Mix Engine — Critic-Driven Mix Improvement

The mix engine runs an iterative critic loop: analyze, plan, execute, measure, evaluate, keep or undo. Every mix change is measured before and after. Nothing stays unless it scores better than the original.

Character-First Default

Do not treat the full loop as the default for vague requests like "make it better", "more character", "more alive", "punchier", "warmer", or "more interesting". Those are usually sound-design or creative-direction requests. Start from analyzer character (sonic_character, get_spectral_shape, get_novelty, get_onsets, get_mel_spectrum) and prefer source, instrument, device-chain, envelope, filter, saturation, modulation, and transient-shape decisions before generic level changes.

Use set_track_volume, set_track_pan, and broad send-level balancing only when the user explicitly asks for balance/level/pan/send work, or when analyzer evidence shows a safety/translation problem such as clipping, headroom collapse, mono collapse, or a severe masking issue. Producers can adjust simple loudness by ear quickly; LivePilot's value is in hearing spectral character and choosing a smarter musical intervention.

For normal work, cap mix-engine action to one high-value move plus a short verdict. Enter the repeated full loop only for explicit requests like "deep mix pass", "mastering prep", "fix all mix issues", or an exact target such as LUFS/headroom/mono compatibility.

The Mix Critic Loop

Follow these steps in order. Do not skip the evaluation step.

Step 1 — Analyze

Call analyze_mix or get_mix_issues to build a MixState and run all critics against the current session. The response contains an issues array, each with a critic, severity, track_index, and evidence dict.

If the M4L analyzer bridge is absent, critics fall back to role-based heuristics only (track names, device chains, volume/pan positions). Inform the user that spectral analysis is unavailable and recommendations are less precise.

For detailed frequency collision data, call get_masking_report. For a quick status overview without the full critic pass, call get_mix_summary.

Step 2 — Plan

Pick the highest-severity issue from the issues array. Call plan_mix_move with the issue data. The planner returns the smallest intervention that addresses the problem — a single parameter change, not a chain of edits.

Read the move object: it contains move_type, target_track, target_device, target_parameter, target_value, and rationale. Consult the move vocabulary in references/mix-moves.md for parameter ranges.

Step 3 — Capture Before

Take a measurement snapshot before executing anything:

1. Call get_master_spectrum — save the 9-band spectral data (sub_low → air)
2. Call get_master_rms — save the RMS and peak values

Optionally call get_mix_snapshot if you need per-track volume/pan/send state for the evaluation.

Step 4 — Execute

Execute the planned move. Use the appropriate tool for the move type:

• set_device_parameter for EQ cuts/boosts, compressor thresholds, saturation drives
• set_track_volume for gain staging
• set_track_pan for stereo placement
• set_track_send for bus routing levels
• toggle_device for bypassing/enabling processors
• batch_set_parameters when the move requires multiple related parameter changes on the same device

Execute exactly one move. Do not chain multiple interventions before measuring.

Step 5 — Capture After

Repeat the same measurements from Step 3:

1. Call get_master_spectrum — save the post-change spectral data
2. Call get_master_rms — save the post-change RMS and peak values

Step 6 — Evaluate

Call evaluate_mix_move with the before and after snapshots:

evaluate_mix_move(
  before_snapshot: { spectrum: [...], rms: float, peak: float },
  after_snapshot:  { spectrum: [...], rms: float, peak: float },
  targets: { ... },     # what the move aimed to improve
  protect: { ... }      # what must not get worse
)

Read the response: keep_change (bool), score (0.0-1.0), improvements (list), regressions (list), explanation (string).

Step 7 — Keep or Undo

If keep_change is false, call undo() immediately. Tell the user what was tried and why it was reverted, citing the regressions list.

If keep_change is true, report the improvement to the user with the score and explanation.

Step 8 — Learn (Optional)

If the move scored above 0.7 and the user confirms satisfaction, call memory_learn(name="...", type="mix_template", qualities={"summary": "..."}, payload={...}) to save the technique for future recall.

Step 9 — Repeat

Return to Step 1 and re-analyze only when the user requested a deep/full mix pass. Otherwise stop after the first measured high-value intervention and report the remaining optional issues as suggestions. Avoid spending a turn on small volume-balancing loops unless they are the requested task.

Quick Mix Checks

Not every request needs the full loop:

• "How's my mix?" — Call get_mix_summary for a one-shot status report with no changes
• "What's clashing?" — Call get_masking_report for detailed per-pair frequency collision data
• "What are the issues?" — Call get_mix_issues for the critic list without executing any fixes

Critic Types

Six critics run during analysis. See references/mix-critics.md for thresholds and evidence format:

• masking — frequency collisions between overlapping tracks
• over_compressed — excessive compression reducing dynamic range
• flat_dynamics — insufficient volume variation across sections
• low_headroom — master peak too close to 0 dBFS
• stereo_width — mono collapse or excessive width on specific elements
• spectral_balance — overall tonal balance skew (too bright, too dark, mid-heavy)

Move Vocabulary

The planner draws from six move types. See references/mix-moves.md for parameter ranges:

• gain_staging — volume adjustments to establish proper level hierarchy
• bus_compression — glue compression on groups or master
• transient_shaping — attack/sustain manipulation for punch or smoothness
• eq_cut — subtractive EQ to clear masking or remove resonances
• eq_boost — additive EQ to bring out character (use sparingly)
• pan_spread — stereo placement adjustments for width and separation

Analyzer Dependency

The mix engine works in two modes:

• Full mode (M4L analyzer connected): spectral data, RMS, key detection available. Critics use measured evidence.
• Heuristic mode (no analyzer): critics infer from track names, device chains, and parameter positions. Always inform the user: "Spectral analysis unavailable — recommendations are based on track structure and device settings only."

Call get_capability_state to check which mode is active before starting the loop.

Extended Perception Toolkit

Beyond get_master_spectrum / get_master_rms / get_detected_key, the analyzer domain exposes six more measurements that give finer evidence than the 9-band spectrum alone. Use them when the standard snapshot is too coarse for the move you are evaluating:

• `get_spectral_shape` — centroid, spread, skewness, kurtosis, rolloff, flatness, crest. Use for tonal balance judgments ("is this bright?", "is the energy concentrated or spread?") that 9 discrete bands cannot describe.
• `get_mel_spectrum` — perceptual mel-band energies. Use when an EQ move needs to be evaluated against how the change is heard, not against linear-frequency bin energies.
• `get_chroma` — 12-bin pitch-class energy. Use to detect harmonic clashes or to confirm a key without trusting get_detected_key alone.
• `get_onsets` — transient detection. Use for groove / rhythm evaluations where you need to know when hits land, not just how loud the average is.
• `get_novelty` — spectral change score with boundary flag. Use to confirm an arrangement boundary actually creates a perceived event, or to detect static sections that need disruption.
• `get_momentary_loudness` — momentary LUFS + true-peak dBTP. Use during mastering moves where peak/RMS is insufficient and EBU R128 is the gauge.

All six are bridge-dependent — they return helpful errors if the analyzer is not on master. They do not replace the before/after snapshot pattern; they enrich what "snapshot" means when the move warrants it.