# Immersive Two-Channel Recordings Based on Personalized BRIRs and Their Applications in Industry
## 1 Introduction  
In recent years, immersive audio technology has witnessed several important breakthroughs; from IVAS (Immersive Voice and Audio Services), a communication codec for 5G mobile systems [1], to AMBEO 2-Channel Spatial Audio, a renderer designed to translate any original immersive or surround mix into two channels [2]. In professional audio production, immersive audio is becoming a critical component and a standard in creating engaging soundscapes for music, film, and gaming [3, 4]. Nowadays, the applications can even extend to areas such as acoustic metamaterials [5]. One of the primary applications of immersive two-channel audio in industry is in the field of virtual and augmented reality (VR/AR) [6, 7]. There is also a rapid growth in extended reality (XR) applications, which encompass both VR and AR as well as mixed reality (MR) [8]. Enhancing the sense of presence and immersion in such environments, making them more effective for training, simulation, and entertainment purposes is the main focus these days [9]; especially if the importance of three-dimensional immersive audio in XR technology is explored through the user-perspective approach [10]. Generally speaking, immersive audio aims to replicate the natural human perception of sound in a three-dimensional space, thereby offering a more engaging and realistic auditory experience. The most natural method of capturing this perception is through binaural recordings made by placing two microphones at the ears of a dummy head. There are more technologies in 3D sound acquisition, e.g., higher-order ambisonics [11]; however, binaural room impulse responses (BRIRs) obtained with binaural microphones are perfectly capable of creating a lifelike immersive experience on their own. However, with the industry moving forward and audio technology presenting new challenges, simple BRIRs may not be enough. Personalizing these responses is an easily adjustable task, whichshifts the focus from recording BRIRs using a dummy head to capturing them with the presence of a real person. This article highlights the importance of BRIR creation and the unique characteristics crucial for creating the best virtual immersive sound on any two-channel device. This article is structured into several sections. Section 2 presents an overview and basics of immersive sound as well as how human ears capture spatial sound. Section 3 outlines the capturing and creation of BRIRs and differences between them and HRIRs. Section 4 focuses on the externalization effect and its importance in any headphone based immersive audio. In Section 5, a few methods for creating two-channel audio are described. Section 6 presents the newest and most intriguing applications in the audio industry featuring personalized BRIRs and HRIRs. Finally, Section 7 concludes the article, summarizing the key findings and suggesting directions for future research. The importance of the approach using personalized BRIRs lies in the simple but fundamental differences in human sound perception. The most popular yet generic head-related impulse responses (HRIRs) obtained from standard Head-Related Transfer Function (HRTF) databases, which carry spatial cues and are traditionally used in rendering immersive audio, are comparable to the BRIRs obtained using a dummy head. Because of how both BRIRs and HRIRs are typically captured [12], they can fall short in providing a truly personalized experience due to individual differences in ear shape and head geometry. By tailoring the audio experience to the listener's specific anatomy, personalized BRIRs significantly enhance the realism and spatial accuracy of immersive audio [13; 14]. Moreover, immersive audio technologies are being increasingly integrated into consumer electronics, and not only headphones but even hearing aids, to expound the natural environment and recreate normal spatial hearing experience.