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

Chapter 4: Amplitude CalibrationI = p 2ρc(4.1)where I = intensity (in watts/m 2 ), p = RMS pressure (in pascals; one pascalequals one newton/m 2 ), ρc = the characteristic impedance of the medium (inmks rayls), ρ = the density of the medium (in kg/m 3 ), and c = the speed ofsound in the medium (in m/sec).In the electrical paradigm, the waveform represents a time-varying voltage inan electric circuit. In a given time interval, this voltage delivers some averagepower to the circuit. The power delivered by a given voltage depends on theimpedance of the circuit, according to the relationshipP = v2Rwhere P = power (in watts), v = RMS voltage, and R = impedance (in ohms).(4.2)A signal is considered to be an acoustic signal or an electric signal depending onwhich paradigm is selected in the Set Calibration dialog box, discussed later inthis chapter.Canary can express any amplitude-related quantity either in acoustical or inelectrical units. Table 4.1 shows the correspondence between quantitiesexpressed using the two paradigms.Table 4.1. Correspondence between acoustical and electrical quantities.SOUNDELECTRICITYQuantity Units Quantity Unitspressure pascals voltage voltsintensity watts/m 2 power wattscharacteristicimpedanceenergy fluxdensityrayls line impedance ohmsjoules / m 2 energy joulesThe remainder of this chapter discusses the calibration procedure for sounds.The procedure for electrical signals is the same, except that electrical units aresubstituted for acoustical units according to the correspondences in Table 4.1.Signal calibration in Canary: an overviewCanary’s internal representation of a digitized signal consists of a sequence ofsample values output by an analog-to-digital converter sampling an inputvoltage at some regular sampling frequency (see Appendix A). The samplevalues are integers ranging from -(2 n-1 ) to 2 n-1 -1, where n is the number of bits68 Canary 1.2 User’s Manual