OM performs at August Hall in San Francisco on Feb. 26, 2019. Photos: Gary Chancer

SAN FRANCISCO — In the 1984 film Amadeus, Emperor Joseph II criticizes Mozart‘s performance saying, “There are simply too many notes.” The period drama portrays the ruler as an idiot who’s unable to appreciate Mozart’s genius. But maybe he had a point.

Spiritual sludge rockers Om and Tunisian singer Emel Mathlouthi epitomized the less-is-more approach on Tuesday night when they shared a bill at August Hall.

Om performs at August Hall in San Francisco on Feb. 26, 2019.

Taking the stage dressed in all black, Om began with a few notes played in slow succession by bassist-vocalist Al Cisneros. The growling bass filled the room with an ominous rumble. Drummer Emil Amos soon struck up a jazzy shuffle beneath the resonant mud, as Cisneros climbed up the bass neck. The San Francisco luminaries rocked the room using rudimentary but transfixing elements.

Founded by ex-members of stoner metal legends Sleep, Om creates music composed largely of a wall of sound—tar-like sediments that throb and groove underneath Cisneros’ ominous vocal blather. The music has an otherworldly flavor to it, evoking the angular and psychedelic elements of Middle Eastern music. It evokes the aftermath of a hard day of spice mining on Dune‘s mystical planet Arrakis. The results beg the question: Is it possible to appropriate culture from beyond the stars?

Between the lengthy songs, Cisneros would swap basses. While the band tuned up, samples of what sounded like a Bulgarian women’s choir music maintained the atmosphere. Some songs emphasized multi-instrumentalist Tyler Trotter’s spacey synthscapes, but he also broke out his guitar and tanpura, a Middle Eastern folk instrument. He contented himself simply playing the tambourine during older, more minimalist numbers.

Drummer Emil Amos pummeled his cymbals, enhancing the Middle Eastern influence with discordant pitches. These cymbal splashes often functioned similarly to horror movie jump scares. His drum fills approached high art, imparting expression and bombast to the slowest and simplest music. His nimble and frenetic percussive assault provided the necessary counterpoint to Cisneros’ monolithic thunder.

Later in the set, woody timbre of a hurdy-gurdy—an ancient Celtic “mechanical violin”—joined the mix. Cisneros also cranked distortion, revealing another layer of sonic complexity to his loping throb. On first listen, Om’s simple songs might seem interchangeable, but they reveal their nuances for the patient and perceptive. Dynamic interplay underscores the minimalist instrumentation and hypnotic riffage. The band seamlessly shifted from one droning groove to the next, balancing ornate arrangements and tasteful ambience.

The show began with an opening set from Tunisian singer, songwriter and activist Emel Mathlouthi. Accompanied by a keyboard player and a drummer, Mathlouthi enchanted with her powerful voice and stage presence.

Mathlouthi’s music is as confrontational as it is emotive. It’s actually banned on Tunisian radio. Amalgamating heavy metal and Joan Baez’s folk music and political activism, Mathlouthi helped spark a political revolution when she dedicated her version of Baez’s “Here’s to Him” to Mohamed Bouazizi—the young street vendor who set himself on fire in an act of defiance. The song came to embody an act that started the series of Middle Eastern anti-government protests known as Arab Spring. In 2015, she performed at the Nobel Peace Prize Ceremony.

Emel Mathlouthi at August Hall in San Francisco on Feb. 26, 2019.

During her set, Mathlouthi set her beautiful voice against a wash of synthesized sounds and EDM-style bass and electronic percussion. Her voice evoked comparisons to Dead Can Dance’s Lisa Gerrard or a more tuneful Diamanda Galas. Musically, the sound occupied some mystical territory between the sinewy quarter tones of Middle Eastern music and lush melancholy.

After her second song, Mathlouthi thanked the audience and explained, “We just drove 26 hours through the snow and mountains to be here, but it was very beautiful and exciting and inspiring.”

Like Om’s set, Mathlouthi’s achieved her atmospheric effect by embellishing a droning note with a series of wavering tones. The varying intervals between the tones and the drone produced unique, immersive melodies. At times, it was difficult to tell if Matlouthi was singing in English or some more primal and universal lexicon of evocation.

After a 50-minute set, Mathlouthi announced the final song would be from her forthcoming album, telling the audience, “Just keep it in your heart, and I’ll see you sometime soon.”

Follow writer David Gill at Twitter.com/songotaku and Instagram/songotaku.