Supports Bluetooth multi-channel sound

Bluetooth has a completely new audio architecture

If you consider that Bluetooth audio was already specified in the early 2000s, it is amazing what has been achieved with this old-fashioned radio architecture in recent years. Above all, the popular wireless earphones should be mentioned, which are not connected to each other with a cable.

But these devices are also a prime example of how creative developers have to be in the meantime in order to achieve their goal with the completely outdated Bluetooth audio technology: Since Bluetooth can only transmit a single stereo signal, and this can only be done via point-to-point. Point connection, the mobile phone first sends the data stream to the (mostly) right in-ear. It plays the right audio channel and transmits the left channel to the other in-ear.

The situation is similarly difficult when it comes to better Bluetooth audio quality: there are alternatives to the Low Complexity Subband Codec (SBC) such as aptX and aptX-HD. However, these are proprietary, cost license fees and are not supported by all operating systems.

The next generation of audio

The Special Interest Group (Bluetooth SIG) responsible for the further development of Bluetooth stated some time ago that the current standard had reached its limits. The members of the SIG therefore decided to call it “Classic Audio” in future and to launch a new generation of Bluetooth audio - called “LE Audio”. According to the group, the techniques and concepts introduced for this purpose are so extensive that they will “enable audio innovations to be implemented over the next 20 years”.

The Bluetooth SIG used the CES to present LE Audio - knowing full well that the required set of around 20 specifications is not yet ready: The most important components will not be published until the first half of 2020. Only the new core specification has already been published, so Bluetooth 5.2 is up to date with immediate effect. Classic Audio should continue to exist, so that there will be devices in the future that support one of the two or both operating modes.

New codec

At the center of LE Audio is a new codec called LC3 (Low Complexity Communications Codec) with sampling rates of 8, 16, 24, 32, 44.1, 48 kHz, data rates from 16 to 320 kBit / s and frame sizes of 7.5 and 10 milliseconds supported. Developers should be able to better adapt the audio transmission to the respective needs. As with SBC, no license fees are due for using LC3 for Bluetooth audio transmission.

According to SIG, users benefit from better audio quality compared to SBC. According to SIG, listening tests have shown that the current standard codec at a maximum (stereo) data rate of 345 kBit / s still sounds audibly worse than the LC3 at 160 kBit / s. At a data rate of 248 kBit / s, LC3 is said to have received 50 percent better average marks than SCB with comparable 237 kBit / s.

According to SIG, LC3 can also be used to transmit audio data at a lower data rate and thus save electricity while maintaining the same or slightly better quality than SBC.

According to SIG, LE Audio also scores very well in terms of latency. It is said to have decreased from 100 to 10 milliseconds at the protocol level compared to SBC. In keeping with this, Dialog Semicoductor demonstrated at the presentation of LE Audio how 5.1-channel sound, LC3-coded, can be transferred from a TV to a surround system via Bluetooth LE Audio without losing lip-synchronicity when playing videos.

Multistream audio

LE Audio can transmit individual audio channels separately from one another, which in turn can be combined into groups. In the case of the "True Wireless" earphones mentioned, this means that the cell phone will in future send the data for the right and left channels separately to the respective in-ear. Isochronous communication is used, the signals are transmitted at constant intervals. Bluetooth SIG speaks of 25 microseconds.

This “multistream audio” is intended to ensure more robust transmission and better stereo imaging. Since the forwarding of an audio channel is no longer necessary, smaller and energy-saving devices can be developed. Voice control should also be easier to implement, since control commands and any audio return channel (for voice transmission with headsets) are transmitted separately.

The combination of low power consumption, high audio quality and multi-stream connections made possible by LE Audio enables SIG to specify Bluetooth audio for hearing aids for the first time.

Broadcast audio

A new broadcast mode is new at LE Audio. Here, a transmitter transmits audio data streams to any number of receivers without being individually coupled to them.

In combination with multistream audio, groups can be formed, even several in parallel. The transmission of an audio data stream in stereo is just as possible as the transmission of several streams with different language versions - either in mono or stereo. This technology is to be used for what is known as “Bluetooth audio sharing”.

In a private environment, for example, several friends could listen to music together through headphones. The main area of ​​application is likely to be found in public spaces in the future. In museums, for example, audio sharing could ensure that you can use your own earphones when using audio guides. Conference participants can have translations in their own language streamed onto the headphones.

In the USA in particular, gyms and airports are also a large potential market for audio sharing. At the moment, TVs with subtitles are often running in silence in these places. In the future, you could hook up to the TV audio stream with the push of a button.

According to the SIG, audio sharing will also become standard in many cinemas and even in theatrical performances. This is not only about alternative language versions, but users with hearing deficits can have the sound sent directly to their hearing aid. A solution that can also be used at home on TV.

So that unauthorized persons cannot latch into the transmission, the system provides an optional encrypted transmission, which can only be viewed after entering a passcode on the receiving device. The Bluetooth SIG sees this "audio sharing" as a completely new application for its radio protocol.

Time schedule

Numerous chip manufacturers support Bluetooth LE Audio, functional prototypes are available from Qualcomm and Nordic Semiconductor. Due to the lack of specifications, SIG currently assumes that the first chipsets will be ready in about a year and that LE Audio will be found in the first products in one to two years.

According to the group, there will then be devices that only support Bluetooth LE audio, e.g. for hearing aids. The typical Bluetooth audio sources such as cell phones, tablets or laptops will usually continue to support the “Classic Audio” mode in the future. (nij)

This article comes from c't 3/2020.