SECT. 4] 



SOUND PRODUCTION BY MARINE ANIMALS 



547 



C. Spectrum Analysis 



By far the most use has been made of visible speech analysis equipment such 

 as the Kay Electric Company's Sonagraph and Vibralyzer, These were the 

 commercial outgrowths of the original sound spectrograph developed at the Bell 

 Telephone Laboratories. They have been used in many different studies of 

 animal sounds. Both instruments present a time and frequency analysis of 

 transient or steady-state wave-forms as a graph in which time is the abscissa, 

 frequency the ordinate, and the intensity is shown by relative blackening of 

 the paper (see Figs. 4 and 6-10). 



These spectrograms give a pictorial representation of sound which satisfies 

 many of the requirements for definitive description of a transient sound, 

 especially the means for comparing and contrasting different sounds. The in- 

 tensity display is qualitative, except that the dividing line between recording 



0.3 0.4 



. r/Me isec) 



Fig. 4. Sound spectrogram of squeal and clicks of Delphinus delphis (saddleback porpoise), 

 made on a Kay Electric Co. Vibralyzer. 



and not-recording is reproducible and can be used to determine one contour 

 of equal intensity. By re-playing the analysis at gain settings according to a 

 desired pattern, the whole sound can be presented in contours of intensity on 

 a map of time and frequency (see Hersey, 1957, fig. 19). For many animal 

 sound investigations, great refinement of this sort is not needed ; we have seen 

 that the contour technique has proved very useful in scattering-layer studies. 

 Another function of these instruments, known as "sectioning", presents the 

 average intensity spectrum over a short time near a selected instant. 



The principal drawback of this type of instrument is its program ; the sound 

 is recorded on a magnetic drum and must be re-played for each setting of the 

 wave analyzer throughout the spectrum. This is a tedious occupation requiring 

 5 min to analyze sounds from 2.4 to 24 sec long. In recent years several manu- 

 facturers have been making matched sets of magnetostriction or crystal filters 

 which all receive the sample at once. With these filters, analyses can be com- 

 pleted in the time of the original sound while providing the same information 



