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@565: function [car_out, state] = CARFAC_CAR_Step(x_in, CAR_coeffs, state)
dicklyon@534: % function [zY, state] = CARFAC_CAR_Step(x_in, CAR_coeffs, state)
dicklyon@534: %
dicklyon@534: % One sample-time update step for the filter part of the CARFAC.
dicklyon@534: 
dicklyon@534: % Most of the update is parallel; finally we ripple inputs at the end.
dicklyon@534: 
dicklyon@565: 
dicklyon@565: % do the DOHC stuff:
dicklyon@565: 
dicklyon@565: g = state.g_memory + state.dg_memory;  % interp g
dicklyon@565: zB = state.zB_memory + state.dzB_memory; % AGC interpolation state
dicklyon@565: % update the nonlinear function of "velocity", and zA (delay of z2):
dicklyon@534: zA = state.zA_memory;
dicklyon@565: v = state.z2_memory - zA;
dicklyon@565: % nlf = CARFAC_OHC_NLF(v .* widen, CAR_coeffs);  % widen v with feedback
dicklyon@565: nlf = CARFAC_OHC_NLF(v, CAR_coeffs);
dicklyon@565: % zB * nfl is "undamping" delta r:
dicklyon@565: r = CAR_coeffs.r1_coeffs + zB .* nlf; 
dicklyon@565: zA = state.z2_memory;
dicklyon@534: 
dicklyon@534: 
dicklyon@534: % now reduce state by r and rotate with the fixed cos/sin coeffs:
dicklyon@534: z1 = r .* (CAR_coeffs.a0_coeffs .* state.z1_memory - ...
dicklyon@534:   CAR_coeffs.c0_coeffs .* state.z2_memory);
dicklyon@534: % z1 = z1 + inputs;
dicklyon@534: z2 = r .* (CAR_coeffs.c0_coeffs .* state.z1_memory + ...
dicklyon@534:   CAR_coeffs.a0_coeffs .* state.z2_memory);
dicklyon@534: 
dicklyon@534: zY = CAR_coeffs.h_coeffs .* z2;  % partial output
dicklyon@534: 
dicklyon@534: % Ripple input-output path, instead of parallel, to avoid delay...
dicklyon@534: % this is the only part that doesn't get computed "in parallel":
dicklyon@534: in_out = x_in;
dicklyon@534: for ch = 1:length(zY)
dicklyon@534:   % could do this here, or later in parallel:
dicklyon@534:   z1(ch) = z1(ch) + in_out;
dicklyon@534:   % ripple, saving final channel outputs in zY
dicklyon@534:   in_out = g(ch) * (in_out + zY(ch));
dicklyon@534:   zY(ch) = in_out;
dicklyon@534: end
dicklyon@534: 
dicklyon@534: % put new state back in place of old
dicklyon@565: % (z1 is a genuine temp; the others can update by reference in C)
dicklyon@534: state.z1_memory = z1;
dicklyon@534: state.z2_memory = z2;
dicklyon@534: state.zA_memory = zA;
dicklyon@534: state.zB_memory = zB;
dicklyon@534: state.zY_memory = zY;
dicklyon@534: state.g_memory = g;
dicklyon@534: 
dicklyon@565: car_out = zY;
dicklyon@565: 
dicklyon@565: