Routing and the Listener Twin

Two buses

Each voice contributes to two independent mono buses:

• presentation bus → cpal output / offline render / UI metering (the work as presented)
• habitat bus → NSGT analysis → landscape (what the ALife ecology responds to)

By default both buses receive the voice. Use send() when a voice should feed only one side, or combine buses with |:

// Reference anchor: sensed by the ecology, absent from the presented sound.
let anchor = harmonic().brain("drone").send(habitat_bus);

// Presented decor that does not influence the ecology.
let decor = sine().send(presentation_bus);

// Explicitly both (the default).
let normal = harmonic().send(habitat_bus | presentation_bus);

place(anchor, at(110.0));
place(decor, at(880.0));
place(normal, consonance(110.0).peak().count(3));
wait(4.0);

Keeping the buses separate is a composition tool. A hidden anchor on send(habitat_bus) can shape how the population organizes without ever becoming audible, and presented decor on send(presentation_bus) can be heard without perturbing the ecology.

Both buses receiving every voice is the default because it is Direct Cognitive Coupling: what the listener hears and what the ecology senses are the same physical event. Splitting the buses is a deliberate departure. send(habitat_bus) casts terrain — the director’s work, shaping the field without being heard. send(presentation_bus) casts decor — heard, but outside the ecology’s world. The samples’ design rule applies: scaffolding is inaudible or embodied.

The Listener Twin

conchordal keeps a ListenerTwin: a listener-side model of the presented sound only. It never reads the habitat bus, so hidden scaffolds cannot create fake listener tension. Its listener_state report contains four perceptual levels:

• stability_level: how stable / consonant the current audible sound is.
• resolvability_level: whether a nearby audible state offers a plausible, more stable continuation.
• tension_level: (1 - stability) * resolvability — unstable now, but with a reachable path toward improvement.
• attention_level: presentation-derived onset / spectral-flux salience.

It also contains the listener-side meter estimate:

• beat_hz, beat_phase, and beat_confidence;
• subdivision_ratio and subdivision_confidence;
• measure_hz, measure_ratio, and measure_confidence.

generated_frame_id, analysis_frame_id, and analysis_lag_frames make the perceptual delay explicit. They matter when comparing a report event with the sound that caused it.

There is no scripting verb for the twin. It is observed, not commanded: when you run with reporting enabled it emits listener_state records, and the GUI shows the same state. Use it to check whether the tension you hear matches what the twin reports before coupling it back into generation.

DCC: coupling the twin back

That optional coupling is DCC, configured in config.toml (or the file selected with --config), not in script:

[dcc]
# Listener pressure is report/UI-only by default.
# coupling_strength = 0.0
# max_temperature_bonus = 0.10

• coupling_strength (0.0–1.0, default 0.0): at 0.0 the twin is report/UI-only and generation is unchanged. Above 0.0 it applies tension_pressure = tension_level * resolvability_level * coupling_strength as a transient pitch-exploration bonus only. It never sets target pitches or changes rhythm synchronization.
• max_temperature_bonus (default 0.10): ceiling on that transient bonus.

Raise coupling_strength gradually, and only after the reported listener_state looks musically legible. When coupling is active, dcc_pressure report records show both the pressure and the resulting temperature bonus.