Propane Blue JI Sequence – click on the score above to enlarge it.
I have to admit I sometimes get obsessed with a musical idea – and Paul’s Extreme Sound Stretch (PES) by Nasca Octavian Paul is a musical tool I am very obsessed with because it lets me perform a variety of unique operations on samples. In this case I use PES to take a sample of metallic noise from the Propane sound set called crissement2 I downloaded in the 90’s and turn it into a ethereal pad in John O’Sullivan’s Blue JI tuning. According to the documentation Propane came from sampling an actual propane warehouse.
The frequency domain view of crissement2 looks like this:
It is not very well pitched as a traditional music source material – but it is rich in harmonics which is what this technique requires.
So then I used the following PES settings: 
What this setting does is isolate a harmonic series starting from a root note of 55 Hz (A1 or in other words second to lowest A on the piano) of 10 harmonics, that is 110, 165, 220, and so on. The amplitude of the harmonic series set is dependent on the content of the source material at any given instant and I do not try to control it. This means that a series based on 55Hz will probably have a different amplitude verses time profile than a harmonic series based on 62 Hz for instance. That is ok since it adds some fine texture to the overall piece.
John’s Blue JI tuning is a series of JI ratios 1/1 15/14 9/8 6/5 5/4 4/3 7/5 3/2 8/5 5/3 9/5 15/8 2/1 which I multiply against 55 Hz to generate 13 files. The frequencies for each ratio can be seen in the score on the samples. Then I gave each file its own track in Sonar and arrange them in dyads and chords. The frequency domain view of the score looks like this: 
in stereo. The cut-off of the harmonic series around 1000 Hz is clearly visible. A better view of the harmonics and their inter-relationship is found by zooming in on the monaural version: 
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