THE CONTROL OF THE CHANT SYNTHESIZER IN OPENMUSIC: MODELLING CONTINUOUS ASPECTS IN SOUND SYNTHESIS

Transcription

1 THE CONTROL OF THE CHANT SYNTHESIZER IN OPENMUSIC: MODELLING CONTINUOUS ASPECTS IN SOUND SYNTHESIS Jean Bresson STMS: IRCAM-CNRS-UPMC 1, place I. Sravisnky Paris, France Marco Sroppa Universiy of Music and Performing Ars Urbansr. 25, Sugar, Germany ABSTRACT The specific model and conrol paradigm of he CHANT synhesizer raise ineresing issues and possibiliies for he conrol of coninuous aspecs in sound synhesis. New objecs for he conrol of CHANT in OpenMusic and in he OMChroma library provide high-level ools and srucures for inegraing hese aspecs in composiional frameworks. 1. BASICS AND HISTORICAL OVERVIEW The CHANT program [16] was developed in he early 80s for conrolling sung voice synhesis models. In his program sounds are produced by assembling synhesis modules mainly compound of FOFs 1 and filers, while conrol processes deermine he evoluion of hese modules parameers. The fine uning and conrol of differen parameers of he FOFs and filers allows o reproduce highqualiy vocal sounds by modelling he real behavior of he vocal sysem. Despie his voice-based model, he modular aspecs and conrol possibiliies of CHANT make i capable of generaing wide ranges of specra and sounds more or less relaed o a vocal simulaion. The conrol of he CHANT modules was iniially performed following a rule-based model. Algorihmic processes (rules) could be acivaed or plugged o he synhesizer and generae he values of a deermined se of parameers a a given conrol rae: An acive rule process knows abou he synhesizer s curren sae and abou he curren ime, and can se or modify any parameer accordingly. Predefined rules derived from signal and psychoacousic analyses have been implemened, such as he auomaic deerminaion of he forman relaive ampliudes or bandwidhs, or heir evoluions depending on he variaion of oher exernal or inernal parameers. More complex or specific rules could also be programmed and applied o personalize he synhesizer s behavior. The Formes environmen [14] was creaed shorly afer in order o handle he generaion and applicaion of such rules in higherlevel and larger-scale emporal srucures. 1 FOF synhesis (Foncions d Onde Formaniques, or Forman Wave Funcions [13]) consiss in defining funcions corresponding o he differen formans of a sound specrum, ha is, o generae he signal resuling from impulses going hrough differen resonan filers. The parameers of he FOFs (cenral frequency, bandwidh, ampliude, ec.) allow o deermine and conrol he posiion and shape of he formans, which is well adaped o he simulaion of he singing voice. In he 90s CHANT was pored and used in several differen conexs, such as he PW-Chan library in Pach- Work [11] or in he Diphone sofware [15], bu for he mos par, rules and oher conrol aspecs were lef ou of he synhesizer. More recenly, wo CHANT libraries were developed in he OpenMusic compuer-aided composiion environmen [3]: Chan-lib and OM-Chan. In Chan-lib 2 he synhesis kernel of CHANT was re-implemened in he Csound language, and he main conrol rules from PW- Chan were pored o OpenMusic. The work presened in his paper concerns OM-Chan and is inegraion o he OMChroma sysem [1]. I uses he original CHANT kernel and provides means o generae and forma adequae parameers for his synhesizer, which consiues an original complemenary approach regarding conrol paradigms and applicaions CONTROL OF CHANT SYNTHESIS Sound synhesis wih CHANT is performed and conrolled a wo differen layers: a synhesis pach runs coninuously and is parameers are periodically modified by exernal conrol changes (see Figure 1). The modules in he synhesis pach are FOF banks (FOF generaors acivaed by a fundamenal frequency exciaion signal), filer banks, noise generaors and inpu sounds. 4 The laes CHANT implemenaion is conrolled via files in he SDIF forma [17] where all parameer values and evoluions are se and sored in precisely imeagged frames. These parameers changes are neiher necessarily equally sampled nor synchronous: each module can be conrolled individually a any momen or a any rae. Beween each specified value change for he synhesis parameers, CHANT performs linear inerpolaions producing smooh variaions and ransiions beween he successive saes of he synhesizer s modules. This conrol scheme induces an original coninuous approach o he conrol of sound synhesis, which is concepually differen (and complemenary) o he even-based approach used by many exising synhesis conrol sysems. 2 Chan-lib by Romain Michon, hp://elecro-m.fr/ romainm/ 3 See [7] for a descripion / comparison of Chan-lib and OM-Chan. 4 In heory he pach modules can be combined freely, bu he curren CHANT implemenaion only provides a se of predefined paches idenified by a pach number (e.g. Pach 0 = FOFs only; Pach 1 = FOFs + Noise Filer; Pach 2 = Noise + Sound Filer; ec.)

