Apply Vibrato to Your Arrangements
Especially when played slowly, the traditional melody “Amazing Grace” in Example 2 provides several long notes for experimenting with pitch modulation. This is an articulation that can vary so greatly, that in practice, it’s best left to the individual player to decide when to use it and at what speed and depth. Play the melody at 60 bpm and experiment with playing anywhere from a partial cycle to one or two cycles on the notes marked with the pitch modulation symbol.
Vary the depth as well. Use a somewhat faster modulation for the quarter note in measure 14 with the traditional vibrato marking. Pay attention to all the other articulations and to the fingerings.
Excerpted from The Alex de Grassi Fingerstyle Guitar Method