diff --git a/modules/audio_processing/agc2/rnn_vad/BUILD.gn b/modules/audio_processing/agc2/rnn_vad/BUILD.gn
index 12e32e544c..814a7f5b44 100644
--- a/modules/audio_processing/agc2/rnn_vad/BUILD.gn
+++ b/modules/audio_processing/agc2/rnn_vad/BUILD.gn
@@ -19,6 +19,7 @@ source_set("lib") {
     "common.h",
     "ring_buffer.h",
     "sequence_buffer.h",
+    "symmetric_matrix_buffer.h",
   ]
   deps = [
     "../../../../api:array_view",
@@ -32,6 +33,7 @@ if (rtc_include_tests) {
     sources = [
       "ring_buffer_unittest.cc",
       "sequence_buffer_unittest.cc",
+      "symmetric_matrix_buffer_unittest.cc",
     ]
     deps = [
       ":lib",
diff --git a/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer.h b/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer.h
new file mode 100644
index 0000000000..f0282aaed5
--- /dev/null
+++ b/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer.h
@@ -0,0 +1,94 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_SYMMETRIC_MATRIX_BUFFER_H_
+#define MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_SYMMETRIC_MATRIX_BUFFER_H_
+
+#include <algorithm>
+#include <array>
+#include <cstring>
+#include <utility>
+
+#include "api/array_view.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace rnn_vad {
+
+// Data structure to buffer the results of pair-wise comparisons between items
+// stored in a ring buffer. Every time that the oldest item is replaced in the
+// ring buffer, the new one is compared to the remaining items in the ring
+// buffer. The results of such comparisons need to be buffered and automatically
+// removed when one of the two corresponding items that have been compared is
+// removed from the ring buffer. It is assumed that the comparison is symmetric
+// and that comparing an item with itself is not needed.
+template <typename T, size_t S>
+class SymmetricMatrixBuffer {
+  static_assert(S > 2, "");
+
+ public:
+  SymmetricMatrixBuffer() = default;
+  SymmetricMatrixBuffer(const SymmetricMatrixBuffer&) = delete;
+  SymmetricMatrixBuffer& operator=(const SymmetricMatrixBuffer&) = delete;
+  ~SymmetricMatrixBuffer() = default;
+  // Sets the buffer values to zero.
+  void Reset() {
+    static_assert(std::is_arithmetic<T>::value,
+                  "Integral or floating point required.");
+    buf_.fill(0);
+  }
+  // Pushes the results from the comparison between the most recent item and
+  // those that are still in the ring buffer. The first element in |values| must
+  // correspond to the comparison between the most recent item and the second
+  // most recent one in the ring buffer, whereas the last element in |values|
+  // must correspond to the comparison between the most recent item and the
+  // oldest one in the ring buffer.
+  void Push(rtc::ArrayView<T, S - 1> values) {
+    // Move the lower-right sub-matrix of size (S-2) x (S-2) one row up and one
+    // column left.
+    std::memmove(buf_.data(), buf_.data() + S, (buf_.size() - S) * sizeof(T));
+    // Copy new values in the last column in the right order.
+    for (size_t i = 0; i < values.size(); ++i) {
+      const size_t index = (S - 1 - i) * (S - 1) - 1;
+      RTC_DCHECK_LE(static_cast<size_t>(0), index);
+      RTC_DCHECK_LT(index, buf_.size());
+      buf_[index] = values[i];
+    }
+  }
+  // Reads the value that corresponds to comparison of two items in the ring
+  // buffer having delay |delay1| and |delay2|. The two arguments must not be
+  // equal and both must be in {0, ..., S - 1}.
+  T GetValue(size_t delay1, size_t delay2) const {
+    int row = S - 1 - static_cast<int>(delay1);
+    int col = S - 1 - static_cast<int>(delay2);
+    RTC_DCHECK_NE(row, col) << "The diagonal cannot be accessed.";
+    if (row > col)
+      std::swap(row, col);  // Swap to access the upper-right triangular part.
+    RTC_DCHECK_LE(0, row);
+    RTC_DCHECK_LT(row, S - 1) << "Not enforcing row < col and row != col.";
+    RTC_DCHECK_LE(1, col) << "Not enforcing row < col and row != col.";
+    RTC_DCHECK_LT(col, S);
+    const int index = row * (S - 1) + (col - 1);
+    RTC_DCHECK_LE(0, index);
+    RTC_DCHECK_LT(index, buf_.size());
+    return buf_[index];
+  }
+
+ private:
+  // Encode an upper-right triangular matrix (excluding its diagonal) using a
+  // square matrix. This allows to move the data in Push() with one single
+  // operation.
