User's Manual - Cornell Lab of Ornithology - Cornell University

Chapter 3: Spectrum AnalysisRemember that a spectrogram or spectrum made with negative frameoverlaps ignores some of the available data, and can give an extremelymisleading picture of a signal. Negative frame overlaps should generally beavoided unless you have some specific reason for wanting to omit some partsof a signal from analysis.Figures 3.6 and 3.7 show pairs of spectra and spectrograms that differ only intime grid resolution.(a)(b)(c)Figure 3.6. Effect of varying time grid resolution in spectrograms. The signalis part of a song of a western meadowlark, digitized at 22.3 kHz. The twospectrograms differ only in time grid resolution (frame overlap). In all threespectrograms, filter bandwidth = 353 Hz (frame length = 256 points = 11.5mS), frequency resolution = 22.7 Hz (FFT size = 1024 points), window =Hamming. (a) Time grid resolution = .719 mS (frame overlap = 93.8%). (b)Time grid resolution = 5.73 mS (frame overlap = 50%). (c) Time grid resolution= 11.5 mS (frame overlap = 0%).Canary 1.2 User’s Manual 49