1 /* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
2 
3 Licensed under the Apache License, Version 2.0 (the "License");
4 you may not use this file except in compliance with the License.
5 You may obtain a copy of the License at
6 
7     http://www.apache.org/licenses/LICENSE-2.0
8 
9 Unless required by applicable law or agreed to in writing, software
10 distributed under the License is distributed on an "AS IS" BASIS,
11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 See the License for the specific language governing permissions and
13 limitations under the License.
14 ==============================================================================*/
15 #ifndef TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_NOISE_REDUCTION_H_
16 #define TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_NOISE_REDUCTION_H_
17 
18 #define kNoiseReductionBits 14
19 
20 #include <stdint.h>
21 #include <stdlib.h>
22 
23 #ifdef __cplusplus
24 extern "C" {
25 #endif
26 
27 struct NoiseReductionState {
28   int smoothing_bits;
29   uint16_t even_smoothing;
30   uint16_t odd_smoothing;
31   uint16_t min_signal_remaining;
32   int num_channels;
33   uint32_t* estimate;
34 };
35 
36 // Removes stationary noise from each channel of the signal using a low pass
37 // filter.
38 void NoiseReductionApply(struct NoiseReductionState* state, uint32_t* signal);
39 
40 void NoiseReductionReset(struct NoiseReductionState* state);
41 
42 #ifdef __cplusplus
43 }  // extern "C"
44 #endif
45 
46 #endif  // TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_NOISE_REDUCTION_H_
47