‘sifting’ for piano – a little bit on compositional ideas behind the piece.
1. Pitch Sets
A selection of the pitch material for the piece was a two levelled process. At first I have used simple sieve generators (such as arithmetic series, sieve of Eratosthenes – a simple, ancient algorithm for finding all prime numbers up to any given limit) to generate lists of values of a range between 21 and 107 (a midi range of a piano instrument). Second stage consisted in logical operations (a binary operators – union, intersection and symmetric difference; a unary operator – complementation) on these lists. An inspiration for this way of working with musical material was sifting used by Iannis Xenakis. In numerous publications Xenakis developed an elegant and powerful system for creating integer-sequence generators. Xenakis used sieves (cribles) for the generation of pitch scales and rhythm sequences in many compositions, and he suggested their application to a variety of additional musical parameters (see an implementation of the algorithm by Christopher Ariza http://www.mitpressjournals.org/doi/pdf/10.1162/0148926054094396). Additionally in ‘sifting’ this technique had been used to generate values for pattern chop algorithm.
2. Rhythm Material and rhythm chop
The basis of a rhythmic structures of the piece were traditional – existing largely in aural tradition – folk tunes from Wielkopolska region. A five short (1 bar length) rhythm sequences were declared as a source material for the pattern chop algorithm (based on Michael Edwards’ chop example) and values from a sifting algorithm were used to select a section of a sequence. The resulting material still has a distinct feel of a folk tune – I think – with added complexity of expanded pitch content and a break-beat style rhythm processing.
Here is a version of the piece as played at the concert