Diagram of the subject enclosure. Panel (a) shows the side view and panel (b) shows the top view of the enclosure. A schematic (c) of the directivity microphone array is shown. All microphones were placed from the center of the petri dish. The angular coordinate system is also shown. The angles and are referred to as elevation and azimuth, respectively.
A spectrogram of a typical call recorded with the wide-bandwidth system is shown in (a). The highest persistent frequency component that appears above the noise occurs at . FFTs are shown in (b) from four times within the spectrogram of (a). The thick black spectrum is close to the noise floor, past the end of the call. The three remaining spectra are from near the beginning of the call. Peaks lower in frequency than the peak labeled are persistent over time and correspond to the call. Peak appears by itself. The thin black spectrum and the blue spectrum do not have corresponding peaks at this frequency. Peaks higher in frequency than are not persistent over time but vary randomly; hence they are considered noise.
Time waveforms of a typical túngara frog call recorded with the microphone array are shown in (a). The SPL, relative to the root-mean-square pressure recorded at microphone E (directly above the frog), is calculated for each channel. The broadband directivity in elevation plane is presented in (b), using the SPLs shown in (a).
In this spectrogram (a) of a typical call, lighter shades of gray indicate higher amplitude. The time that corresponds to the highest frequency is indicated by the vertical line, at approximately . The FFTs at that time and all angles are shown in (b). At frequencies below peaks rise up to above the noise, whereas at frequencies approaching the peaks become indistinguishable from the noise. In (c), the relative amplitude received at different elevation angles is shown for the second harmonic. These narrowband SPLs are presented (in Fig. 5) in the form of directivity plots for each harmonic, and for various azimuthal angles using calls from the same frog. The data in Fig. 5 were all taken at times within the call that corresponded to the highest frequency, as illustrated by the solid line at in Fig. 4(a).
Narrowband elevation directivity plots for a single frog at several azimuth angles are shown. Thirteen calls recorded at are shown in (a). Six calls at are shown in (b). Four calls at are shown in (c). Five calls at are shown in (d).
Narrowband elevation directivity exhibited by four frogs at various azimuth angles is shown. Six calls by Frog 18 at are shown in (a). Nineteen calls by Frog 19 at are shown in (b). Twenty-five calls at are shown in (c). Thirteen calls at are shown in (d).
Model geometry and the results of directivity calculations are shown. The source location is indicated by the open circle at and . The directivity of a simple source above a rigid plane of infinite extent is shown in (a). The infinite plane lies along the -axis and is perpendicular to the -axis. Directivity at 2 and is shown. Directivity due to a finite-sized rigid reflecting plane is shown in (b) for a range of frequencies. The extent of the reflector is indicated by . Directivities due to various representations of an idealized natural environment are shown in (c). A flat rigid reflector resides along the -axis with radius . Beyond , four different realizations are shown: a continuation of the flat rigid reflector, a flat soft layer, a rough rigid layer, and a rough soft layer. Additional details are in the text.
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