Drop D is not just for grunge and metal – Joe Bonamassa explains how he uses it for blues guitar

If you really want to get adventurous, try dropping both your low and high E strings down to D, what's called double drop-D tuning (low to high: D, A, D, G, B, D). This will get you into some CSN&Y ...
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3 Alt-Rock Songs That Use Drop D Tuning in Creative Ways

Ah, drop-D tuning. Long beloved by nu-metal bands, with usage dating back to The Doors, Led Zeppelin, and many more. Guitarists and bands really began implementing it in songwriting in the 1990s, with ...