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

Chapter 3: Spectrum AnalysisSpectraSignificance of thespectrum valuesNumber of framesto averageThe values shown in a spectrum represent either the spectrum intensity level(in dB) or the spectrum intensity (in watts/m 2 Hz) at each frequency,depending on whether a Logarithmic or Quadratic amplitude axis wasselected. Spectrum intensity level and spectrum intensity are defined as theintensity level or intensity in a band one hertz wide centered at the specifiedfrequency. The numerical values for intensity level or intensity at eachfrequency (which are displayed by the spectrum measurement panel) dependon the current calibration settings. The intensity or intensity level values on aspectrum are meaningless unless the signal has been properly calibratedaccording to the procedures outlined in Chapter 4. 1If part of the waveform is selected (highlighted) when you request a spectrum,the number of frames selected is shown in the spectrum dialog box. Thenumber of frames that a given selection encompasses depends on both theframe length and the frame overlap. Consequently, the frame count shown inthe dialog box may change if you change either of these parameters. If morethan one frame is selected, Canary calculates the spectrum for each frameindependently, then averages the spectra of all the frames. The averagedspectrum is then displayed. If the selected part of the signal is at least oneframe long, but is not an integral number of frames in length, Canary uses justthose frames that are completely contained in the selection (i.e., the selection istruncated to an integer number of frames). If the selection encompasses lessthan one whole frame, the selection is zero-padded to make one full frame,which is then used for the spectrum.If no part of the waveform is selected, Canary makes a spectrum of a singleframe, which begins at the blinking insertion point.Once a spectrum is displayed, you can double-click on it to highlight theinterval in the waveform from which the spectrum was made (the spectrumsource interval). This function is particularly useful with single-frame spectraif you want to see exactly how much of the signal was actually used for thespectrum. You can determine how many frames were used to make anexisting spectrum using the spectrum measurement panel (see Chapter 6).1 If you are interested only in differences in decibel levels between parts of one signal,you do not have to calibrate the signal.58 Canary 1.2 User’s Manual