2nd intervals are pretty damn cool. They are most commonly heard in suspended 2nd chords. Well, that's at least where I typically seem to hear and see them being used.
Used correctly, 2nd intervals can add a very unique sound to what you're playing/writing.
What is a 2nd interval? A 2nd interval is one whole step up from a root note. For example: the 2nd interval of G is A. A is one whole step above G (in other words, 2 frets higher).
You can also have a flat 2nd interval, aka: minor 2nd. A flat 2nd interval is a half step above the root note. For example, the flat 2nd interval of B is C. C is one half step above B (in other words, 1 fret higher).
Joel Hoekstra put together some really cool sounding exercises to help you get familiar with the sounds of 2nds. Here's the video lesson he did with Guitar World:
Tabs for this lesson can be found here: www.guitarworld.com/lessons-artist-lessons-rock/applying-second-intervals-arpeggiated-riff-ideas/29966
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