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

Chapter 3: Spectrum AnalysisLogarithmic vs.quadraticamplitude axisThe Amplitude radio buttons allow you to choose either a logarithmic orquadratic 1 amplitude axis. In a logarithmic spectrum, intensity levels areplotted in dB relative to the intensity dB reference value specified in the SetCalibration dialog; a quadratic spectrum plots intensities in W/m 2 /Hz. For aspectrogram, the choice of amplitude axis determines whether the grayscalevalues are proportional to the intensity at each point or the log (base 10) of theintensity.Logarithmic displays are usually more useful for spectra and spectrograms ofbiological sounds because of their large dynamic range.When you select Quadratic amplitude axis, the Clipping Level parameter isautomatically set to -∞ dB.Figures 3.12 and 3.13 show spectrograms and spectra plotted with logarithmicand quadratic amplitude axes.1 If you choose a quadratic amplitude axis, the values displayed are intensity spectrumvalues (in W/m 2 /Hz) rather than intensity spectrum levels (decibels/Hz). If thesignal is calibrated using the electrical paradigm, quadratic amplitudes are powerspectrum values (J/Hz). These spectra are considered “quadratic” because the valuesshown are proportional to the square of the signal amplitude (sound pressure orvoltage).Canary 1.2 User’s Manual 55