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diff --git a/src/3rdparty/resonance-audio/resonance_audio/dsp/gain.h b/src/3rdparty/resonance-audio/resonance_audio/dsp/gain.h
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+++ b/src/3rdparty/resonance-audio/resonance_audio/dsp/gain.h
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+/*
+Copyright 2018 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS-IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#ifndef RESONANCE_AUDIO_DSP_GAIN_H_
+#define RESONANCE_AUDIO_DSP_GAIN_H_
+
+#include <cstddef>
+#include "base/audio_buffer.h"
+
+namespace vraudio {
+
+// Implements a linearly-interpolated application of gain to a buffer channel.
+//
+// @param ramp_length Length of interpolation ramp in samples. Must be > 0.
+// @param start_gain Starting gain value for ramp.
+// @param end_gain Finishing gain value for ramp.
+// @param input_samples Channel buffer to which interpolated gain is applied.
+// @param output_samples Channel buffer to contain scaled output.
+// @param accumulate_output True if the processed input should be mixed into the
+//     output. Otherwise, the output will be replaced by the processed input.
+// @return Next gain value to be applied to the buffer channel.
+float LinearGainRamp(size_t ramp_length, float start_gain, float end_gain,
+                     const AudioBuffer::Channel& input_samples,
+                     AudioBuffer::Channel* output_samples,
+                     bool accumulate_output);
+
+// Applies a gain value to a vector of buffer samples starting at some offset.
+//
+// @param offset_index Starting index for gain application in buffer.
+// @param gain Gain value applied to samples.
+// @param input_samples Channel buffer to which gain is applied.
+// @param output_samples Channel buffer to contain scaled output.
+// @param accumulate_output True if the processed input should be mixed into the
+//     output. Otherwise, the output will be replaced by the processed input.
+void ConstantGain(size_t offset_index, float gain,
+                  const AudioBuffer::Channel& input_samples,
+                  AudioBuffer::Channel* output_samples, bool accumulate_output);
+
+// Checks if the gain factor is close enough to zero (less than -60 decibels).
+//
+// @param gain Gain value to be tested.
+// @return true if the current gain factors are near zero, false otherwise.
+bool IsGainNearZero(float gain);
+
+// Checks if the gain state is close enough to Unity (less than -60 decibels
+// below or above).
+//
+// @param gain Gain value to be tested.
+// @return true if the current gain factors are near unity, false otherwise.
+bool IsGainNearUnity(float gain);
+
+}  // namespace vraudio
+
+#endif  // RESONANCE_AUDIO_DSP_GAIN_H_