1) Primarily a pronounced midranged (can vary low to upper) grrrrrrrrr-like tone. Often enhanced by 600Hz boost, Aggressive technique, playing near the bridge, and accenting the bridge pup.
2) Gallien-Krueger defines growl as-a small amount of even order harmonic Distortion (UrbanAssault415)
3) strings can produce a "string growl" exhibited during slides resulting from the strings lightly grazing the frets - becoming String rattle when the Action is too low.
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