You can't miss Brian Eno's imprint on "Violet Hill," the lead single from Coldplay's fourth studio album, "Viva La Vida or Death and All His Friends." The legendary U2 producer, with Markus Dravs, takes the London-based quartet from straightforward balladry to a more blues-based approach. A dramatic departure from hits like "Clocks" and "The Scientist," "Violet Hill" shifts effortlessly from piano to distorted guitars and back again, anchored by a fervent beat. Vocalist Chris Martin sticks to favored themes like love and reconciliation, but the mood has changed from optimism to wariness. So far, the experimentation has been warmly received: After "Violet Hill" was offered as a free download on coldplay.com in April, fans responded by promptly crashing the site. The release, which showcases Coldplay's renewed energy and purpose, is now crashing onto playlists across multiple formats.—Alexandra Cahill