International Computer Music Conference 2014, 2014. [4] J. Beskow and K. Sjölander, “WaveSurfer-a Short overview in parametric loudspeakers array public domain speech tool,” Proc. ICSLP 2000, technology and its implications in spatialization in electronic 2000. [5] T. Giannakopoulos, “pyAudioAnalysis: An music Open-Source Python Library for Audio Signal Analysis,” PLoS One, vol. 10, no. 12, p. Jaime Reis e0144610, Dec. 2015. INET-md (FCSH-UNL), Festival DME, Portugal [6] O. Lartillot and P. Toiviainen, “A Matlab toolbox [email protected] for musical feature extraction from audio,” Int. Conf. Digit. Audio …, 2007. [7] S. E. Meinard Müller, “Chroma Toolbox: MATLAB implementations for extracting computer as a source of musical sounds” [3], a variants of chroma-based audio features.” ABSTRACT text that then was mentioned by composers [8] E. Pampalk, “A Matlab Toolbox to Compute who changed the history of computer music, Music Similarity from Audio.,” ISMIR, 2004. such as John Chowning, as very promising [9] T. Park and Z. Li, “Not just prettier: FMS toolbox In late December of 1962, a Physics Professor ideas [4], who certainly influenced this and marches on,” Proc. ICMC 2009, 2009. from Brown University, Peter J. Westervelt, other composers. submitted a paper called Parametric Acoustic [10] T. H. Park, B. Miller, A. Shrestha, S. Lee, J. A relation between Westervelt Array [1] considered primary waves interacting Turner, and A. Marse, “Citygram One : discoveries and further developments in Visualizing Urban Acoustic Ecology,” in within a given volume and calculated the scattered pressure field due to the non-linearities parametric loudspeakers array technology were Proceedings of the Conference on Digital described by Croft and Norris [2], including Humanities 2012, 2012. within a small portion of this common volume in the medium [2]. Since then, many outputs of this the technological developments by different [11] C. Shamoon and T. Park, “New York City’s New technology were developed and applied in scientists and in different countries and how it Noise Code and NYU's Citygram-Sound contexts such as military, tomography, sonar has moved from theory and experimentation to Project,” in … -NOISE and NOISE-CON technology, artistic installations and others. implementation and application. Congress and …, 2014. Such technology allows perfect sound It’s important to clear that such [12] T. H. Park, J. Turner, J. You, J. H. Lee, and M. directionally and therefore peculiar expressive terminology isn’t fixed and that it’s possible to Musick, “Towards Soundscape Information techniques in electroacoustic music, allowing a find different definitions to similar projects Retrieval (SIR),” in International Computer very particular music dimension of space. For (commercial, scientific or of other nature), Music Conference Proceedings (ICMC), 2014. such reason, it’s here treated as a idiosyncrasy uses, products and implementations of such [13] T. H. Park, J. Turner, M. Musick, J. H. Lee, C. worth to discuss on its on terms. theoretical background, sometimes even by the Jacoby, C. Mydlarz, and J. Salamon, “Sensing In 2010-2011 I composed the piece "A same authors and in the same articles. Some of Urban Soundscapes,” in Workshop on Mining Anamnese das Constantes Ocultas", them being “parametric loudspeakers” [2], [5], Urban Data, 2014. commissioned by Grupo de Música “parametric speakers “ [6], [7], “parametric [14] C. Mydlarz, S. Nacach, T. Park, and A. Roginska, Contemporânea de Lisboa, that used a acoustic array” [1], [8], “parametric array” [5], “The design of urban sound monitoring devices,” parametric loudspeakers array developed by [7], “parametric audio system” [9], Audio Eng. Soc. …, 2014. engineer Joel Paulo. The same technology was “hypersonic sound” [10], “beam of sound” [1], used in the 2015 acousmatic piece “Jeux de “audible sound beams” [11], “superdirectional l'Espace” for eight loudspeakers and one sound beams” [12], “super directional parametric loudspeaker array. This paper is organized as follows. A loudspeaker” [13], “focused audio” [14], theoretical framework of the parametric “audio spotlight” [15], [16], “phased array loudspeaker array is first introduced, followed by sound system” [17], among others. The term a brief description of the main theoretical aspects PLA is being used here since it seems to of such loudspeakers. Secondly, there is a reunite the main concepts that converge in this description of practices that use such technology technology. Nevertheless, it isn’t meant to be and their applications. The final section presented as an improved terminology over describes how I have used it in my music others. This discussion solely has the purpose compositions. of showing that one who might not be familiar with such technology, and wish to research more about it, will find different terms that 1. Introduction were originated due to particular historical contexts, manufacturers patents and arbitrary The fundamental theoretical principles of a grounds. parametric loudspeaker array (PLA) were discovered and explained by Westervelt [1]. 