# Camera-Sourced Heart Rate Synchronicity: A Measure of Immersion in Audiovisual Experiences
## 3 Methodology
### Audiovisual Setup  
The basic audio presentation condition was implemented using the built-in loudspeakers of the _Mitsubishi LDT422V_ TV [48] (purchased in the UK). This 42-inch monitor was selected to fit between the existing loudspeakers configured in the listening room. In the high-end presentation: for the centre channel, a _Genelec 8010A_[49] model was used; for the height channels, _Genelec 8030 Cs_[50] were used; and for the subwoofer, a _Genelec 7040A_[51] was used. All of the remaining loudspeakers in the configuration were _Genelec 8040 As_[52]. All loudspeakers were purchased in the UK. The location of the loudspeakers in the 7.1.4 system matched the _Dolby_ guidelines [15]. As the distance from the listening position to the height channels (1545 mm) was slightly more than the distance to the other loudspeakers in the array (1250 mm), a delay compensation of 0.86 ms was applied for phase alignment. Figure 1 shows a diagram of the audiovisual setup.  
Each loudspeaker was calibrated at a loudness of 80 dB SPL (A-weighted) using _Room EQ Wizard (V5.30.9)_[53], an _Earthworks M30_ (purchased in the UK)microphone [54], and the built-in calibration switches to achieve a flat frequency response. An 80 dB SPL was chosen as the calibration loudness, as this is a reasonable and realistic listening level. The subwoofer crossover was set to 85 Hz, meaning frequencies below this threshold were produced by a dedicated bass speaker. The frequency response of each channel, excluding the low-frequency effect channel, was measured about a flat target response of 80 dB SPL from 20 Hz and 20 kHz. For all of these channels, the MAE between the measured and target response was less than 1 dB SPL. The media was decoded from the special edition version of the _Gravity_ Blu-ray, which contains both stereo sound encoded with _Dolby Digital_ at 320 kbps and _Dolby Atmos_ sound encoded with _Dolby TrueHD_ (48 kHz, 24 Bit) as versions of the soundtrack [8]. To enable this decoding, the _Dolby Reference Player_ was used [55].  
The room in which the system was set up is an acoustically treated studio control room. The background noise level was measured at 30.6 LAEq (15 min) using an NTI Audio XL2 analyser [56]. Participants were seated in the system's acoustically optimal area, commonly known as the _sweet spot_, with the 42-inch television screen being placed 1.61 m away. This distance was chosen based on guidance from the International Telecommunication Union (ITU) for pairing moving images with multichannel audio [57].  
Measurements of the stimuli loudness were performed in both conditions, initially objectively using a _Tenma 72-860A_[58] loudness meter (purchased in the UK) and then subjectively using two expert listeners. Using the objective approach, loudness was initially set to peak at 85 dB SPL (A-weighted). Subsequently, an expert listener was tasked with switching between the two conditions and adjusting them so they were both at a comfortable listening level and also had no perceivable difference in loudness. After the loudness had been matched perceptually, a binaural recording was made using a _Neumann KUI 100_[59] dummy head microphone (purchased in the UK) to allow for an objective  
Figure 1: Diagram of the listening room where the study took place. The subwoofer was placed under the desk, seven loudspeakers were placed around the listener 1.3 m above the ground, and four loudspeakers were placed above the listener, mounted on a frame attached to the ceiling. The angles subtended between the loudspeakers and the listener aligned with the _Dolby Atmos 7.1.4_ specifications [15]. The camera was mounted at desk height. The TV loudspeakers were on either side of the screen.  
comparison of the frequency content. The frequency analyses of these two recordings can be seen in Figure 2.