From f027a59fa490e1ca521a0f4a8ff5a23522a980b7 Mon Sep 17 00:00:00 2001
From: Chris Cannam <cannam@all-day-breakfast.com>
Date: Mon, 8 Aug 2022 16:55:53 +0100
Subject: [PATCH] I don't like adjusting the rational approximation - it
 changes (even if only nominally) the effective ratio based on quality. I
 think this is more appropriate

---
 src/common/BQResampler.cpp | 27 ++++++++++++++++++---------
 src/common/BQResampler.h   |  2 +-
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/common/BQResampler.cpp b/src/common/BQResampler.cpp
index 384e159..a3ae269 100644
--- a/src/common/BQResampler.cpp
+++ b/src/common/BQResampler.cpp
@@ -122,7 +122,7 @@ BQResampler::QualityParams::QualityParams(Quality q)
         k_snr = 70.0;
         k_transition = 0.2;
         cut = 0.9;
-        rational_max = 48000;
+        length_max = 576000;
         break;
     case FastestTolerable:
         p_multiple = 62;
@@ -130,7 +130,7 @@ BQResampler::QualityParams::QualityParams(Quality q)
         k_snr = 90.0;
         k_transition = 0.05;
         cut = 0.975;
-        rational_max = 96000;
+        length_max = 1024000;
         break;
     case Best:
         p_multiple = 122;
@@ -138,7 +138,7 @@ BQResampler::QualityParams::QualityParams(Quality q)
         k_snr = 100.0;
         k_transition = 0.01;
         cut = 0.995;
-        rational_max = 192000;
+        length_max = 0;
         break;
     }
 }
@@ -378,12 +378,7 @@ BQResampler::pick_params(double ratio) const
 {
     // Farey algorithm, see
     // https://www.johndcook.com/blog/2010/10/20/best-rational-approximation/
-    int max_denom;
-    if (m_dynamism == RatioMostlyFixed) {
-        max_denom = 192000;
-    } else {
-        max_denom = m_qparams.rational_max;
-    }
+    int max_denom = 192000;
     double a = 0.0, b = 1.0, c = 1.0, d = 0.0;
     double pa = a, pb = b, pc = c, pd = d;
     double eps = 1e-9;
@@ -500,6 +495,20 @@ BQResampler::state_for_ratio(BQResampler::state &target_state,
     target_state.filter_length =
         int(parameters.peak_to_zero * m_qparams.p_multiple + 1);
 
+    if (m_qparams.length_max > 0 &&
+        target_state.filter_length > m_qparams.length_max) {
+        int reduced_multiple =
+            int(floor(double(m_qparams.length_max) / parameters.peak_to_zero));
+        int reduced_length =
+            int(parameters.peak_to_zero * reduced_multiple + 1);
+        if (m_debug_level > 0) {
+            cerr << "BQResampler: reducing filter length from "
+                 << target_state.filter_length << " to "
+                 << reduced_length << " based on quality settings" << endl;
+        }
+        target_state.filter_length = reduced_length;
+    }
+    
     if (target_state.filter_length % 2 == 0) {
         ++target_state.filter_length;
     }
diff --git a/src/common/BQResampler.h b/src/common/BQResampler.h
index 7319c5d..99a7ef7 100644
--- a/src/common/BQResampler.h
+++ b/src/common/BQResampler.h
@@ -71,7 +71,7 @@ private:
         double k_snr;
         double k_transition;
         double cut;
-        int rational_max;
+        int length_max;
         QualityParams(Quality);
     };