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%
% Copyright 2001 Free Software Foundation, Inc.
%
% This file is part of GNU Radio
%
% GNU Radio is free software; you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation; either version 2, or (at your option)
% any later version.
%
% GNU Radio is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with GNU Radio; see the file COPYING. If not, write to
% the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
% Boston, MA 02111-1307, USA.
%% find the N-dB width of the given filter
%% E.g., to find the 3-dB width, use width = db_width (taps, -3.0)
%% the result is normalized to nyquist == 1
function width = db_width (taps, db)
[H,w] = freqz (taps, 1, 4096);
Habs = abs(H);
max_H = max(Habs);
min_H = min(Habs);
threshold = max_H * 10^(db/20);
if (min_H > threshold)
error ("The %g dB point is never reached", db);
end
above = Habs >= threshold;
width = sum(above) / length (above);
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