"Conventional loudspeakers emit sound in a nondirectional way (Gan et al. 2012). However, ultrasonic parametric arrays transmit a highly directional sound beam much like a spotlight (Yoneyama et al. 1983, Pompei 1999, Gan et al. 2012). The beam starts out as a mixture of 2 ultrasonic frequencies. "
"They have attracted intensive interest since almost half century ago . A great deal of achievements have been made in theory and practice –. Yoneyama et al.  first modulated ultrasonic signals with audio signals using double sided band amplitude modulation (DSBAM) and fed to parametric loudspeakers to produce audio sounds through the demodulation process provided by the nonlinearity of the air, which however, also generates harmonic distortion degrading the sound quality of the desired sounds. "
[Show abstract][Hide abstract] ABSTRACT: Recently, the general Volterra filter (VF) has been adopted for the modeling of parametric loudspeakers. However, the computation complexity of the VF is too high for real-time implementation. In this paper, a one-dimension Volterra filter (ODVF) with much lower complexity is introduced to model and compensate for the nonlinearity of parametric loudspeakers. A theoretical framework for ODVF model identification is established and a method of measuring the ODVF kernels using the exponential swept-sine signal is provided. The validity of modeling the nonlinearity of the parametric loudspeaker using the ODVF is verified theoretically and experimentally. Based on the established ODVF model, an inverse filter is designed to compensate for the 2nd harmonic distortion of the parametric loudspeakers. To further reduce the 3rd harmonic distortion, an improved compensation method is also proposed. Experimental results show that the performance of the ODVF-based compensation is comparable to that of the Volterra-filter based compensation.
IEEE/ACM Transactions on Audio, Speech, and Language Processing 12/2014; 22(12):2169-2181. DOI:10.1109/TASLP.2014.2363414
"Therefore, the single sideband amplitude modulation (SSBAM) was proposed to result in the same envelope function as the SRAM but with a relaxed bandwidth requirement . Meanwhile, a double integral operator was introduced into the SRAM as an equalizer to further reduce harmonic distortions . However, till now, the most widely applied preprocessing method is still the DSBAM . "
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