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The inconvenient truth about Bluetooth audio

  • We need to talk about Bluetooth. Specifically, Bluetooth as it relates to digital audio transmission from smart device / computer to wireless headphone, streamer or loudspeaker.

    Not at all Bluetooth audio connections are the same. Some hardware pairings sound noticeably better than others, not just with detail retrieval but with their ability to communicate tone and texture. Audible differences come down to the codec (and therefore the hardware) in play: aptX or AAC over Bluetooth will withstand audiophile scrutiny in all but uber-high-end hifi systems; SBC over Bluetooth might not be so lucky.

    Bluetooth audio’s dirty secret is not that it doesn’t sound very good, it’s that it will only sound good if certain conditions are met. We must pay strict attention to our hardware’s specifications sheets if we are to realise Bluetooth’s full potential.

    Overseeing Bluetooth (audio’s) standards and development is the Bluetooth Special Interest Group. We sometimes hear this group referred to as the “The Bluetooth SIG”.

    From Wikipedia: “The SIG is a not-for-profit, non-stock corporation founded in September 1998. The SIG is headquartered in Kirkland, Washington. The SIG has local offices in Beijing, Seoul, Tokyo, and Malmö. The SIG does not make, manufacture or sell Bluetooth enabled products.”

    Bluetooth audio’s specifics can be found in the Advanced Audio Distribution Profile (A2DP). A2DP mandates SBC support as a bare minimum. In other words, every Bluetooth audio device, transmitter or receiver, must support SBC. This is our Bluetooth baseline. If no other codec presents, we still get sound.

    Again from Wikipedia: “The Low Complexity Subband Coding or (SBC), is an audio subband codec specified by the Bluetooth Special Interest Group (SIG) for the Advanced Audio Distribution Profile (A2DP)….As of A2DP version 1.3, the Low Complexity Subband Coding remains the default codec and its implementation is mandatory for devices supporting that profile.”

    Unfortunately, for listeners with an ear for better sound quality, SBC won’t satisfy. I liken its sound to Spotify’s ‘Normal’ streaming setting; tonally grey with cymbals that crunch more than shimmer. That’s fine for the mainstreamer squarely focussed on Bluetooth’s wireless convenience but less for those of who also demand better sound quality.

    Fortunately, higher quality Bluetooth audio is possible. The Bluetooth SIG have allowed for additional audio codecs to be slipstreamed into the A2DP, opening the door for hardware manufacturers to takes listeners beyond SBC’s baseline: MP2, MP3, AAC and Sony’s ATRAC. Oddly, we don’t hear much about those codecs’ deployment in the Bluetooth audio world.

    Making a bigger splash is Qualcomm’s aptX (HD) – a lossy codec like any other. Per MP3 or AAC, aptX can be used to compress digital audio into a less bandwidth-intensive stream. And like the early days of MP3, aptX’s owner Qualcomm claim their codec capable of “near CD quality”. The operative word is “near”. aptX (HD) isn’t lossless. At time of writing, A2DP isn’t yet capable of lossless codec deployment.

    Fortunately for us, an aptX-compressed Bluetooth stream sounds better than its SBC-compressed equivalent. Problem solved, right? Not so fast.

    Remember: aptX is an optional codec. It must be present at both ends of the Bluetooth connection – in the smartphone/laptop AND headphones/streamer. If it isn’t, the Bluetooth audio connection reverts to the inferior sounding SBC. Apple macOS/OS X users can verify aptX’s presence with a simple right click – details here.

    Let’s exemplify. Sennheiser’s promotional copy promises the following of their Momentum Wireless headphones: “…the high-definition aptX® codec carves out every aural nuance in even finer detail. Thus, the trademark MOMENTUM sound becomes still more brilliant.”

    That might be true. But Sennheiser are only giving us, quite literally, half of the story. In order to realise aptX’s aural nuance carving capabilities, it must also be present in the transmitting device. And this is where the devilish details reside.

    Windows 10 supports aptX – no problems there. Ditto MacOS but according to Streamlength USB code developer Gordon Rankin, “If WIFI=2.4 or more than 2 BT desktop, or 1 BT laptop it will revert to SBC.” This information reportedly came from Apple directly.

