Music from an evil subterranean beast

Transcription

1 Music fom an evil subteanean beast Novembe 4, 2011 Abstact Two ecent compositions have capitalized on the geat expessive ange of a custom-designed music synthesis algoithm. The "Animal" plays a pat in Tomato Quintet (a music installation) and Phaso (a contabass and compute piece). The algoithm is played with live contols, espectively, updates fom envionmental sensos and signals fom a senso bow. Nuanced deections of paamete values elicit chaacteistic and sometimes quiky behavio. The bounded set of sonic behavios go into making up an identiable pesonality whose moods o tempeaments can be tavesed in the music which exploits it. "The computeized sounds wee spacey and sometimes menacing, sounding at times like Chafe was tying to tame an evil subteanean beast." [1] Animal's algoithm is compised of two paallel esonatos with the logistic map in thei feedback path. Animal can be categoized as a "meta-physical" model o modeling abstaction as seen in ealie integations of families of physical models [2] and ecombinations of physical model components in physically-impossible ways [3]. Abstaction opens the doo to inclusion of mathematical "pats" fom othe domains. In Animal's case, the logistic map[7] has been boowed fom population biology. 1 Intoduction Building chaacte into musical synthesis is a quest simila to giving life to chaactes in compute gaphics. The quest fo ceation of ecognizable pesonalities is basic in time-based at foms, some of them vey old whethe theate, novels, lm, animation, o othe media. In the musical ealm, physical instuments ae identiable by type e.g., ute and can be manpulated to ll distinctly dieent musical oles. One identity can assume a ole which mimics anothe's (ute pecussion) o boows fom exta-musical identities (bid song). Expession comes into the game when a musical voice communicates a musical something o idea. This could be an idea like a melodic constuction o gestual gue, o it could be a modest change in compotment. No list of these somethings could eve be complete. Of inteest hee, ae the essential components of the caies of musical ideas. In conventional usage, these ae easily descibed and ae tagets fo modeling: the instument is that which sounds when manipulated by a pefome. The pefome is esponsible fo communicating ideas. They may be inventing the ideas on-the-y as in impovised music o atfully endeing ideas which have been pe-baked into a composition. 2 Easy instument-ness Algoithms based on geneal-pupose synthesis techniques like additve synthesis and waveshaping (which includes FM) can be factoed into multiple instument identities. A specic synth instument implies an algoithm tuning endowed with instument identity. The Animal algoithm cannot be factoed into moe than a single identity. To take this a bit futhe fo the sake of claity, FM's many algoithms and thei timbe tuning possibilities have poduced a magnicent ange of synthesis instuments acoss many families (bass, winds, keyboads, vocals, and new identities). Voicing o tuning an FM algoithm is an at in its own ight equiing specialized knowledge, intuition and some amount of luck [4]. Voicing in this sense is ceating both a coase identity (ecognizable) and a nely-tuned instument esponsive to the pefomance of subtle shades of expession (like voicing a piano). 1

2 Figue 1: The Animal algoithm is two paallel esonatos with the logistic map in thei feedback path. In contast, Animal's algoithm is mono-identity. No amount of voicing distots its one identity. The same can be said of many algoithms such as the Kaplus-Stong plucked sting [5] belonging to the physical model class of techniques (though not all). Futhe endowing this one identity with chaacte is up to the pefome. In the case of Animal, two pefomes will be discussed below. Fist, the algoithm itself will be descibed. The idea that non-linea iteated maps might be of inteest in music synthesis dates back to studies of physical acoustics of instuments in the ealy 80's [6]. Self-sustained oscillations wee newly descibed as dynamical systems. The edge tone instuments (utes), eed instuments and bowed stings wee shown to be negative feedback systems coupling a esonant system to a non-linea excitation mechanism. Animal's paallel esonatos ae delay / low-pass lte units with delay times in the pitch ange. Fistode Buttewoth low-pass ltes ae used in seies with the delays. The logistic map x n+1 = x n (1 x n ) is applied to the sum of the esonato outputs and fed back to thei inputs. A dc blocking lte is applied to the output and a tiny dc souce biases the system to kickstat it and avoid computing of subnomal numbes. The algoithm is self-excited as opposed to having the usual extenal enegy souce common in physical models (which ae blown, bowed o stuck in simulation). The use of dual esonatos in feedback though a chaotic system poduces acoustical behavios including mode quenching, dual sidebands (fom AM), peiod doubling, multimodal egimes and vaious distotions. The basic paametes available ae gain length of esonatos of esonato delays fequency of esonato lte cutos of logistic map epesenting the ate of combined epoduction and stavation in population dynamics [7] The algoithm doesn't mimic any paticula physical instument intentionally though at times it has a clainet-like o bassy tone that depends on paamete manipulations. It does intend to poduce a palette of sounds whose time-vaying tansitions ae ich in featues, lling simila spaces of tempoal / spectal vaiation in which odinay instuments and human voice ae also pojected. 3 Rening chaacte What does it mean to say that ceating chaacte is up to the pefome? Fist of all, it equies that identity of instument type be stable. O, if multi-identity, that the choice of identity is being made by the pefome. Eithe way, the choice of instumental souce is bound and sounding it is in thei hands. A melodic gue with an always coaky timbe when at its most lethagic, and a shap cisp, ippling, piecing 2

