## 2 Indoor Soundscape Approach  
Soundscape definition underpins three main pillars that are the \"acoustic environment\", \"people\" and the \"context\" where the perception occurs. The concept was originally developed from studies conducted at an urban scale and in outdoor spaces, with the aim of shifting the focus from the negative to the positive effects of environmental sounds [47; 48]. Standard ISO/TS 12913-2:2018 requires the integration through triangulation of multiple methods (soundwalks, questionnaires, guided interviews, non-participatory observations, and binaural measurements) for a holistic assessment of the acoustic experience, in context [49]. Nevertheless, a gap exists in linking perceptual metrics to acoustic or psychoacoustic measurements and, at the current stage, a straightforward characterization of a soundscape as positive is only possible through measurements by people. For this reason, the soundscape research community is putting great effort into the definition of indices able to objectively describe soundscapes, thus integrating or even replacing decibel-based metrics to reflect human comfort levels [48]. The soundscape concept has been recently applied to buildings and built indoor spaces, in order to characterize how people perceive, experience, and understand the indoor acoustic environment in the context of their working, living or leisure environments [50]. Indeed, the building itself plays a fundamental role in defining the acoustic environment, the people-related and contextual factors in the indoor soundscape concept, because, depending on its geometry and materials, outdoor sounds are filtered and the indoor acoustic environment is shaped, and depending on its function, users' expectations and needs are built. Soundscape assessment methods, as defined by ISO/TS 12913-2:2018 technical specifications, have been mainly derived from listening tests playing outdoor sounds and it is not clear whether they are equally valid indoors [51]. If research on indoor soundscape is still at its embryonic stage, a general model for indoor soundscapes has been proposed, based on three main concepts that are \"acoustical variables\", \"contextual factors\", and \"architectural factors\" [52; 53; 54; 55]. With reference to residential buildings, factors influencing indoor soundscapes have been recently reviewed and proposed as reference [51]. They include factors properly related to the acoustic environment (e.g., sound level, spectral content, roughness, loudness, fluctuation strength, and sound type), urban context and building characteristics, personal traits, socioeconomic features, situational circumstances, and environmental conditions [51]. General assessment methodologies for indoor soundscapes were investigated by several studies, such as questionnaires [56] or sound walks [57; 58], also integrated into post-occupancy evaluations [54]. In residential buildings, questionnaires and guided interviews have been the assessment methods most commonly used to capture people's perception, whereas the adoption of soundwalks and non-participatory behavioral studies appears to be limited in an indoor context and need further investigation [51]. As regards the application of the semantic differential method for a subjective evaluation of indoor soundscapes, nine adjective pairs were proposed to describe three main perceptual dimension of sound (\"evaluation\", \"potency\", and \"activity\") in indoor and outdoor environments [59]. Methods such as \"grounded theory\" coupled with interviews have been specifically investigated in the field of indoor soundscapes, to systematically extract information on subjective perception from qualitative data gathered during questionnaires or interviews [60; 61; 62].