tom@516: % Copyright 2012, Google, Inc.
tom@516: % Author: Richard F. Lyon
tom@516: %
tom@516: % This Matlab file is part of an implementation of Lyon's cochlear model:
tom@516: % "Cascade of Asymmetric Resonators with Fast-Acting Compression"
tom@516: % to supplement Lyon's upcoming book "Human and Machine Hearing"
tom@516: %
tom@516: % Licensed under the Apache License, Version 2.0 (the "License");
tom@516: % you may not use this file except in compliance with the License.
tom@516: % You may obtain a copy of the License at
tom@516: %
tom@516: %     http://www.apache.org/licenses/LICENSE-2.0
tom@516: %
tom@516: % Unless required by applicable law or agreed to in writing, software
tom@516: % distributed under the License is distributed on an "AS IS" BASIS,
tom@516: % WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
tom@516: % See the License for the specific language governing permissions and
tom@516: % limitations under the License.
tom@516: 
tom@516: function [ihc_out, state] = CARFAC_IHCStep(filters_out, coeffs, state);
tom@516: % function [ihc_out, state] = CARFAC_IHCStep(filters_out, coeffs, state);
tom@516: %
tom@516: % One sample-time update of inner-hair-cell (IHC) model, including the
tom@516: % detection nonlinearity and one or two capacitor state variables.
tom@516: 
tom@516: just_hwr = coeffs.just_hwr;
tom@516: 
tom@516: if just_hwr
tom@516:   ihc_out = max(0, filters_out);
tom@516:   state.ihc_accum = state.ihc_accum + max(0, ihc_out);
tom@516: else
tom@516:   one_cap = coeffs.one_cap;
tom@516: 
tom@516:   detect = CARFAC_Detect(filters_out/2);  % detect with HWR or so
tom@516: 
tom@516:   if one_cap
tom@516:     ihc_out = detect .* state.cap_voltage;
tom@516:     state.cap_voltage = state.cap_voltage - ihc_out .* coeffs.out_rate + ...
tom@516:       (1 - state.cap_voltage) .* coeffs.in_rate;
tom@516:   else
tom@516:     % change to 2-cap version more like Meddis's:
tom@516:     ihc_out = detect .* state.cap2_voltage;
tom@516:     state.cap1_voltage = state.cap1_voltage - ...
tom@516:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.out1_rate + ...
tom@516:       (1 - state.cap1_voltage) .* coeffs.in1_rate;
tom@516: 
tom@516:     state.cap2_voltage = state.cap2_voltage - ihc_out .* coeffs.out2_rate + ...
tom@516:       (state.cap1_voltage - state.cap2_voltage) .* coeffs.in2_rate;
tom@516:   end
tom@516: 
tom@516:   % smooth it twice with LPF:
tom@516: 
tom@516:   state.lpf1_state = state.lpf1_state + coeffs.lpf_coeff * ...
tom@516:     (ihc_out - state.lpf1_state);
tom@516: 
tom@516:   state.lpf2_state = state.lpf2_state + coeffs.lpf_coeff * ...
tom@516:     (state.lpf1_state - state.lpf2_state);
tom@516: 
tom@516:   ihc_out = state.lpf2_state;
tom@516: 
tom@516:   state.ihc_accum = state.ihc_accum + max(0, ihc_out - coeffs.rest_output);
tom@516: end