No, Bluetooth cannot deliver hi-res audio

  • From a 2016 IFA press conference in Berlin, Sony launched the MDR-1000X to the European market: a Bluetooth headphone that would debut the company’s ‘hi-res-capable’ (but lossy) LDAC codec. If that has your brow furrowed, you’re not alone. Enter Australian hi-fi journalist Jez Ford: if (hi-res) audio carried over Bluetooth via LDAC and then upscaled via Sony’s DSEE HX algorithm is audibly indistinguishable from hi-res audio (as Sony had claimed), why bother with hi-res audio?

    Regular (or sharp) readers will know of my general indifference toward hi-res audio – especially DSD – but the answer to Ford and other hi-res enthusiasts is that we still need ‘traditional’ hi-res audio – as streamed by Tidal or Qobuz or Amazon – because network streams are lossless and LDAC installed as part of Bluetooth’s A2DP is not. Losslessness isn’t a nice-to-have bonus. It’s fundamental to hi-res audio’s premise of ‘studio-quality sound’.

    According to Sony, LDAC compresses data streams down to a maximum of 990kbps. That bitrate then drops to 660kbps and again to 330kbps as Bluetooth connection quality diminishes. Even 990kbps is insufficient for the higher bitrates demanded by lossless CD-quality audio carriage: typically anywhere between 600kbps and 1411kbps. A lossless hi-res stream, therefore, would call for kbps in their thousands. LDAC can’t get close. And neither can any other Bluetooth audio codec where maximum bitrates fall below LDAC’s 990kbps: Qualcomm aptX HD (570kbps), AAC (320kbps) or SBC (342kbps).

    Those numbers tell us that allย Bluetooth audio codecs are lossy. They throw data away in order to squeeze the digital audio signal through the Bluetooth pipe. And we cannot get back what we throw away.

    Why then did Sony take the time and money to develop LDAC? For headphone manufacturers, Bluetooth offers some pointed advantages over a traditional analogue connection. It permits digital domain signal reception and, therefore, DSP for 1) easier optimisation of the driver’s frequency response and 2) varying degrees of active noise cancellation. The way I hear it, ANC gives us more than Bluetooth’s lossy compression takes away; the 1000X series has been my goto Bluetooth headphone for winter walkabouts since its 2016 debut.

    For Sony, improving a Bluetooth codec’s compression technique potentially improves the listening experience and thus gives it an edge over the competition. LDAC offers up to 1.5x the data throughput of Qualcomm’s aptX HD.

    At home, it’s a different story. Audiofolk like yours truly don’t need Bluetooth transmission to facilitate digital connections (and DSP). With wires connecting gear that is never required to be portable, Bluetooth is relegated to a convenience input — for friends and family. And for those who prioritise convenience over audio quality, Bluetooth audio receivers like iFi’s Zen Blue and Shanling’s BA1 (announced this week) bridge the phone-to-hifi gap very nicely. But there’s a wrinkle…

    Shanling’s website copy describes their LDAC-supporting BA1 Bluetooth streamer as offering “a hi-fi level [sic] hi-res audio playback over Bluetooth”. I’m sure the company lawyers have been over the promo blurb but is it not just a bit misleading? ‘Hi-fi level’ is subjective enough but what of ‘hi-res audio playback’? Does this not imply hi-res audio as many of us already know it – lossless audio at 24bit/48kHz and above – can be streamed over Bluetooth? “High bitrate” is not the same as “lossless” and the lossy nature of LDAC’s compression algorithm isn’t made clear to would-be customers.

    Similarly, iFi describes their LDAC-loaded Zen Blue as a “High-resolution wireless streamer” which, to the unwitting buyer, could read as if Bluetooth alone will take care of his/her hi-res streaming needs. Does ‘high-resolution’ here mean highly resolving or does it imply, say, 24bit/96kHz without data being trashed?

    Like Sony’s 1000X headphones, neither the iFi Zen Blue nor the Shanling BA1 will flat out refuse to play a hi-res file over an LDAC-fuelled connection but the codec will still discard musical information (data) for the stream to squeeze down Bluetooth audio’s tunnel. And just like Sony in 2016, we now find iFi and Shanling (unwittingly?) blurring the lines between networked hi-res audio streaming and Bluetooth hi-res audio streaming. Lossy hi-res could be likened to vegetables being described as “fresh frozen” — oxymoronic!

    That all of this LDAC talk is irrelevant to iPhone users. Like Qualcomm’s aptX, Apple flatly refuses to implement anything other than AAC whose 320kbps ceiling makes a mockery of any iOS-derived hi-res-over-Bluetooth intent. This doesn’t mean that Bluetooth audio streaming can’t sound good – it can. Hardware implementation is as crucial as codec support.

    To wit, iFi’s slippery use of language recently tripped up a well-known hi-fi YouTube reviewer who marvelled about the Zen Blue’s hi-res support and how far Bluetooth audio technology had come in recent years. Indeed it has, but lossless transmission of digital audio isn’t part of that progress. The Bluetooth SIG – the organisation who effectively determine what Bluetooth audio can and can’t do – has gone in a different direction with Bluetooth LE. What would it take for the SIG to implement lossless FLAC carriage over Bluetooth (is the million-dollar question)?

    Until that question is answered, Bluetooth cannot take CD-quality audio from phone to headphone (or streamer) without loss. Hi-res audio? A Bluetooth pipe dream! And if ‘hi-res Bluetooth streams’ are audibly indistinguishable from the lossless hi-res audio that we pull down from the cloud over Ethernet or WiFi, why should we bother with lossless hi-res?

    Further information: Sony | iFi | Shanling

    Written by John

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

    Darko.Audio is a member of EISA.

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