/* AudioEffectCompressor Created: Chip Audette, Dec 2016 - Jan 2017 Purpose; Apply dynamic range compression to the audio stream. Assumes floating-point data. This processes a single stream fo audio data (ie, it is mono) MIT License. use at your own risk. */ #ifndef _AudioEffectCompressor_F32 #define _AudioEffectCompressor_F32 #include //ARM DSP extensions. https://www.keil.com/pack/doc/CMSIS/DSP/html/index.html #include class AudioEffectCompressor_F32 : public AudioStream_F32 { //GUI: inputs:1, outputs:1 //this line used for automatic generation of GUI node public: //constructor AudioEffectCompressor_F32(void) : AudioStream_F32(1, inputQueueArray_f32) { setThresh_dBFS(-20.0f); //set the default value for the threshold for compression setCompressionRatio(5.0f); //set the default copression ratio setAttack_sec(0.005f, AUDIO_SAMPLE_RATE); //default to this value setRelease_sec(0.200f, AUDIO_SAMPLE_RATE); //default to this value setHPFilterCoeff(); enableHPFilter(true); //enable the HP filter to remove any DC offset from the audio resetStates(); }; //here's the method that does all the work void update(void) { //Serial.println("AudioEffectGain_F32: updating."); //for debugging. audio_block_f32_t *audio_block = AudioStream_F32::receiveWritable_f32(); if (!audio_block) return; //apply a high-pass filter to get rid of the DC offset if (use_HP_prefilter) arm_biquad_cascade_df1_f32(&hp_filt_struct, audio_block->data, audio_block->data, audio_block->length); //apply the pre-gain...a negative gain value will disable if (pre_gain > 0.0f) arm_scale_f32(audio_block->data, pre_gain, audio_block->data, audio_block->length); //use ARM DSP for speed! //calculate the level of the audio (ie, calculate a smoothed version of the signal power) audio_block_f32_t *audio_level_dB_block = AudioStream_F32::allocate_f32(); calcAudioLevel_dB(audio_block, audio_level_dB_block); //returns through audio_level_dB_block //compute the desired gain based on the observed audio level audio_block_f32_t *gain_block = AudioStream_F32::allocate_f32(); calcGain(audio_level_dB_block, gain_block); //returns through gain_block //apply the desired gain...store the processed audio back into audio_block arm_mult_f32(audio_block->data, gain_block->data, audio_block->data, audio_block->length); //transmit the block and release memory AudioStream_F32::transmit(audio_block); AudioStream_F32::release(audio_block); AudioStream_F32::release(gain_block); AudioStream_F32::release(audio_level_dB_block); } // Here's the method that estimates the level of the audio (in dB) // It squares the signal and low-pass filters to get a time-averaged // signal power. It then void calcAudioLevel_dB(audio_block_f32_t *wav_block, audio_block_f32_t *level_dB_block) { // calculate the instantaneous signal power (square the signal) audio_block_f32_t *wav_pow_block = AudioStream_F32::allocate_f32(); arm_mult_f32(wav_block->data, wav_block->data, wav_pow_block->data, wav_block->length); // low-pass filter and convert to dB float c1 = level_lp_const, c2 = 1.0f - c1; //prepare constants for (int i = 0; i < wav_pow_block->length; i++) { // first-order low-pass filter to get a running estimate of the average power wav_pow_block->data[i] = c1*prev_level_lp_pow + c2*wav_pow_block->data[i]; // save the state of the first-order low-pass filter prev_level_lp_pow = wav_pow_block->data[i]; //now convert the signal power to dB (but not yet multiplied by 10.0) level_dB_block->data[i] = log10f_approx(wav_pow_block->data[i]); } //limit the