Applications

BLE Audio Hearing Aids

Image Source: highwaystarz/stock.adobe/com

By Bonnie Baker for Mouser Electronics

Published January 25, 2022

Introduction

Strip away headphone- and speaker-wire hassles with Bluetooth^® Low Energy (LE) Audio. The Bluetooth approach revolutionizes audio by changing how we hear the world and experience audio. While the basis of Bluetooth LE audio is on the low power LE standard, it offers many new and improved audio features, including Multi-Stream—which synchronizes or separates left and right stereo channel transmission directly to the left and right hearing aid or earplugs. But the largest Bluetooth technology solution area is Bluetooth's LE audio streaming (Figure 1).

Bluetooth LE Audio with lines leading to LC3, Broadcast, Multi-Stream, and Hearing Aids logos

Figure 1: Bluetooth LE Audio wireless options. (Image Source: Bonnie Baker)

Automotive Audio Streaming

High-quality, low-power codecs support true multi-stream audio Bluetooth headphones and earbuds. An updated Bluetooth audio streaming system improves the management and sharing of wireless audio streams between devices without overworking the batteries in phones, smartwatches, or headphones.

Bluetooth audio streaming units allow you to wirelessly send music and other sound files to your car stereo from your phone. If you have music and audiobooks on your phone, a Bluetooth car stereo will play them by using Bluetooth's advanced audio distribution profile (A2DP).

Multi-stream and broadcast Audio support allows you to control multiple, independent, synchronized audio streams from a source device—like a smartphone—to many headphones, speakers, and audio sinks. Bluetooth LE will implement audio sharing between headphones, allowing you to broadcast audio.

The new Bluetooth audio standard provides audio streams simultaneously to their customers in public spaces, such as malls or gyms. This transmission style can be instrumental in museums, where tour guides stream places of interest directly to visitors' phones in various languages.

Synchronous Left and Right Channels

The high-performance synchronization capability of independent receiving devices supports advanced audio applications such as True Wireless Sound (TWS) earbuds and 3D sound. Typically, two audio sink devices receive the left and right audio frames. Each audio sink device independently decodes and renders the audio samples with a precision of fewer than three microseconds between left and right devices.

Bluetooth LE Audio Features

The critical communication channels for Bluetooth LE Audio are low power, high quality, high speed, and low latency.

Low Power

The primary claim to fame of the Bluetooth LE Audio format is its low power capability. The Bluetooth Low-Energy (LE) Audio module can transmit data over 40 channels at a 2.4GHz frequency band. The Bluetooth LE modules can operate for about four to five years with a small battery. In addition to this, Bluetooth SIG also announced a new codec—the Low Complexity Communication Codec (LC3)—providing high-quality audio at lower power and data rates.

Speed

Unlike classical Bluetooth, the Bluetooth LE modules do not have heating problems. Because the silicon temperature is lower, data transmission can occur faster. The Bluetooth LE Audio module has higher throughput and a more extended range.

Low Latency

It takes time to do the coding work at one end and then the encoding at the other. This circular coding process is typically less than ten milliseconds. What is the impact of this latency characteristic? This excessive time may seem like the circular process is slow. However, suppose you look at it from a human perspective. In that case, the ability for a person to discern if they hear an "echo" occurs with latency higher than one hundred milliseconds. This speed means that a perceived sent sound over a Bluetooth link gets to the listener as fast as the actual sound does (Figure 2).

Father and son with a bowl of popcorn cheering at a tv

Figure 2: An entire family, with or without hearing aids, can enjoy synchronized television sound together. (Image Source: fizkes/stock.adobe.com)

LC3 Codec Features

LC3 is an efficient Bluetooth audio codec for use in LE Audio profiles. It encodes speech and music at various bitrates and incorporates them in any Bluetooth audio profile. A good recommendation is to implement PLC (Packet Loss Concealment) at the receiving ends of audio connections, increasing audio quality.

The LC3 codec modules use the optional LC3plus codec to achieve low power optimization and exceptionally high sound quality. Bluetooth Low Energy (LE) is not LE Audio. The new LC3 codec promises better sound quality than the previously mandatory subband codec (SBC). The LC3 codec code uses spectrum and airtime more efficiently by creating shorter code and using a lower bit rate.

Further Enhancements with Bluetooth Version 5.3

A few of the future enhancements with Bluetooth LE Audio include the addition of periodic advertising, encryption key size control, connection subrating, and channel classification.

