mirror of https://github.com/thesofproject/sof.git
118 lines
2.8 KiB
Mathematica
118 lines
2.8 KiB
Mathematica
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function [emp_coefs, deemp_coefs] = iir_gen_quant_coefs(params);
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stage_gain = params.stage_gain;
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stage_ratio = params.stage_ratio;
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anchor_freq = params.anchor;
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emp = cell(1, 2);
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deemp = cell(1, 2);
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% Generate the coefficients of (de)emphasis for the 1-st stage of biquads
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[emp(1), deemp(1)] = emp_deemp_stage_biquad(stage_gain, anchor_freq,
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anchor_freq / stage_ratio);
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anchor_freq = anchor_freq / (stage_ratio * stage_ratio);
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% Generate the coefficients of (de)emphasis for the 2-nd stage of biquads
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[emp(2), deemp(2)] = emp_deemp_stage_biquad(stage_gain, anchor_freq,
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anchor_freq / stage_ratio);
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% Adjust the stage gain (push gains to the last stage) of emphasis filter
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[emp(1), emp(2)] = stage_gain_adjust(emp(1), emp(2));
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% Print emp and deemp
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emp
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deemp
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% Convert the coefficients to values usable with SOF
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emp_coefs = iir_coef_quant(emp);
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deemp_coefs = iir_coef_quant(deemp);
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end
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function [emp, deemp] = emp_deemp_stage_biquad(gain, f1, f2);
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[z1, p1] = emp_stage_roots(gain, f1);
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[z2, p2] = emp_stage_roots(gain, f2);
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b0 = 1;
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b1 = -(z1 + z2);
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b2 = z1 * z2;
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a0 = 1;
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a1 = -(p1 + p2);
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a2 = p1 * p2;
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% Gain compensation to make 0dB at 0Hz
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% For emphasis filter, alpha should be > 1. Record the alpha gain and then we
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% will do the stage gain adjustment afterwards.
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alpha = (a0 + a1 + a2) / (b0 + b1 + b2);
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% [ a2 a1 b2 b1 b0 shift gain]
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emp = [-a2, -a1, b2, b1, b0, 0, alpha];
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% For deemphasis filter, beta should be < 1. Multiply beta directly to b coeffs
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% to have a healthy scaling of biquads internally.
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beta = (b0 + b1 + b2) / (a0 + a1 + a2);
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% [ a2 a1 b2 b1 b0 shift gain]
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deemp = [-b2, -b1, a2 * beta, a1 * beta, a0 * beta, 0, 1.0];
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end
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function [zero, pole] = emp_stage_roots(gain, normalized_freq);
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gk = 1 - gain / 20;
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f1 = normalized_freq * gk;
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f2 = normalized_freq / gk;
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zero = exp(-f1 * pi);
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pole = exp(-f2 * pi);
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end
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function quant_coefs = iir_coef_quant(coefs);
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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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addpath ../eq
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quant_coefs = cell(1, 2);
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for i = 1:length(coefs)
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coef = cell2mat(coefs(i));
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quant_ab = eq_coef_quant(coef(1:5), bits_iir, qf_iir);
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quant_gain = eq_coef_quant(coef(7), bits_gain, qf_gain);
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quant_coefs(i) = [quant_ab coef(6) quant_gain];
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end
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quant_coefs = cell2mat(quant_coefs);
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rmpath ../eq
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end
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function [bq1, bq2] = stage_gain_adjust(prev_bq1, prev_bq2);
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prev_bq1 = cell2mat(prev_bq1);
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prev_bq2 = cell2mat(prev_bq2);
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[rshift, gain] = decompose_gain(prev_bq1(7) * prev_bq2(7));
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bq1 = [prev_bq1(1:5) 0 1.0];
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bq2 = [prev_bq2(1:5) rshift gain];
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end
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function [rshift, gain] = decompose_gain(prev_gain);
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max_abs_val = 2; % Q2.14
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rshift = 0;
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gain = prev_gain;
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while (abs(gain) >= max_abs_val)
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gain = gain / 2;
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rshift--; % left-shift in shift stage
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endwhile
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end
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