annotate carfac/carfac_common.cc @ 626:586b0677aae8

Fourth revision of Alex Brandmeyer's C++ implementation. Fixed more style issues, changed AGC structures to vectors, replaced FloatArray2d with vector<FloatArray>, implemented first tests using GTest to verify coefficients and monaural output against Matlab values (stored in aimc/carfac/test_data/). To run tests, change the path stored in carfac_test.h in TEST_SRC_DIR. Added CARFAC_GenerateTestData to the Matlab branch, fixed stage indexing in CARFAC_Cross_Couple.m to reflect changes in AGCCoeffs and AGCState structs.

//
//  carfac_common.cc
//  CARFAC Open Source C++ Library
//
//  Created by Alex Brandmeyer on 5/10/13.
//
// This C++ file is part of an implementation of Lyon's cochlear model:
// "Cascade of Asymmetric Resonators with Fast-Acting Compression"
// to supplement Lyon's upcoming book "Human and Machine Hearing"
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "carfac_common.h"

FPType ERBHz (const FPType cf_hz, const FPType erb_break_freq,
              const FPType erb_q) {
  FPType erb;
  erb = (erb_break_freq + cf_hz) / erb_q;
  return erb;
}

FloatArray CARFACDetect (const FloatArray& x) {
  FloatArray conductance, z, set;
  FPType a = 0.175;
  // This offsets the low-end tail into negative x territory.
  // The parameter is adjusted for the book, to make the 20% DC response
  // threshold at 0.1.
  z  = x + a;
  // Zero is the final answer for many points.
  conductance = (z < 0).select(0.0, (z*z*z) / (z*z*z + z*z + 0.1));
  return conductance;
}