diff carfac/carfac_common.cc @ 609:aefe2ca0674f

First version of a C++ implementation by Alex Brandmeyer

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/carfac/carfac_common.cc	Mon May 13 22:51:15 2013 +0000
@@ -0,0 +1,60 @@
+//
+//  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;
+}
+
+//An IHC-like sigmoidal detection nonlinearity for the CARFAC.
+//Resulting conductance is in about [0...1.3405]
+FPType CARFACDetect (FPType x) {
+  
+  FPType conductance, z;
+  FPType a = 0.175;
+  //offset of low-end tail into neg x territory
+  //this parameter is adjusted for the book, to make the 20% DC response
+  //threshold at 0.1
+  z  = x + a;
+  conductance = pow(z,3) / (pow(z,3) + pow(z,2) + 0.1);
+  //zero is the final answer for many points:
+  return conductance;
+}
+
+FloatArray CARFACDetect (FloatArray x) {
+  
+  FloatArray conductance, z;
+  FPType a = 0.175;
+  //offset of low-end tail into neg x territory
+  //this parameter is adjusted for the book, to make the 20% DC response
+  //threshold at 0.1
+  z  = x + a;
+  conductance = (z * z * z) / ((z * z * z) + (z * z) + 0.1);
+  //zero is the final answer for many points:
+  return conductance;
+}
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