Page  00000001 A NEW INTERACTIVE PERFORMANCE SYSTEM FOR REAL-TIME SOUND SYNTHESIS Giorgio Nottoli*, Mario Salerno**, Giovanni Costantini** * Conservatorio di Musica "L. Refice" via Roma, 25 03100 Frosinone, Italy ** Department of Electronic Engineering "Tor Vergata" University of Rome via di Tor Vergata 110 00133 Rome, Italy Abstract A new electronic system has been developed for real-time sound synthesis. It is called Betel Orionis and it is based on the dedicated DSP Orion. This system is intended for live performances in concert halls and it is interfaced with personal computer and MIDI controls that allow the composer or performer to interact with it. Interesting features are its complete programmability from the lowest level (DSP) up to the highest level (control algorithms and interactive interface for the user) and its processing power that allows complex realtime synthesis. Introduction The project goal is to meet the expressive demands of the musicians; these demands have been subject to a radical change in the course of this century. The research for new sonorities and new dynamic possibilities together with the vast progress within the field of electronics and computer science have contributed towards the birth and development of computer music. Today, within the field of contemporary art music, electronic synthesis and sound processing systems are very regularly applied. AUDIO BUS MIDI GESTUAL AUDIO 110 CONTROL SYNTESIS PROCESSING SPATIALISATION MVIODULE MO1DULE MODULE MODULE PC CONTROL BUS Fig. 1 - SAIPH block scheme

Page  00000002 A system has been designed which allows synthesis, processing and spatialization of sound in real-time (it is intended to be used live in a concert hall): this system is SAIPH. SAIPH is designed as a modular system: it is made of modules which are dedicated to perform specific musical signal processing. A SAIPH system block scheme is illustrated in Fig. 1. The Betel Orionis system, presented in this paper, is the module of the SAIPH system allotted for sound synthesis. It has been utilised for a live performance at the MACBA (Museum of Contemporary Art of Barcelona) on 31 January 1998. In that performance, Betel Orionis synthesized eight independent sound structures in parallel using a kind of granular synthesis with both sine-waves and PCM grain events with the maximum polyphony of 512 sinewaves oscillators and 240 PCM oscillators. The 16 independent Betel Orionis outputs have been connected to two 8x8 digital mixers/spatializers Mixtral (Giorgio Nottoli, Carlo Alberto Paterlini, Attila Baldini, 1997) driving 16 speakers positioned in the MACBA museum. Before describing the Betel Orionis system, a brief description of the Orion DSP architecture will be given. The DSP Orion has been designed in 1990 by one of the authors (Giorgio Nottoli, 1991). It is a DSP dedicated to the musical signal synthesis and it is the core of this system. The Orion microcircuit Orion is a Digital Signal Processor specifically designed to synthesize sound events according to all the principal synthesis algorithms utilised in computer music. Moreover, it allows high performances compared with most of the actual DSPs. This is obtained thanks to its architecture based on a set of top-level units interconnected by an unidirectional multi-bus structure. In particular, the interconnection architecture has been properly designed to support the implementation of the synthesis primitives. So, the basic primitives are implemented by special hardware units designed for maximum execution speed. Each main unit has the complexity of a subsystem and has a bit of it's own local intelligence. In particular, it is able to execute elementary sequence of operations under the supervision of the main chip microcontroller. As an example, to implement an interpolating table look-up algorithm, the T_ALU (Tables ALU main unit) executes two external memory read cycles and interpolates between the two samples with a dedicated parallel multiplier using local intelligence only. Orion is constituted of four specialized Arithmetic Logic Units, three data RAMs and three I/O units. Executing music oriented digital signal processing algorithms, the computing work is distributed among the four ALUs to maximize parallelism while the data transfer work takes advantage of the three data rams structure. Additive, phase and frequency modulation synthesis algorithms can be implemented using the internal sine-wave generator. The Orion DSP can address up to 16 Msamples of dynamic memory in witch you can store waveforms to make more complex sounds with PCM looping algorithms. The set of microinstructions enable a complete support to carry out hardware envelopes for high quality sound generation and reduction of the control microprocessor computing charge. The Betel Orionis system The hardware Betel Orionis is a multiprocessor system for real-time sound synthesis based on the dedicated DSP Orion and it is a hardware module of the SAIPH system, described previously. It is an open system because of complete programmability of the Orion DSP. The project is based on a multiprocessor architecture and implements all the most important algorithms for real-time sound synthesis with a capacity of eight stereo output audio channels. In particular, each channel is controlled by an Orion DSP driven in real-time by a host personal computer. Each Orion DSP can work alone

