## 3 Environmental Noise Database
### Urban and Suburban Pilot Areas On-Site Inspections and Recording Campaign  
The main goal of the recording campaign was to collect widely diverse samples of road traffic noise and anomalous noise events in order to provide a general picture of the real-life scenarios the dynamic noise mapping system will be working on. To that effect, several recordings were conducted between the 18 and 21 May 2015 in specific locations of the two pilot areas of the DYNAMAP project, covering both urban (Milan) and suburban (Rome) scenarios. These locations were selected according to representative traffic conditions and acoustic characteristics of the pilot areas (see [36; 37] for further details). The WASN of the DYNAMAP project is based on low-cost acoustic sensors from Bluewave [38]. According to the project requirements, the recordings were conducted using two measuring devices simultaneously: the low-cost sensor connected to a ZOOM H4n digital recorder (see Figure 1b), and a Bruel & Kjaer 2250 sonometer (see Figure 1a), being the latter used as a certified reference according to the project requirements. However, only the audio data obtained from the low-cost sensor is used for the subsequent analyses. The recording setup was the following:  
* Situation of both measuring devices: 50 cm distance between them. * Sampling: 48 kHz sampling rate with 24 bits/sample. * Sensitivity verification using a 94 dBSPL, 1 kHz calibration tone. * Clapping: in order to align the audio recordings from both measuring devices, a sequence of 5 s. of clapping was performed between both sensors with a separation that assured a very good signal to noise ratio despite the environmental noise. * Gain adjustment: the input gain of each recorder was selected to guarantee enough room for in-site audio dynamics (no saturation). * Installation: both recording systems were installed on a tripod and included a windscreen to protect the sensor from wind. * Orientation: the final orientation of the DYNAMAP low-cost sensors with respect to the traffic flow is still undefined. For this reason, recordings were made with three orientations: putting the sensor in the direction of the traffic -forward orientation-, in the opposite direction -backward-, or orthogonal to the vehicles flow. Moreover, three elevation angles of the sensors positions were also employed: \(0^{\circ}\), \(45^{\circ}\) and \(-45^{\circ}\). Figure 1: Recording equipment. Between 18 and 19 May 2015, the recordings were conducted in six sites along the A90 highway in Rome to collect suburban audio samples. They constituted a representative subset of the 17 sites in this pilot area according to the following four classes [36]: single road, additional crossing or parallel roads, railway lines running parallel or crossing the A90 motorway, and a complex scenario including multiple connections. In particular, the recording equipment was installed in six highway portals owned by the DYNAMAP partner ANAAS S.p.A.(see Figure 2), a government-owned company under the control of the Ministry of Infrastructure and Transport in Italy. During these recordings, the weather conditions were dry and sunny, and with an average temperature of 19 \({}^{\circ}\)C.  
From 20 to the 21 May 2015, the recording campaign was moved to district 9 pilot area in Milan to collect urban road traffic noise samples in twelve locations at different times of day and night following [37] (see Figure 3 for examples of recording setup). More precisely, the recordings were conducted on the following locations:  
1. Near a hospital, including tramways and low traffic. 2. One-way road with very-low traffic. 3. Highly dense but slow traffic, with tramways, stone road surface, traffic lights and retentions. 4. Railways, very-low traffic. 5. Tram and railways, fast fluid traffic flow (multi-lane). 6. City center, shopping road, crossroad with traffic lights. Wet road surface. 7. Very low fluid traffic two-way road at night (multi-lane). 8. Two-way road with fluid traffic near university (multi-lane). 9.