diff --git a/src/VisualizerWidget.cpp b/src/VisualizerWidget.cpp
index 2bfcc02..78a5357 100644
--- a/src/VisualizerWidget.cpp
+++ b/src/VisualizerWidget.cpp
@@ -390,7 +390,43 @@ void VisualizerWidget::render(QRhiCommandBuffer *cb) {
     m_lastBuildW = w;
     m_lastBuildH = h;
     if (m_mirrored) {
-      buildVertices(w * 0.55f, h / 2 + 2);
+      buildVertices(w * 0.55f, h / 2);
+
+      // Expand half-size vertices into all 4 quadrants (eliminates mirror seam)
+      {
+        int fillFloats = m_fillVertexCount * 6;
+        int lineFloats = m_lineVertexCount * 6;
+        float fw = (float)w, fh = (float)h;
+
+        auto expand = [&](const float *src, int nVerts, std::vector<float> &dst) {
+          for (int q = 0; q < 4; q++) {
+            bool fx = (q == 1 || q == 3);
+            bool fy = (q == 2 || q == 3);
+            for (int v = 0; v < nVerts; v++) {
+              int b = v * 6;
+              dst.push_back(fx ? fw - src[b] : src[b]);
+              dst.push_back(fy ? fh - src[b + 1] : src[b + 1]);
+              dst.push_back(src[b + 2]);
+              dst.push_back(src[b + 3]);
+              dst.push_back(src[b + 4]);
+              dst.push_back(src[b + 5]);
+            }
+          }
+        };
+
+        std::vector<float> expFill, expLine;
+        expFill.reserve(fillFloats * 4);
+        expLine.reserve(lineFloats * 4);
+        expand(m_vertices.data(), m_fillVertexCount, expFill);
+        expand(m_vertices.data() + fillFloats, m_lineVertexCount, expLine);
+
+        m_vertices.clear();
+        m_vertices.insert(m_vertices.end(), expFill.begin(), expFill.end());
+        m_vertices.insert(m_vertices.end(), expLine.begin(), expLine.end());
+        m_fillVertexCount *= 4;
+        m_lineVertexCount *= 4;
+      }
+
       buildCepstrumVertices(w, h);
     } else {
       buildVertices(w, h);
@@ -398,8 +434,6 @@ void VisualizerWidget::render(QRhiCommandBuffer *cb) {
     }
   }
 
-  int numPasses = m_mirrored ? 4 : 1;
-
   // Prepare resource updates
   QRhiResourceUpdateBatch *u = m_rhi->nextResourceUpdateBatch();
 
@@ -420,43 +454,13 @@ void VisualizerWidget::render(QRhiCommandBuffer *cb) {
     }
   }
 
-  // Upload MVP matrices
+  // Upload single full-screen ortho MVP (slot 0)
   QMatrix4x4 correction = m_rhi->clipSpaceCorrMatrix();
-
-  for (int i = 0; i < numPasses; i++) {
+  {
     QMatrix4x4 proj;
     proj.ortho(0, (float)w, (float)h, 0, -1, 1);
-
-    if (m_mirrored) {
-      switch (i) {
-      case 0: break;
-      case 1:
-        proj.translate(w, 0, 0);
-        proj.scale(-1, 1, 1);
-        break;
-      case 2:
-        proj.translate(0, h, 0);
-        proj.scale(1, -1, 1);
-        break;
-      case 3:
-        proj.translate(w, h, 0);
-        proj.scale(-1, -1, 1);
-        break;
-      }
-    }
-
     QMatrix4x4 mvp = correction * proj;
-    u->updateDynamicBuffer(m_ubuf.get(), i * m_ubufAlign, 64,
-                           mvp.constData());
-  }
-
-  // Upload full-screen ortho MVP for cepstrum (slot 4)
-  if (m_mirrored && m_cepstrumVertexCount > 0) {
-    QMatrix4x4 cepProj;
-    cepProj.ortho(0, (float)w, (float)h, 0, -1, 1);
-    QMatrix4x4 cepMvp = correction * cepProj;
-    u->updateDynamicBuffer(m_ubuf.get(), 4 * m_ubufAlign, 64,
-                           cepMvp.constData());
+    u->updateDynamicBuffer(m_ubuf.get(), 0, 64, mvp.constData());
   }
 
   // Begin render pass
@@ -465,30 +469,26 @@ void VisualizerWidget::render(QRhiCommandBuffer *cb) {
                    (float)outputSize.height()});
 
   const QRhiCommandBuffer::VertexInput vbufBinding(m_vbuf.get(), 0);
+  QRhiCommandBuffer::DynamicOffset dynOfs(0, 0);
 
-  for (int i = 0; i < numPasses; i++) {
-    QRhiCommandBuffer::DynamicOffset dynOfs(0, quint32(i * m_ubufAlign));
-
-    if (m_fillVertexCount > 0) {
-      cb->setGraphicsPipeline(m_fillPipeline.get());
-      cb->setShaderResources(m_srb.get(), 1, &dynOfs);
-      cb->setVertexInput(0, 1, &vbufBinding);
-      cb->draw(m_fillVertexCount);
-    }
-
-    if (m_lineVertexCount > 0) {
-      cb->setGraphicsPipeline(m_linePipeline.get());
-      cb->setShaderResources(m_srb.get(), 1, &dynOfs);
-      cb->setVertexInput(0, 1, &vbufBinding);
-      cb->draw(m_lineVertexCount, 1, m_fillVertexCount, 0);
-    }
+  if (m_fillVertexCount > 0) {
+    cb->setGraphicsPipeline(m_fillPipeline.get());
+    cb->setShaderResources(m_srb.get(), 1, &dynOfs);
+    cb->setVertexInput(0, 1, &vbufBinding);
+    cb->draw(m_fillVertexCount);
   }
 
-  // --- Cepstral Thread (single full-screen pass, after mirror loop) ---
-  if (m_mirrored && m_cepstrumVertexCount > 0) {
-    QRhiCommandBuffer::DynamicOffset cepOfs(0, quint32(4 * m_ubufAlign));
+  if (m_lineVertexCount > 0) {
     cb->setGraphicsPipeline(m_linePipeline.get());
-    cb->setShaderResources(m_srb.get(), 1, &cepOfs);
+    cb->setShaderResources(m_srb.get(), 1, &dynOfs);
+    cb->setVertexInput(0, 1, &vbufBinding);
+    cb->draw(m_lineVertexCount, 1, m_fillVertexCount, 0);
+  }
+
+  // --- Cepstral Thread ---
+  if (m_mirrored && m_cepstrumVertexCount > 0) {
+    cb->setGraphicsPipeline(m_linePipeline.get());
+    cb->setShaderResources(m_srb.get(), 1, &dynOfs);
     cb->setVertexInput(0, 1, &vbufBinding);
     cb->draw(m_cepstrumVertexCount, 1, m_fillVertexCount + m_lineVertexCount, 0);
   }