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Bluetooth LE Audio: multi-streaming, new codec (but no lossless)

  • Active noise-cancelling (ANC) headphones have been around for a number of years but in 2019, the technology made the leap to True Wireless Earphones (TWE). First came the Sony WF-1000XM3, then Apple’s AirPods Pro. From the floor of CES 2020, Klipsch, Panasonic, Technics, 1MORE and Audio-Technica are joining the TWE ANC party; lest they are left behind by an ever-expanding corner of the personal audio market where consumer dollars are often won on feature set alone.

    Also announced in Las Vegas this week, a more fundamental development in the bedrock on which TWE and wireless headphones are built. The Bluetooth Special Interest Group (SIG), the organisation that oversees the Bluetooth’s specifications, has announced at CES 2020 the forthcoming availability of Bluetooth Low Energy (LE) Audio, where lossy compressed digital audio will be streamed using a lower energy spectrum hitherto reserved for smartwatches and other wearables.

    Underpinning Bluetooth LE Audio will be a new codec: Low Complexity Communications Codec (LC3) promises superior audible performance to (the somewhat weak-sounding) SBC and from a 50% reduction in data rates. For hardware manufacturers, that means greater runtimes from existing earphone/headphone batteries or the same runtime but from smaller batteries. The upshot, in time, will likely be the introduction of smaller, lighter Bluetooth headphones/earphones.

    Furthermore, an optional LC3plus codec seeks to standardise how high-res audio sources are handled by the Bluetooth audio stack. LC3plus provides a data-compressed transmission pipe for PCM source files up to 24bit/96kHz. Like Qualcomm’s aptX (HD) and Sony’s LDAC, LC3plus’ data compression will still be lossy — just because a Bluetooth audio codec claims hi-res audio compatibility doesn’t mean it’s not discarding data along the way. However, unlike aptX (HD) and LDAC, LC3plus will be an open standard.

    LE Audio also brings some big functional changes to the way Bluetooth audio is streamed. As of right now, most TWE operate in a master/slave configuration: one earbud receives a single Bluetooth audio stream, keeps one set of channel data for itself and then feeds the other channel to the other earbud. Hardware manufacturers must ensure that L/R channel audio is kept in sync. LE Audio sidesteps this engineering challenge by permitting one separate stream per channel. The source – smartphone or computer – will instead transmit TWO fully synchronised data streams, one to each earbud.

    This new multistream capability can be scaled to multiple headsets where one LE Audio source can transmit the same audio to multiple pairs of headphones/TWE and in perfect sync. That’s useful for anyone wanting to host their own Silent Disco or for venues wanting to send the same audio stream to many wireless ear/headphone wearers.

    The original Bluetooth audio stack has been renamed Classic Audio and, according to the Bluetooth SIG, can co-exist with LE Audio implementations, thus ensuring backwards compatibility with legacy source devices.

    Alas, LE Audio brings us no closer to the Bluetooth audio holy grail: lossless transmission. For that, we still need hardwired connections.

    Further information: Bluetooth SIG | LC3

    John Darko

    Written by John Darko

    John currently lives in Berlin where creates videos and podcasts and pens written pieces for Darko.Audio. He has also contributed to 6moons, TONEAudio, AudioStream and Stereophile.

    Darko.Audio is a member of EISA.

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