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view main/signal/interp.m @ 0:6b33357c7561 octave-forge
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author | pkienzle |
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date | Wed, 10 Oct 2001 19:54:49 +0000 |
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## Copyright (C) 2000 Paul Kienzle ## ## This program 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 of the License, or ## (at your option) any later version. ## ## This program 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 this program; if not, write to the Free Software ## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA ## usage: y = interp(x, q [, n [, Wc]]) ## ## Upsample the signal x by a factor of q, using an order 2*q*n+1 FIR ## filter. Note that q must be an integer for this rate change method. ## n defaults to 4 and Wc defaults to 0.5. ## ## Example ## # Generate a signal. ## t=0:0.01:2; x=chirp(t,2,.5,10,'quadratic')+sin(2*pi*t*0.4); ## y = interp(x(1:4:length(x)),4,4,1); # interpolate a sub-sample ## stem(t(1:121)*1000,x(1:121),"-g;Original;"); hold on; ## stem(t(1:121)*1000,y(1:121),"-r;Interpolated;"); ## stem(t(1:4:121)*1000,x(1:4:121),"-b;Subsampled;"); hold off; ## ## See also: decimate, resample function y = interp(x, q, n, Wc) if nargin < 1 || nargin > 4, usage("y=interp(x, q [, n [, Wc]])"); endif if q != fix(q), error("decimate only works with integer q."); endif if nargin<3 n=4; Wc=0.5; elseif nargin<4 Wc=0.5; endif if rows(x)>1 y = zeros(length(x)*q+q*n+1,1); else y = zeros(1,length(x)*q+q*n+1); endif y(1:q:length(x)*q) = x; b = fir1(2*q*n+1, Wc/q); y=q*fftfilt(b, y); y(1:q*n+1) = []; # adjust for zero filter delay endfunction %!demo %! ## Generate a signal. %! t=0:0.01:2; x=chirp(t,2,.5,10,'quadratic')+sin(2*pi*t*0.4); %! y = interp(x(1:4:length(x)),4,4,1); # interpolate a sub-sample %! plot(t(1:121)*1000,y(1:121),"r-+;Interpolated;"); hold on; %! stem(t(1:4:121)*1000,x(1:4:121),"ob;Original;"); hold off; %! %! % graph shows interpolated signal following through the %! % sample points of the original signal.