Update the alpha value in the echo detector.

webrtc/modules/audio_processing/residual_echo_detector_unittest.cc

 /*
  *  Copyright (c) 2016 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.
  */
 
@@ skipping 70 matching lines @@
     if (i % 100 == 0) {
       // This is causing the simulated clock drift.
       echo_detector.AnalyzeRenderAudio(zeros);
     }
   }
   // We expect to detect echo with high likelihood. Clock drift is harder to
   // correct on the render side than on the capture side. This is due to the
   // render buffer, clock drift can only be discovered after a certain delay.
   // A growing buffer can be caused by jitter or clock drift and it's not
   // possible to make this decision right away. For this reason we only expect
-  // an echo likelihood of 80% in this test.
-  EXPECT_GT(echo_detector.echo_likelihood(), 0.8f);
+  // an echo likelihood of 75% in this test.
+  EXPECT_GT(echo_detector.echo_likelihood(), 0.75f);
 }
 
 TEST(ResidualEchoDetectorTests, EchoWithCaptureClockDrift) {
   ResidualEchoDetector echo_detector;
   std::vector<float> ones(160, 1.f);
   std::vector<float> zeros(160, 0.f);
 
   // In this test the capture signal has a delay of 10 frames w.r.t. the render
   // signal, but is otherwise identical. Both signals are periodic with a 20
   // frame interval. There is a simulated clock drift of 1% in this test, with
@@ skipping 12 matching lines @@
     if (i % 100 == 0) {
       // This is causing the simulated clock drift.
       echo_detector.AnalyzeCaptureAudio(zeros);
     }
   }
   // We expect to detect echo with near certain likelihood.
   EXPECT_NEAR(1.f, echo_detector.echo_likelihood(), 0.01f);
 }
 
 }  // namespace webrtc