How to Play Fast Riffs Cleanly With a Metronome
The progressive speed method (see [[alternate-picking-speed-exercises:the article on alternate picking speed]]) works on a real riff too (see [[first-electric-guitar-riffs:the article on first riffs]]), but a riff has one quirk: it's rarely even in difficulty from start to finish, and that changes the training itself.
Find the hardest bar, don't drill the whole riff
In almost any riff, one specific bar or transition caps the speed of everything else - spreading equal attention across the whole riff is inefficient if nine bars out of ten are already at the target tempo. Find that actual bottleneck and drill it first.
Muting needs to stay as even as the notes
At high tempo, palm muting (see the article on muting) often drifts first, before the notes themselves do - the palm either loosens its grip or shifts slightly. Check muting stability at the same tempo you check the notes at, not separately.
Downpicked riffs tire the hand faster than it feels like
If a riff is played entirely with downstrokes (see the article on downpicking), the hand tires noticeably faster than with alternate picking at the same tempo - and fatigue on its own ruins cleanliness before raw speed even becomes the limiting factor. Take short rests inside the practice session instead of playing until the hand clearly gives out.
The +5 BPM method applies to the whole riff
The same progressive method as for an isolated technique (see the article on alternate picking speed): raise the metronome in small steps, only after several clean passes in a row of the entire riff, bottleneck included, not just the easy bars.
Record a pass at the target tempo
Record yourself at the intended final tempo and listen back separately from playing - a recording makes it far clearer whether the riff is actually clean at that speed, or whether cleanliness has already started slipping unnoticed during the playing itself.
Try it in practice
Open the metronome