chirp

% error: y = chirp(t [, f0 [, t1 [, f1 [, form [, phase]]]]])
%
% Evaluate a chirp signal at time t.  A chirp signal is a frequency
% swept cosine wave.
%
% t: vector of times to evaluate the chirp signal
% f0: frequency at time t=0 [ 0 Hz ]
% t1: time t1 [ 1 sec ]
% f1: frequency at time t=t1 [ 100 Hz ]
% form: shape of frequency sweep
%    'linear'      f(t) = (f1-f0)*(t/t1) + f0
%    'quadratic'   f(t) = (f1-f0)*(t/t1)^2 + f0
%    'logarithmic' f(t) = (f1-f0)^(t/t1) + f0
% phase: phase shift at t=0
%
% Example
%    specgram(chirp([0:0.001:5])); % linear, 0-100Hz in 1 sec
%    specgram(chirp([-2:0.001:15], 400, 10, 100, 'quadratic'));
%    soundsc(chirp([0:1/8000:5], 200, 2, 500, 'logarithmic'),8000);
%
% If you want a different sweep shape f(t), use the following:
%    y = cos(2*pi*integral(f(t)) + 2*pi*f0*t + phase);