dicklyon@534: % Copyright 2012, Google, Inc.
dicklyon@534: % Author: Richard F. Lyon
dicklyon@534: %
dicklyon@534: % This Matlab file is part of an implementation of Lyon's cochlear model:
dicklyon@534: % "Cascade of Asymmetric Resonators with Fast-Acting Compression"
dicklyon@534: % to supplement Lyon's upcoming book "Human and Machine Hearing"
dicklyon@534: %
dicklyon@534: % Licensed under the Apache License, Version 2.0 (the "License");
dicklyon@534: % you may not use this file except in compliance with the License.
dicklyon@534: % You may obtain a copy of the License at
dicklyon@534: %
dicklyon@534: %     http://www.apache.org/licenses/LICENSE-2.0
dicklyon@534: %
dicklyon@534: % Unless required by applicable law or agreed to in writing, software
dicklyon@534: % distributed under the License is distributed on an "AS IS" BASIS,
dicklyon@534: % WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
dicklyon@534: % See the License for the specific language governing permissions and
dicklyon@534: % limitations under the License.
dicklyon@534: 
dicklyon@534: function [ihc_out, state] = CARFAC_IHC_Step(filters_out, coeffs, state);
dicklyon@534: % function [ihc_out, state] = CARFAC_IHC_Step(filters_out, coeffs, state);
dicklyon@534: %
dicklyon@534: % One sample-time update of inner-hair-cell (IHC) model, including the
dicklyon@534: % detection nonlinearity and one or two capacitor state variables.
dicklyon@534: 
dicklyon@534: just_hwr = coeffs.just_hwr;
dicklyon@534: 
dicklyon@534: if just_hwr
dicklyon@534:   ihc_out = max(0, filters_out);
dicklyon@534:   state.ihc_accum = state.ihc_accum + ihc_out;
dicklyon@534: else
dicklyon@534:   one_cap = coeffs.one_cap;
dicklyon@534: 
dicklyon@534:   detect = CARFAC_Detect(filters_out);  % detect with HWR or so
dicklyon@534: 
dicklyon@534:   if one_cap
dicklyon@534:     ihc_out = detect .* state.cap_voltage;
dicklyon@534:     state.cap_voltage = state.cap_voltage - ihc_out .* coeffs.out_rate + ...
dicklyon@534:       (1 - state.cap_voltage) .* coeffs.in_rate;
dicklyon@534:   else
dicklyon@534:     % change to 2-cap version more like Meddis's:
dicklyon@534:     ihc_out = detect .* state.cap2_voltage;
dicklyon@534:     state.cap1_voltage = state.cap1_voltage - ...
dicklyon@534:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.out1_rate + ...
dicklyon@534:       (1 - state.cap1_voltage) .* coeffs.in1_rate;
dicklyon@534: 
dicklyon@534:     state.cap2_voltage = state.cap2_voltage - ihc_out .* coeffs.out2_rate + ...
dicklyon@534:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.in2_rate;
dicklyon@534:   end
dicklyon@534: 
dicklyon@534:   % smooth it twice with LPF:
dicklyon@534: 
dicklyon@534:   state.lpf1_state = state.lpf1_state + coeffs.lpf_coeff * ...
dicklyon@534:     (ihc_out - state.lpf1_state);
dicklyon@534: 
dicklyon@534:   state.lpf2_state = state.lpf2_state + coeffs.lpf_coeff * ...
dicklyon@534:     (state.lpf1_state - state.lpf2_state);
dicklyon@534: 
dicklyon@534:   ihc_out = state.lpf2_state - coeffs.rest_output;
dicklyon@534: 
dicklyon@534:   state.ihc_accum = state.ihc_accum + max(0, ihc_out);
dicklyon@534: end