2 1 CHANT pach #1 (FOF, Noise, Filer) FOF bank Noise FOFs Fundamenal freq. Forman parameers: - freq1, amp1, bw1,... - freq2, amp2, bw2, Filer Pach sae parameers: Parameers inerpolaion beween 1 and 2 2 Noise Disribuion, Ampliude Filers - freq1, amp1, bw1,... - freq2, amp2, bw2, Figure 1. The conrol of he CHANT synhesizer: imed sae modificaion and coninuous inerpolaions. n case coninuous evoluions are conrolled by processes compuing periodically he signal or sound synhesis parameers, possibly saring from reference saes also inegraed in he conrol level. 6 A a meeing poin of hese wo complemenary approaches, composiion wih sound synhesis should herefore no only posiion synhesis evens and parameers in ime, bu also access he coninuous srucures of sound exures. This dual concepion requires dedicaed sysems for he specificaion and conrol of sound characerisics. 4. OM-CHANT A oolki in he new OpenMusic OM-Chan library allows o forma conrol srucures and creae SDIF files adaped o he conrol of CHANT (see Figure 2). Uiliies are also provided in order o faciliae seing he CHANT parameers (daa base of forman values, implemenaion of he differen CHANT predefined rules, ec.) 3. CONTINUOUS VS. DISCRETE PARADIGM The disincion beween discree and coninuous emporal srucures in sounds is a long-sanding issue [8]. Indeed, i is no always sraighforward o discriminae in sounds and sound generaion processes wha comes wihin discree or coninuous ime: Sounds can be considered as coninuous objecs (acousic waves wih coninuously varying inernal/specral morphologies), or as discree srucures (sequences of samples, for digial sounds, bu also a a higher level, as significan or self-consisen musical objecs). In he radiion of he Music N languages [12], he noe concep has been preserved as basic specificaion in sound synhesis processes: There is a clear disincion beween he sound microsrucure (DSP processes defined in he synhesis insrumens ) and he score where discree evens are scheduled. Composiional issues herefore come under discree ime, organizing evens inside he sound, or organizing sound evens hemselves. Coninuous aspecs (for insance modulaions, evoluions or ransiions beween saes of he parameers) are mosly handled inside evens using saic srucures (ables or breakpoin funcions, for insance) or appropriae modules wihin he DSP pach. 5 This approach, however, makes i difficul o handle and conrol he ransiions and ariculaions beween evens, which occur naurally and are fundamenal in he percepion of sounds. On he oher hand, sysems like CHANT/Formes, bu also oher funcional languages such as Arcic [9], end o consider sound as a unique coninuous flow undergoing global composiional processing (from microsrucure o high-level musical forms). In his 5 Soluions o generae more elaboraed ime funcions in music or synhesis environmens have been proposed, see for insance [2, 10]. Figure 2. OM-Chan: Generaion of SDIF daa for he conrol of CHANT in OpenMusic. OpenMusic processes using OM-Chan generae a sequence of SDIF frames conaining values for he differen parameers of he synhesizer s modules. 7 SDIF conrol frames can be arbirarily disribued in ime, eiher very sparsely, in which case CHANT will inerpolae beween 6 Real-ime sound processing environmens ofen perform such coninuous conrol of he synhesis parameers bu do no allow high-level musical formalizaion of he relaed processes [18], and are herefore no addressed in he curren discussion. 7 The specificaion of he SDIF conrol srucure for CHANT is available a hp://sdif.sourceforge.ne/sandard/sdif-sandard.hml. See also [6] for an overview of SDIF daa manipulaion ools in OpenMusic.