    I have no issue in getting my 11” MacBook Air to talk aptX to the Momentum Wireless – they sound great too. Less so when cutting over to an iPhone 6S Plus. What gives? iOS does not support aptX and so the Bluetooth audio connection reverts to the inferior-sounding SBC. And it will do invisibly to the end user.

    For the audio-centric iPhone user considering a pair of aptX Bluetooth headphones, this is essential intel. Ditto any iPhone/iPad owner eyeing KEF’s Motion One earphones. Their spec sheet reads “Bluetooth v4.1 with aptX codec”. Does that mean a complete absence of AAC support or did KEF just not list it on their website? We note a similar story with KEF’s LS50 Wireless loudspeaker: “Bluetooth 4.0 with aptX® codec” – it’s all she wrote.

    What can we do to get the Bluetooth connection away from SBC?

    There are two options:

    1) Swap out the smartphone for an aptX-capable model. Qualcomm maintain a list on their website. Choice is currently restricted to Android and Windows smartphones where the hardware manufacturer – not the OS developer – has licensed aptX from Qualcomm.

    2) Swap out the headphones for an AAC-capable model. iOS might not talk aptX but it does do AAC. When used as a Bluetooth audio codec, AAC sounds every bit as good as aptX. Telling us this in the real world are Sony’s MDR-1000X Bluetooth headphones which offer the best of both worlds: support for aptX and support for AAC. Sony understandably make a big noise about AAC in their promo material – the MDR-1000X are goto ‘phones for the iOS user. Without AAC support I might not have seen their Bluetooth-derived appeal.

    A similar two-pronged attack on SBC can be seen on the specifications sheet for iFi Audio’s iONE DAC. It too supports aptX and AAC. That means decent sounding Bluetooth audio for all iPhones and iPads plus selected Android and Windows phones. For this iPhone and iPad user, AAC support is the killer feature, not aptX. And if your smartphone supports neither codec, you’re back to SBC.

    Don’t believe the aptX hype. Despite its ubiquity in the audio hardware space, perhaps amplified by manufacturers seeking instant audiophile credibility, consumer caution is advised.

    This week noise was made about the addition of Sony’s LDAC codec to Android O, the next version of Google’s mobile operating system, scheduled for mass market rollout in Q3 2017.

    From the horse’s mouth, “LDAC™ is a new audio technology from Sony that allows you to enjoy high quality wireless audio via Bluetooth. With 3x the data transmitted, LDAC provides an enhanced wireless listening experience for all your music.”

    SBC transmits audio data at around 330kbps, LDAC at 990kbps. Irrespective of Sony’s frequent use of hi-res audio verbiage in talking up LDAC’s capabilities, it too remains a lossy codec. Its inclusion in both the aforementioned MDR-1000X and it turn paired with the Sony NW-ZX2 make for a seriously compelling listening experience.

    This all-Sony hardware combo underlines the need for the better sounding codec to be present in both transmitter and receiver. Just like aptX. Just like AAC.

    Before dropping cash on the counter, consumers have work to do — dig into a Bluetooth headphone’s (or DAC’s or loudspeaker’s) codec inclusivity. Does it do aptX, AAC or LDAC? Experience tells us that if it’s on the spec sheet, it can also be found in the promotional material. Then look for the same codec in your favoured transmission device: smartphone, tablet, Mac or PC. A mismatch will lead to SBC and possible disappointment. How very inconvenient.

    Further information (for 2019): Tangled up in Bluetooth

    CORRECTION: an earlier version of this article stated that Astell&Kern’s XB10 Bluetooth dongle was not AAC-capable. It is.


    John H. Darko

    Written by John H. 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.

    Follow John on YouTube or Instagram


    1. Device manufacturers sometimes don’t pay much attention to AAC Bluetooth.

      Cambridge audio make a Bluetooth dongle for their integrated amps for $99 which only supports aptX- which could end in disappointment for the uninformed customer who owns an iOS device

        • But how does one know their iPhone is actually connecting over AAC to a headphone like the. MDR-1000X, instead of reverting to SBC? As I’ve explained in the post below, I can clearly hear an audio issue with certain tones, when connecting over Bluetooth to an iOS device that doesn’t surface when using the cable.

