Opportunities and Challenges for Bluetooth LE Audio Assistive Listening Systems

Assistive listening systems (ALSs) for people with hearing difficulties have traditionally utilized magnetic induction hearing loops compatible with hearing aids (HAs) or headset systems connected via RF or IR links. The HA industry has been working with the Bluetooth SIG over the past decade to develop a new low-energy audio standard with broadcast capabilities. Released in 2022 as Bluetooth LE Audio with Auracast, it is poised to replace legacy ALSs, with potential compatibility across all future HAs and smart earbuds (a.k.a. "hearables"). However, several technical and practical challenges remain for the replacement of traditional ALSs by Auracast. Firstly, the recommended calibration of sound volume levels in Auracast transmitters and receivers mirrors the standard for calibrating hearing loops, but hearing loops are normally installed by trained professionals, whereas the relative simplicity of Auracast transmitters means that there is a likelihood that they will be set up by non-experts in many cases. Similarly, in large venues it is possible for installers of hearing loops to insert a time delay in the loop signal processing to match the time delay of the acoustic signal arriving through the air at the position of the loop in the venue. However, since Auracast users will not necessarily be constrained to one position in the venue, they will experience a range of different acoustic time delays. In this paper, we: i) review the development of the Bluetooth LE Audio with Auracast standard and how it compares to traditional ALS technologies, and ii) discuss signal processing approaches to sound level calibration and variable audio delay implementation in Auracast transmitters and receivers.