Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011
HYPOTHESISHYPOTESIS FOR THE FOUNDATION OF A LAPTOP ORCHESTRA
Marco Gasperini Meccanica Azione Sonora [email protected]
ABSTRACT been, but as for the use of the word, up to our our days (at least the last two centuries), it is possible to trace In this article some theoretical issues about the some constant features (among many others) which are foundations of a laptop orchestra will be presented, worth considering in the present perspective: prompted by the actual involvement in the design of the • it is a relatively wide instrumental group (there S. Giorgio Laptop Ensemble in Venice. The main are no voices); interest is in the development of an eco-systemic [10] • it is divided in sections of instruments of similar kind of communication/interaction between performers. timbres or of similar playing techniques (strings, First some phenomenological features of orchestra and woods, brass, percussions, etc.); laptop will be reviewed, followed by a brief summary of • it is generally conducted. the history of laptop orchestras. A coherent system Starting from these considerations it can be said that according to the premises will then be developed an orchestra is characterized by a specific sound quality defining what will be an orchestral player and what will which depends on the mix of all the instrumental sounds be a conductor and how they will be musically produced by the musicians, that is to say by all the interacting. Technical issues regarding the set-up of the different timbres of the instruments, by their distribution orchestra and the means of communication between the in the performance place and, last but not least, by the elements of the orchestra will then be approached. The quality of the performers and of their instruments. most versatile solution for this last issue (audio An orchestral player is responsible: communication) has been found exploiting possibilities • of playing his/her part, as close as possible to the of Local Area Network communications on ethernet indications contained in the score; interfaces. Finally the partial results of the research will • of the musical quality of the produced sounds. be summarized. Each orchestral should have developed, through years of practice and studies, technical and musical skills in a 1. INTRODUCTION very high degree on an instrument which, besides a more or less wide range of variations of its timbric and Based on recent research in the development of laptop playing techniques, sounds always the same, it always orchestras [5] [13] [14] [15] [21] [23] [24], digital manifest its systemic identity, and for this reason is ensembles and diffused network performances [1] [3] recognized. [6] [7] [12] [16] [26], a laptop section has been Beside all this the musicians are subject to a developed according to the hereafter described performing stress caused by the care in following the architecture. A similar musical network has already score and the director, and a physical stress caused by been developed and tested in the frame of the S. Giorgio the playing position and by the gestural expressiveness Laptop Ensemble in the course of the 2009 in Venice typical of each instrument. It can be said that the good [8]. The author will try to show how could be developed quality of an execution depends on the way a similar from scratch a musical ensemble made up by laptops, stream of strains (by no way to be intended in a negative taking care of evolving from basic considerations on the sense: a string must be strained to be musically useful) nature of instruments and inserting the least possible is musically managed. number of heterogeneous elements. The director is responsible of this and of all the other global sounding factors of the whole ensemble: 2. SOME PHENOMENOLOGICAL ASPECTS OF • the acoustic mixture, which depends on the ORCHESTRA AND LAPTOP intonation, the use of the playing techniques of the various instruments, the dynamic balance Orchestra is a Greek word whose etymon may be traced between sections, etc.; back to the verb to dance. According to this, it was used • of the rhythmic precision and synchrony which to name the space between the stage and the audience in is a fundamental feature for the perception of the the ancient Greek theatre, a space where there used to orchestra as a unified sounding body, internally take place the performances of the chorus. articulated; It is not the aim of this paper to attempt an exhaustive • of the actual realization in sounds of what is description of all musical, historical and social features contained as signs in a musical score. of such a complex system as the orchestra is and has The figure of the director, as has been defined from the nineteenth century onward, does not play a sounding 602 Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 part in the performance, that is to say that he does not communication between digital machines. The main has a musical part in the score but he has to control and interesting fact is the shift of the function of the manage all the parts. computer from a compositional instrument to a As for the first term it is a definitely primitive term: performance instrument: the members of these laptop is the abbreviation for laptop computer which is ensembles must design the network of relationships referred (as his predecessor desktop computer) to the which should exist between their devices, according to position in which a portable computer may be held. the performance strategies (and so instrumental) they As for its acoustical and playing qualities a laptop have adopted; moreover they should design their sound (cfr. [24]): production algorithms which they will be playing and • is a neutral instrument (or, said otherwise, not merely use to produce sounds to be recorded on passive), not directly linked to a specific intrinsic tape. sonority (apart from that of the CPU fan or that produced by pressing the keyboard); 3.2. …to the Third millennium • is potentially ever-changing: the algorithm used However not before the XXI sec. was it possible to for the local production of sounds may change conceive a laptop orchestra for the wide diffusion of the during the same performance, making it technological facilities (network communication, wide impossible to univocally link the source and its bandwidths, stable and quite standardized protocols, acoustical appearance, even for the fact that its