fir_halfband_decimator.cpp

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#include "fir_halfband_decimator.h"
#include "poly_utils.h"
 
namespace vital {
 
  FirHalfbandDecimator::FirHalfbandDecimator() : Processor(kNumInputs, 1) {
    static const mono_float coefficients[kNumTaps] = {
      0.000088228877315364f,  0.000487010018128278f,  0.000852264975437944f,  -0.001283563593466774f,
      -0.010130591831925894f, -0.025688727779244691f, -0.036346596505004387f, -0.024088355516718698f,
      0.012246773417129486f,  0.040021434054637831f,  0.017771298164062477f,  -0.046866403416502632f,
      -0.075597513455990611f,  0.013331126342402619f,  0.202889888191404910f,  0.362615173769444080f,
      0.362615173769444080f,  0.202889888191404910f,  0.013331126342402619f,  -0.075597513455990611f,
      -0.046866403416502632f,  0.017771298164062477f,  0.040021434054637831f,  0.012246773417129486f,
      -0.024088355516718698f, -0.036346596505004387f, -0.025688727779244691f, -0.010130591831925894f,
      -0.001283563593466774f,  0.000852264975437944f,  0.000487010018128278f,  0.000088228877315364f,
    };
 
    // Pack every pair of coefficients into taps_
    for (int i = 0; i < kNumTaps / 2; ++i)
      taps_[i] = poly_float(coefficients[2 * i], coefficients[2 * i + 1]);
 
    reset(constants::kFullMask);
  }
 
  void FirHalfbandDecimator::saveMemory(int num_samples) {
    int input_buffer_size = 2 * num_samples;
    poly_float* audio = input(kAudio)->source->buffer;
 
    // Compute where in the input buffer we should start saving
    int start_audio_index = input_buffer_size - kNumTaps + 2;
    for (int i = 0; i < kNumTaps / 2 - 1; ++i) {
      int audio_index = start_audio_index + 2 * i;
      // Consolidate two channels/samples at a time for poly_float
      memory_[i] = utils::consolidateAudio(audio[audio_index], audio[audio_index + 1]);
    }
  }
 
  void FirHalfbandDecimator::process(int num_samples) {
    const poly_float* audio = input(kAudio)->source->buffer;
    int output_buffer_size = num_samples;
 
    // Basic checks to ensure buffer sizes are valid
    VITAL_ASSERT(output_buffer_size > kNumTaps / 2);
    VITAL_ASSERT(input(kAudio)->source->buffer_size >= 2 * output_buffer_size);
 
    poly_float* audio_out = output()->buffer;
 
    // First, use memory_ from the previous block to fill the early samples
    for (int memory_start = 0; memory_start < kNumTaps / 2 - 1; ++memory_start) {
      poly_float sum = 0.0f;
 
      // Use stored memory first
      int tap_index = 0;
      int num_memory = kNumTaps / 2 - memory_start - 1;
      for (; tap_index < num_memory; ++tap_index) {
        sum = utils::mulAdd(sum, memory_[tap_index + memory_start], taps_[tap_index]);
      }
 
      // Then move on to the current block's audio
      int audio_index = 0;
      for (; tap_index < kNumTaps / 2; ++tap_index) {
        // Consolidate two adjacent samples into a poly_float
        poly_float consolidated = utils::consolidateAudio(audio[audio_index], audio[audio_index + 1]);
        sum = utils::mulAdd(sum, consolidated, taps_[tap_index]);
        audio_index += 2;
      }
 
      // Write out a decimated sample (sum both lanes)
      audio_out[memory_start] = utils::sumSplitAudio(sum);
    }
 
    // Process the rest of the block
    int out_index = kNumTaps / 2 - 1;
    int audio_start = 0;
    for (; out_index < output_buffer_size; ++out_index) {
      poly_float sum = 0.0f;
      int audio_index = audio_start;
 
      // Sum over all taps for each output sample
      for (int tap_index = 0; tap_index < kNumTaps / 2; ++tap_index) {
        poly_float consolidated = utils::consolidateAudio(audio[audio_index], audio[audio_index + 1]);
        sum = utils::mulAdd(sum, consolidated, taps_[tap_index]);
        audio_index += 2;
      }
      audio_start += 2;
 
      audio_out[out_index] = utils::sumSplitAudio(sum);
    }
 
    // Save the end of this block to memory for seamless continuity next time
    saveMemory(num_samples);
  }
 
  void FirHalfbandDecimator::reset(poly_mask reset_mask) {
    for (int i = 0; i < kNumTaps / 2 - 1; ++i)
      memory_[i] = 0.0f;
  }
 
} // namespace vital