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The authoring form (score §2.3) is the definition, yet a note holding both "start":0 and "start":5 built with start 5 (serde_json keeps the last value) and the same hash as a note with start 5 alone; another JSON reader could keep the first. wai_cli/strict_json.rs reads JSON with every object's members distinct and refuses a repeat, and build reads its document through it. Two refused cases are added: a note field and a document member, each given twice. Co-Authored-By: Claude Opus 5.5 <[email protected]>
138 lines
6 KiB
Markdown
138 lines
6 KiB
Markdown
# WAI Extension: Score (Music as Instructions)
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> Status: Draft. Phase 6 — the deepest audio lever. Ship the
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> composition, not the recording: a score of note events the sink
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> synthesizes. Conformance is **mixdown-equivalence**, the music
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> counterpart of spatial audio. Reference impl: the `score` feature of
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> `wai-rs`; corpus: `score-conformance/`; live sink:
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> wai.transaction.science/score.
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Keywords **MUST**, **MUST NOT**, **SHOULD**, **MAY** are RFC 2119/8174.
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## 1. Scope and model
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A `wai.audio.score` object carries **no recorded audio** — only note
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events. Where `wai.audio.scene` mixes recorded sound *objects*, a score
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is reconstructed from instructions: a deterministic reference synth
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turns the notes into a canonical PCM mixdown, and a sink with a richer
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instrument (soundfont, neural) renders the same score for presentation.
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It is lever 3 (instructions-at-the-sink) for music — a minute of music
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is kilobytes of notes, not megabytes of samples.
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In scope: the container, the note model, the deterministic reference
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synthesis, the **mixdown-equivalence** conformance criterion, the
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receipt profile. Out of scope: a transport; the sink's instrument
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(soundfonts, neural synths — presentation, not conformance); MIDI-file
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import (an authoring concern).
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Relationship to the core spec: mirrors spatial audio. The reconstruct
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runs in the `wai.det.fixed64` floor; `media` takes the value `"audio"`;
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`wai.audio.score` is authoritative.
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## 2. Container (`WSCR`)
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```
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"WSCR" | u16 n_sections | section table (u8 kind, u32 off, u32 len) | sections
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```
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| kind | section | required |
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|---|---|---|
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| `0x01` | contract (canonical JSON) | REQUIRED |
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| `0x02` | note events | REQUIRED |
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### 2.1 Contract
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```json
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{ "channels": 1, "duration": 34000, "numeric": "wai.det.fixed64",
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"sample_rate": 22050 }
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```
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`duration` is the rendered mixdown length in samples.
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### 2.2 Notes
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`n_notes u32`, then per note (65 bytes):
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`start u64 | dur u64 | phase_inc i64 Fx | gain i64 Fx | waveform u8 |
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attack u64 | decay u64 | sustain i64 Fx | release u64`.
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`phase_inc` is the per-sample phase advance `freq / sample_rate`,
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authored off-line from the pitch — so the floor never evaluates an
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exponential to turn a note into a frequency (the same authoring
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discipline as the avatar quaternion). `waveform` selects a reference
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timbre: `0` saw, `1` square, `2` triangle, `3` 25%-pulse.
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### 2.3 Authoring form (informative)
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`wai score build` writes a `WSCR` from a JSON document that holds every
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field as an integer, so the committed document is the definition and no
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platform's floating-point `pow` can change a pitch:
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```json
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{ "sample_rate": 22050, "channels": 1, "duration": 34000,
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"numeric": "wai.det.fixed64",
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"notes": [ { "start": 0, "dur": 3500, "phase_inc": 50960238,
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"gain": 1717986918, "waveform": 0, "attack": 220,
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"decay": 600, "sustain": 2791728742, "release": 1500 } ] }
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```
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`phase_inc`, `gain` and `sustain` are the raw Q32.32 bits. `numeric` may
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be left out. The tool refuses a number with a fraction or an exponent, a
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member it does not name, a member given twice (readers differ on which of
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the two values they keep), more than one channel, a `phase_inc` of a whole
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cycle or more, a `gain` or `sustain` above 1.0, a waveform above 3, and a
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note whose release would end after `duration`, so the mixdown always
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holds every note whole. `score-conformance/notes/` holds each vector in
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this form, and `wai score build` turns it back into the committed `WSCR`
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byte for byte.
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## 3. Reference synthesis (trig-free)
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For each note, a phase accumulator advances by `phase_inc` each sample
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(wrapping at `1.0`); a **piecewise-linear** oscillator maps the phase to
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`[-1, 1]` (no trig); a **linear ADSR** envelope (attack ramp → decay to
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`sustain` → held until `dur` → release to zero over `release`) scales
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it; the result times `gain` accumulates into the mixdown buffer. Each
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output sample is quantized to `i16` (`round(v · 32767)`, half away from
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zero, clamped) in integer space. The whole path is `+ − × ÷` in the
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`Fx` floor — bit-identical on every machine.
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## 4. Conformance — mixdown-equivalence
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> Given the same `wai.audio.score`, a conforming sink MUST reconstruct
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> the identical canonical `i16` PCM via the reference synth, hence the
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> identical BLAKE3 — on every machine, no tolerance parameter.
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```
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mixdown_hash = BLAKE3("wai:score-mixdown\x01" || i16le PCM)
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score_hash = BLAKE3("wai:score\x01" || contract || notes) // identity
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```
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A conformance vector also states `pcm_sha256`, the SHA-256 of the same
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`i16le` PCM (the audio buffer of SPEC §7 *Digests*), so a verifier that
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holds only SHA-256 checks the samples. `wai score render` prints both
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and, with `--pcm`, writes the samples.
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A sink MAY play a soundfont/neural instrument instead; that is
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presentation and does not affect conformance, exactly as the audio-scene
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HRTF render or the worlds renderer does not.
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## 5. Receipt (JWP profile)
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`score_hash` is the identity; the group's objects are the mix PCM blocks
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(per a fixed sample span), Merkle-bound; one Ed25519 signature (verified as
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SPEC §7 *Signatures* requires) over score_hash + root + exact work (= duration × notes) + carried
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`joules_micro`; `parent_receipt_hash` chains — the worlds/audio receipt
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shape reused. The figure's acquisition class rides beside it as an optional signed label
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([energy-measurement](energy-measurement.md) §2.8): absent, the receipt keeps
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its legacy bytes and the figure is unlabelled; present, it is inside the
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signature. The reference meter labels every figure it measures
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`OnChipCounter`, with its declared uncertainty.
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## Appendix
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Mixdown-equivalence is spatial audio's criterion with the recorded
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objects replaced by note events: both render a deterministic `i16` mix
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in the `Fx` floor and hash it. The score is the most extreme
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instructions-at-the-sink case in audio — there is no recording anywhere
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in the payload, only the composition. Sight, hearing, touch, motion,
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state, captured-content provenance — and now the composition itself —
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are one floor, one verification.
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