amount that the state of the smoothing filter can go toward negative infinity if (prev_level_lp_pow < (1.0E-13)) prev_level_lp_pow = 1.0E-13; //never go less than -130 dBFS //scale the wav_pow_block by 10.0 to complete the conversion to dB arm_scale_f32(level_dB_block->data, 10.0f, level_dB_block->data, level_dB_block->length); //use ARM DSP for speed! //release memory and return AudioStream_F32::release(wav_pow_block); return; //output is passed through level_dB_block } //This method computes the desired gain from the compressor, given an estimate //of the signal level (in dB) void calcGain(audio_block_f32_t *audio_level_dB_block, audio_block_f32_t *gain_block) { //first, calculate the instantaneous target gain based on the compression ratio audio_block_f32_t *inst_targ_gain_dB_block = AudioStream_F32::allocate_f32(); calcInstantaneousTargetGain(audio_level_dB_block, inst_targ_gain_dB_block); //second, smooth in time (attack and release) by stepping through each sample audio_block_f32_t *gain_dB_block = AudioStream_F32::allocate_f32(); calcSmoothedGain_dB(inst_targ_gain_dB_block,gain_dB_block); //finally, convert from dB to linear gain: gain = 10^(gain_dB/20); (ie this takes care of the sqrt, too!) arm_scale_f32(gain_dB_block->data, 1.0f/20.0f, gain_dB_block->data, gain_dB_block->length); //divide by 20 for (int i = 0; i < gain_dB_block->length; i++) gain_block->data[i] = pow10f(gain_dB_block->data[i]); //do the 10^(x) //release memory and return AudioStream_F32::release(gain_dB_block); AudioStream_F32::release(inst_targ_gain_dB_block); return; //output is passed through gain_block } //Compute the instantaneous desired gain, including the compression ratio and //threshold for where the comrpession kicks in void calcInstantaneousTargetGain(audio_block_f32_t *audio_level_dB_block, audio_block_f32_t *inst_targ_gain_dB_block) { // how much are we above the compression threshold? audio_block_f32_t *above_thresh_dB_block = AudioStream_F32::allocate_f32(); arm_offset_f32(audio_level_dB_block->data, //CMSIS DSP for "add a constant value to all elements" -thresh_dBFS, //this is the value to be added above_thresh_dB_block->data, //this is the output audio_level_dB_block->length); // scale by the compression ratio...this is what the output level should be (this is our target level) arm_scale_f32(above_thresh_dB_block->data, //CMSIS DSP for "multiply all elements by a constant value" 1.0f / comp_ratio, //this is the value to be multiplied inst_targ_gain_dB_block->data, //this is the output above_thresh_dB_block->length); // compute the instantaneous gai...which is the difference between the target level and the original level arm_sub_f32(inst_targ_gain_dB_block->data, //CMSIS DSP for "subtract two vectors element-by-element" above_thresh_dB_block->data, //this is the vector to be subtracted inst_targ_gain_dB_block->data, //this is the output inst_targ_gain_dB_block->length); // limit the target gain to attenuation only (this part of the compressor should not make things louder!) for (int i=0; i < inst_targ_gain_dB_block->length; i++) { if (inst_targ_gain_dB_block->data[i] > 0.0f) inst_targ_gain_dB_block->data[i] = 0.0f; } // release memory before returning AudioStream_F32::release(above_thresh_dB_block); return; //output is passed through inst_targ_gain_dB_block } //this method applies the "attack" and "release" constants to smooth the //target gain level through time. void calcSmoothedGain_dB(audio_block_f32_t *inst_targ_gain_dB_block, audio_block_f32_t *gain_dB_block) { float32_t gain_dB; float32_t one_minus_attack_const = 1.0f - attack_const; float32_t one_minus_release_const = 1.0f - release_const; for (int i = 0; i < inst_targ_gain_dB_block->length; i++) { gain_dB = inst_targ_gain_dB_block->data[i]; //smooth the gain using the attack or release constants if (gain_dB < prev_gain_dB) { //are we in the attack phase? gain_dB_block->data[i] = attack_const*prev_gain_dB + one_minus_attack_const*gain_dB; } else { //or, we're in the release phase gain_dB_block->data[i] = release_const*prev_gain_dB + one_minus_release_const*gain_dB; } //save value for the next time through this loop prev_gain_dB = gain_dB_block->data[i]; } //return return; //the output here is gain_block } //methods to set parameters of this module void resetStates(void) { prev_level_lp_pow = 1.0f; prev_gain_dB = 0.0f; //initialize the HP filter. (This also resets the filter states,) arm_biquad_cascade_df1_init_f32(&hp_filt_struct, hp_nstages, hp_coeff, hp_state); } void setPreGain(float g) { pre_gain = g; } void setPreGain_dB(float gain_dB) { setPreGain(pow(10.0, gain_dB / 20.0)); } void setCompressionRatio(float cr) { comp_ratio = max(0.001, cr); //limit to positive values updateThresholdAndCompRatioConstants(); } void setAttack_sec(float a, float fs_Hz) { attack_sec = a; attack_const = expf(-1.0f / (attack_sec * fs_Hz)); //expf() is much faster than exp() //also update the time constant for the envelope extraction setLevelTimeConst_sec(min(attack_sec,release_sec) / 5.0, fs_Hz); //make the level time-constant one-fifth the gain time constants } void setRelease_sec(float r, float fs_Hz) { release_sec = r; release_const = expf(-1.0f / (release_sec * fs_Hz)); //expf() is much faster than exp() //also update the time constant for the envelope extraction setLevelTimeConst_sec(min(attack_sec,release_sec) / 5.0, fs_Hz); //make the level time-constant one-fifth the gain time constants } void setLevelTimeConst_sec(float t_sec, float fs_Hz) { const float min_t_sec = 0.002f; //this is the minimum allowed value level_lp_sec = max(min_t_sec,t_sec); level_lp_const = expf(-1.0f / (level_lp_sec * fs_Hz)); //expf() is much faster than exp() } void setThresh_dBFS(float val) { thresh_dBFS = val; setThreshPow(pow(10.0, thresh_dBFS / 10.0)); } void enableHPFilter(boolean flag) { use_HP_prefilter = flag; }; //methods to return information about this module float32_t getPreGain_dB(void) { return 20.0 * log10f_approx(pre_gain); } float32_t getAttack_sec(void) { return attack_sec; } float32_t getRelease_sec(void) { return release_sec; } float32_t getLevelTimeConst_sec(void) { return level_lp_sec; } float32_t getThresh_dBFS(void) { return thresh_dBFS; } float32_t getCompressionRatio(void) { return comp_ratio; } float32_t getCurrentLevel_dBFS(void) { return 10.0* log10f_approx(prev_level_lp_pow); } float32_t getCurrentGain_dB(void) { return prev_gain_dB; } void setHPFilterCoeff_N2IIR_Matlab(float32_t b[], float32_t a[]){ //https://www.keil.com/pack/doc/CMSIS/DSP/html/group__BiquadCascadeDF1.html#ga8e73b69a788e681a61bccc8959d823c5 //Use matlab to compute the coeff for HP at 20Hz: [b,a]=butter(2,20/(44100/2),'high'); %assumes fs_Hz = 44100 hp_coeff[0] = b[0]; hp_coeff[1] = b[1]; hp_coeff[2] = b[2]; //here are the matlab "b" coefficients hp_coeff[3] = -a[1]; hp_coeff[4] = -a[2]; //the DSP needs the "a" terms to have opposite sign vs Matlab } private: //state-related variables audio_block_f32_t *inputQueueArray_f32[1]; //memory pointer for the input to this module float32_t