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Audio: EQIIR/Selector: Add scripts to produce crossover blobs
This patch adds to script sof_selector_blobs.m export of stereo stream upmix to duplicated channels. The duplicated channels are then filtered with desired crossover characteristics. The added script for IIR EQ sof_example_lr4.m exports 4th order Linkwitz-Riley files for crossover low-pass and high-pass. The added example should be quite typical for laptop PCs. With larger speakers the frequency could be lower, with smaller higher. Also the crossover order could be changed to lower and higher. The 4th order should be quite typical. Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>
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‎src/audio/eq_iir/tune/sof_example_lr4.m‎

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%% Design 4th order Linkwitz–Riley filter bank
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% SPDX-License-Identifier: BSD-3-Clause
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%
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% Copyright (c) 2025, Intel Corporation.
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%
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% Author: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>
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function sof_example_lr4()
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%% Common definitions
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fs = 48e3;
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fc = 2e3;
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sof_tools = '../../../../tools';
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tpath = fullfile(sof_tools, 'topology/topology2/include/components/eqiir');
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cpath = fullfile(sof_tools, 'ctl/ipc4/eq_iir');
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sof_eq_paths(1);
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%% --------------------------------------------------
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%% Example: Band-split 2ch to 4ch low and high bands
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%% --------------------------------------------------
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design_name = sprintf('xover_lr4_%dhz_lhlh_%dkhz', fc, round(fs/1000));
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blob_fn = fullfile(cpath, [design_name '.bin']);
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alsa_fn = fullfile(cpath, [design_name '.txt']);
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tplg_fn = fullfile(tpath, [design_name '.conf']);
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comment = 'LR4 filter bank coefficients';
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howto = 'cd src/audio/eq_iir/tune; octave sof_example_lr4.m';
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% Design low-pass and high-pass filters
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eq_lo = lo_band_iir(fs, fc);
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eq_hi = hi_band_iir(fs, fc);
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% Quantize and pack filter coefficients plus shifts etc.
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bq_lo = sof_eq_iir_blob_quant(eq_lo.p_z, eq_lo.p_p, eq_lo.p_k);
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bq_hi = sof_eq_iir_blob_quant(eq_hi.p_z, eq_hi.p_p, eq_hi.p_k);
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% Build blob
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channels_in_config = 4; % Setup max 4 channels EQ
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assign_response = [0 1 0 1]; % Order: lo, hi, lo, hi
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num_responses = 2; % Two responses: lo, hi
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bm = sof_eq_iir_blob_merge(channels_in_config, ...
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num_responses, ...
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assign_response, ...
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[bq_lo bq_hi]);
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% Pack and write file
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sof_eq_pack_export(bm, blob_fn, alsa_fn, tplg_fn, comment, howto)
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%% --------------------------------------------------
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%% Example: Same but filters order is lo, lo, hi, hi
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%% --------------------------------------------------
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design_name = sprintf('xover_lr4_%dhz_llhh_%dkhz', fc, round(fs/1000));
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blob_fn = fullfile(cpath, [design_name '.bin']);
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alsa_fn = fullfile(cpath, [design_name '.txt']);
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tplg_fn = fullfile(tpath, [design_name '.conf']);
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assign_response = [0 0 1 1]; % Order: lo, lo, hi, hi
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num_responses = 2; % Two responses: lo, hi
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bm = sof_eq_iir_blob_merge(channels_in_config, ...
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num_responses, ...
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assign_response, ...
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[bq_lo bq_hi]);
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% Pack and write file
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sof_eq_pack_export(bm, blob_fn, alsa_fn, tplg_fn, comment, howto)
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%% ------------------------------------
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%% Done.
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%% ------------------------------------
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sof_eq_paths(0);
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end
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%% -------------------
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%% EQ design functions
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%% -------------------
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function eq = lo_band_iir(fs, fc)
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%% Get defaults for equalizer design
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eq = sof_eq_defaults();
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eq.fs = fs;
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eq.enable_iir = 1;
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eq.iir_norm_type = 'peak';
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eq.iir_norm_offs_db = 0;
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% Parametric EQs are PEQ_HP1, PEQ_HP2, PEQ_LP1, PEQ_LP2, PEQ_LS1,
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% PEQ_LS2, PEQ_HS1, PEQ_HS2 = 8, PEQ_PN2, PEQ_LP4, and PEQ_HP4.
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%
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% Parametric EQs take as second argument the cutoff frequency in Hz
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% and as second argument a dB value (can use 0 for LP2). The
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% Third argument is a Q-value (can use 0 for LP2).
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% Two 2nd order butterworth low-pass filters for 4th order Linkwitz–Riley
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eq.peq = [ ...
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eq.PEQ_LP2 fc 0 0 ; ...
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eq.PEQ_LP2 fc 0 0 ; ...
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];
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%% Design EQ
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eq = sof_eq_compute(eq);
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%% Plot
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sof_eq_plot(eq);
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end
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function eq = hi_band_iir(fs, fc)
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%% Get defaults for equalizer design
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eq = sof_eq_defaults();
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eq.fs = fs;
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eq.enable_iir = 1;
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eq.iir_norm_type = 'peak';
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eq.iir_norm_offs_db = 0;
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% Two 2nd order high-pass filters for 4th order Linkwitz–Riley
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eq.peq = [ ...
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eq.PEQ_HP2 fc 0 0 ; ...
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eq.PEQ_HP2 fc 0 0 ; ...
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];
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%% Design EQ
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eq = sof_eq_compute(eq);
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%% Plot
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sof_eq_plot(eq);
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end
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% Pack and write file common function for all exports
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function sof_eq_pack_export(bm, bin_fn, ascii_fn, tplg_fn, note, howto)
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bp = sof_eq_iir_blob_pack(bm, 4); % IPC4
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if ~isempty(bin_fn)
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sof_ucm_blob_write(bin_fn, bp);
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end
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if ~isempty(ascii_fn)
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sof_alsactl_write(ascii_fn, bp);
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end
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if ~isempty(tplg_fn)
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sof_tplg2_write(tplg_fn, bp, 'IIR', note, howto);
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end
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end

‎src/audio/selector/tune/sof_selector_blobs.m‎

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write_blob(sel, "upmix_stereo_to_51");
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write_blob(sel, "upmix_stereo_to_71");
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% Stereo to L,L,R,R
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sel.coeffs = [ 1 0 0 0 0 0 0 0 ; ...
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1 0 0 0 0 0 0 0 ; ...
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0 1 0 0 0 0 0 0 ; ...
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0 1 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ];
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write_blob(sel, "xover_selector_lr_to_llrr");
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% Stereo to L,R,L,R
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sel.coeffs = [ 1 0 0 0 0 0 0 0 ; ...
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0 1 0 0 0 0 0 0 ; ...
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1 0 0 0 0 0 0 0 ; ...
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0 1 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ; ...
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0 0 0 0 0 0 0 0 ];
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write_blob(sel, "xover_selector_lr_to_lrlr");
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sof_selector_paths(false);
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end
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