This is written in 17 notes per octave for piano and tenor. I used pianoteq with a grand piano virtually rebuilt to 17 for both parts using scordatura - that is play these notes on a 12 equal keyboard tuned to 17 and you will hear this.
(Sibelius 8 which is the version I use does not have native support for 17)
The vocal is provided by Synthesizer V which used the midi of the vocal part and then retuned by hand to 17 equal and the two parts married up in Cakewalk by Bandlab. Synth V uses samples of a human singer that is then reconstructed on the fly using an AI model - much more flexible than a traditional sample set.