gusucode.com > 信号处理工具箱 - signal源码程序 > signal\signal\signal\chirp.m
function y = chirp(t,f0,t1,f1,method,phi) %CHIRP Swept-frequency cosine generator. % Y = CHIRP(T,F0,T1,F1) generates samples of a linear swept-frequency % signal at the time instances defined in array T. The instantaneous % frequency at time 0 is F0 Hertz. The instantaneous frequency F1 % is achieved at time T1. By default, F0=0, T1=1, and F1=100. % % Y = CHIRP(T,F0,T1,F1,'method') specifies alternate sweep methods. % Available methods are 'linear','quadratic', and 'logarithmic'; the % default is 'linear'. Note that for a log-sweep, F1>F0 is required. % % Y = CHIRP(T,F0,T1,F1,'method', PHI) allows an initial phase PHI to % be specified in degrees. By default, PHI=0. % % Default values are substituted for empty or omitted trailing input % arguments. % % EXAMPLE 1: Compute the spectrogram of a linear chirp. % t=0:0.001:2; % 2 secs @ 1kHz sample rate % y=chirp(t,0,1,150); % Start @ DC, cross 150Hz at t=1sec % specgram(y,256,1E3,256,250); % Display the spectrogram % % EXAMPLE 2: Compute the spectrogram of a quadratic chirp. % t=-2:0.001:2; % +/-2 secs @ 1kHz sample rate % y=chirp(t,100,1,200,'q'); % Start @ 100Hz, cross 200Hz at t=1sec % specgram(y,128,1E3,128,120); % Display the spectrogram % % See also GAUSPULS, SAWTOOTH, SINC, SQUARE. % Author(s): D. Orofino, T. Krauss, 3/96 % Copyright (c) 1988-98 by The MathWorks, Inc. % $Revision: 1.1 $ % $Revision: 1.1 $ $Date: 1998/06/03 14:42:18 $ % Parse inputs, and substitute for defaults: error(nargchk(1,6,nargin)); if nargin<6, phi=[]; end if nargin<5, method=[]; end if nargin<4, f1=[]; end if nargin<3, t1=[]; end if nargin<2, f0=[]; end if isempty(phi), phi=0; end if isempty(method), method='linear'; end if isempty(f1), f1=100; end if isempty(t1), t1=1; end if isempty(f0), f0=0; end % Parse the method string: % Set p=1 for linear, 2 for quadratic, 3 for logarithmic method=lower(method); p=strmatch(method,strvcat('linear','quadratic','logarithmic')); if isempty(p), error('Unknown method selected.'); elseif length(p)>1, error('Ambiguous method selected.'); end if p==3, % Logarithmic chirp: if f1<f0, error('F1>F0 is required for a log-sweep.'); end beta = log10(f1-f0)/t1; y = cos(2*pi * ( (10.^(beta.*t)-1)./(beta.*log(10)) + f0.*t + phi/360)); else % Polynomial chirp: p is the polynomial order beta = (f1-f0).*(t1.^(-p)); y = cos(2*pi * ( beta./(1+p).*(t.^(1+p)) + f0.*t + phi/360)); end % end of chirp.m