# Objective Assessment of Porcine Voice Acoustics for Laryngeal Surgical Modeling
## 1 Introduction  
Voice impairment is a major factor in public health, affecting the economic prosperity of society as a whole, as well as the social functioning and quality of life of individuals [1, 2, 3]. [PERSON] et al. interviewed a random sample of 1326 adults in Iowa and Utah and found that the lifetime prevalence of a voice disorder was 29.9%. Of the interviewed participants, 7.2% reported an absence from work for one day or more due to their voice during the last year [1]. Another study by [PERSON] et al., reviewing data of 386 patients with a short-term disability claim due to a laryngeal disorder, found that voice disorders were associated with an average missed work attendance of 39.2 days in 12 months. This resulted in an average wage loss of $4437.89 per patient [2]. The effect on quality of life was shown by [PERSON] et al. One of their findings was that patients with reported voice problems experienced nearly twice the likelihood of depressive symptoms [3]. Accordingly, the human voice is an ongoing subject of research with novel treatments under development for many human voice disorders [4, 5, 6, 7]. Testing new treatments obviously carries certain risks, and translating research into humans often requires pre-clinical animal models to demonstrate safety and efficacy before enrolling human subjects. Due to their similar anatomy, physiology, and genetics, pigs have emerged as an important animal model. Additionally, they are easy to breed, have no complex husbandry needs, and produce large litters. In biomedical research, miniature pigs are particularly useful because their full adult size is more manageable than traditional farm pigs [8, 9]. For voice research, pig and human vocal folds exhibit similar physical characteristics, most notably the vocal fold thickness and distribution of elastic and collagen fibers. Pigs are also highlyvocal in a similar frequency range as humans, unlike other animal models such as rabbits and small rodents [10; 11; 12]. However, understanding the voice in non-humans has complexities, as there are obvious differences between pig and human vocalizations. Besides the anatomic differences of tongue position, position of the larynx, and vocal tract length, pig vocalizations exhibit nonlinear qualities such as subharmonics and chaotic episodes that occur without complex nervous system control [13; 14]. Pigs also cannot be instructed to phonate on command, to hold a vowel, or to phonate using a variety of call types. In general, lower frequency calls like grunts are highly variable and may be attributed to non-laryngeal origins [11], although there is no unanimity on this subject [13]. In contrast to grunts, which are emitted nasally, higher frequency calls like screams and squeals are emitted orally [15] and are in general assumed to originate from the vocal folds [13]. Prior studies have presented various methods of classifying normal porcine phonation, differentiating between call types in an agricultural and animal communication context. However, no unanimous differentiation rules have emerged [11; 15; 16; 17; 18]. Considerable blurring between call types is evident due to the indiscrete nature of the calls and their existence on a sound continuum [16; 18]. Extensive variation in \"normal\" pig calls is also widely documented [11; 15]. Other complexities include noisy irregular data, pigs moving during phonation, nonlinear distortion, and recording noise, which complicate interpretation [14]. Further, results of these studies assessing more natural pig phonation are not necessarily transferable to the situation of pigs undergoing laryngeal surgery, i.e., in a post-surgery setting. For these reasons, we avoid a more specific differentiation between call types in this work and focus on higher frequency calls such as squeals and screams in general. Few studies have addressed porcine voice function after laryngeal tissue engineering.