Constant LEVEL_SPREAD_CONVENTION 

pub const LEVEL_SPREAD_CONVENTION: &str = "the 90th minus the 10th percentile of the full-band \
level of the pooled notes, quantiles by linear interpolation; a note's full-band level is the peak \
of the centred RMS of the mono mix in dB of full-scale power over one period of the fundamental, \
or the fewest whole periods that span 2 ms, on a 1 ms hop from its onset to its note-off knee, or \
to 50 ms before its end in the note list without one, and on a mono line, one whose voices layer \
reads at most one voice at a time, never past the next later onset; always low confidence, a rule no stem has tested; null under 3 pooled notes with a level";

The convention of the level spread.