mirror of https://github.com/thesofproject/sof.git
71 lines
2.6 KiB
Mathematica
71 lines
2.6 KiB
Mathematica
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function b = stdlpf_get(fu, fs)
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%% b = stdlpf_get(fu, fs)
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%
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% Standard loww-pass filter
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%
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% Input
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% fu - upper band-edge frequency
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% fs - sample rate
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%
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% Output
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% b - coefficients for FIR filter
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%
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% Reference AES17 5.2.5
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%%
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% Copyright (c) 2017, 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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%% Design filter
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rp = 0.001; % Since this may need to be in frequency response measurement the ripple must be very small
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rs = -65; % Some margin vs. requirement
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a = [1 0];
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% Note: The fc-fu for digital low-pass is not feasible. Use of fu*1.2 instead
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% results to example 24 kHz for 20 kHz upper band-edge. This could be a mistake
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% in specification.
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fc = min(fu*1.2, 0.99*fs/2);
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f = [fu fc];
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dev = [ (10^(rp/20)-1)/(10^(rp/20)+1) 10^(rs/20) ];
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[n, wn, beta, ftype] = kaiserord(f, a, dev, fs);
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b = fir1(n, wn, ftype, kaiser(n+1,beta));
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if 0
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f = linspace(0, fs/2, 1000);
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h = freqz(b,1, f, fs);
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figure
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plot(f, 20*log10(abs(h)))
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hold on;
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plot( [fc fs/2], [-60 -60], 'r', [0 fu], [-0.1 -0.1], 'r', [0 fu], [0.1 0.1], 'r');
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hold off;
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grid on;
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end
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end
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