Example 3 The last introductory example presented here is a transient signal embedded in a -5dB white gaussian noise. This transient signal is a constant frequency modulated by a one-sided exponential amplitude (see fig. 1.10): >> trans=amexpo1s(64).*fmconst(64); >> sig=[zeros(100,1) ; trans ; zeros(92,1)]; >> sign=sigmerge(sig,noisecg(256),-5); >> plot(real(sign)); >> dsp=fftshift(abs(fft(sign)).^2); >> plot((-128:127)/256,dsp); Figure 1.10: Time- and frequency- representation of a noisy transient signal From these representations, it is difficult to localize precisely the signal in the time-domain as well as in the frequency domain. Now let us have a look at the spectrogram of this signal calculated using the M-file tfrsp.m (see fig. 1.11): >> tfrsp(sign); Figure 1.11: Spectrogram of the noisy transient signal the transient signal appears distinctly around the normalized frequency 0.25, and between time points 125 and 160.
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