alexbrandmeyer@609: //
alexbrandmeyer@609: //  carfac_common.cc
alexbrandmeyer@609: //  CARFAC Open Source C++ Library
alexbrandmeyer@609: //
alexbrandmeyer@609: //  Created by Alex Brandmeyer on 5/10/13.
alexbrandmeyer@609: //
alexbrandmeyer@609: // This C++ file is part of an implementation of Lyon's cochlear model:
alexbrandmeyer@609: // "Cascade of Asymmetric Resonators with Fast-Acting Compression"
alexbrandmeyer@609: // to supplement Lyon's upcoming book "Human and Machine Hearing"
alexbrandmeyer@609: //
alexbrandmeyer@609: // Licensed under the Apache License, Version 2.0 (the "License");
alexbrandmeyer@609: // you may not use this file except in compliance with the License.
alexbrandmeyer@609: // You may obtain a copy of the License at
alexbrandmeyer@609: //
alexbrandmeyer@609: //     http://www.apache.org/licenses/LICENSE-2.0
alexbrandmeyer@609: //
alexbrandmeyer@609: // Unless required by applicable law or agreed to in writing, software
alexbrandmeyer@609: // distributed under the License is distributed on an "AS IS" BASIS,
alexbrandmeyer@609: // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
alexbrandmeyer@609: // See the License for the specific language governing permissions and
alexbrandmeyer@609: // limitations under the License.
alexbrandmeyer@609: 
alexbrandmeyer@609: #include "carfac_common.h"
alexbrandmeyer@609: 
alexbrandmeyer@609: //Auditory filter nominal Equivalent Rectangular Bandwidth
alexbrandmeyer@609: //Ref: Glasberg and Moore: Hearing Research, 47 (1990), 103-138
alexbrandmeyer@609: FPType ERBHz (FPType cf_hz, FPType erb_break_freq, FPType erb_q) {
alexbrandmeyer@609:   
alexbrandmeyer@609:   FPType erb;
alexbrandmeyer@609:   erb = (erb_break_freq + cf_hz) / erb_q;
alexbrandmeyer@609:   return erb;
alexbrandmeyer@609: }
alexbrandmeyer@609: 
alexbrandmeyer@609: //An IHC-like sigmoidal detection nonlinearity for the CARFAC.
alexbrandmeyer@609: //Resulting conductance is in about [0...1.3405]
alexbrandmeyer@609: FPType CARFACDetect (FPType x) {
alexbrandmeyer@609:   
alexbrandmeyer@609:   FPType conductance, z;
alexbrandmeyer@609:   FPType a = 0.175;
alexbrandmeyer@609:   //offset of low-end tail into neg x territory
alexbrandmeyer@609:   //this parameter is adjusted for the book, to make the 20% DC response
alexbrandmeyer@609:   //threshold at 0.1
alexbrandmeyer@609:   z  = x + a;
alexbrandmeyer@609:   conductance = pow(z,3) / (pow(z,3) + pow(z,2) + 0.1);
alexbrandmeyer@609:   //zero is the final answer for many points:
alexbrandmeyer@609:   return conductance;
alexbrandmeyer@609: }
alexbrandmeyer@609: 
alexbrandmeyer@609: FloatArray CARFACDetect (FloatArray x) {
alexbrandmeyer@609:   
alexbrandmeyer@609:   FloatArray conductance, z;
alexbrandmeyer@609:   FPType a = 0.175;
alexbrandmeyer@609:   //offset of low-end tail into neg x territory
alexbrandmeyer@609:   //this parameter is adjusted for the book, to make the 20% DC response
alexbrandmeyer@609:   //threshold at 0.1
alexbrandmeyer@609:   z  = x + a;
alexbrandmeyer@609:   conductance = (z * z * z) / ((z * z * z) + (z * z) + 0.1);
alexbrandmeyer@609:   //zero is the final answer for many points:
alexbrandmeyer@609:   return conductance;
alexbrandmeyer@609: }