3 he specified values, or precisely sampled, describing specific and fine parameers evoluions (see Secion 2). The conrol approach emphasized in OM-Chan herefore follows he CHANT paradigm and circumvens he usage of imed evens in he conrol of sound synhesis: Processes of arbirary complexiy can be programmed o generae he coninuous evoluion of he differen synhesis parameers. coninuous evoluions can be specified for all or par of he synhesis parameers during he even ime inerval. Each even is responsible for he generaion of a se of ime-agged SDIF frames. A sored lis of CHANT evens herefore allows o generae he SDIF file conaining he full conrol sequence for a given CHANT pach, hen synhesized using OM-Chan ools (see Figure 3). 5. CHANT EVENTS: AN IMPLEMENTATION IN OMCHROMA Discree evens specified wih ime localizaion and exen are convenien for composiional conrol, bu no sraighforward o inegrae in he OM-Chan oolki and concepual framework [7]. The consideraion of imed evens wihin a coninuous ime flow and he descripion of heir morphology and ariculaions imply specific decisions. An exension of he OMChroma sysem o he conrol of CHANT synhesis, which we creaed recenly, inroduces hese conceps in he composiional environmen. OMChroma is a sysem for he conrol of sound synhesis inegraed in OpenMusic, where he main conrol srucures are ime-agged marices represening compound sound evens. The differen componens of an OMChroma marix describe parameer values for differen insances of a synhesis module [1]. This sysem was iniially designed o conrol Csound or concepually similar sound synhesizers based on he even concep (he marix componens generae he differen score saemens ). I was however mean o be modular and easily exensible o oher sound synhesizers. This new exension will indeed bring new synhesis possibiliies o OMChroma, while providing a srucured framework for he emporal organizaion and conrol of he CHANT processes CHANT Even Classes Five new classes have been creaed in OMChroma o represen CHANT evens. Each class is aached o an elemen of he CHANT pach, and is insances will deermine and conrol he evoluion of his elemen s parameers during a given ime inerval. CH-F0 represens FOF fundamenal frequency evens, CH-FOF represens FOF formans evens (he combinaion of CH-F0 and CH-FOF values deermines he full parameers for he FOF generaor), CH-FLT represens filer evens, CH-NOISE represens noise evens, and CH-SND represens sound evens (audio inpu playback from a sound file). 8 CHANT classes have an onse and a duraion slo, and can be considered as evens organized in a global emporal conex. Evens can have an arbirarily long duraion, and 8 Noe ha only CH-FOF and CH-FLT are acual marices, whose columns represen he differen componens or formans of a FOF or filer bank and whose rows represen heir differen parameers. CH-F0 and CH-NOISE are one-dimensional descripions, and CH-SOUND is a simple reference o a file on he disk. Figure 3. CHANT synhesis in OMChroma: Using highlevel srucures o represen CHANT evens Coninuous Conrol Two conrol processes from he original CHANT program have been implemened in OMChroma for he seing and modulaion of differen synhesis parameers and he general design of he inernal morphology of CHANT evens: he jier and he vibrao. 9 Boh effecs can be applied o he iniial values eiher by addiion or muliplicaion (see Figure 4). Anoher conrol uiliy available is he pulse-rain funcion, which generaes impulses wih precise uning of consan or coninuous values of he period, ampliude, aack and release, ec. This funcion is principally mean o generae ampliude envelopes (e.g. for noise generaors, see Figure 5) Temporal Represenaion using he Maquee The OpenMusic Maquee can be used o represen composiional objecs and processes embedded in ime srucures, including he parameers of a synhesis process [5]. I consiues a convenien inerface o represen CHANT synhesis evens in a emporal conex and beer handle and conrol heir emporal characerisics (see Figure 6). 9 Jier and vibrao produce respecively aleaoric variaions and sinusoïdal modulaions wih given frequencies and ampliudes around iniial, consan or coninuous parameers.

