There's a nice documentary film on recording engineer Tom Dowd that is available for on-line viewing through Netflix (as well as for rental, as a regular DVD which is presumably available elsewhere as well).

Dowd was an incredible technician and musician who recorded many many great artists and was responsible for several generations of technical advances. One of his many accomplishments was the "Layla" album, as well as all the early Allman Brothers Band releases and the rest of the Derek and the Dominoes catalog.

I'm mentioning this here and now because one of the more interesting moments in this wonderful musical film shows Mr Dowd playing back and discussing the tapes of "Layla," isolating Duane's guitar part (slide-guitar harmonies that are fairly deeply buried in the final mix as released), and discussing Duane's great talent.