3 Figue 2: Tavesing atios of esonato delay lengths fom 1.04 to 8.0. One esonato delay length is held constant while the othe's length is shotened. Vaying atios ceate a vaiety of pitches simila to oveblowing o sul ponticello eects. Figue 3: Ramping up feedback gain to both esonatos fom 0.0 to 1.0. Animal is self-excited by the slight bias injection which is constantly pesent. The algoithm will not speak with a feedback gain of 0.0. Inceasing feedback gain enegizes the system and tonal quality taveses fom muted to billiant eventually hitting modes which ae gavelly and foceful. quality when awakened and leading would constitute a ecognizable chaacte. As a thought expeiment, call this one Animal `A' and conjue an Animal `B' of contasting sets of elements. Animal `B' might simply be a stuttee that ties to hit pitches but only spoadically manages it. Both `A' and `B' ae ecognizably instances of Animal. They ae both necessaily constucted fom the set of sonic moves aoded by Animal's identity so they shae the identity but die in chaacte. As musical voices they ae sepaable and could play contasting oles. O because this is music and anything goes, these chaactes could hold foth with a duo and the duo could stat badly and end happily, etc. all up to the musical ideas being constucted. Can thee be musical expession without chaacte? In simplest tems, no, because if expession is the planting of ideas fom one consciousness into anothe, as listenes we tend to constuct a souce communicating to us even in its absence. Ascibing chaacte is the essence of this tendency. We conjue the pefome whethe the povenance of the music is human o mechanical. A obot is a valid chaacte, as ae the actos in the ecoded sound of a topical ain foest. Once we take it in as music that is communicating to us its souce entities ae endowed with what can be called chaacte. If that fails, does the music fail? Can the ainfoest itself be communicating? (fo my pat: yes, music sometimes fails and yes, we can hea music in many ways and things) The following will illustate timbal moves which ae available to the pefome constucting a chaacte with Animal. As a lab expeiment, all but one paamete is held at a its medium value. The independent paamete is vaied in a linea amp fom a low value to a high value. Many acoustical featues pesent themselves in these isolated contexts. In paticula, envelopes shaping amplitude and spectal evolution pitches eects suppoted by hamonic and subhamonic seies, possibly multiple at the same time simila to oveblowing, sul ponticello, sul tasto, and ceaky voice non-hamonic sideband modulation and distotion 3

4 Figue 4: Sweeping the balance between esonatos. With esonatos holding non-coincidental tunings of delay length and/o lowpass fequency, e ects can be deived fom alteing thei elative contibution. The gue shows thee pitch egimes obtained, including subhamonics. Figue 5: Ramping the lowpass fequency fom 550 to 9000 Hz. Akin to inceasing feedback gain, but without the gavelly sound in Figue 3, the highe lowpass cuto fequency towad the end of the sound ceates a bightness e ect. Figue 6: Tavesing atios of esonato lowpass fequencies fom to 4.0. Almost indetectable in the sonogam, but visible in a zoomed spectal slice, the atio of esonato lowpass fequencies ceates a quality shift by tavesing a egion with sidebands. The oveall pecept is stongly pitched. An in ection in tone is caused by sidebands gowing and diminishing in stength. Figue 7: Ramping up the paamete of the logistic map. Inceasing the logistic map paamete the second (octave lowe) subhamonic as seen in the end of the gue. 4 gows

5 4 Applications To summaize, Animal is a compute algoithm manifesting a single instument identity. Fom it, its pefome can constuct pesonalities of dieent chaacte t to the intended musical ole. Its sonic moves o capabilities ae intended to be manipulated expessively. The pefome is fee to constuct chaactes that ae as convincing as the music itself. Its application in the multi-media piece Tomato Quintet stetches this notion to its limit. Its pefomes ae ipening tomatoes. A tansfeence is its goal, in which listenes ascibe to the tomatoes the quality of chaacte which they infe fom the music. Tomato Quintet is a digital museum / galley installation employing eal-time music geneation. Its coceato, Geg Niemeye, consides it a new media still life. The music contasts slow time scale mateial (the ipening pocess) with much faste time scales (coesponding to human activities and attention). Animal povides chaacteistic music on both levels. An ambient voice consists of pitched mateial ceated with the algoithm and diven by slowly-changing signals fom CO 2 gas level sensos nea the ipening tomatoes (othe ambient layes use othe algoithms and include sounds of wind and tansient, pecussive phenomena eminiscent of hail on a oof). Faste time scale guations ae also synthesized using Animal and come fom motion of acceleometes induced by visitos touching the senso systems. Phaso is a concet piece fo solo contabass plus compute-geneated sound. The composition employs Animal (along with seveal othe mateials). A chous of Animals achieve a pitched textue pefomed via bowing gestues. The bassist uses a special-pupose bow, the K-Bow, to povide gestue signals fom its acceleometes and stain gauges which ae connected to the accompanying sound geneating compute via Bluetooth. The chaacte evoked is one of pitch-based stuctue whose modulations ae intespesed with abupt hythmic supises and textual intusions. Refeences [1] H. Ying, Aual challenge, Global Times (2011) [music eview 25-May-2011] [2] P. Cook, A Meta-Wind-Instument Physical Model, and a Meta-Contolle fo Real Time Pefomance Contol, Intenational Compute Music Confeence, San Jose (1992) [3] C. Buns, Heo and Leande (2003) [composition fo eight-channel audio] [4] J. Chowning, D. Bistow, FM Theoy & Applications - By Musicians Fo Musicians, Tokyo: Yamaha (1986) [5] K. Kaplus, A. Stong Digital Synthesis of Plucked Sting and Dum Timbes, Compute Music Jounal (MIT Pess) 7 (2): 4355 (1983) [6], M. McIntye, R. Schumache, J. Woodhouse, On the oscillations of musical instuments, Jounal of the Acoustical Society of Ameica, 74: (1983) [7] R. May, Simple mathematical models with vey complicated dynamics, Natue 261 (5560): (1976) 5