diff --git a/webrtc/modules/audio_coding/codecs/isac/fix/source/filters_neon.c b/webrtc/modules/audio_coding/codecs/isac/fix/source/filters_neon.c
new file mode 100644
index 0000000000..e703a5caac
--- /dev/null
+++ b/webrtc/modules/audio_coding/codecs/isac/fix/source/filters_neon.c
@@ -0,0 +1,114 @@
+/*
+ *  Copyright (c) 2014 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 <arm_neon.h>
+#include <assert.h>
+
+#include "webrtc/modules/audio_coding/codecs/isac/fix/source/codec.h"
+
+// Autocorrelation function in fixed point.
+// NOTE! Different from SPLIB-version in how it scales the signal.
+int WebRtcIsacfix_AutocorrNeon(int32_t* __restrict r,
+                               const int16_t* x,
+                               int16_t n,
+                               int16_t order,
+                               int16_t* __restrict scale) {
+  int i = 0;
+  int16_t scaling = 0;
+  uint32_t temp = 0;
+  int64_t prod = 0;
+  int64_t prod_tail = 0;
+
+  assert(n % 4 == 0);
+  assert(n >= 8);
+
+  // Calculate r[0].
+  int16x4_t x0_v;
+  int32x4_t tmpa0_v;
+  int64x2_t tmpb_v;
+
+  tmpb_v = vdupq_n_s64(0);
+  const int16_t* x_start = x;
+  const int16_t* x_end0 = x_start + n;
+  while (x_start < x_end0) {
+    x0_v = vld1_s16(x_start);
+    tmpa0_v = vmull_s16(x0_v, x0_v);
+    tmpb_v = vpadalq_s32(tmpb_v, tmpa0_v);
+    x_start += 4;
+  }
+
+#ifdef WEBRTC_ARCH_ARM64
+  prod = vaddvq_s64(tmpb_v);
+#else
+  prod = vget_lane_s64(vadd_s64(vget_low_s64(tmpb_v), vget_high_s64(tmpb_v)),
+                       0);
+#endif
+  // Calculate scaling (the value of shifting).
+  temp = (uint32_t)(prod >> 31);
+
+  scaling = temp ? 32 - WebRtcSpl_NormU32(temp) : 0;
+  r[0] = (int32_t)(prod >> scaling);
+
+  int16x8_t x1_v;
+  int16x8_t y_v;
+  int32x4_t tmpa1_v;
+  // Perform the actual correlation calculation.
+  for (i = 1; i < order + 1; i++) {
+    tmpb_v = vdupq_n_s64(0);
+    int rest = (n - i) % 8;
+    x_start = x;
+    x_end0 = x_start + n - i - rest;
+    const int16_t* y_start = x_start + i;
+    while (x_start < x_end0) {
+      x1_v = vld1q_s16(x_start);
+      y_v = vld1q_s16(y_start);
+      tmpa0_v = vmull_s16(vget_low_s16(x1_v), vget_low_s16(y_v));
+#ifdef WEBRTC_ARCH_ARM64
+      tmpa1_v = vmull_high_s16(x1_v, y_v);
+#else
+      tmpa1_v = vmull_s16(vget_high_s16(x1_v), vget_high_s16(y_v));
+#endif
+      tmpb_v = vpadalq_s32(tmpb_v, tmpa0_v);
+      tmpb_v = vpadalq_s32(tmpb_v, tmpa1_v);
+      x_start += 8;
+      y_start += 8;
+    }
+    // The remaining calculation.
+    const int16_t* x_end1 = x + n - i;
+    if (rest >= 4) {
+        int16x4_t x2_v = vld1_s16(x_start);
+        int16x4_t y2_v = vld1_s16(y_start);
+        tmpa0_v = vmull_s16(x2_v, y2_v);
+        tmpb_v = vpadalq_s32(tmpb_v, tmpa0_v);
+        x_start += 4;
+        y_start += 4;
+    }
+#ifdef WEBRTC_ARCH_ARM64
+    prod = vaddvq_s64(tmpb_v);
+#else
+    prod = vget_lane_s64(vadd_s64(vget_low_s64(tmpb_v), vget_high_s64(tmpb_v)),
+                         0);
+#endif
+
+    prod_tail = 0;
+    while (x_start < x_end1) {
+      prod_tail += WEBRTC_SPL_MUL_16_16(*x_start, *y_start);
+      ++x_start;
+      ++y_start;
+    }
+
+    r[i] = (int32_t)((prod + prod_tail) >> scaling);
+  }
+
+  *scale = scaling;
+
+  return order + 1;
+}
+