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refactor(processor): move pre-gain calculation before Pass 3 #59

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Merged
flexiondotorg merged 4 commits into from
Mar 15, 2026
Merged

refactor(processor): move pre-gain calculation before Pass 3 #59

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530d762
refactor(processor): extract calculatePreGain and buildPreLimiterPrefix
flexiondotorg Mar 15, 2026
3177f1f
refactor(processor): reorder computation and simplify loudnorm signat…
flexiondotorg Mar 15, 2026
fabed9f
docs(processor): document Pass 3 filter prefix in diagnostics and arc…
flexiondotorg Mar 15, 2026
ecf6eeb
style(processor): align NormalisationResult struct fields with gofumpt
flexiondotorg Mar 15, 2026
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4 changes: 2 additions & 2 deletions AGENTS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ internal/

1. **Pass 1 (Analysis):** Measures LUFS, true peak, LRA, noise floor, spectral characteristics; detects silence/speech regions via 250ms interval sampling
2. **Pass 2 (Processing):** Applies adaptive filter chain tuned to measurements; output measured for before/after comparison
3. **Pass 3 (Measuring):** Runs loudnorm in measurement mode (JSON output via FFmpeg log capture) to get input stats for linear mode
3. **Pass 3 (Measuring):** Optionally prepends `volume` (pre-gain) + `alimiter` (Volumax) when limiting is active, then runs loudnorm in measurement mode (JSON output via FFmpeg log capture) to get input stats for linear mode; measures the post-limiter signal so `measured_I`/`measured_TP` are accurate
4. **Pass 4 (Normalising):** Applies `volume` (pre-gain, when ceiling clamped) + `alimiter` (Volumax) + `loudnorm` (linear mode) + `adeclick`; pre-gain raises very quiet recordings so the alimiter can use a viable ceiling; `alimiter` creates headroom so loudnorm achieves full linear gain to reach -16 LUFS

**Filter chain order (Pass 2):**
Expand All @@ -72,7 +72,7 @@ Order rationale: downmix to mono first; HP/LP removes frequency extremes before

**Normalisation (Pass 3/4):**
```
Pass 3: loudnorm (measure-only, print_format=json) → captures LoudnormStats JSON
Pass 3: [volume (pre-gain, when clamped) → alimiter (Volumax)] → loudnorm (measure-only, print_format=json) → captures LoudnormStats JSON
Pass 4: volume (pre-gain, when clamped) → alimiter (Volumax, peak reduction) → loudnorm (linear mode, input stats from Pass 3) → adeclick
```

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8 changes: 8 additions & 0 deletions internal/logging/report.go
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Expand Up @@ -1891,6 +1891,14 @@ func writeDiagnosticPeakLimiter(f *os.File, result *processor.NormalisationResul
fmt.Fprintln(f, "")
}

if result.Pass3FilterPrefix != "" {
fmt.Fprintln(f, "Pass 3 measurement:")
fmt.Fprintf(f, " Prefix applied: %s -> loudnorm\n", result.Pass3FilterPrefix)
fmt.Fprintln(f, " Pass 3 measures the post-limiter signal so loudnorm receives accurate")
fmt.Fprintln(f, " measured_I and measured_TP values in Pass 4.")
fmt.Fprintln(f, "")
}

fmt.Fprintln(f, "Filter parameters:")
fmt.Fprintln(f, " Attack: 5 ms (gentle - preserves transient shape)")
fmt.Fprintln(f, " Release: 100 ms (smooth recovery, eliminates pumping)")
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