# Immersive Two-Channel Recordings Based on Personalized BRIRs and Their Applications in Industry
## 3 Personalized BRIRs  
Reproducing stereo sound through headphones provides some directional sensation on the plane of the ears but cannot place sounds above or below the head. The head and ears, particularly the auric, not only naturally block but also shape and filter sound as it travels around a person. Under standard listening conditions in a room with its own acoustics, there is always some source of sound and reflections occur. The interference of acoustic waves and the way they enter a person's ears can be artificially simulated using special impulse responses. This unique way of shaping sound for each individual, using not only the ears but also the shape of the head and upper body, is most often measured in a laboratory anechoic  
Figure 1: Timeline of most significant events in the history of BRIRs. chamber with dozens to hundreds of speakers located at different heights and angles. Under such conditions, an excitation signal is played from each source, and the impulse response is recorded in the listener's blocked ear canal using binaural microphones. A discrete stop-and-go method is commonly used, where the speakers for the measurements are placed in different positions and played back one at a time, while simultaneously recording the responses from the microphones. HRIRs recorded this way can then be processed into HRTFs. This method can take many hours and is therefore very cumbersome for listeners. Proposed techniques to reduce the total measurement time include interpolation, which reduces the angular resolution of HRTF measurements [27], and the Multiple Exponential Sweep Method (MESM) [28], which uses multiple speakers reproducing ESS signals in an interleaved or overlapping fashion. To reduce listener limitations, continuous HRTF acquisition combined with head movement recording is often used. This allows subjects to move their head freely in both the horizontal and vertical planes to best cover the position of their head across the 3D grid. VR equipment with head motion tracking and synchronized binaural recording is often used for this [7]. If, instead of a human, a dummy head is recorded, also with binaural microphones mounted in the dummy ear canals, then it is possible to create a database of HRTF functions with averaged impulse responses for each angle. The use of such a base, especially in the initial stages of research on spatial acoustics topics, is simpler than creating individual response sets; however, as mentioned earlier, the results are not always conclusive in being satisfactory. As mentioned, the creation of individual sets of HRIRs for each person is possible, as in the case of dummies, using binaural microphones. Objectively, such measurements should also be made in an anechoic chamber. However, recording signals from binaural microphones can be performed in any room that has its own acoustics. The responses obtained in this way are called BRIRs (binaural room impulse responses) and are responses carrying both HRIR properties and information about the rooms' spatial acoustics [29]. A simplified comparison of HRIRs and BRIRs is shown in Figure 2.  
BRIRs capture how sound propagates from a source, interacts with the environment, and reaches the listener's ears, encompassing direct sound, early reflections, and reverberation [30]. This makes BRIRs capable of providing listeners with more accurate spatial cues, thus improving their ability to locate sound sources in three-dimensional space [31]. Nowadays, the realism offered by BRIRs is crucial for VR and AR applications, where auditory accuracy significantly enhances the sense of presence and immersion in virtual environments [32]. BRIRs are also essential in architectural acoustics, aiding in the design of spaces such as concert halls and theaters by simulating how sound behaves in different environments [33]. Personalized binaural room impulse responses (BRIRs) represent a significant leap forward in the quest for high-fidelity spatial audio.