The guitar doubles the bass for much of the riff, so match the timing and note length of the bass to get a tight, powerful sound. Use downstrokes to add weight to the ascending chromatic phrase and pay attention to where the upstrokes fall within the guitar fills. They keep the more intricate phrases flowing, and reset the picking hand so you land back on the beat with a downstroke. The last three notes of the riff are accented by the whole band, so add definition to this phrase by relaxing the fretting finger after each note and palm muting in the spaces.
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