+  std::array<T, (S - 1) * (S - 1)> buf_{};
+};
+
+}  // namespace rnn_vad
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_SYMMETRIC_MATRIX_BUFFER_H_
diff --git a/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer_unittest.cc b/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer_unittest.cc
new file mode 100644
index 0000000000..408467a259
--- /dev/null
+++ b/modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer_unittest.cc
@@ -0,0 +1,111 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/audio_processing/agc2/rnn_vad/symmetric_matrix_buffer.h"
+
+#include "modules/audio_processing/agc2/rnn_vad/ring_buffer.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace test {
+namespace {
+
+using rnn_vad::RingBuffer;
+using rnn_vad::SymmetricMatrixBuffer;
+
+template <typename T, size_t S>
+void CheckSymmetry(const SymmetricMatrixBuffer<T, S>* sym_matrix_buf) {
+  for (size_t row = 0; row < S - 1; ++row)
+    for (size_t col = row + 1; col < S; ++col)
+      EXPECT_EQ(sym_matrix_buf->GetValue(row, col),
+                sym_matrix_buf->GetValue(col, row));
+}
+
+using PairType = std::pair<int, int>;
+
+// Checks that the symmetric matrix buffer contains any pair with a value equal
+// to the given one.
+template <size_t S>
+bool CheckPairsWithValueExist(
+    const SymmetricMatrixBuffer<PairType, S>* sym_matrix_buf,
+    const int value) {
+  for (size_t row = 0; row < S - 1; ++row) {
+    for (size_t col = row + 1; col < S; ++col) {
+      auto p = sym_matrix_buf->GetValue(row, col);
+      if (p.first == value || p.second == value)
+        return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+// Test that shows how to combine RingBuffer and SymmetricMatrixBuffer to
+// efficiently compute pair-wise scores. This test verifies that the evolution
+// of a SymmetricMatrixBuffer instance follows that of RingBuffer.
+TEST(RnnVadTest, SymmetricMatrixBufferUseCase) {
+  // Instance a ring buffer which will be fed with a series of integer values.
+  constexpr int kRingBufSize = 10;
+  RingBuffer<int, 1, static_cast<size_t>(kRingBufSize)> ring_buf;
+  // Instance a symmetric matrix buffer for the ring buffer above. It stores
+  // pairs of integers with which this test can easily check that the evolution
+  // of RingBuffer and SymmetricMatrixBuffer match.
+  SymmetricMatrixBuffer<PairType, kRingBufSize> sym_matrix_buf;
+  for (int t = 1; t <= 100; ++t) {  // Evolution steps.
+    SCOPED_TRACE(t);
+    const int t_removed = ring_buf.GetArrayView(kRingBufSize - 1)[0];
+    ring_buf.Push({&t, 1});
+    // The head of the ring buffer is |t|.
+    ASSERT_EQ(t, ring_buf.GetArrayView(0)[0]);
+    // Create the comparisons between |t| and the older elements in the ring
+    // buffer.
+    std::array<PairType, kRingBufSize - 1> new_comparions;
+    for (int i = 0; i < kRingBufSize - 1; ++i) {
+      // Start comparing |t| to the second newest element in the ring buffer.
+      const int delay = i + 1;
+      const auto t_prev = ring_buf.GetArrayView(delay)[0];
+      ASSERT_EQ(std::max(0, t - delay), t_prev);
+      // Compare the last element |t| with |t_prev|.
+      new_comparions[i].first = t_prev;
+      new_comparions[i].second = t;
+    }
+    // Push the new comparisons in the symmetric matrix buffer.
+    sym_matrix_buf.Push({new_comparions.data(), new_comparions.size()});
+    // Tests.
+    CheckSymmetry(&sym_matrix_buf);
+    // Check that the pairs resulting from the content in the ring buffer are
+    // in the right position.
+    for (size_t delay1 = 0; delay1 < kRingBufSize - 1; ++delay1) {
+      for (size_t delay2 = delay1 + 1; delay2 < kRingBufSize; ++delay2) {
+        const auto t1 = ring_buf.GetArrayView(delay1)[0];
+        const auto t2 = ring_buf.GetArrayView(delay2)[0];
+        ASSERT_LE(t2, t1);
+        const auto p = sym_matrix_buf.GetValue(delay1, delay2);
+        EXPECT_EQ(p.first, t2);
+        EXPECT_EQ(p.second, t1);
+      }
+    }
+    // Check that every older element in the ring buffer still has a
+    // corresponding pair in the symmetric matrix buffer.
+    for (size_t delay = 1; delay < kRingBufSize; ++delay) {
+      const auto t_prev = ring_buf.GetArrayView(delay)[0];
+      EXPECT_TRUE(CheckPairsWithValueExist(&sym_matrix_buf, t_prev));
+    }
+    // Check that the element removed from the ring buffer has no corresponding
+    // pairs in the symmetric matrix buffer.
+    if (t > kRingBufSize - 1) {
+      EXPECT_FALSE(CheckPairsWithValueExist(&sym_matrix_buf, t_removed));
+    }
+  }
+}
+
+}  // namespace test
+}  // namespace webrtc