Christina Aguilera’s new album is entitled Liberation, although it is not entirely clear from what or whom she might be seeking to escape. Editorial control, perhaps. Despite portentous orchestral interludes and a cappella links intended to suggest a work of thematic import, Liberation has no discernible centre other than Aguilera’s extraordinary voice.

The album is a sprawling rag bag of pop styles and guest spots, encompassing rock, R&B, soul, hip hop, reggaeton and anthemic balladry – pretty much standard fare for a fading pop star desperate for a hit.

It has been six years since Aguilera released an album but considerably longer since she has enjoyed solo success. Her previous two albums were poorly received and you would have to go back to Stripped in 2002 to recall when Aguilera really ruled the pop roost.

She has, however, maintained a presence in the public eye as a powerhouse guest vocalist on collaborative tracks (notably with Maroon 5 and Pitbull) and as an actress in country music drama series Nashville. She also serves on the panel of American TV talent show The Voice, judging wannabe stars trying to imitate exactly the kind of overwrought delivery in which she herself excels. She is a vocalist who never sings one note when half a dozen will do.

This is not necessarily a bad thing. Just like listening to a particularly skilful guitarist, it is inherently exciting to witness supreme technical ability firing on all cylinders. In terms of range, command, flexibility, tone, timbre, power, sensitivity and all the pyrotechnical melisma of the modern diva, Aguilera is right up there with Whitney Houston and Mariah Carey. Yet in pop music virtuosity has never been as important as character, style and songcraft, departments in which Aguilera has often been found lacking.

There are moments on Liberation when you can only sit back and applaud her skill. Harmonising with herself on ballad Twice, she sounds like a one-woman Fleetwood Mac, her rich low notes fluttering effortlessly up to falsetto with no loss of control. She lets rip with a raw rock energy reminiscent of Janis Joplin on Sick Of Sittin’.

Every track is polished and purposeful, but the sheer busy quality of her singing and overactive variety of the production ensures that Liberation never settles into a coherent listening experience. One moment she is roaring feminist soul anthem Fall In Line with Demi Lovato, urging young girls to take control of their lives. The next, she is playing second fiddle to a couple of pedestrian rappers (Ty Dolla $ign and 2 Chainz) on Accelerate, a generic modern hip hop track. She tries so hard to cover all pop bases, Aguilera ends up sounding more like one of the contestants on her talent show than the superstar her ability warrants.