4 Figure 6. CHANT objecs in he OpenMusic Maquee. This process is funcionally equivalen o he pach in Figure 3. Each box represens an OpenMusic objec or pach producing a CHANT even. In a maquee, he onse and duraion of he evens are represened by he posiion and exen of heir conaining box. Compuaion of he whole emporal srucure can be riggered, allowing o synhesize and hear he resuling sounds. Figure 4. Applying a vibrao and a double jier o he F0 from Figure 3. Effecs are applied by addiion a a sampling rae specified in param-process. 6. EVENTS PROPERTIES Musical evens sar a a specific ime and generally run for a given duraion. In order o obain he seady sae of a se of parameer during a given ime inerval, he CHANT evens duplicae heir values a wo momens b and e deermined by heir beginning ime and duraion (see Figure 7). Beween hese wo momens, he defaul synhesizer behavior will produce a sable sound (inerpolaion beween wo idenical saes). Concreely, his simple process occurs a wriing he daa frames corresponding o he CHANT objec in he SDIF file, ha is, jus before synhesis. If no coninuous evoluion exiss inside he evens, wo SDIF frames are produced for each one of hem a b and e. E b e Figure 7. Represenaion of an even in he coninuous ime line. Figure 5. Using pulse-rain o generae he ampliude envelope of a noise even. Sequences of evens may however leave possible ambiguous inervals in he ime line (see Figure 8). In his case, CHANT would in principle inerpolae and produce a coninuous ransiion beween he wo evens (i.e. beween e 1 and b 2, from he final sae of o he iniial sae of ). In order o obain silence beween he successive evens, anoher opional aribue of he CHANT evens makes hem duplicae again heir se of parameers from b and e respecively o b + ε and e ε, wih ampliude values

5 b1 e1? b2 e2 Figure 8. Represenaion of a sequence of evens in he coninuous ime line. se o 0 a b and e (see Figure 9). In his case he value ε will deermine a fade-in/ou ime during which he ampliude is inerpolaed from 0 o is value in En beween b n and b n + ε and from he value in En o 0 beween e n ε e n. Beween he successive evens, he synhesizer s parameers are sill inerpolaed bu he ampliude is zero. b1 b1+ε e1-ε e1 b2 b2+ε e2-ε Figure 9. Generaing silence and fade-in/fade-ou beween CHANT evens. The case where wo evens overlap is also worh being considered. In a configuraion such as he one in Figure 10, he overlapping of wo evens (wih seady inernal parameers) would produce he following defaul behavior: Sae a b 1, hen inerpolaion from o beween b 1 and b 2, inerpolaion from back o beween b 2 and e 1, and finally inerpolaion from o beween e 1 and e 2. b1 b2? e1 Figure 10. Overlapping evens. e2 A simple rick allows o produce a more inuiive resul: by swiching he parameers values a e 1 and b 2, he parameers become sable beween b 1 and b 2 and beween e 1 and e 2. On he overlapping inerval (beween b 2 and e 1) he synhesizer will inerpolae beween he saes and, which is a more likely desired ransiion behavior (see Figure 11). This mehod may work in some cases, bu some problems remain. If coninuous evoluions are specified wihin he evens, i is simply no applicable: Parameers from and would be inerleaved in he conrol flow, which would produce unpredicable (and probably undesired) effecs in sound synhesis. A soluion in his case is o e2 b1 e1 b2 e2 Figure 11. Generaing a ransiion on he evens overlapping inerval. rescale and shrink he parameers curves from he original even duraion o he seady inervals only, hen o perform he inerpolaions beween ending and iniial saes of he evens. Oher soluions could simply be o cu he evoluion a he ime were overlapping/ransiion sars, or o define a way o coninuously go from one se of parameers o he oher (as a kind of fade-in/fade-ou ransiion). Due o he mulipliciy of choices and subjecive decisions involved, he possibiliy o program and personalize he process seems necessary in order o allow for he definiion of specific behaviors, he personalizaion of inerpolaion profiles, or he applicaion of individual ransiions for he differen synhesis parameers. 