By the end of the 1990s, Sigh were quite certainly Japan's best-known black metal export, but come the flip to a new millennium and their mind-blowing fifth album, 2001's Imaginary Sonicscape, their radical evolutionary curve arguably transcended even their eclectic genre's ultra-forgiving boundaries.

With their startling combination of progressive, orchestral, jazz, psychedelic, and, yes, heavy metal music, that album's songs held themselves together as if by a miracle -- despite repeatedly challenging both songwriting convention and common sense to achieve a true triumph of "sonic imagination," as it were.

Unfortunately, even the most daring and visionary musical creations can be undone by technical issues, and Sigh's would-be next musical coup, 2005's Gallows Gallery, was ultimately struck down by something as puerile as mucky production.

What a shame, since underneath what sounds like a rough studio mix, two or three passes removed from a satisfactory final product, one can actually discern the same stellar musicianship and obsessive attention to arranging detail that Sigh built their legend and fan base upon.

Granted, this fidelity problem isn't as overt on the album's two softer cuts.

"The Tranquilizer Song" is a simply glorious amalgam of bandleader Mirai Kawashima's waltzing synthesized strings, swirling Hammond organs, keyboard lullabies, and timid falsettos -- more suited to classical music conservatories than mosh pits.

And "Gavotte Grim" clashes thundering drum work with dainty harpsichords, industrial ambience, hypnotizing doom chords, and soaring solos from guitarist Shinichi Ishikawa, the Japanese Michael Schenker.

But the remainder of Gallows Gallery's predominantly heavy tracks ("Pale Monument," "In a Drowse," "Silver Universe," "Messiahplan," etc.) are bogged down by fuzzy, oversaturated guitars and muddy vocalizing.

Without such deterrents, their shocking contrasts of bright synth parts and almost childlike choruses with extreme metal brutality and hyperactive percussion (think Mayhem going to town on the Carpenters!) would have proved all the more fascinating and unique.

At least Sigh's spirit of experimentation is still intact, but until their next effort rectifies these technical issues, fans will have to approach Gallows Gallery with a forgiving ear and a grain of salt.