Power Reduction Using Periodic Advertising

The Periodic Advertising enhancement rejects redundant transmission while also reducing the system's power. The Periodic Advertising packets include the AdvDataInfo field to implement this advertising process.

Any Bluetooth LE product broadcasts data by utilizing the Period Advertising function. This function creates redundancy to increase the probability of receiving accurate data by reducing noise. The automatic transmission in rapid succession of multiple data packets containing the same data is designed to increase the probability of receiving the data and thus increases the reliability of the wireless transmission.

On the other end of the transmission, the receiving device often already has the data and engages in re-processing the acquisition of the new data packet. With the AdvDataInfo field in the device, the receiving device now recognizes when a data packet contains redundant data. As opposed to re-processing the data, the device discards it immediately. The sooner a receiving device identifies and discards redundant data packets, the less energy it spends processing those packets. With this additional bonus time, the device spends time scanning other channels. This process presents the energy-saving activity of rejecting redundant, fully processed packages, but it can also increase the duty cycle of one of the other channels.

Encryption Key Size Control—Improved Efficiency

Bluetooth version 5.3 offers enhanced Host Controller Interface (HCI) commands. These commands provide efficient host methods that ensure the encrypted connection between Bluetooth Classic (BR/EDR) devices uses a minimum acceptable key length. The HCI enhancements improve signaling efficiency in many Bluetooth Classic products, where encryption is mandatory or highly encouraged.

Bluetooth wireless devices ensure unauthorized third parties cannot access transmitted data between two connected devices by using encryption. One key factor determining the strength of the protection provided is the encrypted data key's size or length. In Bluetooth Classic (BR/EDR), the encrypt key size used by the two controllers negotiate data during connection establishment. Subsequently, the hosts query their controllers to select an acceptable minimum length key, and if not, the hosts can choose not to send data over the connection. Although this method is inefficient, data is not transmitted over connections that hosts see as appropriately protected.

Bluetooth Core Specification version 5.3 introduces a new optional Host Controller Interface (HCI) command (Set Min Encryption Key Size) to improve the situation. This command enables a host to specify the minimum key size a controller may accept when connecting to another device. In addition, the current HCI command controllers inform the hosts of a change of the encryption settings (Encryption Change Event).

In Bluetooth BR/EDR, controllers in connected devices negotiate encryption key sizes. With this change, the host informs, with the Host Controller Interface (HCI), its Bluetooth BR/EDR controller of the minimum acceptable key size. This enhancement also improves the outcome of the Bluetooth BR/EDR controllers and host key length negotiations.

Connection Subrating and Power Saving

Some product types spend much of their time in a low-duty cycle connection to conserve power. But when a particular application needs higher bandwidth, a quick change must occur with the connection parameters. Minimally-delayed connection parameters with connection subrating delivers a better user experience. This complete update occurs while retaining the power-saving properties of low-duty cycle connections.

Channel Classification

Bluetooth LE Peripheral devices can now provide a Central device with radio channel classification data. This action may be used by the Central device when performing channel selection during adaptive frequency hopping. This improves throughput and reliability by reducing susceptibility to interference at the Peripheral when the Peripheral and Central devices are not physically close to each other.

Conclusion

Once again, the Bluetooth Special Interest Group has pushed the wireless industry for the good. The enhancement of the new Bluetooth LE Audio format outperforms the Classical Bluetooth by introducing a new, more efficient codec and various new features. This article explored why Bluetooth LE Audio has become a game-changer for a new wireless audio generation. Bluetooth headphones will expect a surge in growth over the next five years. Additionally, TVs will rely on Bluetooth connectivity by delivering premium home audio and entertainment experiences. By 2025, this environment will contribute to an expected 150 million annual shipments. The Bluetooth speaker demand will continue to rise, meaning the Bluetooth LE Audio is here to stay.

Author Bio

Bonnie Baker is a seasoned analog, mixed-signal, and signal chain professional and electronics engineer. Baker has published and authored hundreds of technical articles and blogs in industry publications. She is also the author of A Baker's Dozen: Real Analog Solutions for Digital Designers as well as coauthor of several other books. In past roles, she worked as a modeling, strategic marketing, IC architect, and designer engineer. Baker has an Electrical Engineering Masters from University of Arizona, Tucson, Arizona, and a bachelor’s degree in music education from Northern Arizona University (Flagstaff, AZ). Enjoy reading Bonnie’s work as much as she enjoys sharing her career’s learned electrical nuggets.