< CASE STUDY >

Device supporting hard of hearing children with BLE Audio

15 msAudio delay

16 kHzSample rate

48 kbpsBitrate

16 bitSample res.

Client

Audinor - a company dealing with innovative hearing aid solutions, specializes in creating and supplying devices supporting hard of hearing children in schools and kindergartens. Every day, Audinor tries to improve access to education for all students, and for this purpose it constantly strives to implement the latest technologies to break down communication barriers as efficiently as possible.

nRF Connect SDK

The documentation and sample applications provided as part of the nRF Connect SDK enable easy understanding and implementation of the system. They offer the function of updating the device software via DFU, which increases its usability and security.

Zephyr

An open-source real-time operating system that provides support for many processor architectures, which allows its flexible use in a variety of technological projects.

LC3

LC3 (liblc3)

An audio codec designed specifically for BLE Audio, available under the open-source Apache 2.0 license and offering support for LC3 Plus extensions, which increases its adaptability and functionality in modern audio systems.

Challenge

A company supporting the education of hard of hearing children has encountered significant technological barriers with their current product. The proprietary communication protocol used so far not only limited the possibilities of integration with other systems, but also became obsolete in the face of new standards such as BLE Audio (Auracast) technology. The effects of this situation were:

Minimizing delays

Optimizing application code to minimize audio latency to ensure user comfort. Minimizing delays in sound transmission is key to avoiding the annoying echo effect.

Reliability and range

Maintaining and improving high levels of reliability and coverage, even when both protocols are used simultaneously. Coexistence of proprietary protocol with BLE Audio.

Integration with BLE Auracast

Integration with the new BLE Audio technology (Auracast) and maintaining compatibility with existing systems with the possibility of future expansions. Adaptation of the existing communication protocol to the requirements imposed by the BLE Audio specification.

The project was aimed not only at integration with Auracast, but also at maintaining and even improving high sound quality, minimizing delays and also increasing the range and transmission reliability.

The customer decided to use the Nordic nRF5340 microcontroller, which offers support for BLE Audio technology and is similar to the previously used nRF52840. An important aspect of the project was verifying the correctness of the hardware provided by the client. The project required good time and resource management to deliver the finished solution within the agreed deadline.

One of the requirements was to update the communication protocol of the existing solution to enable better integration with the new technology.

An important element of the project was testing the solution in terms of operation with other BLE Audio solutions available on the market. This required collaboration with other solution providers and a solid understanding of technical specifications.

What is Bluetooth Auracast™?

Bluetooth Auracast™, formerly known as Bluetooth LE Audio Broadcast, is a new technology whose application in technologies supporting the hard of hearing is a revolution in the way hearing aid users can experience sound in their surroundings. Auracast allows you to wirelessly share audio from one device to multiple receivers. For example, in public spaces such as cinemas, theaters or lecture halls, sound from the audio system can be transmitted directly to the hearing aids, eliminating interference and improving the clarity of the received signal. This means that Auracast can significantly improve the quality of life of people with hearing loss, enabling them to participate more comfortably and fully in everyday and cultural life.

Solution

Due to the decision to use the nRF5340 microcontroller, we decided to use the C language and tools (SDK) provided by the manufacturer. The project was based on nRF Connect SDK provided by the microcontroller manufacturer and the open source Zephyr RTOS. Extensive documentation and a multitude of sample applications allowed us to quickly start working on the project.

In order to update the existing communication protocol, we decided to use a 10 millisecond packet size to make the existing protocol as similar to BLE Audio as possible. The previously used Opus audio codec has been replaced with LC3 to ensure compatibility with the new technology. At the same time, we have improved the sound quality. Among the many available options, we chose LC3 because it is an audio codec designed specifically for BLE Audio.

We used the implementation of the LC3 codec provided by Google - liblc3. Its advantages are:

full compliance with the LC3 codec specification, which ensures compatibility with other devices
open-source Apache 2.0 license, which allows free use of the code
availability of the source code, enabling the creation of a codec for any platform, including nRF52, on which the previous version of the system was based
support for LC3 Plus extensions that may be used in the future. LC3 Plus offers wider codec configuration options, such as selecting bitrate, sample rate, and sample resolution

Audio latency has been minimized to ~15ms using proprietary protocol and to ~30ms using BLE Audio. Low latency is crucial to our system because it avoids the tiring echo effect.

The final application supports DFU (Device Firmware Update), which allows for remote software updates of the device. Thanks to this, the customer can easily update the software of their devices in the future using the mobile application. This limits the risk associated with system maintenance and allows for quick response to possible software errors.