125 lines
4.3 KiB
Matlab
125 lines
4.3 KiB
Matlab
function iir_resp = eq_iir_blob_quant(eq_b, eq_a)
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%% Convert IIR coefficients to 2nd order sections and quantize
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%
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% iir_resp = eq_iir_blob_quant(b, a, bits)
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%
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% b - numerator coefficients
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% a - denominator coefficients
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% bits - number of bits to quantize
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%
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% iir_resp - vector to setup an IIR equalizer with number of sections, shifts,
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% and quantized coefficients
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%
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%%
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% Copyright (c) 2016, Intel Corporation
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% All rights reserved.
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%
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% Redistribution and use in source and binary forms, with or without
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% modification, are permitted provided that the following conditions are met:
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% * Redistributions of source code must retain the above copyright
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% notice, this list of conditions and the following disclaimer.
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% * Redistributions in binary form must reproduce the above copyright
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% notice, this list of conditions and the following disclaimer in the
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% documentation and/or other materials provided with the distribution.
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% * Neither the name of the Intel Corporation nor the
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% names of its contributors may be used to endorse or promote products
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% derived from this software without specific prior written permission.
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%
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% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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% AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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% IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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% ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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% LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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% CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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% SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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% INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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% CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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% ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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% POSSIBILITY OF SUCH DAMAGE.
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%
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% Author: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>
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%
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%% Settings
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bits_iir = 32; % Q2.30
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qf_iir = 30;
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bits_gain = 16; % Q2.14
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qf_gain = 14;
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scale_max = -3; % dB, scale biquad L-inf norm
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plot_pz = 0;
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plot_fr = 0;
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%% Convert IIR to 2nd order sections
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if exist('OCTAVE_VERSION', 'builtin')
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[sos, gain] = tf2sos(eq_b, eq_a);
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else
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% TODO: tf2sos produces in Matlab EQs with zero output due to
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% very high gain variations within biquad. Need to investigate if
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% this is incorrect usage and a bug here.
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[sos, gain] = tf2sos(eq_b, eq_a, 'UP', Inf);
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fprintf('Warning: Problems have been seen with some IIR designs.\n');
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fprintf('Warning: Please check the result.\n');
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end
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sz = size(sos);
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nbr_sections = sz(1);
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n_section_header = 2;
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n_section = 7;
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iir_resp = int32(zeros(1,n_section_header+nbr_sections*n_section));
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iir_resp(1) = nbr_sections;
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iir_resp(2) = nbr_sections; % Note: All sections in series
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for n=1:nbr_sections
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b = sos(n,1:3);
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a = sos(n,4:6);
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if plot_pz
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figure
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zplane(b,a);
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tstr = sprintf('SOS %d poles and zeros', n);
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title(tstr);
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end
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np = 1024;
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[h, w] = freqz(b, a, np);
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hm = max(abs(h));
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scale = 10^(scale_max/20)/hm;
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gain_remain = 1/scale;
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gain = gain*gain_remain;
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b = b * scale;
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ma = max(abs(a));
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mb = max(abs(b));
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if plot_fr
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figure
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[h, w] = freqz(b, a, np);
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plot(w, 20*log10(abs(h))); grid on;
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xlabel('Frequency (w)');
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ylabel('Magnitude (dB)');
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tstr = sprintf('SOS %d frequency response', n);
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title(tstr);
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end
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%% Apply remaining gain at last section output
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if n == nbr_sections
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section_shift = -fix(log(gain)/log(2));
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section_gain= gain/2^(-section_shift);
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else
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section_shift = 0;
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section_gain = 1;
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end
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%% Note: Invert sign of a!
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%% Note: a(1) is omitted, it's always 1
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m = n_section_header+(n-1)*n_section+1;
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iir_resp(m:m+1) = eq_coef_quant(-a(3:-1:2), bits_iir, qf_iir);
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iir_resp(m+2:m+4) = eq_coef_quant( b(3:-1:1), bits_iir, qf_iir);
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iir_resp(m+5) = section_shift;
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iir_resp(m+6) = eq_coef_quant( section_gain, bits_gain, qf_gain);
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end
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end
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