well as Duke Ellington 's example , that inspired the creation of a large group including a french horn and a tuba . Evans had been the arranger for the Claude Thornhill orchestra , and it was the sound of this group , as well as Duke Ellington 's example , that suggested the creation of an unusual line-up : a nonet including a French horn and a tuba ( this accounts for the `` tuba band '' moniker that was to be associated with the combo ) .