The story goes that in 1890 a 13 year old Casals found the complete manuscripts for Grutzmacher's edition of Bach's six Cello Suites in a thrift shop in Barcelona; practiced them for 13 years before he felt worthy of their performance.
He committed them to tape in 1925, and, in search of perfection, continued re-recording them, culminating in the famous recordings of 1936/38/39.
The sound quality is slightly compromised by tape hiss but you cease to hear that once you lose yourself in these wondrous performances. And performance is the name of the game. Casals attacks what were once regarded as merely practice pieces with such gusto that it's difficult not to be swept away by his obvious rapture. It's said the Liszt was the first real pop star; he invested such personality into the performance of his own writings that his character and profile became as important to the moment as the music. There are elements of that here too; I'm no classicist but there are imperfections in Casal's dynamic playing that can only be regarded as willful interpretation; like a Hendrix of the cello.