# Singing-Voice Timbre Evaluations Based on Transfer Learning
## 1 Introduction  
Singing is one of the most common forms of artistic performance that can be achieved by vibrations of the vocal cords, without the use of any external apparatus. This artistic expression is internalized in various aspects, such as melody, pitch, rhythm, and timbre, and it can be said that singing evaluation is a complex multidimensional task. In the context of the quantitative evaluation and analysis of singing by human experts, which is often expensive and is low in terms of the availability of resources, tools for automatic evaluation of singing are of great use. Professional singers can pursue higher levels of progress based on feedback, singing enthusiasts can aid their daily learning to help progress based on feedback evaluations, and in the education industry, these tools can be used in aiding teaching. Singing analysis, as a complex task, consists of various small tasks. Currently, well-developed systems contain automatic evaluation systems for pitch, articulation, and other dimensions. Some evaluation tasks have clear definitions and objective indicators, such as pitch, that are easier to quantify and analyze. Meanwhile, for timbre and other abstract and subjective evaluation dimensions, it is more difficult to quantify, and an automatic evaluation system is not easy to achieve. In 2008, [PERSON] et al. [1] concluded from their experiments that among many musical criteria, the first is pitch accuracy, the second is rhythmic consistency, and the third is tonal brightness, ranked according to their importance. Singing timbre is not only a person's own voice but includes the person's singing style and breath control, and singing timbre has a crucial influence on whether a song is performed properly. Therefore, the research of timbre evaluation is important for improving singing evaluations. Timbre is a misleadingly, simple, and vague word encompassing a very complex set of auditory attributes, in addition to a plethora of psychological and musical issues [2]. There are numerous versions of the definition of timbre in the currently available literature. Timbre is the attribute of auditory sensation with respect to which a listener can judge two sounds that are similarly presented and possessing the same loudness and pitch as dissimilar [3]. This definition by the Acoustical Society of America is also an intuitive idea when one sees the term timbre, and it clarifies that timbre is strongly distinctive and highly recognizable; however, it is an oversimplified description of timbre. The definition of timbre in the _Columbia Encyclopedia_ is as follows: Sound Quality is determined by the overtones, the distinctive timbre of any instrument being the result of the number and relative prominence of the overtones it produces. This definition more clearly shows what timbre specifically is, but with some errors. Timbre is not only related to frequency in the frequency domain, but it is also related to the amplitude envelope in the temporal direction, and different envelope curves can affect the audience's perception; for example, piano timbre is difficult to identify when played backward. Although the literary formulation is controversial, the point of consensus is that timbre is influenced by different frequencies that make up the sound, and the quality of timbre is mainly determined by overtones. Although overtones are clearly documented with numerical values and distribution statistics on spectrograms, representing them in a uniform and orderly sequence, similarly to pitch, is difficult. It is also difficult to describe timbre in terms of a single dimension, as multiple words are often used with respect to different dimensions. For example, a trumpet has a bright and sharp timbre, while a cello has a thick and low timbre. Timbre as a multidimensional musical attribute has many evaluation terms, such as rich and barren, cold and warm, sharp and staccato, etc.