From 53eca719fb47c99f8eaaa6dacbf0ac74351589d6 Mon Sep 17 00:00:00 2001
From: Chris Cannam <cannam@all-day-breakfast.com>
Date: Thu, 18 Aug 2022 16:41:43 +0100
Subject: [PATCH] Apply gradual phase-reset on unity in the R2 stretcher (R3
 already does this)

---
 src/faster/StretcherChannelData.cpp |  2 ++
 src/faster/StretcherChannelData.h   |  1 +
 src/faster/StretcherProcess.cpp     | 21 +++++++++++++++++++--
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/faster/StretcherChannelData.cpp b/src/faster/StretcherChannelData.cpp
index 376b76c..483c572 100644
--- a/src/faster/StretcherChannelData.cpp
+++ b/src/faster/StretcherChannelData.cpp
@@ -87,6 +87,8 @@ R2Stretcher::ChannelData::construct(const std::set<size_t> &sizes,
     interpolator = allocate_and_zero<float>(maxSize);
     interpolatorScale = 0;
 
+    unityResetLow = 16000.f;
+
     for (std::set<size_t>::const_iterator i = sizes.begin();
          i != sizes.end(); ++i) {
         ffts[*i] = new FFT(*i);
diff --git a/src/faster/StretcherChannelData.h b/src/faster/StretcherChannelData.h
index 1b2d673..b0ce210 100644
--- a/src/faster/StretcherChannelData.h
+++ b/src/faster/StretcherChannelData.h
@@ -113,6 +113,7 @@ public:
     float *ms; // only used when mid-side processing
     float *interpolator; // only used when time-domain smoothing is on
     int interpolatorScale;
+    float unityResetLow; // for gradual phase-reset on unity ratio
 
     float *fltbuf;
     process_t *dblbuf; // owned by FFT object, only used for time domain FFT i/o
diff --git a/src/faster/StretcherProcess.cpp b/src/faster/StretcherProcess.cpp
index 5074a93..4757d5e 100644
--- a/src/faster/StretcherProcess.cpp
+++ b/src/faster/StretcherProcess.cpp
@@ -744,12 +744,29 @@ R2Stretcher::modifyChunk(size_t channel,
     int bandlow = lrint((150 * m_fftSize) / rate);
     int bandhigh = lrint((1000 * m_fftSize) / rate);
 
+    float r = getEffectiveRatio();
+
+    bool unity = (fabsf(r - 1.f) < 1.e-6f);
+    if (unity) {
+        if (!phaseReset) {
+            phaseReset = true;
+            bandlimited = true;
+            bandlow = lrint((cd.unityResetLow * m_fftSize) / rate);
+            bandhigh = count;
+            if (bandlow > 0) {
+                m_log.log(2, "unity: bandlow & high", bandlow, bandhigh);
+            }
+        }
+        cd.unityResetLow *= 0.9f;
+    } else {
+        cd.unityResetLow = 16000.f;
+    }
+
     float freq0 = m_freq0;
     float freq1 = m_freq1;
     float freq2 = m_freq2;
-
+    
     if (laminar) {
-        float r = getEffectiveRatio();
         if (r > 1) {
             float rf0 = 600 + (600 * ((r-1)*(r-1)*(r-1)*2));
             float f1ratio = freq1 / freq0;