Implement tail processing for AudioNodes

third_party/WebKit/Source/platform/audio/DynamicsCompressorKernel.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 477 matching lines @@
   // Predelay section.
   for (unsigned i = 0; i < pre_delay_buffers_.size(); ++i)
     pre_delay_buffers_[i]->Zero();
 
   pre_delay_read_index_ = 0;
   pre_delay_write_index_ = kDefaultPreDelayFrames;
 
   max_attack_compression_diff_db_ = -1;  // uninitialized state
 }
 
+double DynamicsCompressorKernel::TailTime() const {
+  // The reduction value of the compressor is computed from the gain
+  // using an exponential filter with a time constant of
+  // |kMeteringReleaseTimeConstant|.  We need to keep he compressor
+  // running for some time after the inputs go away so that the
+  // reduction value approaches 0.  This is a tradeoff between how
+  // long we keep the node alive and how close we approach the final
+  // value.  A value of 5 to 10 times the time constant is a
+  // reasonable trade-off.
+  return 5 * kMeteringReleaseTimeConstant;
+}
+
 }  // namespace blink