Hip-hop beatmaster Timbaland's record as a producer is unparalleled for sheer bulk of hits and unstinting quality, but his track record as a performer, to put it charitably, is mixed.

The pride of Virginia Beach has not turned himself into Jay-Z on his solid if unspectacular new album, "Timbaland Presents Shock Value," but Timothy Mosley, wise enough to know his limitations, turns over the bulk of his album to guest stars. As would be expected from a producer as beloved and well-connected as Timbaland, the guest list is star-studded.

Surprisingly, it is the mash ups that are the most successful, with Timbaland taking emo and piano rock under his capacious wing. These experimental efforts are crammed into the last third of "Shock Value," which is front-loaded with radio-friendly hip-hop tracks. After a torrid start with the remarkable "Oh Timbaland" -- in which the producer samples Nina Simone's "Sinnerman," tweaking Simone's voice to substitute his name for the song's title -- the next batch of songs are occasionally thrilling but mostly familiar takes on Timbaland's hip-hop-pop formula.

Timbaland has always been more comfortable with tweaking the mainstream than messing around at the margins, and so the most successful mash up is the Fall Out Boy collaboration "One and Only," which manages to simultaneously be a lighter-waving emo anthem and a Timbaland gem in the vein of Aaliyah's "We Need a Resolution." On "2 Man Show," even Sir Elton gets into the mix, dropping some lovely piano (but no vocals).

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