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/*
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* AudioFilterFIR_F32 |
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*
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* Created: Chip Audette (OpenAudio) Feb 2017 |
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* - Building from AudioFilterFIR from Teensy Audio Library (AudioFilterFIR credited to Pete (El Supremo)) |
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*
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*/ |
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#ifndef _filter_iir_f32 |
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#define _filter_iir_f32 |
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#include "Arduino.h" |
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#include "AudioStream_F32.h" |
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#include "arm_math.h" |
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// Indicates that the code should just pass through the audio
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// without any filtering (as opposed to doing nothing at all)
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#define IIR_F32_PASSTHRU ((const float32_t *) 1) |
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#define IIR_MAX_STAGES 1 //meaningless right now
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class AudioFilterIIR_F32 : public AudioStream_F32 |
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{ |
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public: |
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AudioFilterIIR_F32(void): AudioStream_F32(1,inputQueueArray), coeff_p(FIR_F32_PASSTHRU) { |
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} |
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void begin(const float32_t *cp, int n_stages) { |
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coeff_p = cp; |
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// Initialize FIR instance (ARM DSP Math Library)
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if (coeff_p && (coeff_p != IIR_F32_PASSTHRU) && n_stages <= IIR_MAX_STAGES) { |
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//https://www.keil.com/pack/doc/CMSIS/DSP/html/group__BiquadCascadeDF1.html
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arm_biquad_cascade_df1_init_f32(&iir_inst, n_stages, (float32_t *)coeff_p, &StateF32[0]); |
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} |
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} |
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void end(void) { |
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coeff_p = NULL; |
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} |
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void setBlockDC(void) { |
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//https://www.keil.com/pack/doc/CMSIS/DSP/html/group__BiquadCascadeDF1.html#ga8e73b69a788e681a61bccc8959d823c5
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//Use matlab to compute the coeff for HP at 40Hz: [b,a]=butter(2,40/(44100/2),'high'); %assumes fs_Hz = 44100
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float32_t b[] = {8.173653471988667e-01, -1.634730694397733e+00, 8.173653471988667e-01}; //from Matlab
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float32_t a[] = { 1.000000000000000e+00, -1.601092394183619e+00, 6.683689946118476e-01}; //from Matlab
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setFilterCoeff_Matlab(b, a); |
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} |
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void setFilterCoeff_Matlab(float32_t b[], float32_t a[]) { //one stage of N=2 IIR
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//https://www.keil.com/pack/doc/CMSIS/DSP/html/group__BiquadCascadeDF1.html#ga8e73b69a788e681a61bccc8959d823c5
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//Use matlab to compute the coeff, such as: [b,a]=butter(2,20/(44100/2),'high'); %assumes fs_Hz = 44100
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hp_coeff[0] = b[0]; hp_coeff[1] = b[1]; hp_coeff[2] = b[2]; //here are the matlab "b" coefficients
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hp_coeff[3] = -a[1]; hp_coeff[4] = -a[2]; //the DSP needs the "a" terms to have opposite sign vs Matlab
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uint8_t n_stages = 1; |
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arm_biquad_cascade_df1_init_f32(&iir_inst, n_stages, hp_coeff, &StateF32[0]);
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} |
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virtual void update(void); |
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private: |
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audio_block_f32_t *inputQueueArray[1]; |
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float32_t hp_coeff[5 * 1] = {1.0, 0.0, 0.0, 0.0, 0.0}; //no filtering. actual filter coeff set later
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// pointer to current coefficients or NULL or FIR_PASSTHRU
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const float32_t *coeff_p; |
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// ARM DSP Math library filter instance
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arm_biquad_casd_df1_inst_f32 iir_inst; |
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float32_t StateF32[4*IIR_MAX_STAGES]; |
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}; |
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void AudioFilterIIR_F32::update(void) |
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{ |
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audio_block_f32_t *block, *b_new; |
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block = AudioStream_F32::receiveWritable_f32(); |
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if (!block) return; |
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// If there's no coefficient table, give up.
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if (coeff_p == NULL) { |
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AudioStream_F32::release(block); |
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return; |
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} |
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// do passthru
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if (coeff_p == IIR_F32_PASSTHRU) { |
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// Just passthrough
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AudioStream_F32::transmit(block); |
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AudioStream_F32::release(block); |
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return; |
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} |
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// do IIR
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arm_biquad_cascade_df1_f32(&iir_inst, block->data, block->data, block->length); |
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AudioStream_F32::transmit(block); // send the IIR output
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AudioStream_F32::release(block); |
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} |
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#endif |
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