IIRFilter.h (2048B)
1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef IIRFilter_h 6 #define IIRFilter_h 7 8 #include "nsTArray.h" 9 10 typedef nsTArray<double> AudioDoubleArray; 11 12 namespace blink { 13 14 class IIRFilter final { 15 public: 16 // The maximum IIR filter order. This also limits the number of feedforward 17 // coefficients. The maximum number of coefficients is 20 according to the 18 // spec. 19 const static size_t kMaxOrder = 19; 20 IIRFilter(const AudioDoubleArray* feedforwardCoef, 21 const AudioDoubleArray* feedbackCoef); 22 ~IIRFilter(); 23 24 void process(const float* sourceP, float* destP, size_t framesToProcess); 25 26 void reset(); 27 28 void getFrequencyResponse(int nFrequencies, const float* frequency, 29 float* magResponse, float* phaseResponse); 30 31 bool buffersAreZero(); 32 33 private: 34 // Filter memory 35 // 36 // For simplicity, we assume |m_xBuffer| and |m_yBuffer| have the same length, 37 // and the length is a power of two. Since the number of coefficients has a 38 // fixed upper length, the size of xBuffer and yBuffer is fixed. |m_xBuffer| 39 // holds the old input values and |m_yBuffer| holds the old output values 40 // needed to compute the new output value. 41 // 42 // m_yBuffer[m_bufferIndex] holds the most recent output value, say, y[n]. 43 // Then m_yBuffer[m_bufferIndex - k] is y[n - k]. Similarly for m_xBuffer. 44 // 45 // To minimize roundoff, these arrays are double's instead of floats. 46 AudioDoubleArray m_xBuffer; 47 AudioDoubleArray m_yBuffer; 48 49 // Index into the xBuffer and yBuffer arrays where the most current x and y 50 // values should be stored. xBuffer[bufferIndex] corresponds to x[n], the 51 // current x input value and yBuffer[bufferIndex] is where y[n], the current 52 // output value. 53 int m_bufferIndex; 54 55 // Coefficients of the IIR filter. 56 const AudioDoubleArray* m_feedback; 57 const AudioDoubleArray* m_feedforward; 58 }; 59 60 } // namespace blink 61 62 #endif // IIRFilter_h