# Indoor Acoustic Requirements for Autism-Friendly Spaces
## 2 Materials and Methods
### Literature Results on Acoustic Devices Requirements and Their Uses  
At present, the most widely used devices for indoor monitoring include infra-red sensors, open/closed detectors, weather stations, kinematic sensors, webcams, and microphones for sound and speech recognition [21]. Sound and voice recognition systems represent a good compromise between privacy and support [22]. They can monitor sound levels without \"being seen\", featuring the option to whether to record signals or not. Sound and speech recognition technologies are classified as acoustic event detection (AED) and sound source recognition systems (SSR). AED is designed to detect anomalous acoustic events and were first developed only to assist video surveillance monitoring [23]. They are based on sound signal peculiarities, which can be composed of many different time or spectral characteristics, amplitude levels (consequently different signal-to-noise ratio), and durations. The detection algorithms are based on pre-processing techniques, necessary to detect potential alarm signals [24]. These systems are mainly used for \"security\" in outdoor environments or large spaces (garages, airports, stations, etc.). SSR are devices that have been recently developed. They permit the switch from a help button-driven request to an immediate sending of a distress call by means of the use of people's own voice or a specific event recognition. These technologies are becoming increasingly popular today, especially thanks to the development of home automation techniques within smart homes [25]. Sensors can provide information about a person's posture and movement or detect falls, etc. [26]. Smart homes are therefore useful to monitor activities or to help with cognitive or physical disabilities in daily events [27]. In this case, they would make it possible to monitor situations of annoyance or nervousness such as sudden noises coming from outside (a loud horn or an individual streaming from the street), or from nearby  
Figure 1: Flowchart of the research approach. environments (neighbor's noise, etc.) and trigger the appropriate mechanism, if the individual suffers emotional stress related to these factors [28]. Nowadays, there are many available solutions of acoustic recognition algorithms [29]. The involved systems feature one or more microphones or are even embedded in robots, permitting them to follow individuals very closely. As far as voice command is concerned, these systems are able to analyze and recognize many characteristics including intensity, timbre, rhythm, and level [30]. This permits to distinguish whether to send an early warning to the caregivers or not. Such systems therefore permit non-autonomous people to maintain control of their environment, activities, health, well-being, and sense of dignity [31]. Many of the above-presented studies identify disabled people as the main stakeholders, in particular when they are able to look after themselves, but they may need help when facing some difficult tasks or any situations of risk, danger, and accident. Recognition systems can also be implemented in order to emit reassurance signals (voices, music, light variation) in order to avoid crises and panic. Most problems encountered during the implementation phases are related to the background noise and indoor reverberation conditions [32]. Accordingly, recognition performance decreases significantly as devices are located away from the user's mouth (e.g., when positioned on the ceiling), due to reverberation increasing, and background noise effect (masking) [33]. Indoor sound environment may be characterized by many objective parameters. One of the most important is the measure of the energy decay in time (reverberation time RT). This parameter depends on the sound-absorbing characteristics of the finishing and on the volume of the room. Reverberation time is short for very sound absorbent rooms or small close environments and increases proportionally to volume or the decrease in the presence of sound absorbing materials [34].