To defy categorization in today’s music world is truly a feat. With all the different labels placed on music, it is hard to believe there are bands that can’t be classified.

Tool is one of those rare enigmas.

They’re too loud and abrasive to be called rock, but too melodic for metal. And since there is no category for inventive bands that touch upon all the aspects of songwriting while covering every corner of the music spectrum, Tool will always stand out.

On their latest release, “Aenima,” Tool continues to dwell in the realm of the unknown. As on the platinum selling “Undertow,” the band grabs the listener and doesn’t ease its grip until the album’s conclusion. This edge-of-your-seat tension helped boost “Undertow’s” sales through the roof, and will undoubtedly do the same for “Aenima.”

Many tracks on “Aenima” focus on Tool’s uncanny ability for the start/stop, fast/slow technique popular in much of today’s music. But where many bands use the technique simply to create a catchy attention-getter for their music, Tool takes it to the extreme. Every time the band goes slow, they manage to hold the listener in suspense. You just wait for the explosion, but often it’s slow in coming. Instead, the slower moments are fully developed and add an incredible tension to the impending feeling of doom. Think of it as the not-so-peaceful calm before the storm.

These slow moments work largely thanks to the voice of singer Maynard James Keenan. On previous offerings Keenan’s vocals have been mixed evenly with the music, causing the lyrics to be at times muddled. This time around Keenan’s voice is a level above the instruments. Not only does this help clarify what he is saying, it also displays his talent as a vocalist. His wide vocal range acts as an additional instrument and often carries the songs. This is especially evident on the longer tracks such as “H.” and “Pushit.”

But don’t think that Tool’s signature sound has changed, because is hasn’t. It has simply progressed. Keenan’s partners in crime still pack the same energy with their instruments, only now they have learned how and when to bring it down a notch.

And, of course, they haven’t forgotten how to be loud. “Hooker with a Penis” is an unrelenting, fast-paced attack on fans who have called Tool sell-outs. “I sold my soul to make a record, dipshit/ And you bought one,” Keenan tells the fan before repeatedly yelling “Fuck you, buddy.” The grinding “Die Eier Von Satan” speeds along while the lyrics are screamed in German, describing how to make the perfect cookie (there are no eggs and an added secret ingredient).

But there’s more to “Aenima” than a bunch of songs. With the help of sound effects and melodic introductions, the songs flow from one to the next, creating a cohesive entity. This is a trick Tool has not attempted before and it helps the album fly by despite its 78-minute length.

And then there is the album’s finale, the 14-minute “Third Eye.” Perfectly summing up the entire album, it begins with snippits of comedy from the late Bill Hicks, who is also mentioned in the CD’s liner notes. Hicks’ words slowly fade into the growing guitar distortion and tribal drumwork. As the song builds, Keenan steps in slowly and tentatively against the music. After a few minutes, though, he is wailing like a banshee. The music picks up to challenge him while his voice starts to strain from yelling. Then after an extended musical interlude, everything dies, except for Keenan’s whispered voice. As it grows, so does the music and the noise level, leading up to one final explosion.

As the tune fades, Tool slowly loosens its vice-tight grip, and allows the listener to relax and breathe freely again. The damage is done, though, as Tool has forced their way into the cerebral cavity of their listeners and created a deep, dark hole where they will lurk forever.