annotate carfac/carfac_common.cc @ 610:01986636257a

Second check-in of Alex Brandmeyer's C++ implementation of CARFAC. Addressed style issues and completed implementation of remaining functions. Still needs proper testing of the output stages against the MATLAB version, and runtime functions need improvements in efficiency.

//
//  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"

// Auditory filter nominal Equivalent Rectangular Bandwidth
// Ref: Glasberg and Moore: Hearing Research, 47 (1990), 103-138
FPType ERBHz (FPType cf_hz, FPType erb_break_freq, FPType erb_q) {
  FPType erb;
  erb = (erb_break_freq + cf_hz) / erb_q;
  return erb;
}

FloatArray CARFACDetect (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;
}