prev_level_lp_pow = 1.0; float32_t prev_gain_dB = 0.0; //last gain^2 used //HP filter state-related variables arm_biquad_casd_df1_inst_f32 hp_filt_struct; static const uint8_t hp_nstages = 1; float32_t hp_coeff[5 * hp_nstages] = {1.0, 0.0, 0.0, 0.0, 0.0}; //no filtering. actual filter coeff set later float32_t hp_state[4 * hp_nstages]; void setHPFilterCoeff(void) { //https://www.keil.com/pack/doc/CMSIS/DSP/html/group__BiquadCascadeDF1.html#ga8e73b69a788e681a61bccc8959d823c5 //Use matlab to compute the coeff for HP at 20Hz: [b,a]=butter(2,20/(44100/2),'high'); %assumes fs_Hz = 44100 float32_t b[] = {9.979871156751189e-01, -1.995974231350238e+00, 9.979871156751189e-01}; //from Matlab float32_t a[] = { 1.000000000000000e+00, -1.995970179642828e+00, 9.959782830576472e-01}; //from Matlab setHPFilterCoeff_N2IIR_Matlab(b, a); //hp_coeff[0] = b[0]; hp_coeff[1] = b[1]; hp_coeff[2] = b[2]; //here are the matlab "b" coefficients //hp_coeff[3] = -a[1]; hp_coeff[4] = -a[2]; //the DSP needs the "a" terms to have opposite sign vs Matlab } //private parameters related to gain calculation float32_t attack_const, release_const, level_lp_const; //used in calcGain(). set by setAttack_sec() and setRelease_sec(); float32_t comp_ratio_const, thresh_pow_FS_wCR; //used in calcGain(); set in updateThresholdAndCompRatioConstants() void updateThresholdAndCompRatioConstants(void) { comp_ratio_const = 1.0f-(1.0f / comp_ratio); thresh_pow_FS_wCR = powf(thresh_pow_FS, comp_ratio_const); } //settings float32_t attack_sec, release_sec, level_lp_sec; float32_t thresh_dBFS = 0.0; //threshold for compression, relative to digital full scale float32_t thresh_pow_FS = 1.0f; //same as above, but not in dB void setThreshPow(float t_pow) { thresh_pow_FS = t_pow; updateThresholdAndCompRatioConstants(); } float32_t comp_ratio = 1.0; //compression ratio float32_t pre_gain = -1.0; //gain to apply before the compression. negative value disables boolean use_HP_prefilter; // Accelerate the powf(10.0,x) function static float32_t pow10f(float x) { //return powf(10.0f,x) //standard, but slower return expf(2.302585092994f*x); //faster: exp(log(10.0f)*x) } // Accelerate the log10f(x) function? static float32_t log10f_approx(float x) { //return log10f(x); //standard, but slower return log2f_approx(x)*0.3010299956639812f; //faster: log2(x)/log2(10) } /* ---------------------------------------------------------------------- ** Fast approximation to the log2() function. It uses a two step ** process. First, it decomposes the floating-point number into ** a fractional component F and an exponent E. The fraction component ** is used in a polynomial approximation and then the exponent added ** to the result. A 3rd order polynomial is used and the result ** when computing db20() is accurate to 7.984884e-003 dB. ** ------------------------------------------------------------------- */ //https://community.arm.com/tools/f/discussions/4292/cmsis-dsp-new-functionality-proposal/22621#22621 //float log2f_approx_coeff[4] = {1.23149591368684f, -4.11852516267426f, 6.02197014179219f, -3.13396450166353f}; static float log2f_approx(float X) { //float *C = &log2f_approx_coeff[0]; float Y; float F; int E; // This is the approximation to log2() F = frexpf(fabsf(X), &E); // Y = C[0]*F*F*F + C[1]*F*F + C[2]*F + C[3] + E; //Y = *C++; Y = 1.23149591368684f; Y *= F; //Y += (*C++); Y += -4.11852516267426f; Y *= F; //Y += (*C++); Y += 6.02197014179219f; Y *= F; //Y += (*C++); Y += -3.13396450166353f; Y += E; return(Y); } }; #endif