From 2f8b91e1e2602bd37a3f44a245bafeed2047b1d7 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 20 Jul 2026 01:36:18 +0000
Subject: [PATCH] Stream LoudnessMeter blocks through a ring buffer (drops ~127
 MB analysis spike)
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integratedLUFS allocated a full-length [Double] weighted buffer (~127 MB
for a 6-minute track) on top of the mono analysis buffer — a transient
spike that ran while music plays and fed the jetsam budget. The weighted
samples now stream through a single block-sized ring (~140 KB); each
400 ms block's mean-square is summed from the ring in the same order as
before, so results are bit-identical (regression test compares against
the old implementation verbatim, including at sample rates where the
block isn't a whole multiple of the hop).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013TJoWkqg8bzkGdzxWhWjWP
---
 .../ContinuityCore/LoudnessMeter.swift        | 26 +++++----
 .../LoudnessMeterTests.swift                  | 53 +++++++++++++++++++
 2 files changed, 69 insertions(+), 10 deletions(-)

diff --git a/Packages/ContinuityCore/Sources/ContinuityCore/LoudnessMeter.swift b/Packages/ContinuityCore/Sources/ContinuityCore/LoudnessMeter.swift
index 7e8738d..a56ab8b 100644
--- a/Packages/ContinuityCore/Sources/ContinuityCore/LoudnessMeter.swift
+++ b/Packages/ContinuityCore/Sources/ContinuityCore/LoudnessMeter.swift
@@ -23,26 +23,32 @@ public enum LoudnessMeter {
         var highPass = Biquad.highPass(f0: 38.13547087602444, q: 0.5003270373238773,
                                        sampleRate: sampleRate)
 
-        var weighted = [Double](repeating: 0, count: samples.count)
-        for i in 0..<samples.count {
-            weighted[i] = highPass.process(shelf.process(Double(samples[i])))
-        }
-
         // 400 ms blocks, 100 ms hop (75% overlap).
         let block = Int(0.4 * sampleRate)
         let hop = Int(0.1 * sampleRate)
-        guard block > 0, hop > 0, weighted.count >= block else { return nil }
+        guard block > 0, hop > 0, samples.count >= block else { return nil }
 
+        // Single streaming pass: weighted samples land in a block-sized ring instead of a
+        // full-length buffer (which cost ~127 MB on a 6-minute track — a jetsam-feeding spike
+        // while analysis runs during playback). Each block's mean-square is summed from the
+        // ring in logical order, so the arithmetic — order included — matches the old
+        // whole-buffer implementation exactly.
+        var ring = [Double](repeating: 0, count: block)
         var blockLoudness: [Double] = []
         var blockMeanSquare: [Double] = []
-        var start = 0
-        while start + block <= weighted.count {
+        for i in 0..<samples.count {
+            ring[i % block] = highPass.process(shelf.process(Double(samples[i])))
+            let filled = i + 1
+            guard filled >= block, (filled - block) % hop == 0 else { continue }
+            let start = filled - block
             var sum = 0.0
-            for i in start..<(start + block) { sum += weighted[i] * weighted[i] }
+            for j in start..<filled {
+                let w = ring[j % block]
+                sum += w * w
+            }
             let ms = sum / Double(block)
             blockMeanSquare.append(ms)
             blockLoudness.append(-0.691 + 10 * log10(max(ms, .leastNormalMagnitude)))
-            start += hop
         }
 
         // Absolute gate: drop blocks below −70 LUFS.
diff --git a/Packages/ContinuityCore/Tests/ContinuityCoreTests/LoudnessMeterTests.swift b/Packages/ContinuityCore/Tests/ContinuityCoreTests/LoudnessMeterTests.swift
index 8892745..8af345d 100644
--- a/Packages/ContinuityCore/Tests/ContinuityCoreTests/LoudnessMeterTests.swift
+++ b/Packages/ContinuityCore/Tests/ContinuityCoreTests/LoudnessMeterTests.swift
@@ -54,4 +54,57 @@ final class LoudnessMeterTests: XCTestCase {
         XCTAssertEqual(LoudnessMeter.makeupGainDB(measuredLUFS: -30, targetLUFS: -14), 6, accuracy: 1e-9)   // boost cap
         XCTAssertEqual(LoudnessMeter.makeupGainDB(measuredLUFS: -1, targetLUFS: -14), -12, accuracy: 1e-9)  // cut cap
     }
+
+    /// The streaming ring-buffer implementation must reproduce the straightforward
+    /// whole-buffer measurement bit-for-bit — including at sample rates where the 400 ms
+    /// block is NOT an exact multiple of the 100 ms hop (integer truncation, e.g. 44056 Hz).
+    func testStreamingMatchesReferenceImplementation() {
+        for rate in [44_100.0, 48_000.0, 44_056.0] {
+            let n = Int(3.7 * rate)   // non-whole block count exercises the tail handling
+            let samples = (0..<n).map { i -> Float in
+                // Deterministic multi-tone with a quiet stretch so both gates engage.
+                let t = Double(i) / rate
+                let quiet = t > 2.5 ? 0.001 : 1.0
+                return Float(quiet * (0.08 * sin(2 * .pi * 997 * t) + 0.04 * sin(2 * .pi * 210 * t)))
+            }
+            let streamed = LoudnessMeter.integratedLUFS(samples: samples, sampleRate: rate)
+            let reference = Self.referenceLUFS(samples: samples, sampleRate: rate)
+            XCTAssertEqual(streamed, reference, "sample rate \(rate)")
+        }
+    }
+
+    /// The pre-optimization implementation: full-length weighted buffer, then blocks.
+    private static func referenceLUFS(samples: [Float], sampleRate: Double) -> Double? {
+        guard sampleRate > 0, !samples.isEmpty else { return nil }
+        var shelf = LoudnessMeter.Biquad.highShelf(f0: 1681.974450955533, gainDB: 3.999843853973347,
+                                                   q: 0.7071752369554196, sampleRate: sampleRate)
+        var highPass = LoudnessMeter.Biquad.highPass(f0: 38.13547087602444, q: 0.5003270373238773,
+                                                     sampleRate: sampleRate)
+        var weighted = [Double](repeating: 0, count: samples.count)
+        for i in 0..<samples.count {
+            weighted[i] = highPass.process(shelf.process(Double(samples[i])))
+        }
+        let block = Int(0.4 * sampleRate)
+        let hop = Int(0.1 * sampleRate)
+        guard block > 0, hop > 0, weighted.count >= block else { return nil }
+        var blockLoudness: [Double] = []
+        var blockMeanSquare: [Double] = []
+        var start = 0
+        while start + block <= weighted.count {
+            var sum = 0.0
+            for i in start..<(start + block) { sum += weighted[i] * weighted[i] }
+            let ms = sum / Double(block)
+            blockMeanSquare.append(ms)
+            blockLoudness.append(-0.691 + 10 * log10(max(ms, .leastNormalMagnitude)))
+            start += hop
+        }
+        var gated = zip(blockMeanSquare, blockLoudness).filter { $0.1 > -70 }
+        guard !gated.isEmpty else { return nil }
+        let meanMS = gated.reduce(0) { $0 + $1.0 } / Double(gated.count)
+        let relativeThreshold = -0.691 + 10 * log10(meanMS) - 10
+        gated = gated.filter { $0.1 > relativeThreshold }
+        guard !gated.isEmpty else { return nil }
+        let finalMS = gated.reduce(0) { $0 + $1.0 } / Double(gated.count)
+        return -0.691 + 10 * log10(finalMS)
+    }
 }