Where does he say that? There are documents online claiming otherwise; it seems to be common knowledge (whether or not it's correct) that the Beatles first used DI for bass on 1 February 1967 while recording the title track for Sgt. Pepper. See here, for example: The Beatles' recording technology (Wikipedia) That article cites as its source a quote from Abbey Road engineer Ken Townsend in Mark Lewisohn's Complete Beatles Recording Sessions. That same article notes that British producer Joe Meek and Motown had both used DI for guitars and bass earlier, which means the Beatles were not actually the first to do so, though Ken Townsend apparently thought they were. Anyway, it seems from this that even if the Beatles did use DI for bass, they did not do so until Pepper, so there are no DI bass tracks on earlier albums such as Revolver and Rubber Soul.