Pelog is a seven-note Indonesian scale whose pitches do not correspond to any notes in 12-TET

Pelog is a seven-note scale used in Indonesian gamelan music. Unlike Western scales built from 12-TET semitones, pelog’s pitches fall between the cracks of standard chromatic tuning — “there is no association with the 12 notes available in Western music.” Moreover “both the intervals and the specific pitches vary widely,” so pelog is a family of tunings that differs between gamelan ensembles and regions rather than a single fixed scale. This makes pelog a clear example of how many of the world’s music traditions use tunings incommensurable with 12-TET, and why pitch-bend or sample-based approaches are needed to reproduce them digitally.

Examples

A gamelan saron (metallophone) tuned to pelog: its pitches cannot be mapped to piano keys; reproducing it needs custom MIDI tuning or samples tuned by ear to the physical instruments.

Assessment

Why can pelog pitches not be played accurately on a piano? What does “both the intervals and the specific pitches vary widely” imply about trying to define a single canonical pelog scale?