Recently, Deutsche Grammophon released a remastered vinyl box set of Karajan's Bruckner recordings. In this video, the two sound engineers explain the remastering process from the original analog 8-track master tapes. If you are not interested in the discussions, start the video directly at 17:40 minutes.
EDIT:
Here is the documentary from DG without the discussions
EDIT:
Here is the documentary from DG without the discussions
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