Reference ranges

DEBUSSY grades each analysis against the three-tier framework of the companion review. The tiers come from a four-dimension evidence score — Effect Evidence, Mechanistic Confirmation, Appraisal Independence, Designability — summed to 0–12 per parameter:

Composite score	Tier	Meaning
9–12	Tier 1	Universal fixed design principles
5–8	Tier 2	Established direction, but optimise per individual
0–4	Tier 3	Exploratory adjuncts; further validation needed

Tier 1 is the only gate that can fail. Tiers 2 and 3 are reported.

Tier 1 — universal design checks

Parameter	Score	Design strategy	How DEBUSSY grades it
Roughness	12	Minimise; target < 0.3 asper	mean < 0.3 asper and ≤ 2 % of duration above it
Event structure	11	Stable mean level; minimise transients	INFO — dynamic range + crest reported, not gated
Onset dynamics	11	Gradual attack; onset-to-peak > ~50 ms	attack median > 50 ms
Predictability †	9	Regular patterns; avoid abrupt structural change	MANUAL — structural, not auto-detectable

† Predictability sits at the Tier-1 lower boundary. It is placed in Tier 1 because predictive-coding mechanisms are appraisal-independent — they operate automatically regardless of musical background.

Roughness status logic

Time above 0.3 asper	Status
≤ 2 %	PASS
2–10 %	CAUTION (intermittent)
> 10 %	FAIL (frequent)

A high whole-file mean fails regardless of coverage — the verdict is the more severe of the two, so coverage can only make it more conservative, never rescue a high mean. On long files coverage is sampled from probes, so a clean reading is never certified: the status is capped at CAUTION.

The 0.3 asper threshold follows the amygdala-activation roughness literature. The 2 % / 10 % coverage bands are provisional screening heuristics, not validated cut-offs.

Attack status logic

The verdict is the median-onset rule (> 50 ms). A high share of sub-50 ms onsets can downgrade a PASS to CAUTION, but only when the pattern is both substantial (> 25 % of onsets) and non-incidental (n ≥ 5). It never fails on its own: envelope rise time ignores absolute level, so it describes onset shape rather than measuring startle.

Tier 2 — directional guidelines

Direction is established; the optimum is person- and context-specific, so these are reported in-range vs out-of-range rather than passed or failed.

Parameter	Score	Design strategy
Tempo / rhythm ‡	10	Default 60–80 BPM; adapt toward individual resting heart rate
Sharpness	8	Limit energy above 3–4 kHz (provisional target)
Pitch	7	Low-mid frequency centre; descending contours
Spectral slope	6	Negative slope; avoid flat-spectrum noise
Complexity	5	Low-complexity instrumental textures
Semantic content	5	Instrumental by default; lyrics only if controlled

‡ Tempo scores 10, inside the Tier-1 band, but is assigned to Tier 2 because musical training and cultural rhythmic conventions modulate the tempo–arousal relationship, which rules out a universal fixed value.

DEBUSSY reports spectral centroid as the measured stand-in for pitch height, and lyrics presence for semantic content.

Tier 3 — exploratory

Parameter	Score	Why not prescribable
Harmonicity / HNR	3	Tonal clarity raises pleasantness, but large cross-cultural variation
Familiarity	2	Reward activation observed; direction depends on the individual

Spectral flatness is reported here too: it earns a slot in the reporting guideline as the tonal-to-noise continuum measure, without a design threshold.

Programmatic access

from debussy import tier1_items, tier2_items, tier3_items, format_compliance

for item in tier1_items(result):
    print(item["parameter"], item["status"], item["note"])

print(format_compliance(result))   # printable summary

Each item carries parameter, value, unit, target, status and note. Tier-1 statuses are PASS, CAUTION, FAIL, INFO, MANUAL or N/A.