2. Theoretical framework Interestingly, this was in the same year of the publication of an article by Max Mathews A parametric loudspeaker is guided by a where the author said there were “no principle described by Westervelt as: theoretical limits to the performance of the two plane waves of differing frequencies 240 Proceedings of the International Computer Music Conference 2016 Proceedings of the International Computer Music Conference 2016 241 generate, when traveling in the same direction, two not [12]. Such systems are quite peculiar, even Defining the application of PLA in performer’s neck like the strap for an new waves, one of which has a frequency equal to when compared to the so-called narrow artistic fields or within musical practices isn’t accordion player [38]. Other artists that have the sum of the original two frequencies and the coverage loudspeakers, that feature dispersion obvious. In that sense, Blacking clears that “no been using such technology relate to the other equal to the difference frequency [1]. in the 50 degree range, such as some Meyer musical style has ‘its own terms’: its terms are the DXARTS - Seattle Arts and Technology, such However, to trace a proper theoretical Speakers [21], and potentially have new terms of its society and culture, and of the bodies of as Michael McCrea Acoustic Scan [39] and framework of the parametric acoustic array in applications in many diverse fields. the human beings who listen to it, and create and Juan Pampin that have present in 2007, with modern applications, Gan et al. makes a more perform it" [27]. In such terms, is Hiroshi other colleagues, works that were using PLA clear description, based on Westervelt’s Mizoguchi human-machine interface (named technology as ultrasonic waveguides, as an theory: ‘Invisible Messenger’), that integrates real acoustic mirror and as wearable sound [40]. When two sinusoidal beams are radiated time visual tracking of face and sound beam Furthermore, Pampin has used PLA from an intense ultrasound source, a spectral forming by speaker array [28], an art work? technology in musical pieces such as 2014 component at the difference frequency is For the purpose of the present paper, secondarily generated along the beams due to the “Respiración Artificial”, for bandoneon, string Mizoguchi’s work will not be considered as an nonlinear interaction of the two primary waves. At quartet, and electronics using PLA, as he the same time, spectral components such as a sum- art form, since the authors don’t consider mentions in an interview: frequency component and harmonics are generated. themselves as doing art. As Bourdieu The piece is about breathing cycles. The However, only the difference-frequency component mentions, one may view the ‘eye’ as being a bandoneon has a big bellow and is able to hold a can travel an appreciable distance because sound product of history reproduced by education, note for a very long time. The timing of the inhale absorption is generally increased with frequency, being true for the mode of “artistic perception and exhale of the instrument was used to define the and amplitudes of higher-frequency components now accepted as legitimate, that is, the aesthetic time structure of the piece. The beginning of my decay greatly compared with the difference disposition, the capacity to consider in and for piece is all in the very upper register (above 1000 frequency. The secondary source column of the themselves, as form rather than function, not only Hertz, around the C above treble clef). When you difference frequency (secondary beam) is virtually hear up there, you hear in a different way. Your ear the work designated for such apprehension, i.e. created in the primary beam and is distributed along Figure 1. Comparison between hypothetical legitimate works of art, but everything in the world, is not able to resolve what is happening with pitch, a narrow beam, similar to an end-fire array reported dispersion patterns for a conventional loudspeaker including cultural objects which are not yet the notes tend to shimmer, it builds sensation. This in antenna theory. Consequently, the directivity of and for a PLA. consecrated” [29]. piece is all sensorial it’s not theoretical. Its more the difference-frequency wave becomes very For the purpose of the present paper, neurological if you want. In terms of the electronics, narrow. This generation model of the difference 3. Parametric