User's Manual - Cornell Lab of Ornithology - Cornell University
User's Manual - Cornell Lab of Ornithology - Cornell University
User's Manual - Cornell Lab of Ornithology - Cornell University
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Chapter 4Signal Amplitude CalibrationAbout this chapterThis chapter discusses how to use Canary for making calibrated absoluteamplitude measurements. If the only measurements you need to make aretime and frequency measurements, or measurements <strong>of</strong> the relativeamplitudes <strong>of</strong> parts <strong>of</strong> a signal, you do not need to set the signal calibration asdiscussed below.BEWARE!Amplitude measurements provided by Canary are meaningless unless the signalhas been properly calibrated!In most cases, making calibrated amplitude measurements requires the use <strong>of</strong>calibrated microphones and tape recorders, and/or the use <strong>of</strong> a calibratedsound source to generate a calibration signal <strong>of</strong> known amplitude (see“Recording a calibration signal” below).This chapter assumes a working knowledge <strong>of</strong> the relationships among soundpressure, intensity, and characteristic impedance in elastic media, and amongvoltage, power, and impedance in electric circuits, and with decibelmeasurements. If you are not familiar with these concepts, or need to reviewthem, see Appendix C.Acoustical and electrical paradigmsCanary allows you to make amplitude measurements from waveforms,spectrograms, and spectra using either an acoustical or an electrical paradigm.In the acoustical paradigm, the waveform represents a time-varying pressureat some point in space in an elastic medium such as air or water. In a plane orspherical free-progressive sound wave, the squared effective (RMS) soundpressure is proportional to the average sound intensity over a given timeinterval at a given point in space. The proportionality constant relatingsquared sound pressure 1 and sound intensity is the inverse <strong>of</strong> thecharacteristic impedance <strong>of</strong> the medium. Characteristic impedance is theproduct <strong>of</strong> the medium’s density and the speed <strong>of</strong> sound in the medium.Sound pressure, sound intensity, and characteristic impedance are thusrelated by1 The term “sound pressure” here and elsewhere in this manual means RMS soundpressure, unless otherwise noted.Canary 1.2 User’s <strong>Manual</strong> 67
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