Duality is an album of luminous, tranquil and moving music created with voice, percussion, electronic keyboards and samplers. Lisa Gerrard described it as ‘classical contemporary, a mosaic of cultural influences and in the voice of what we’ve gone through in the past 20 years of our artisanship.’ The album crystalized the musical partnership between Pieter Bourke and Lisa Gerrard, setting a template for future collaborations together.

Bourke had been brought into Gerrard's ensemble several years earlier as percussionist and keyboardist on her 1995 solo album The Mirror Pool and the accompanying European and North American concert tour. On that tour the two began writing some pieces together, percussion jams that were developed solely for the concerts but which were never recorded. Following the 1996 Spiritchaser album and tour by Dead Can Dance, Gerrard took a month and a half off before beginning work on her second solo album at her home studio in Gippsland, Australia.

In November 1996 she invited Bourke to her studio to engineer and play percussion on a track that she had begun recording. Originally Bourke thought he would be there for just a short time, do a few pieces with percussion and voice, then leave and let Gerrard integrate the results into a larger whole. However, as the sessions progressed the two artists found their creative energies fusing into a singular musical vision, which blossomed into a co-writing venture and the album Duality.

‘We were working on some minimal vocal pieces, which we called 'interludes', not full blown songs as such’, recalls Bourke. ‘Lisa would improvise over a drone note, then she would build up layers of vocals to add highlights, weight and dimension. When recording the third interlude we felt that it wanted to be a much bigger piece of work, outside of the interlude concept.’ The two musicians decided to explore it and see where it would lead, eventually spending seven weeks expanding the piece with added layers of percussion, keyboards and vocals. When they were finished they had created the 8 minute opening track Shadow Magnet. Bourke says that, ‘from there we realized there was potential for a whole lot more than we initially realized.’

They eventually spent a year working on the album, working at a relaxed pace that both enjoyed. With the exception of a few pieces developed from their initial writing forays, Bourke says, ‘everything else started from one fragment and was built up through a process of improvisation and spontaneity in the studio. We were both always present there, so no one went away and worked on a vocal part or a drum part. It was all done together, just the two of us. Our working method was to record each idea as soon as it surfaced, and it was the same for vocal parts or melodic keyboard parts or rhythm parts. Each idea was a direct response to what was already there in the music. We just kept exploring, recording things in such a way that Lisa could evolve a vocal idea without having to stop the tape machine. In this way, a real momentum was gathered, and over the course of many hours we’d arrive at something that really unlocked the piece of music further. Then we would build on that again. Layering was an integral part of the recording process, particularly with Lisa’s vocals.’

‘Most parts were recorded live, although it sounds quite sculptured’, Gerrard adds. ‘Even the string pieces were performed and sung live.’ The challenge was to put all these parts into arrangements that, as Bourke explains, ‘had to be connected in a way that the story unfolded. And we spent just as much time in that area as we did in the finding the actual parts. We were flexible in moving parts around and trying various arrangements, until we found the one that felt right.’

One of the standout songs on Duality is the majestic Sacrifice. Featuring a soaring vocal performance over an emotive string arrangement, this composition has gone on to appear in countless films, trailers, documentaries, and advertisements. The song forms the soundtrack to the Telecom Italia Ghandi commercial which was directed by Spike Lee. In 2012 the ad won the prestigious Italian Advertising Key Award in the category Best Ever Forever as one of the best commercials of the last 30 years. Sacrifice also featured as a main theme in Bourke and Gerrard's filmscore for The Insider, directed by Michael Mann.

Duality was completed in December 1997 and released on the 4AD record label on April 13th 1998. ‘I had never experienced the fluidity and trust that existed between Lisa and I in creating this work’, recalls Bourke. ‘So much was unspoken while we were working, but whatever idea came up, we would take it as far as we could and that was sometimes magical. I often felt like we were working on music for the first time, which was an amazing feeling to have after having already spent 15 years making music. Duality is the purest collaborative project I've been involved with, in the sense that there is nothing on the album that feels like it could have been created without the presence of both collaborators.’ Gerrard agreed, saying ‘the unique quality of this situation is that we were able to find such a gentle equilibrium, an unspoken common ground that allowed us to be liberated by what we were making and not ashamed, not afraid.’