Simultaneous imaging of sound propagations and spatial distribution of acoustic frequencies.

We propose a simultaneous imaging technique of both sound propagations and spatial distribution of acoustic frequencies. We experimentally demonstrated the proposed technique for the acoustic waves of frequencies 39,500 and 40,500 Hz, which have close sound pressure. The sounds were recorded at the framerate of 100,000 fps by parallel phase-shifting digital holography. To obtain the distribution of the acoustic frequencies, the short-time Fourier transform analysis was applied. The simultaneous imaging was carried out by assigning the frequencies and the pixel values of the phase-difference images to the components of HSL color space. The images obtained by the proposed technique represent the frequencies with the hue in addition to the sound propagations with the luminance. We succeeded in imaging the spatiotemporal evolution of the spatial frequencies of the sounds.