{"id": "card_music_pitch", "kind": "reference", "title": "Pitch — A440 and the measured reference", "body": "Concert pitch fixes A above middle C at 440 Hz (MIDI note 69), sealed; the ensemble tunes to it under f = 440 * 2^((n-69)/12). Pitch is a measured frequency, and the interval arithmetic is sealed through the engine's music verifier.", "source": {"label": "Narrow Highway — music", "url": "", "authority_tier": "engine_derived"}, "shelf": "codex", "box": "music", "bands": ["music", "pillar", "pitch", "one map"], "subject": "Pitch — A440 and the measured reference", "connections": [{"to_card_id": "card_floor_music", "relationship": "part_of", "evidence": "a pillar (Pitch)"}, {"to_card_id": "card_floor_metrology", "relationship": "connects_at", "evidence": "A440 is a reference frequency - measurement"}, {"to_card_id": "card_floor_the_instruments", "relationship": "connects_at", "evidence": "the music verifier seals the interval and tuning arithmetic"}], "author": "engine", "created_at": 0.0, "updated_at": 0.0, "visibility": "public", "lifecycle_stage": "public", "volatility": "permanent", "surface": "secular", "generated": false, "call": "codex.music", "facets": {"subject": ["one map", "pillar", "pitch"]}, "presentation": {"glyph": "•", "kind_label": "music", "by": "Narrow Highway — music", "authority": "engine_derived", "posted": "", "standing": ""}, "neighbors": [{"id": "card_floor_music", "title": "Music — interval, tuning, and the harmonic series", "relationship": "part of", "why": "a pillar (Pitch)", "href": "/card/card_floor_music", "resolved": true}, {"id": "card_floor_metrology", "title": "Metrology — measurement and the SI", "relationship": "connects at", "why": "A440 is a reference frequency - measurement", "href": "/card/card_floor_metrology", "resolved": true}, {"id": "card_floor_the_instruments", "title": "The instruments — every verifier and validator, and where they join", "relationship": "connects at", "why": "the music verifier seals the interval and tuning arithmetic", "href": "/card/card_floor_the_instruments", "resolved": true}], "house": {"door": "FIND", "kind": "card", "trail": "connections", "seal": "/card/card_music_pitch", "next_step": {"do": "follow a connection: what this card rests on, and what rests on it", "door": "FIND", "tool": "card_connections", "params": {"id": "card_music_pitch"}}, "ends": "a verdict or a card · the trail · a seal · one next step"}}