He feels her extraordinary world of sounds grows from her own improvisatory playing with fellow composer Viktor Suslin, using various folk instruments. I'm reminded of a scene from the Leaving Home documentary in which Gubaidulina is seen in rehearsal, enthusiastically rattling some exotic shaker.
It is this sonic world, imbued with the composer's intensely spiritual outlook, that informs her 1979 In Croce which Rummel and organist James Tibbles perform on Saturday.
In Croce may be better known in its later transcription for cello and bayan or accordion, but the organ version "benefits from a larger range of dynamics", he says, "even if the organ might seem more indirect and less human than the accordion".
But the pair have found a way to heighten the crucial and dramatic meeting between the instruments as they traverse the cross of its title.
Rummel is convinced that In Croce is one of the great works of its century. "I'm sure it will be played in 200 years' time. Absolutely sure."
Also involved in the project is composer Eve de Castro-Robinson, long an enthusiast of Gubaidulina.
"Every Gubaidulina piece is sonically intriguing," she says, "and often there's a mystical element. They're elusive and yet readily musically rewarding."
She talks of Friday's Quasi hoquetus as "suggestive and fleeting, with plaintive, high bassoon lines for Ben Hoadley and Sue Bierre's viola, alongside outbreaks of startling passion from Sarah Watkins' piano".
De Castro-Robinson enthuses about the "gorgeously aphoristic studies of the Ten Preludes", works that also feature in the Friday concert, played by a half-circle of Rummel's cello students.
"That's where a lot of Gubaidulina's string techniques come from," Rummel says, adding that there is also humour to be found in the second of the two Lieder sung by Carmel Carroll. "It's based on 'There's a hole in my bucket' and unfolds in a very funny way."
Inevitably, Gubaidulina's deep faith is at the core of most of the music in the concerts but, Rummel conclu-des, the inner truths lie even deeper.
"This music grows out of the natural combination of the intellect and the emotions. Gubaidulina's compositions are based on a natural ratio of how nature works. It's the same as in architecture where some things work because they have certain proportions.
"Even if you're not consciously aware of this, it's always lying there underneath."
Performance
What: Sofia Gubaidulina Workshop
Where and when: University Music Theatre, 6 Symonds St, Friday at 4pm
What: Dancer on a Tightrope
Where and when: University Music Theatre, Friday at 7.30pm
What: Rejoice!
Where and when: St David's Presbyterian Church, 68-70 Khyber Pass Rd, Saturday August 20 at 7.30pm