powerful processors, compatibility issues, etc.). actual sound source (the loudspeaker/s) may be Now some laptop orchestra experiences will be placed far from the sound-computing engine; reviewed. • does not need the development of specific The most active make-up, both for the documentation playing techniques, at least not comparable to the produced on their activity and for the public instrumental technical skills requested to an performances, is the Princeton Laptop Orchestra1 orchestral player; (PLORK), founded in 2005 by Dan Trueman and Perry • it does not induce any physical nor performing stress. About this fact, Dan Trueman reports the Cook [21] [24]. The main features of this ensemble, critics made by a spectator of a performance of compounded by approximately fifteen people, are: the Princeton Laptop Orchestra: “As far as I • the orchestra is placed on the stage; could tell, they were all just checking their e- • each member has its own laptop, controllers and mail”[24]; sound diffusion system (a six channels hemispherical speaker, permitting different • in any case there is no direct nor necessary link between the gestural expressiveness and the patterns of sound radiation) placed nearby;
sounding result. • the overall sound of the orchestra is localized; • control signals may be transmitted through a Local Area Network by means of the Open 3. A BRIEF HISTORY OF LAPTOP Sound Control (OSC) protocol [27]; ORCHESTRAS • on some occasions acoustical instruments have been included in the performance. 3.1. From the eighties… The composer who wants to write for them should at first imagine and design a possible interaction between With the term laptop orchestra is intended a reasonable the performers and then design the environment itself group of musicians (orchestra) each of them exerting which will become the instrument of an orchestral. The his/her musical skills by means of a portable digital compositions written for PLORK use the figure of the computer (laptop). This kind of musical group may be conductor in heterogeneous ways. seen as one of the possible outcomes of the musical Others laptop orchestras whose activity may be research developed through technological instruments in connected with that of PLORK are the Oslo Laptop the last seventy years. Orchestra (OLO), founded in 20072, and the Standford This perspective was foreshadowed (how much Laptop Orchestra3 (SLORK), founded in 2008 [25]. unconsciously?) in the title of the first historical article A different attitude is that of the Milwaukee Laptop on computer music made widely available: “The Digital Orchestra (MiLO), which defines itself as “a collective Computer as a Musical Instrument” by Max Mathews of musicians and artists dedicated to live audio/visual [18]. performance”4. It is a non-hierarchical ensemble, The first experiments in this field were carried on as inclined toward the free improvisation, in which each soon as personal computers were made available on the member is free to bring his/her musical approach, may market, in the second half of the Seventies; this large use the software of his/her choice, is free to play availability made it possible to use the computers outside of the great institutions and laboratories. At least 1 PLORK:
603 Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 alongside acoustical instruments as well or use some and coherently an ensemble. Although it was not video processing. They developed custom network explicitly present in the premises of this work, the facilities with the software pure-data [20] to improve the outcome get very near to the research on sound eco- interaction between performers, named NRCI [5] [23] systems carried on by the Italian composer Agostino Di and based on the protocol OSC. This facilities are used Scipio [10] [11]. to broadcast to the orchestra the performance data of Let’s consider the setting-up of an audio network each performer: rhythm, melodic envelope, amplitude, with an input signal x(t). In relationship to an audio etc.; each member is free to choose which data to input signal a computer may be considered as a delay receive and how to relate the received data to his/her unit with an arbitrary transfer function which, in the sound processing. simplest case, would be an unitary pulse: in this case the Others laptop orchestras are: the Carnegie Mellon system will be linear and its output, given a fixed delay Laptop Orchestra (CMLO), founded by Roger B. of N samples, will be: Dannenberg, addressed to didactical issues [9]; the Worldscape Laptop Orchestra (WLO), the largest y(t) = x (t-N) (1) ensemble of this type, set-up for just one concert [14]; the Linux Laptop Orchestra (L2ORK5); the The delay is due to the size of the memory buffer Huddersfield Experimental Laptop Orchestra6 (HELO), (I/O vector) used by the audio interface to carry on the an ensemble with interesting suggestions about A/D and D/A conversions. The I/O vector is linked to rehearsals practice [15] 7. the CPU clock: given a same amount of operations the Finally I would like to mention the S. Giorgio Laptop I/O vector size could be decreased as the processor Ensemble, founded in Venice in 20098, who gave its power will increase. first concert in 11.07.2009 at the Foundation “G. Cini” in the island of S. Giorgio Maggiore [8]. This 5. BUILDING THE ENSEMBLE experience has give birth to the research that will be here presented. The work of this group is witnessed by a 5.1. Step one printed score for string quartet and laptop ensemble9. By connecting in series several of the previously described elements, an elementary hierarchical chain of 4. THE LAPTOP AS A MUSICAL INSTRUMENT N computers could be obtained (see Figure 1). The first element S (server) generates the signal, which traverse A laptop musical ensemble will be, by definition, an each client. Each element Cn has a local output outCn ensemble of musicians (performers) each using a laptop which reflects the instantaneous state of the client, and computer, leaded by a conductor. The computers are will introduce in the audio chain a certain dCn samples connected to form a network of musical information. delay. The choice of a single source of audio signal is The whole complex of algorithms used locally by a due to consideration about economy of means and unity computer will be called instrument; each instrument will of results: given a certain audio input each client will be played by the performer through some variable repeat it after a certain delay time and the whole control parameters. One element (built-up by a ensemble will emerge as the succession of a same computer and an instrument, played by a performer) of acoustical sign (canone all’unisono). the network will be called client, while the conductor’s instrument will be called the network’s server. The aim is that to create a system capable of some autonomous dynamics in sound starting from the intrinsic features of the basic elements. To this end it is necessary to consider the devices in their true nature, i.e. to catch their phenomenological essence; doing so will permit, in a constructivist view, to develop consequently Figure 1: audio chain of N clients with control over 5 L2ORK:
