The MORPH project proposes to use sound morphing to investigate musical instrument timbre. In music, timbre is traditionally associated with the musical instrument producing the sound. Thus, it is common to refer to the timbre of the violin, for example. However, musicians talk about timbral variations between different makers or even different pitch registers of the same instrument. In practice, not all violins sound the same due to many factors, ranging from the shape of the instrument to the materials used. For instance, the strings are known to influence the sound quality of the violin, and different materials will produce perceptually different results, such as a “warm” or “dark” sound quality.
Research into timbre perception investigates the ways in which sounds are perceived to differ. The term timbre covers many perceptual parameters that are not accounted for by pitch, loudness, spatial position, and duration. Due to its complexity, timbre is often considered as one of the “last frontiers” in auditory science. Today, we understand timbre from two distinct viewpoints, a categorical contributor to source identification and a sensory quality. Timbre is the primary perceptual vehicle for the recognition of a sound source, and thus involves the absolute categorization of a sound. Categorical timbre is what allows us to recognize that a violin is playing a melody instead of a piano, for example. However, variations such as warmer or darker violin sounds are associated with the sensory quality of timbre perception.
Recent advances in timbre research have investigated the relationship between the sensory and categorical facets of timbre perception. The categorical view assumes that there are “timbral gaps” between musical instruments, whereas the sensory view posits that timbre is potentially continuous in nature and the timbral gaps result from the physical limitations of the sound producing objects. The MORPH project uses sound morphing to create intermediate sounds between two different instruments and then investigate how the morphing transformation affects the timbre of these sounds. Musical instrument sound morphing theoretically allows creating continuous timbre spaces by filling the gaps between traditional musical instruments and therefore breaking the categorical perception of musical instrument timbre by the auditory illusion of hybrid musical instruments.
There are three overall research objectives (RO). RO1 aims to develop a high-quality and accurate model of musical instrument sounds to enable precise and controlled manipulations of acoustic features. The model should be perceptually transparent for orchestral instruments, and the manipulations should be perceptually natural. RO2 aims to investigate timbre perception using the models from RO1. The morphs create hybrid musical instrument sounds that potentially break the absolute categorization of musical instrument perception. RO2 requires perceptual evaluation to validate if morphing connects the musical instruments, essentially creating continuous timbre spaces. Finally, RO3 aims to assist musicians and composers in gaining creative control over musical instrument sound morphing.
The MORPH project has resulted in powerful tools to advance our fundamental understanding of timbre and potentially led to groundbreaking discoveries in timbre perception, as well as impact music technology by transferring the methodology to digital media used in creative musical applications. The MORPH project has advanced music audio processing by developing new modeling techniques specifically tailored for musical instrument sounds. Additionally, the MORPH project has provided powerful analysis tools to further our understanding of musical timbre perception.
