dicklyon@473: % Copyright 2012, Google, Inc.
dicklyon@473: % Author: Richard F. Lyon
dicklyon@473: %
dicklyon@473: % This Matlab file is part of an implementation of Lyon's cochlear model:
dicklyon@473: % "Cascade of Asymmetric Resonators with Fast-Acting Compression"
dicklyon@473: % to supplement Lyon's upcoming book "Human and Machine Hearing"
dicklyon@473: %
dicklyon@473: % Licensed under the Apache License, Version 2.0 (the "License");
dicklyon@473: % you may not use this file except in compliance with the License.
dicklyon@473: % You may obtain a copy of the License at
dicklyon@473: %
dicklyon@473: %     http://www.apache.org/licenses/LICENSE-2.0
dicklyon@473: %
dicklyon@473: % Unless required by applicable law or agreed to in writing, software
dicklyon@473: % distributed under the License is distributed on an "AS IS" BASIS,
dicklyon@473: % WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
dicklyon@473: % See the License for the specific language governing permissions and
dicklyon@473: % limitations under the License.
dicklyon@473: 
dicklyon@473: function [ihc_out, state] = CARFAC_IHC_Step(filters_out, coeffs, state);
dicklyon@473: % function [ihc_out, state] = CARFAC_IHC_Step(filters_out, coeffs, state);
dicklyon@473: %
dicklyon@473: % One sample-time update of inner-hair-cell (IHC) model, including the
dicklyon@473: % detection nonlinearity and one or two capacitor state variables.
dicklyon@473: 
dicklyon@504: % AC couple the filters_out, with 20 Hz corner
dicklyon@504: ac_diff = filters_out - state.ac_coupler;
dicklyon@504: state.ac_coupler = state.ac_coupler + coeffs.ac_coeff * ac_diff;
dicklyon@473: 
dicklyon@504: if coeffs.just_hwr
dicklyon@504:   ihc_out = min(2, max(0, ac_diff));  % limit it for stability
dicklyon@473: else
dicklyon@504:   conductance = CARFAC_Detect(ac_diff);  % rectifying nonlinearity
dicklyon@504: 
dicklyon@495:   if coeffs.one_cap;
dicklyon@495:     ihc_out = conductance .* state.cap_voltage;
dicklyon@473:     state.cap_voltage = state.cap_voltage - ihc_out .* coeffs.out_rate + ...
dicklyon@473:       (1 - state.cap_voltage) .* coeffs.in_rate;
dicklyon@473:   else
dicklyon@473:     % change to 2-cap version more like Meddis's:
dicklyon@495:     ihc_out = conductance .* state.cap2_voltage;
dicklyon@473:     state.cap1_voltage = state.cap1_voltage - ...
dicklyon@473:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.out1_rate + ...
dicklyon@473:       (1 - state.cap1_voltage) .* coeffs.in1_rate;
dicklyon@473: 
dicklyon@473:     state.cap2_voltage = state.cap2_voltage - ihc_out .* coeffs.out2_rate + ...
dicklyon@473:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.in2_rate;
dicklyon@473:   end
dicklyon@473: 
dicklyon@473:   % smooth it twice with LPF:
dicklyon@473: 
dicklyon@499:   ihc_out = ihc_out * coeffs.output_gain;
dicklyon@473:   state.lpf1_state = state.lpf1_state + coeffs.lpf_coeff * ...
dicklyon@473:     (ihc_out - state.lpf1_state);
dicklyon@473:   state.lpf2_state = state.lpf2_state + coeffs.lpf_coeff * ...
dicklyon@473:     (state.lpf1_state - state.lpf2_state);
dicklyon@499:   ihc_out = state.lpf2_state - coeffs.rest_output;
dicklyon@473: end
dicklyon@504: 
dicklyon@504: state.ihc_accum = state.ihc_accum + ihc_out;  % for where decimated output is useful
dicklyon@504: