Ustad Saami is a slightly built man with long graceful hands that sweep skywards and then down as he sings, as though conducting a theremin. His hypnotic voice leaps from octave to octave as he homes in on the precise microtones of the 49-note scale of which the 76-year-old is the world’s last surviving practitioner. He performs cross-legged, his eyes wide and hawk-like, flanked by his four musician sons.

Yet for Grammy-winning US music producer Ian Brennan, who travelled to Pakistan in late 2017 to record Saami’s first ever album, God is Not a Terrorist, the humble master of eastern classical music often frightened the daylights out of him. Recording live on Saami’s Karachi rooftop, in marathon sessions that began after sunset and continued long after sunrise, Saami’s voice, Brennan has said, would suddenly escalate to “10 times heavier than anything Metallica has ever produced”.

“When he loosens his voice and drops multiple octaves, it’s almost sinister – it can be very intimidating,” Brennan tells the Guardian.

Ustad Saami with a tanpura.

Though Saami has passed on to his sons and select students the musical tradition that harks back through the generations to the 13th century, he remains the sole master of the extraordinarily complex 49-note scale (seven times that of the western scale), which his uncle began teaching him at the age of 11. “It’s mind-boggling,” says Brennan. “That’s why the music is at risk of dying with him – because it’s something that is superhuman to be able to do.”

Not only is Saami’s Surti music – infused with pre-Islamic elements, the Indian classical tradition of khayal and Sufi qawwali – at risk of extinction, but in a country where exponents of Sufi devotional music are considered blasphemous by fundamentalists within Islam, he risks his life by continuing to play it. In 2016, famed qawwali singer Amjad Sabri was shot dead by Taliban gunmen not far from where Saami lives. In Pakistan, Saami says, music itself is tossed between halal and haram like a sport.

A few years ago, as Saami’s Surti music languished on the endangered list, two of his students reached out to Brennan and implored him to come to Karachi. Brennan has made a name for himself travelling the world, recording under-heard geniuses and amplifying the voices of marginalised musicians. His collaboration with Tuareg rockers Tinariwen from Mali’s Sahara desert won a Grammy award for best world music album, and Brennan has also produced the music of maximum-security prisoners in Malawi, genocide survivors in Rwanda and slum dwellers in Nairobi.

“When I listened to [Saami’s] music,” Brennan says, “I was instantly struck by the complexity and also by the darkness of it. The foreboding and the more melancholy aspects contrast pretty dramatically with what is stereotypically regarded as music from Pakistan in the west.”

Ustad Saami is rebelling against all the orthodoxy on both sides of the border in India and Pakistan Producer Ian Brennan

It became Brennan’s mission to show the world there was more to Pakistani music than the late qawwali superstar Nusrat Fateh Ali Khan, and for Saami to “take his rightful place” as one of the titans of modern Pakistani music. Brennan’s first step was preserving on record Saami’s unique but commercially sidelined multilingual songs (Saami sings in Farsi, Arabic, Urdu, Hindi, Sanskrit and Vedic Sanskrit). “By embracing the multiculturalism of the music of the region”, says Brennan, Saami has forfeited mainstream success in his homeland.

“[Saami is a proponent of] an ancient system but at the same time it’s a very modern and progressive system – he’s rebelling against all the orthodoxy on both sides of the border in India and Pakistan,” Brennan explains.

“It’s sort of professional suicide in a sense. If he had conformed, the opportunities for him in Pakistan would have been far greater.”

Releasing his first album, God Is Not a Terrorist, at the age of 75 (it came out last year) was “a dream come true”, Saami says. The provocative title represents a counter-narrative to the often hostile way Pakistan is portrayed in the west.

Since its release, God Is Not a Terrorist and Saami’s transcendental live performances have attracted critical acclaim outside Pakistan – and not just from world music circles. Rock music bibles Mojo and Uncut declared the album “electrifying” and “mesmerising”, and when Saami and his sons performed at the Netherlands’ hip tastemaker festival Le Guess Who? last November, Brennan says “jaded indie rock people were crying at the end”.

He also played Womad in England last July, drawing a crowd of around 10,000 festival goers late one night as he played an hour-long song specifically designed to be performed at midnight. Saami was overwhelmed by the reception he received. Afterwards, he says, “I couldn’t sleep all night. I had prepared my whole life for that audience.”

Ustad Saami (left) on the street in his home city of Karachi. Photograph: Marilena Umuhoza Delli

Saami will make his first trip to Australia in March, accompanied by his four sons who play tabla drums, harmonium and tanpura, to perform at the Womadelaide festival in Adelaide. Saami’s music may have its roots in the 13th century, but Brennan describes it as “extremely modern and progressive”.

“That’s largely because it’s improvisatory. So every time he performs it, it’s alive and it’s different.”

• Ustad Saami plays Womadelaide in Botanic Park, Adelaide, 6-9 March 2020