Mimir/docs/audio-field.md

Audio Field

Mimir's audio field is six microphones, loopback/program reference, and two calibration speakers aligned into one presentation timeline.

Live Target

flowchart TD
    A["mic / loopback capture drivers"] --> B["Mimir.Runtime audio buffers"]
    C["speaker probe scheduler"] --> B
    B --> D["native alignment + phase state"]
    D --> E["Faust/native DSP"]
    E --> F["host voice"]
    E --> G["co-streamer voice"]
    E --> H["ambient / transients"]
    E --> I["loopback stems"]
    E --> J["spatial bed"]
    F --> K["OBS"]
    G --> K
    H --> K
    I --> K
    J --> K

Invariants

• Scarlett speaker loopback is the timing authority when calibration chirplets are playing.
• Focusrite dialogue mics are the voice anchors.
• Camera mics are spatial/context witnesses.
• Loopback/program audio is timing evidence where available; it outranks acoustic mics for clock/timing because it is the emitted program surface.
• Distributed inputs must be aligned and resampled before they become program stems.
• The five-second runtime window is allowed to be spent on alignment, resampling, separation, and spatial-field extraction. Low latency loses to a coherent volumetric sound field here.
• Probe signals are budgeted telemetry, not a permanent audio bed.
• Faust/native DSP owns the hot separation and spatialization graph.

Next Cut

The current diagnostic witness is native/probes/wasapi_audio_cadence, which emits timestamped WASAPI audio-block metadata into Mimir.Runtime through the frame-event adapter. It has proven Focusrite mic, Kiyo Pro mic, Kiyo mic, both USB Camera / PS3 Eye mics, and Scarlett speaker loopback in rolling buffers when loopback audio is actively playing. One PS3 Eye mic previously enumerated but produced zero WASAPI packets until that Eye was unplugged and replugged.

The full probe runtime config now enables sample-bearing blocks for every local audio source. MimirChirpletTimeline owns the emitted calibration stream and the matched-filter shape used to analyze it. The default timeline is a deterministic order-3 de Bruijn symbol sequence over 32 chirp symbols. Any three consecutive correctly detected symbols identify the event index inside the current operating horizon, so a receiver can place its audio window on the canonical timeline without being handed Mimir's runtime clock. Mimir queues half-second PCM segments ahead of the audio cursor, and each segment contains short asymmetric chirplets chosen from separated high-frequency slots. The point is not ornament. The timing code is carried by both frequency and rhythm, so it behaves more like a quiet birdsong texture than a repeated sweep.

MimirAudioSynchronizationAnalyzer resamples candidate mic windows into the loopback sample-rate timeline, uses cheap coarse chirplet energy for acquisition, then lets the symbol decoder refine delay from matched event indices. The lag search is wide enough for ordinary remote/network delay, not just local speaker-to-mic delay. Reports carry rounded integer delay, fractional delay from parabolic peak interpolation, and the count/confidence of timeline-symbol events used to refine the report.

MimirSynchronizationHub.BuildAlignedAudioFrame returns a provisional aligned mono frame: loopback is always channel zero, and other channels enter only when their chirplet confidence clears the gate. Delay estimates compare loopback and candidate mic windows at a shared timestamp edge; positive delay means the candidate mic is late relative to loopback. The current chirplet trace uses a 16-sample hop and parabolic peak interpolation. The aligned-frame application still rounds to integer samples; the fractional estimate exists so the next actuator can drive a real fractional-delay line.

The same timeline also starts the frequency-response path. Each report includes per-band matched energy for the chirplet atoms. That is not a finished room/mic normalizer yet, but it is the live surface that will become response-curve estimation: loopback carries what was emitted, each mic carries what survived speaker, air, room, and capsule, and the ratio over the continuous chirplet timeline becomes gain/phase correction evidence.

MimirAudioSynchronizationStateTracker turns continuous observations into state. It confidence-gates reports, smooths fractional delay per source, and estimates delay slope as sampling-rate offset in ppm. This is the control input for the coming actuator. The state can survive a brief weak report, but it is not a license to run blind: loopback must keep receiving the emitted timeline or fresh reports will stop.

The actual Mimir app path now runs this online: MimirRuntime.Update keeps the chirplet timeline queued, polls sources, and updates sync analysis on a fixed cadence. MIMIR_SYNC_TELEMETRY_SECONDS enables console telemetry for live tests. Current runtime testing proves Aquarium output wakes the Scarlett loopback, the mic buffers stay live, and the continuous timeline can produce confident online sync states in the app. The next failure is no longer lock/no-lock; it is stabilizing state filtering enough for the actuator.

Chirplet Calibration Model

flowchart TD
    A["MimirChirpletTimeline"] --> B["Aquarium audio output"]
    B --> C["Scarlett speaker loopback"]
    B --> D["room + speakers + mics"]
    C --> E["loopback rolling buffer"]
    D --> F["mic rolling buffers"]
    E --> G["matched chirplet traces"]
    F --> G
    G --> H["delay observations"]
    H --> L["smoothed sync state + SRO"]
    G --> I["per-band response estimates"]
    L --> J["fractional delay / resampler actuator"]
    I --> K["frequency response normalization"]

The chirplet timeline owns three facts:

• Emission: the PCM that Aquarium sends to the speakers.
• Timing witness: the matched-filter atom bank used to find the stream in loopback and mic buffers.
• Response witness: the per-band atoms used to measure how strongly each mic hears each emitted band.

Continuous chirplet evidence gives both the current delay and the drift/SRO by watching delay change over time. Per-band energy over the same stream gives the normalization curve. The important constraint is that all three measurements must be tied to the same emitted timeline, not three separately invented probes.

The symbol layer is intentionally blunt. Chirp symbols use separated frequency slots instead of subtle variants sharing the same center frequency, because a wrong symbol is worse than a noisy delay. A synthetic runtime check rendered two seconds of canonical timeline audio and decoded events 0, 1, and 2 back to a window start within about 1.5 ms. Real device runs still depend on loopback capture staying live; the local Scarlett loopback has intermittently stopped advancing during short headless sniffs.

Next, replace the diagnostic bridge with native audio capture workers that append typed blocks into Mimir.Runtime, then expose buffer depth, clock state, delay estimates, and stem routing in Aquarium UI.