          The headphones have a ‘Priority on sound quality’ mode that should let them make the highest possible connection, in this case AAC, but that soft crackling does cast some doubt on that and there is no way to check.

          But if it is, might AAC not be as good as we might have thought? Not jumping to conclusions here, but I do wonder.

          • I don’t hear crackling from my MDR-1000X as you do. And as stated in the piece, we don’t know which codec an iPhone is using at any given time.

            And glad you dug that piece – I was worried that for the beginner network audiophile it would be too much in one hit.

            • Thanks for the reply. Thankfully, I only hear it in certain pieces like that Greg Barley song ‘Moonbeams’, but I guess I have to do some more homework then. See if I can find someone with an APTX device or LDAC, see if that makes any difference. The problem not ocurring over cable does imply a BT issue, but like you, I’m not an engineer, so who knows….

              Really appreciate all your pieces by the way, especially was very, very useful.

            • You’ve also highlighted another problem with Bluetooth – connection-type obfuscation makes it tricky to diagnose problems. Try to get your hands on a Sony. My NW-ZX2 Walkman tells me which codec is in play.

    2. Nice article. Great you’re taking the effort to also shine some light on the ‘lesser audiophile’ stuff, that does however make the commuter’s life a whole lot better.

      Bought my MDR-1000X three weeks ago (second hand) and I have to say I am very impressed. It won the direct comparison in the store with the wireless Sennheiser, Bose and B&W’s, so this will replace my broken B&W P5. As a commuter this is quite a leap forward. Suddenly there is peace and quiet during my travels and I actually get to hear the music. All else fades away. The touch controls of the earcup are phenomenal.

      BUT *****: Last week I did find an instance where over bluetooth the Sony couldn’t seem to handle the nuance of a piano song. There seems to be some soft veiled crackling in certain songs. Structurally.

      If anyone is willing to try this: When I play the Greg Barley song Moonbeams on Spotify (streaming quality extreme, bluetooth connection) on my MDR-1000X from my iPhone 6, the crackling starts at about the 30 second mark of the song.

      -Cabled, without power and with the 3,5mm cable it does not seem to occur (but sound isn’t that great that way)
      -Cabled, with power and noise cancellation on it does not seem to occur. Quite a bit of hiss though, but that seems to be the recording. My AKG-701 and Denon 300 also had some hiss, especially the AKG
      – Cabled, with power and noise cancellation off it does not seem to occur

      So it does seem to be a BT issue. It is not just one earcup. Both give this gentle crackle or static, hard describe but evidently there. And very annoying.
      I can’t test if this is the lower iPhone Bluetooth standard (this article claims AAC should be up to snuff), since we don’t have a device with other high(er?) bluetooth standards. NO APTX or LDAC yet in this household.

      Anyone willing to try as well and post the results? I tried the corresponding head-fi topic, but without much results (one person experienced the same thing). The rest is a little busy praising LDAC. If that is the solution, cool, But before reaching for my wallet yet again, I would like to reproduce the problem and make sure it’s actually generic for iPhone Bluetooth or something else might be wrong.

      I could really use some second guessing here. 🙂

    3. What about battery usage? We’ve been told BT lossless is a no-go because of its battery demands. Now comes Sony with a 990 kbips format… Why not go that little bit further and get to CD’s 1411 kbps?

      • I’m not an engineer so I know not. I think the Bluetooth SIG are working on lossless possibilities. I *think*. Perhaps someone else reading this can shed some light on the matter?

    4. Hi John, hope you are feeling refreshed after your holiday!

      It is my understanding from press outlets other than The Verge (e.g. Android Police) that Android O AOSP, rather than merely the proprietary layers to be featured on the Pixel 2 range, will introduce native Bluetooth transmission for aptX and aptX HD in addition to LDAC (and I’ve also found a mention of AAC – but not explicitly aacPlus / HE-AAC – though I cannot find the referenced screenshot: ).

