Proceedings of the 2000 International Computer Music Conference, Berlin, Germany, 27 Aug.-1 Sept. 2000, pp. 50–53 50 Proceedings ICMC 2000 Model-Based Synthesis of the Clavichord Vesa Välimäki 1 , Mikael Laurson 2 , Cumhur Erkut 1 , and Tero Tolonen 1 1 Helsinki University of Technology, Lab. of Acoustics and Audio Signal Processing P.O. Box 3000, FIN-02015 HUT, Espoo, Finland Vesa.Valimaki@hut.fi, Cumhur.Erkut@hut.fi, Tero.Tolonen@hut.fi http://www.acoustics.hut.fi/ 2 Sibelius Academy, Center for Music and Technology, Helsinki, Finland Laurson@siba.fi, http://www.siba.fi/ ABSTRACT A synthesis model for the clavichord is developed applying the principles of digital waveguide modeling. A commuted waveguide synthesis model is used, where each tone is generated with two coupled string models that are excited with a common excitation signal that is obtained from analysis of recorded clavichord tones. The characteristic knock terminating tones played by the clavichord is reproduced by triggering a sample that is separated from a recorded tone. A simple technique enables the realistic variation of the fundamental frequency by using a control function that can be a constant value plus the impulse response of a low-order digital filter. Sound examples will be available at http://www.acoustics.hut.fi/~vpv/publications/icmc00.htm. 1. INTRODUCTION We describe a technique for sound synthesis of the clavi- chord using the physical modeling approach. The clavi- chord is one of the oldest keyboard instruments, which is still used in performances and recordings of renaissance and baroque music [1–5]. The sound of the instrument is pleasant but quiet. The maximum SPL at 1 meter is only about 50 dB or 60 dB—depending on the individual con- struction of the instrument. The reasons are that the strings are thin and their tension is low, the tangent hits the string at its end, which is a nodal point for all its modes, and the soundboard is small and thus does not much amplify the sound [2]. Consequently, the instru- ment can only be used in intimate performances for small audiences. This is the main reason why the clavichord was replaced by the harpsichord and finally by the mod- ern piano. One of our motivations in this research is to give the clavichord a new life in the digital world, where the faint sound level of the instrument can be amplified by simply turning a volume knob. The suggested synthesis model is based on digital waveguide modeling [6], [7]. In Section 2 of this paper, we discuss the acoustical properties of the clavichord. Section 3 describes the synthesis model, and Section 4 presents some synthesis examples. Section 5 concludes the paper. 2. ACOUSTICS OF THE CLAVICHORD For each key of the clavichord, a pair of strings has been tuned in unison [1–5]. The keys are at one end of a lever while a tangent has been attached to its other end. When a key is depressed, the tangent hits the string pair and initiates vibration. One end of the strings has been damped with felt, and the other end goes over a bridge to the tuning machine. Thus, the strings are freely vibrating between the bridge and the tangent, which works as both a hammer and a termination. The tangent mechanism is pretty noisy as it excites modes of the soundboard but also itself causes sound from its moving parts. The string pairs are always slightly detuned, and since they are coupled via a non-rigid bridge, both beats and a two-stage decay result. Figure 1 shows the envelope of a recorded clavichord tone. The irregular (non-exponential) decay of the tone can be observed. When a key is released, the vibration again propagates to the felt, which efficiently attenuates the tone. The key mechanism also generates a loud knock, which is char- acteristic to the sound of the instrument. In Fig. 1, a burst located at 1.1 s corresponds to the knock; at the same time the tone starts to decay fast. The envelope curves of the first 5 harmonics are pre- sented in Fig. 2. It is seen that regular exponential decay (i.e., linear decay on a dB scale) is rare: there is some beating and other irregularities in many harmonics.