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stftb >> stftb > Choice of Particular Signals > chirp

chirp

Evaluate a chirp signal at time t. A chirp signal is a frequency swept cosine wave

Calling Sequence

y = chirp(t)
y = chirp(t, f0)
y = chirp(t, f0, t1)
y = chirp(t, f0, t1, f1)
y = chirp(t, f0, t1, f1, form)
y = chirp(t, f0, t1, f1, form, phase)

Parameters

t:

real vector of times (in seconds) to evaluate the chirp signal

f0:

a positive scalar: the frequency (in Hz) at time t=0 (default: 0). If set to [] the default value is used.

t1:

a positive scalar: the time (in seconds) t1 (default: 1). If set to [] the default value is used.

f1:

a positive scalar: frequency (in Hz) at time t=t1 (default: 100). If set to [] the default value is used.

form:

a character string: the 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

The default value is "linear". If set to [] the default value is used.

phase:

a real scalar: the phase shift (in degree) at t=0 (default: 0). If set to [] the default value is used.

Description

If you want a different sweep shape f(t), use the following: y = cos(2*%pi*integral(f(t)) + 2*%pi*f0*t + phase);

Examples

clf; gcf().color_map = jetcolormap(128);
// Linear
subplot(221);
[TFR,T,F] = tfrsp(chirp([0:0.002:5])',1:2:2501,128);
subTFR = linspace(1, size(TFR, 'c'), 100);
grayplot(T(subTFR),F(1:$/2),TFR(1:$/2,subTFR)');
xtitle "linear, 0-100Hz in 1 sec"

//Quadratic
subplot(222);
[TFR,T,F] = tfrsp(chirp([-2:0.001:15], 400, 10, 100, 'quadratic')',1:2:5001,128);
subTFR = linspace(1, size(TFR, 'c'), 100);
grayplot(T(subTFR),F(1:$/2),TFR(1:$/2,subTFR)');
xtitle "quadratic, 400 Hz at t=0 and 100 Hz at t=10"

//Logarithmic
subplot(223);
[TFR,T,F] = tfrsp(chirp([0:1/8000:5], 200, 2, 500, "logarithmic")',1:20:40001,128);
subTFR = linspace(1, size(TFR, 'c'), 100);
grayplot(T(subTFR),F(1:$/2),TFR(1:$/2,subTFR)');
xtitle "logaritmic, 200 Hz at t=0 and 500 Hz at t=2"

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