604 Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 feedback has been applied, said local feedback for it is signal processing locally implemented. Moreover a exerted at the client level. further improvement may be that to configure each A system as that in Figure 2 is said an IIR comb filter section of the ensemble according to some physical [28], described by the well-known frequency response. model of resonance (for example: string, pipe, plate, It should be noted that this response displays resonant etc. See Figure 3). peaks and attenuation valley: given a certain amount of dCn samples of delay (local I/O vector) at the sampling rate sr, the system will have dCn peaks evenly spaced in the whole spectrum from 0 Hz to sr/2; the distance !P between peaks will be inversely proportional to the delay dCn, according to the following relationship:
!P = sr / dCn [Hz]. (2)
The peaks are thus in harmonic relationship to a fundamental frequency !P. The relationship between peaks (pCn) and valleys (vCn) of the frequency Figure 3: a section of the laptop orchestra arranged to response, which affects the perception of the zones of form a simplified model of a resonant plate [19]. resonance, depends on the gain factor gCn:
5.3. Stability pCn/vCn = (1+gCn) / (1-gCn). (3) The stability of the designed networks is not obtained by resolving the proper polynomial of the particular system but with the use of non-linear energy compensation functions that may be traced back to dynamics compression issues [4] [10] [28]. Before being transmitted to the next client the envelope of the output signal is extracted and its ones’ complement is used to compensate the actual output (see Figure 4). The particular technique of envelope extracting depends on two variable factors: 1. t: delay [sec.], memory of the envelope extractor; 2. g : feedback gain [0, 1], sensitivity to positive derivative of input signal (growth of energy) and length of the decay curve.
Figure 2: client with local feedback and control over the gain factor gCn.
According to the actual gain value the client will have a stronger or weaker presence of its resonances (i.e. on timbre). By imposing local feedbacks we have thus obtained two instrumental possibilities controlled by a single parameter (gain): 1. clients relative independence to input signal Figure 4: energy compressor. (resonance); These two variables have been unified in a single 2. timbric presence of the instrument determined by factor called sensitivity (sCn), directly proportional to the fundamental frequency !P of the comb filter both variables on a 0 to 1 scale. and by ratio (3) above. The combination of feedback and energy It should be noticed how systems as that in Figure 2 compensation corresponds to the act of tending a string. are the building blocks of what is known as physical Such a system has a minimum of autonomous life (not modelling synthesis or, more generally, waveguides algorithmically driven) and has been devised in [10] synthesis [4] [17] [28]. [11]. In a system composed of such elements emerges a The sensitivity could thus be used as a measure of the first possibility of proper subdivision of the ensemble in dynamicity of an instrument, as is the case with several resonance sections, determined by a contingent instrumental sections in a classical ensemble where factor (I/O vector size), and unrelated to the actual some of theme are, historically, characterized by a
605 Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 greater versatility (for example the strings’ section) than Besides this controls each performer should manage others (for example the brass section). the parameters of the signal processing carried on locally on his/her machine. This will be a second order 5.4. The complete client. level of the orchestra design: among the sound elaboration tools used in the S. Giorgio Laptop The complete implementation of a single client can be Ensemble there were vocoders, granular processing, seen in Figure 5. The performer will be able to control at synthesis tools, transpositions, etc., all acting on the least three parameters of his instrument (see Table 1), in incoming sound produced by the string quartet. addition to those proper to the digital signal processing (dsp) algorithm locally implemented. These three 6. THE DIRECTOR parameters may be related to the musical parameters of intensity (local loudness, aCn), rhythmic articulation Having thus defined the clients level it is felt the need to (local sensitivity, sCn) and timbric presence (local improve accordingly the server level. Up to now the feedback gain, gCn). All these features should be only function of the element S has been that to feed the explored, tested and playing skills should be developed network with an audio signal. For a conductor to exert through rehearsal exercises as suggested in [15]. its control over an ensemble it is necessary that (s)he For the local output of the laptop performers non- knows and hears the players’ parts: to obtain a similar standard transducers may be used, made by the coupling condition in the network of audio signals implemented, of an acoustic magnetostrictive actuator [22] with a the clients should feed-back their output signal to the resonant surface. These actuators may be used to put in server. This will be called global feedback whose gain resonance any surface on which they are placed (wood, will be controlled by the director. The stability of this glass, metal, etc.) and are currently widely used for system is obtained at this global level by means of non- environmental sonifications. linear compensation functions as it is at the local level,
and will be called global sensitivity (sS) (see Figure 6).