7. CONCLUSION AND FUTURE WORKS In addiion o giving access and renewed conrol possibiliies for his synhesizer, he use of CHANT in OpenMusic allowed us o invesigae new aspecs in he domain of he conrol of sound synhesis, and o propose adequae ools inegraed in he compuer-aided composiion environmen. The OMChroma objecs presened in his paper, in paricular, migh allow o achieve advanced and powerful conrol over boh high-level composiion and fine uning of he coninuous evoluion of composiional srucures driving CHANT synhesis. Even superimposiion and overlapping are probably he main issues remaining o address. The conrol of ransiions beween successive evens could be implemened eiher as an addiional funcional characerisics of he CHANT even objecs or as independen srucures superimposed o a sequence of evens. Even hough, CHANT synhesis remains inherenly monophonic: Transiions are always pairwise and can be performed beween wo overlapping evens only. In he curren sae of he synhesizer, i is no possible eiher o imagine several simulaneous voices made of differen FOFs and independen inpu frequencies.voice polyphony can however easily be simulaed by generaing differen files and mix hem using he sound processing ools available in OpenMusic [4]. The maquee inerface would moreover provide a hierarchical view and conrol over accordingly srucured processes. Anoher direcion o explore concerns he spaializaion, or disribuion of he differen componens of he

6 CHANT paches (FOFs, filers, ec.) over a given number of audio channels. This feaure is suppored by he CHANT synhesizer and can be conrolled for each individual synhesis componen. 8. REFERENCES [1] C. Agon, J. Bresson, and M. Sroppa, OMChroma: Composiional Conrol of Sound Synhesis, Compuer Music Journal, vol. 35, no. 2, [2] D. P. Anderson and R. Kuivila, Coninuous Absracions for Discree Evens Languages, Compuer Music Journal, vol. 13, no. 3, [3] G. Assayag, C. Rueda, M. Laurson, C. Agon, and O. Delerue, Compuer Assised Composiion a IR- CAM: From PachWork o OpenMusic, Compuer Music Journal, vol. 23, no. 3, [4] J. Bresson, Sound Processing in OpenMusic, in Proceedings of he Inernaional Conference on Digial Audio Effecs, Monréal, Canada, [5] J. Bresson and C. Agon, Temporal Conrol over Sound Synhesis Processes, in Proceedings of he Sound and Music Compuing Conference, Marseille, France, [6], Processing Sound and Music Descripion Daa Using OpenMusic, in Proceedings of he Inernaional Compuer Music Conference, New York / Sony Brook, USA, [7] J. Bresson and R. Michon, Implémenaions e Conrôle du Synhéiseur CHANT dans OpenMusic, in Aces des Journées d Informaique Musicale, Sain-Eienne, France, [8] R. B. Dannenberg, P. Desain, and H. Honing, Programming Language Design for Music, in Musical Signal Processing, C. Roads, S. T. Pope, A. Piccialli, and G. DePoli, Eds. Swes and Zeilinger, [9] R. B. Dannenberg, P. McAvinney, and D. Rubine, Arcic : A Funcional Language for Real-Time Sysems, Compuer Music Journal, vol. 10, no. 4, [10] P. Desain and H. Honing, Towards Algorihmic Descripions of Coninuous Modulaions of Musical Parameers, in Proceedings of he Inernaional Compuer Music Conference, Banff Cener for he Ars, Canada, [11] F. Iovino, M. Laurson, and L. Poier, PW-Chan Reference, IRCAM, Paris, France, [12] M. V. Mahews, Ed., The Technology of Compuer Music. MIT Press, [13] X. Rode, Time-domain Forman-wave Funcion Synhesis, Compuer Music Journal, vol. 8, no. 3, [14] X. Rode and P. Coine, Formes: Composion and Scheduling of Processes, Compuer Music Journal, vol. 8, no. 3, [15] X. Rode and A. Lefevre, The Diphone Program : New Feaures, New synhesis Mehods and Experience of Musical Use, in Proceedings of he Inernaional Compuer Music Conference, Thessaloniki, Greece, [16] X. Rode, Y. Poard, and J.-B. Barrière, The CHANT Projec: From he Synhesis of he Singing Voice o Synhesis in General, Compuer Music Journal, vol. 8, no. 3, [17] D. Schwarz and M. Wrigh, Exensions and Applicaions of he SDIF Sound Descripion Inerchange Forma, in Proceedings of he Inernaional Compuer Music Conference, Berlin, Germany, [18] M. Sroppa, Live elecronics or... live music? Towards a criique of ineracion, Aesheics of Live Elecronic Music - Comemporary Music Review, vol. 18, no. 3, 1999.