Our H 2 O rchestra uses musical instruments that make sound in each of the states-of-matter of H 2 O (dihydrogen monoxide): Pagophone (“pago” is Greek for “ice” and “phone” is Greek for “sound”) represents H 2 O in its solid-state; Hydraulophone: a musical instrument that makes sound from matter (water) in its liquid state; Callio fl ute: a musical instrument that 

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... paper describes a musical instrument consisting of a physical process that acoustically generates sound from the material world (i.e. sound derived from matter such as solid, liquid, gas, or plasma) which is modi fi ed by a secondary input from the informatic world. This informatic input selects attributes such as the frequency range of the musical note be- ing sounded, while the acoustic process is kept in close contact with the user, to ensure a high degree of expressivity. In one example, ice skates with acoustic pickups are used to play music while the skater simultaneously controls a bandpass fi lter with a hand-held keyer and wearable computer. Each skate works much like the bow on a violin, allowing the player to hit, scrape, rub, or “bow”, the ice in various ways to create a wide variety of musical textures. Additionally the player can select sound samples on a per-note basis and then “scratch” out a melody or harmony (playing multiple samples at once) on the ice on the rink like a team of Disk Jockeys (DJs) work- ing together to “scratch” an array of vinyl records. Because the grooves on an ice rink are made by the player in a freeform fashion, there is much more room for variations in musical timbres and textures than with the fi xed grooves of a record. Rather than merely using the keyer to trigger musical notes through MIDI note on/note off commands, we create acoustic sound through a physical process such as skating, and then turn those physical sounds into musical notes with the handheld keyer that functions as a modi fi er input. This combination combines the expressivity of non-electrophonic musical instruments like the violin with the fl exibility of electrophones like the sound synthesizer. As a further contribution of the paper, a general taxonomy of acoustic transducers and a link to physical organology is provided, in which the top-level of the taxonomy is the state- of-matter in which the transducer operates. Index Terms — Hyperacoustic, pagophone, pagolin, hydraulophone, reustophone, poseidophone, idratmosphone, at- mosphone, H2Orchestra, musikeyer, elementary organology Unlike a hyperinstrument[1] in which position sensors, or the like, ADD synthetic sounds to an acoustic instrument, hypera- coustic instruments use position sensors, or the like, to MUL- TIPLICATIVELY combine these. Most notably, hyperacoustic instruments use a synthetic input to modify an acoustically generated sound. See Figures 1 and 2. Organologists and ethnomusicologists often address funda- mental philosophical questions regarding categorization of musical instruments in view of recent developments. Instruments are generally classi fi ed based on initial sound production mechanisms; for example, an electric guitar is still a chordophone, not an electrophone, even though electric- ity (and now computation, i.e. digital effects pedals, etc.) is involved extensively further along the sound production path [2][3]. Hyperacoustic processing of audio signals relies on an acoustic sound source—ie. one which falls outside the “elec- trophones” category. In particular, we focus on acoustic signals from real-life physical processes in which the sound- producing medium is closely linked with the user-interface, in terms of controllability and tactility. A current trend in musical interfaces has been to expand ver- satililty and generality by separating user interfaces from their corresponding sound-producing media. Examples include the piano, harpsichord, and sound synthesizer, which often have a similar user interface that is quite separate from the harp or any physical process. The mechanization and consistency of user-interface allows more intricate and complex pieces to be played by a single person. This paper identi fi es an opposite trend in musical interface design inspired by instruments such as the harp (when the strings are directly plucked by the user), the acoustic or electric guitar, the tin whistle, and the Neanderthal fl ute. These instruments have a directness of user-interface, where the musician is in direct physical contact with the sound-producing medium. We propose the invention of new instruments that are designed to have this expressive intimacy, while also allowing for their high degree of virtuosity. Previous examples included the poseidophone, an instrument made from an array of ripple tanks, each tuned for a particular note [4], and the hydraulophone, an instrument in which sound is produced by pressurized hydraulic fl uid that is in direct physical contact with the fi ngers of the player [5]. To better understand and contextualize some of these new primordial user interfaces, a broader concept of musical instrument classi fi cation has recently been proposed that con- siders the state-of-matter of the sound production medium as well as the state-of-matter of the user-interface [4]. In the early 1980s, author S. Mann formed the concept of an “ H 2 O rchestra” in which dihydrogen monoxide ( H 2 O ), in its various states of solid (ice), liquid (water), and gas (steam/vapour), as well as underwater plasma (fourth state- of-matter) were used to generate acoustic sound. These instruments represent all four “Elements”: “Earth” (solid), “Water” (liquid); “Air” (gas); and “Fire” (plasma), using H 2 O . The resulting four instruments are called the pagophone (Greek for “ice” and “sound” in the same way that “xylophone” is Greek for “wood sound”), the hydraulophone, the idratmosphone, and the plasmaphone. This paper further explores variations of the pagophone. In one embodiment of the pagophone, variously lengthed bars made of ice are struck (see Fig. 3), and the sound is ampli fi ed by a pickup in each bar, or one for all bars. The pickups can also be connected to bandpass fi lters, a separate fi lter for each note, to improve the sound. In other versions there are only 1 or 2 fi lters for 1 or 2 sticks, with input from a computer-vision idioscope [6] to de- termine which bar is struck. In another embodiment of the pagophone, there is only one piece of ice which sounds different depending on geospa- tial or other input data. In one embodiment, the pagophone is “played” on a skating rink (the ice that makes the sound) with skates (or, equivalently with skis on a ski hill, or with a toboggan, mak- ing sound from snow), each skate fi tted with a pickup, passed through a wearable computer to a wearable ampli fi er and speakers. We call this a “pagolin” to draw the analogy of the skates to violin bows. In one version the pagist (pagophone player) uses a musikeyer to select the fi lter (the “note”), while putting expression into the foot scrape or other sound. One version has two keyers, and holds one in each hand. Some but not all embodiments also use computer vision to do object location and adjust the pagophonic sound appropri- ately. For example, vision, radar, sonar, or lidar sensors or a combination of these watch the passing ice, and index through sampled audio fi les to create an effect similar to “scratching” a ...