Everything about Annie Clark, who performs under the name St. Vincent, seems at odds with itself. The singer-songwriter, a wide-eyed, demure-looking Oklahoman, first shattered any image of innocence and one-dimensionality with her 2007 debut “Marry Me.” With lyrics teetering between the outlandish and the soulful, St. Vincent combined her voice with an eclectic mix of instruments to show that her demeanor belied the dark complexity within. After four years and two critically acclaimed albums, St. Vincent has expanded her sonic range through a complex combination of increasingly oblique lyrics, bizarre instrumentation, and irregular song structures. “Strange Mercy” continues to broaden her already experimental style and, though superficially inaccessible, the album is the most successful expression of her sound yet.

This is not a welcoming album. The opening song “Chloe in the Afternoon” sets the overall tone of the album with its immediate blend of woozy synthesizers, spasmodic bursts of guitar, and incongruously dulcet vocals. From there, the album blossoms into a complex and often confusing work comprised of lurching transitions and unanticipated explosions of noise. Her lyrical choices do nothing to contradict this aesthetic. Though the album’s abrasiveness and rapid tonal shifts from sweet simplicity to furious madness challenge her listeners, her care in assembling these seemingly unhinged tracks is exercised with striking precision.

Perhaps the best aspects of “Strange Mercy” are not simply St. Vincent’s expertly varied and calculated combinations of standard instruments and voice, but also her increased and unexpected use of synthesizer. With a gently beating drum or a soft pluck of guitar string, the calm, secure tones of “Marry Me” and second album “Actor” are invoked. However, the retro synthesized sounds one would expect from Passion Pit or MGMT somehow find their way between slow bass thrums and an alto voice. It is this sort of unpredictability that leads the songs’ artful progression and overall ingenuity. Surprising, lip-curling guitar riffs jar and blend with soft vocals, while distorted synthesized sounds join in a mélange of chaos. Clark pushes each instrument to its most extreme range, confidently shifting the music from calm to hysteria, ease to madness. This Pandora’s box of instrumentation contains as much ear-splitting noise as it does traditional guitar, yet these ordinarily abrasive sounds are deployed with such exactness that the unholy becomes otherwise.

Whether in the opening sequence of “Hysterical Strength” or the middle of “Neutered Fruit,” St. Vincent’s jarring synth and electric guitar measures enhance her quirky and understated lyrics. The line “I ate flowers in the backyard / While finding neutered fruit” would sound irredeemably strange and perverse were it not resting on top of her characteristic hypnotic, slightly neurotic bass guitar pulse. There is, in the same song, the line “Don’t run, don’t run / Little rabbit, run,” which is then evoked by a lightly distorted electric guitar passage that mimics the forbidden action. St. Vincent’s instrumentals work well with her vocals, musically miming her lyrics and lending undercurrents of meaning to purposefully vague passages.

Though she is a self-proclaimed killer of poetry, St. Vincent isn’t so much killing poetry as she is creating her own particular brand. Instead of delivering them in voice, “Strange Mercy” delivers them in the more unconventional mode of instrumentation. This album relies on a close connection between eerily subdued lyrics and dynamic melodies, propagating an artful strangeness that thrives along insane lines, and adheres to its own aesthetic logic. St. Vincent’s method is truly impressive, and on “Strange Mercy” her beautiful combination of complex words and aggressively bizarre sounds has come even closer to the sublime.