A Percussive Sound Synthesizer Based on Physical and Perceptual Attributes

Synthesis of impact sounds is far from a trivialtask owing to the high density of modes generallycontained in such signals. Several authors have ad-dressed this problem and proposed different ap-proaches to model such sounds. The majority ofthese models are based on the physics of vibratingstructures, as with for instance modal synthesis(Adrien 1991; Pai et al. 2001; van den Doel, Kry,and Pai 2001; Cook 2002; Rocchesso, Bresin, andFernstrom 2003). Nevertheless, modal synthesis isnot always suitable for complex sounds, such asthose with a high density of mixed modes. Otherapproaches have also been proposed using algorith-mic techniques based on digital signal processing.Cook (2002), for example, proposed a granular-synthesis approach based on a wavelet decomposi-tion of sounds.The sound-synthesis model proposed in this ar-ticle takes into account both physical and percep-tual aspects related to sounds. Many subjectivetests have shown the existence of perceptual cluesallowing the source of the impact sound (its mate-rial, size, etc.) to be identiﬁed merely by listening(Klatzky, Pai, and Krotkov 2000; Tucker and Brown2002). Moreover, these tests have brought to thefore some correlations between physical attributes(the nature of the material and dimensions of thestructure) and perceptual attributes (perceived ma-terial and perceived dimensions). Hence, it hasbeen shown that the perception of the materialmainly correlates with the damping coefﬁcient ofthe spectral components contained in the sound.This damping is frequency-dependent, and high-frequency modes are generally more heavilydamped than low-frequency modes. Actually, thedissipation of vibrating energy owing to the cou-pling between the structure and the air increaseswith frequency (see, for example, Caracciolo andValette 1995). To take into account this fundamental sound be-havior from a synthesis point of view, a time-varying ﬁltering technique has been chosen. It iswell known that the size and shape of an object’sattributes are mainly perceived by the pitch of thegenerated sound and its spectral richness. The per-ception of the pitch primarily correlates with thevibrating modes (Carello, Anderson, and Kunkler-Peck 1998). For complex structures, the modal den-sity generally increases with the frequency, so thathigh frequency modes overlap and become indis-cernible. This phenomenon is well known and isdescribed for example in previous works on roomacoustics (Kuttruff 1991). Under such a condition, the human ear deter-mines the pitch of the sound from emergent spec-tral components with consistent frequency ratios.When a complex percussive sound contains severalharmonic or inharmonic series (i.e., spectral compo-nents that are not exact multiples of the fundamen-tal frequency), different pitches can generally beheard. The dominant pitch then mainly depends onthe frequencies and the amplitudes of the spectralcomponents belonging to a so-called dominant fre-quency region (Terhardt, Stoll, and Seewann 1982)in which the ear is pitch sensitive. (We will discussthis further in the Tuning section of this article.)With all these aspects in mind, and wishing to pro-pose an easy and intuitive control of the model,we have divided it into three parts represented byan excitation element, a material element, and anobject element.The large number of parameters available throughsuch a model necessitates a control strategy. Thisstrategy (generally called a mapping) is of great im-portance for the expressive capabilities of the in-strument, and it inevitably inﬂuences the way itcan be used in a musical context (Gobin et al. 2004).