1 /* //device/include/server/AudioFlinger/AudioPeakingFilter.h 2 ** 3 ** Copyright 2009, The Android Open Source Project 4 ** 5 ** Licensed under the Apache License, Version 2.0 (the "License"); 6 ** you may not use this file except in compliance with the License. 7 ** You may obtain a copy of the License at 8 ** 9 ** http://www.apache.org/licenses/LICENSE-2.0 10 ** 11 ** Unless required by applicable law or agreed to in writing, software 12 ** distributed under the License is distributed on an "AS IS" BASIS, 13 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 ** See the License for the specific language governing permissions and 15 ** limitations under the License. 16 */ 17 18 #ifndef ANDROID_AUDIO_PEAKING_FILTER_H 19 #define ANDROID_AUDIO_PEAKING_FILTER_H 20 21 #include "AudioBiquadFilter.h" 22 #include "AudioCoefInterpolator.h" 23 24 namespace android { 25 26 // A peaking audio filter, with unity skirt gain, and controllable peak 27 // frequency, gain and bandwidth. 28 // This filter is able to suppress introduce discontinuities and other artifacts 29 // in the output, even when changing parameters abruptly. 30 // Parameters can be set to any value - this class will make sure to clip them 31 // when they are out of supported range. 32 // 33 // Implementation notes: 34 // This class uses an underlying biquad filter whose parameters are determined 35 // using a linear interpolation from a coefficient table, using a 36 // AudioCoefInterpolator. 37 // All is left for this class to do is mapping between high-level parameters to 38 // fractional indices into the coefficient table. 39 class AudioPeakingFilter { 40 public: 41 // Constructor. Resets the filter (see reset()). 42 // nChannels Number of input/output channels (interlaced). 43 // sampleRate The input/output sample rate, in Hz. 44 AudioPeakingFilter(int nChannels, int sampleRate); 45 46 // Reconfiguration of the filter. Changes input/output format, but does not 47 // alter current parameter values. Clears delay lines. 48 // nChannels Number of input/output channels (interlaced). 49 // sampleRate The input/output sample rate, in Hz. 50 void configure(int nChannels, int sampleRate); 51 52 // Resets the filter parameters to the following values: 53 // frequency: 0 54 // gain: 0 55 // bandwidth: 1200 cents. 56 // It also disables the filter. Does not clear the delay lines. 57 void reset(); 58 59 // Clears delay lines. Does not alter parameter values. 60 void clear() { mBiquad.clear(); } 61 62 // Sets gain value. Actual change will only take place upon commit(). 63 // This value will be remembered even if the filter is in disabled() state. 64 // millibel Gain value in millibel (1/100 of decibel). 65 void setGain(int32_t millibel); 66 67 // Gets the gain, in millibel, as set. 68 int32_t getGain() const { return mGain - 9600; } 69 70 // Sets bandwidth value. Actual change will only take place upon commit(). 71 // This value will be remembered even if the filter is in disabled() state. 72 // cents Bandwidth value in cents (1/1200 octave). 73 void setBandwidth(uint32_t cents); 74 75 // Gets the gain, in cents, as set. 76 uint32_t getBandwidth() const { return mBandwidth + 1; } 77 78 // Sets frequency value. Actual change will only take place upon commit(). 79 // This value will be remembered even if the filter is in disabled() state. 80 // millihertz Frequency value in mHz. 81 void setFrequency(uint32_t millihertz); 82 83 // Gets the frequency, in mHz, as set. 84 uint32_t getFrequency() const { return mNominalFrequency; } 85 86 // Gets gain[dB]/2 points. 87 // Results in mHz, and are computed based on the nominal values set, not on 88 // possibly rounded or truncated actual values. 89 void getBandRange(uint32_t & low, uint32_t & high) const; 90 91 // Applies all parameter changes done to this point in time. 92 // If the filter is disabled, the new parameters will take place when it is 93 // enabled again. Does not introduce artifacts, unless immediate is set. 94 // immediate Whether to apply change abruptly (ignored if filter is 95 // disabled). 96 void commit(bool immediate = false); 97 98 // Process a buffer of input data. The input and output should contain 99 // frameCount * nChannels interlaced samples. Processing can be done 100 // in-place, by passing the same buffer as both arguments. 101 // in Input buffer. 102 // out Output buffer. 103 // frameCount Number of frames to produce. 104 void process(const audio_sample_t in[], audio_sample_t out[], 105 int frameCount) { mBiquad.process(in, out, frameCount); } 106 107 // Enables the filter, so it would start processing input. Does not 108 // introduce artifacts, unless immediate is set. 109 // immediate Whether to apply change abruptly. 110 void enable(bool immediate = false) { mBiquad.enable(immediate); } 111 112 // Disabled (bypasses) the filter. Does not introduce artifacts, unless 113 // immediate is set. 114 // immediate Whether to apply change abruptly. 115 void disable(bool immediate = false) { mBiquad.disable(immediate); } 116 117 private: 118 // Precision for the mFrequency member. 119 static const int FREQ_PRECISION_BITS = 26; 120 // Precision for the mGain member. 121 static const int GAIN_PRECISION_BITS = 10; 122 // Precision for the mBandwidth member. 123 static const int BANDWIDTH_PRECISION_BITS = 10; 124 125 // Nyquist, in mHz. 126 uint32_t mNiquistFreq; 127 // Fractional index into the gain dimension of the coef table in 128 // GAIN_PRECISION_BITS precision. 129 int32_t mGain; 130 // Fractional index into the bandwidth dimension of the coef table in 131 // BANDWIDTH_PRECISION_BITS precision. 132 uint32_t mBandwidth; 133 // Fractional index into the frequency dimension of the coef table in 134 // FREQ_PRECISION_BITS precision. 135 uint32_t mFrequency; 136 // Nominal value of frequency, as set. 137 uint32_t mNominalFrequency; 138 // 1/Nyquist[mHz], in 42-bit precision (very small). 139 // Used for scaling the frequency. 140 uint32_t mFrequencyFactor; 141 142 // A biquad filter, used for the actual processing. 143 AudioBiquadFilter mBiquad; 144 // A coefficient interpolator, used for mapping the high level parameters to 145 // the low-level biquad coefficients. 146 static AudioCoefInterpolator mCoefInterp; 147 }; 148 149 } 150 151 #endif // ANDROID_AUDIO_PEAKING_FILTER_H 152
