Fix the UHJ all-pass delay

For real this time. The non-all-passed signal needs a one-sample delay over the
all-passed signal. Because of the way the all-pass FIR filter is structured,
it wouldn't otherwise use the last buffered sample, allowing it to be shifted
forward in time by one sample.

Also, remove a couple unnecessary buffers.

2 files changed, 8 insertions, 11 deletions

diff --git a/core/uhjfilter.cpp b/core/uhjfilter.cpp
index 2dd41d15..3fbec3b3 100644
--- a/core/uhjfilter.cpp
+++ b/core/uhjfilter.cpp
@@ -244,13 +244,13 @@ void Uhj2Encoder::encode(const FloatBufferSpan LeftOut, const FloatBufferSpan Ri
     /* Combine the previously delayed mid/side signal with the input. */
 
     /* S = 0.9396926*W + 0.1855740*X */
-    auto miditer = std::copy(mMidDelay.cbegin(), mMidDelay.cend(), mMid.begin());
+    auto miditer = mMid.begin() + sFilterSize;
     std::transform(winput, winput+SamplesToDo, xinput, miditer,
         [](const float w, const float x) noexcept -> float
         { return 0.9396926f*w + 0.1855740f*x; });
 
     /* D = 0.6554516*Y */
-    auto sideiter = std::copy(mSideDelay.cbegin(), mSideDelay.cend(), mSide.begin());
+    auto sideiter = mSide.begin() + sFilterSize;
     std::transform(yinput, yinput+SamplesToDo, sideiter,
         [](const float y) noexcept -> float { return 0.6554516f*y; });
 
@@ -260,10 +260,6 @@ void Uhj2Encoder::encode(const FloatBufferSpan LeftOut, const FloatBufferSpan Ri
     for(size_t i{0};i < SamplesToDo;++i,++sideiter)
         *sideiter += left[i] - right[i];
 
-    /* Copy the future samples back to the delay buffers for next time. */
-    std::copy_n(mMid.cbegin()+SamplesToDo, mMidDelay.size(), mMidDelay.begin());
-    std::copy_n(mSide.cbegin()+SamplesToDo, mSideDelay.size(), mSideDelay.begin());
-
     /* Now add the all-passed signal into the side signal. */
 
     /* D += j(-0.3420201*W + 0.5098604*X) */
@@ -280,4 +276,8 @@ void Uhj2Encoder::encode(const FloatBufferSpan LeftOut, const FloatBufferSpan Ri
     /* Right = (S - D)/2.0 */
     for(size_t i{0};i < SamplesToDo;i++)
         right[i] = (mMid[i] - mSide[i]) * 0.5f;
+
+    /* Copy the future samples to the front for next time. */
+    std::copy(mMid.cbegin()+SamplesToDo, mMid.cbegin()+SamplesToDo+sFilterSize, mMid.begin());
+    std::copy(mSide.cbegin()+SamplesToDo, mSide.cbegin()+SamplesToDo+sFilterSize, mSide.begin());
 }
diff --git a/core/uhjfilter.h b/core/uhjfilter.h
index 7609533b..ff794355 100644
--- a/core/uhjfilter.h
+++ b/core/uhjfilter.h
@@ -14,15 +14,12 @@ struct Uhj2Encoder {
      */
     constexpr static size_t sFilterSize{128};
 
-    /* Delays for the unfiltered signal. */
-    alignas(16) std::array<float,sFilterSize> mMidDelay{};
-    alignas(16) std::array<float,sFilterSize> mSideDelay{};
-
+    /* Delays and processing storage for the unfiltered signal. */
     alignas(16) std::array<float,BufferLineSize+sFilterSize> mMid{};
     alignas(16) std::array<float,BufferLineSize+sFilterSize> mSide{};
 
     /* History for the FIR filter. */
-    alignas(16) std::array<float,sFilterSize*2> mSideHistory{};
+    alignas(16) std::array<float,sFilterSize*2 - 1> mSideHistory{};
 
     alignas(16) std::array<float,BufferLineSize + sFilterSize*2> mTemp{};