      Presumably Google will pay lump licence fees to CSR / Qualcomm and Sony rather than the manufacturer of each Android O device instead paying a model licence fee and per-unit royalty?

      In related news, I notice that V-MODA have just released the Crossfade Wireless 2 Bluetooth (4.1? 4.2? I’ve searched but can’t find a definitive answer) headphones with an SBC receiver on the Matte Black and Matte White colours and an aptX (though not aptX HD) receiver on the Rose Gold colour (and though the predecessor supported AAC and aacPlus / HE-AAC – – V-MODA CEO Val Kolton has not confirmed whether either are supported on the new model):


      “Can I pair my headphones to two devices at the same time?

      Yes, Crossfade Wireless are able to maintain Bluetooth connection with two devices simultaneously such as smartphone+laptop, smartphone+tablet or smartphone+smartwatch”

      The new Samsung Galaxy S8 and S8+ (incidentally based on Android 7.0, not 7.1) also features this functionality:

      “Bluetooth Dual audio – Stream audio from one smartphone to up to two Bluetooth headsets or speakers simultaneously. You can adjust the volume levels for each device independently, allowing users to listen comfortably.”

      along with a Bluetooth 5 transmitter, although I cannot find any explicit references to aptX, aptX HD, AAC or aacPlus / HE-AAC:

      “Bluetooth v 5.0 (LE up to 2Mbps)” /

      Thanks, Nick.

    5. Another aspect here is licensing:

      SBC is free and mandated by the BT SIG. It is a compression algorithm designed to balance fidelity with battery life, and does a pretty good job.

      aptX on the other hand is ADPCM, supports very high bit rates, sounds great, and sucks up more battery life than SBC. But even more importantly, it’s NOT free. There is a license attached to it – I thin Qualcomm owns it now. This always leads to vendor headaches, especially since BT enabled devices have thinner margins.

      I think though given the way the industry is heading, BT will become more and more important – even to us audiophiles.

    6. Totally agree that you need APT-X or equivalent to get decent quality over Bluetooth; I did some testing a while back through my main system (Ayre/Harbeth) and the difference was akin to that between MP3 320 and CD quality.

      Far more than the difference between a cheap £5 adapter and an expensive one for ‘normal’ BT (learning point – for general background work or car the cheap option is surprisingly acceptable)

      I have to say that the obvious solution is to use the phones wired. Yes yes, that sort of negates getting BT phones. Except I’m most interested in the noise cancelling for use when out and about or working in a noisy office. The new Sony’s are top of the list at the moment; the fact that they do wireless as well is a benefit rather than their raison d’etre for me. But then I’m not an iPhone user. And also probably not a typical user. So bit of a pointless post really!

    7. If only the bluetooth latency could be removed . . . oh the possibilities for watching movies and other audio-visual streams.

      And +1 for Sony. My ZX2 and MDR-100ABN headphones really are a joy to listen to on the go (couldn’t stretch to the 1000’s).

    8. For all this nitpicking negativity I’m absolutely loving my sony bt headphones playing youtube and crunchyroll latenight without upsetting anyone else. Being cabless the audio quality is so nice….cheers…

      • If it’s the MDR-1000X, there are no nits to pick. They do aac, aptX and ldac. All bases covered. And yes, convenience is underrated in the audiophile sphere.

    9. One of the things I always point out to people is that listening over Bluetooth is fine, but that the quality of the source material is important. If you’re listening to lossy files the stream will be transcoded for transmission over Bluetooth (be it in AAC, aptX or whatever), which can impact the sound quality. There’s certainly a case to be made for using lossless files or streams (such as from Tidal or Qobuz) even when listening to a pair of Bluetooth headphones. Also, I’m still looking for a definitive answer to what happens when you for example play an AAC file over a Bluetooth connection which also uses AAC for streaming. Is the AAC file transcoded to another AAC file/stream or is the Bluetooth technology smart enough to recognise the file is in the same codec used for streaming, and just pass it on?

    DAP + smartphone = Onkyo Granbeat DP-CMX1

    Difference with a capital D – Audeze’s iSine 20