Page  00000003 or it can communicate with other Orions exchanging samples via a serial link. This feature allows the user to choose the best configuration for his own needs. Thanks to the Orion DSP architecture dedicated to the implementation of methods for sound synthesis, the system reaches a considerably high processing power. In order to get an idea of the efficiency of the system we may refer two very common methods of synthesis: -additive synthesis: in this case, the system offers a capacity of 1024 virtual oscillators -PCM synthesis: the whole system disposes of a capacity of 240 PCM channels with a memory of 128 Msamples. The system core is made of eight Orion DSPs synchronized by an external 32 MHz clock generator. Every Orion is intefaced with: a) the PC ISA bus by the host interface b) another Orion DSP or a stereo DAC device by the synchronous serial interface (the choice is made by the microprogram); the eight DACs, together with anti-aliasing filters, constitute the system audio interface c) a SIMM module up to 32 Mbytes (16 Msamples) by the dynamic memory interface. The Betel Orionis system block scheme is shown in Fig. 2. Fig. 2 - Betel Orionis block scheme The software Betel Orionis automatically generates complex sound textures and allows the composer or the performer to control them in real-time. The system is completely programmable from the lowest level (DSP) to the higher level (control algorithms and interactive interface towards the user), thus making it extremely versatile for the most varied user requests.

Page  00000004 The system software architecture is set on three levels: 1) user interface level,designed in such a way to allows the control of a large number of events via a few high level parameters which are activated via gestual controls (mouse, PC keyboard, sliders and other MIDI controls) 2) control level, with control algorithms based on deterministic and random methods that are located within the host computer (PC) 3) sound generation level, with sound synthesis algorithms that are located within the microprograms for the Orion DSP. There are typologies of synthesis and control algorithms that are already developed; however, it is possible to generate both control and synthesis algorithms via an appropriate editor. The user interface is the most innovative part of the system and it is designed to meet the expressive needs of the musical composition and execution. It allows the control of a large number of complex events via a few high level parameters driven by gestual controls. During the real-time performance, the system is controlled using a set of standard MIDI controllers (buttons joysticks and sliders). The low level parameters of each sound structure (constituted of a group of oscillators) are generated by a control formula using both stocastic and deterministic methods. The formula parameters are mapped into a two dimensional space to allow easy real-time timbral manipulation using the MIDI controllers set. Conclusions In this paper has been described the Betel Orionis system. It is a new electronic system for real-time sound synthesis based on the dedicated DSP Orion and it is driven by personal computer or MIDI controls. The system is based on a multiprocessor architecture and implements all the most important algorithms for realtime sound synthesis with a capacity of eight stereo output audio channels. The user interface is the most innovative part of the system and it is designed to meet the expressive needs of the musical composition and execution. It allows the control of a large number of complex events via a few high level parameters driven by gestual controls, making Betel Orionis very suitable for live performances in concert halls. Reference Giorgio Nottoli: ORION: a single chip digital sound processor/synthesizer, Proc. of IX Colloquium on Musical Informatics, 1991, Genova, Italy Giorgio Nottoli, Giovanni Costantini: Betel Orionis: a real time, multiprocessing sound synthesis system, Proc. of Journees d'Informatique Musicale, May 1998, Agelonde, France Giorgio Nottoli, Carlo Alberto Paterlini, Attila Baldini: Software Aided Mixing on a Low-Cost Digital Console, Proc. of AES /103rd Convention, 1997 Giorgio Nottoli, Mario Salerno, Giovanni Costantini: Betel Orionis: un sistema multiprocessore orientato alla sintesi del segnale musicale in tempo reale, "La terra fertile", September 4-6, 1998, L'Aquila, Italy Giorgio Nottoli, Mario Salerno, Giovanni Costantini: A new real-time sound synthesis system intended for live performance, Proc. of XII Colloquium on Musical Informatics, September 24-26, 1998, Gorizia, Italy. Mario Salerno, Fausto Sargeni, Giorgio Nottoli, Giovanni Costantini: Tecnologia e musica all'Universith "Tor Vergata" di Roma, Proc. of "La terra fertile", Ottobre 1996, L'Aquila, Italy