1 /* Copyright 2017 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 16 // Basic class for applying a mel-scale mapping to a power spectrum. 17 18 #ifndef TENSORFLOW_CORE_KERNELS_MFCC_MEL_FILTERBANK_H_ 19 #define TENSORFLOW_CORE_KERNELS_MFCC_MEL_FILTERBANK_H_ 20 21 #include <vector> 22 #include "tensorflow/core/framework/op_kernel.h" 23 24 namespace tensorflow { 25 26 class MfccMelFilterbank { 27 public: 28 MfccMelFilterbank(); 29 bool Initialize(int input_length, // Number of unique FFT bins fftsize/2+1. 30 double input_sample_rate, int output_channel_count, 31 double lower_frequency_limit, double upper_frequency_limit); 32 33 // Takes a squared-magnitude spectrogram slice as input, computes a 34 // triangular-mel-weighted linear-magnitude filterbank, and places the result 35 // in output. 36 void Compute(const std::vector<double>& input, 37 std::vector<double>* output) const; 38 39 private: 40 double FreqToMel(double freq) const; 41 bool initialized_; 42 int num_channels_; 43 double sample_rate_; 44 int input_length_; 45 std::vector<double> center_frequencies_; // In mel, for each mel channel. 46 47 // Each FFT bin b contributes to two triangular mel channels, with 48 // proportion weights_[b] going into mel channel band_mapper_[b], and 49 // proportion (1 - weights_[b]) going into channel band_mapper_[b] + 1. 50 // Thus, weights_ contains the weighting applied to each FFT bin for the 51 // upper-half of the triangular band. 52 std::vector<double> weights_; // Right-side weight for this fft bin. 53 54 // FFT bin i contributes to the upper side of mel channel band_mapper_[i] 55 std::vector<int> band_mapper_; 56 int start_index_; // Lowest FFT bin used to calculate mel spectrum. 57 int end_index_; // Highest FFT bin used to calculate mel spectrum. 58 59 TF_DISALLOW_COPY_AND_ASSIGN(MfccMelFilterbank); 60 }; 61 62 } // namespace tensorflow 63 64 #endif // TENSORFLOW_CORE_KERNELS_MFCC_MEL_FILTERBANK_H_ 65
