How to play Machine Head - Locust main riff
This track - from Machine Head's album, Unto The Locust - is played in drop B tuning (low to high: B F# B E G# C#). This is the same as drop D tuning, but a minor third lower.
After a Metallica-esque clean intro and a catchy octave riff, Machine Head wheel out the big guns with a bone-crushing riff that combines single notes with natural harmonics. Playing the natural harmonics cleanly is undoubtedly the toughest part of the riff.
The first set of harmonics requires you to quickly skip to the fourth string, while the second set requires you to skip two strings to the third string. Start slowly and focus on keeping your pick movement to a minimum. This stops you wasting time and energy on unwanted movement and helps you get this riff up to full speed.
Get the sound
A guitar fitted with a humbucker is best for Locust. Use the bridge pickup to get some bite and stop the sound becoming too indistinct. You need plenty of distortion. Wind up the gain and then set your EQ control to produce the classic 'scooped' metal sound. Boost the treble and the bass and then lower the middle. Metal rhythm sounds usually have little or no reverb.