Figure 5: client’s architecture Figure 6: the complete audio network. By using different resonators there will be different colouring of the excitation audio signals and the The conductor will also be responsible of the global possibility to distinguish each performer by the sound of the ensemble diffused via a standard P.A. particular timbre of its resonator, independently from system (global loudness level). The global signal will the actual signal processing locally implemented. not be exactly as the sum of the performers‘ local outputs because of the differences in the transduction Variable Exerted Control Perceptible effect elements that are not transmitted in the audio stream. These differences will emerge as spatial dynamics (local gCn local feedback Resonance to output vs. global output) due to timbric factors and not gain input signal and on any pre-arranged simulation of sound movement. timbric presence The laptop performers and the conductor will thus sCn local sensitivity Rhythmic exert their control by means of the same kind of articulation of the variables that have, however, different effects depending audio stream on the level at which this controls are exerted (see Table Can local loudness Loudness 2). produced on the The server should also manage the actual local output configuration of the orchestra, namely the nodes of Table 1: client’s parameters. communication between client and client, in order to configure the sections, for example, as a simple row of
606 Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 clients (see Figure 1) or as a particular physical model • n.1 Public Address System; (see Figure 3). • one or more ethernet switch(es) for audio communication; Laptop Conductor Laptop • n.1 wireless access-point for data Performer Performer communication. Gain Timbric Formal presence articulation 8. FINAL REMARKS Sensibility Rhythmic Dynamics of texture the stream Control parameters have been found that seem relevant Loudness Local Global to the nature of the network: this parameters are in a loudness loudness certain degree automatic, but their actual response depends on the combined actions of performers and Table 2: comparison between client and server conductor. This first control level regards audio parameters. communication between laptops, and to describe it have As for the IN signal fed to the network by the server, been used terms borrowed from network technology: the there are some possible observations: global behaviour will be managed by the server that will • it could come from some acoustical source (one also have to grant the stability of the whole audio or more instruments, ambience noise, etc.); network (avoiding saturation), of its configuration • it could be read from an audio file; (connecting clients) and feeding the clients with an • it could be synthesized on some node of the audio signal. The clients will manage the modality of network; their own local resonance and stability. The server level • different signals may be sent to different nodes is managed by the conductor while the clients level by of the network, in order to feed different section the performers: this is the second control level, the with distinct signals. human level of interaction which is not automatic, depends on performance practice and must be finely 7. TECHNICAL DETAILS tuned through rehearsals. It should be noted that the server/director does not directly take part in the In the S. Giorgio Laptop Ensemble a similar network acoustical matter (i.e. sounds are produced/transformed has somehow been implemented with audio signals by the orchestra) but just manages the relationships being broadcasted on a Local Area Network using UDP between the orchestra elements and the global features protocol on ethernet interfaces. After some test the more (loudness, rhythmic articulation, etc.) of the audio reliable solution was that of using an open source VST stream. plug-in (whormhole210) to manage the audio communication between server and clients. This choice 9. ACKNOWLEDGEMENT was made to avoid the complexities of a physical set-up using audio interfaces, and musically managing the This research has been carried on independently by the shortcomings of network communications (intrinsic writer, who would like to thank Agostino Di Scipio, delays). Riccardo Vaglini and Alvise Vidolin for their support. The network has been used even to broadcast control data streams carrying information on main 10. REFERENCES features of the audio stream (input signal envelope, global audio envelope, etc.) using the OSC protocol; to [1] Barbosa, A. “Displaced Soundscapes: A avoid conflicts with audio signals broadcasting, the Survey of Network Systems for Music and control data were sent through a wireless network. Sonic Art Creation”, «Leonardo Music Each orchestral will thus be equipped: Journal», vol.13, 2003, pp. 53–59. • n.1 laptop (with an ethernet interface); • n.1 acoustic actuator; [2] Brown, C., Bischoff, J., Indigenous to the Net: • n.1 resonance surface; Early Network Music Bands in the San • n.1 ethernet cable; Francisco Bay Area, 2002, available at • n.1 MIDI controller.
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