As in previous Rock Band (see Kennansoft's guide for the same achievement in RB3:
The Vocal Virtuoso achievement in Rock Band 3 worth 30 pointsEarn an Awesome rating on at least 90% of the phrases in 6 songs on Hard Vocals. ) parts, just use tracks that consist of only talking parts. Not all tracks that worked in RB3 seem to work in RB4.
I can confirm that the following tracks are working for this (Beastie Boys tracks used to work fine, but only the DLC are available yet):
- Rage Against the Machine - "Bombtrack" (DLC)
- Rage Against the Machine - "Guerrilla Radio" (DLC)
- Rage Against the Machine - "Killing in the Name" (DLC)
- Rage Against the Machine - "Sleep Now in the Fire" (DLC)
- Red Hot Chili Peppers - "Give it away" (DLC)
- Run DMC - "King of Rock" (DLC)
- Soul Remnants - "Dead Black (Heart of Ice)"
Shout/"sing"/growl into your mic during the parts and you're fine. You probably will also get the "4x Overdrive in 1 track while singing" achievement while going for this achievement.
PS: You may want to check the Rock Band store on the 360 for the DLC tracks, they're cheaper there.