For a band as talented, ambitious and exacting as prog-rock quintet Dream Theater, improving its product is a great challenge.

But the boys from Berklee College of Music have done it consistently. On each album since 1989’s raw but razor-sharp When Dream And Day Unite, themes have become more developed, arrangements more lush and songwriting more focused. Predictably, then, the new double studio CD, Six Degrees Of Inner Turbulence (Elektra ***), is the most accomplished yet.

Disc one’s five songs alone mark unexplored territory. Hip-hop scratches, distorted vocals, and half-speed and backward tracks bolster intricate passages reminiscent of Yes, Styx, Tool and Supertramp. The 42-minute, eight-part title track that fills disc two is more disjointed than the 1995 epic, ‘A Change Of Seasons’, one of metal’s pre-eminent orchestral achievements. There are quirks – John Myung’s bass is too faint. John Petrucci’s guitar still overshreds a solo or two, and James LaBrie’s vocals can seem strained. But Six Degrees Of Inner Turbulence solidifies Dream Theater’s reputation as rock’s version of Albert Einstein.

—Mike Daniel, The Dallas Morning News