Review Index:

Qualcomm aptX Bluetooth Review: Improving Wireless Sound

Subject: General Tech
Manufacturer: Qualcomm aptX

Listening Impressions - Putting aptX to the test

Beyond the technical aspects of aptX, I can provide an account of my own experience with the technology. Rather than just write about it, I had requested to try aptX out myself with compatible hardware, and Qualcomm sent over an LG G5 smartphone and a pair of Sennheiser Momentum wireless headphones for a demo. As a skeptic of Bluetooth quality, this demo is something I never would have done independently - having no interest in purchasing any wireless headphones myself. But I wanted to give aptX a fair shake, and my loaner equipment arrived in time for some holiday listening.

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Let me begin by saying this: not only does perceived audio quality depend on how critical you are when listening, but it also depends on the type of music you listen to. I set out to see if I could actually tell the difference between wired and wireless sound from the same source, and with the same headphones. The music I selected alternated between pop and jazz, with pop an example of modern music production (dynamic range compression, synthesized sounds, drum machine beats, etc.) and jazz an example of extremely complex sound, with live mic’d instruments, congested passages, and a full spectrum of frequencies with full dynamic range intact (ok, some mastering engineers will apply a little DRC, depending on the record, but still nothing like today’s “brick wall” music with a grand total of about 6dB dynamic range).

I started by listening to compressed pop music (tracks from the current top 40, played via Amazon Music or official YouTube/Vevo streams), and these sounded identical with the wireless connection vs. wired with Momentum headphones and the LG G5. One of the biggest advantages of aptX audio with compressed music is the fact that it avoids re-compressing via frequency-domain (psychoacoustic auditory masking) techniques that the audio is already compressed with from these sources. Having a format much closer to straight PCM - which works in the time domain, instead - prevents the rather unpleasant sound that can occur over standard (SBC codec) Bluetooth connections. There is (again) science behind claims of distortion from re-compression, with something described as the "cumulative effects of concatenating compression codecs" which you can read about here (PDF).

When I switched to lossless music files (FLAC and ALAC, played back using the VLC app), I specifically selected tracks that I know to be difficult to reproduce accurately. I was still very impressed by the performance of the wireless headphones, even though the jazz tracks I listened to the most critically are a "worst-case" scenario for compression. There were still moments when I thought I was hearing a difference, but it was only when I was listening for it. Overall the sound was fantastic, and by far the best wireless experience I’ve had to date (I'll add that the Sennheiser Momentum headphones are incredible in their own right). This standard implementation of aptX was perhaps a little behind the wired sound with complex passages, but that was with CD-quality audio. (I must point out that aptX HD audio exists, and I would love to compare that to wired sound with my library of 24-bit music!)

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If you don’t listen to jazz (I do, but I am very particular and only listen to select styles from specific time periods) then it’s hard to explain just how hard to reproduce on even “hi-fi” equipment it can be. I am not attempting to convince anyone that 'highbrow' music choices are necessary, but it did make a great test of the aptX streaming technology with the wireless headphones. Passages with crashing cymbals, thumping upright bass notes, complex chords on piano, and blasts of upper midrange horn will exercise every part of a sound system; and can often sound a little congested as a result. With these sorts of passages in jazz I find it far easier to hear problems with lossy compression, and particularly in the treble. It is also difficult to describe exactly how compression sounds to me, but perhaps 'synthetic' is the word. (I wish I didn’t notice this sort of thing, but I always have, and it means I can only carry lossless files around with me if it's something I care about - to the detriment of my available storage space.)

  • Here’s the short version: using the Sennheiser Momentum headphones in their aptX Bluetooth mode with the LG G5 phone, modern (less complex) music from typical compressed sources was indistinguishable a wired connection in my listening sessions; and with the most complex music (uncompressed acoustic jazz) there was a slight difference that I don't think the vast majority of people would notice.


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Here’s why I came away highly impressed with aptX, even if I think I could tell the difference from wired headphones with some music: I had to really push the technology, listening carefully using the most complex audio I could think of, to hear a noticeable difference. What I mean is that, had I been using the aptX-connected headphones purely for enjoyment, then I would be hard pressed to tell you “I can hear a difference”. For the most part I forgot that they were wireless, and just listened - and thoroughly enjoyed myself in the process.

In closing, I urge anyone considering a high-quality Bluetooth audio solution to look for the aptX logo. More and more products are being introduced using an implementation of aptX (be it the standard version or HD and low-latency variants), and it clearly makes a difference. I categorize it as 'audiophile-approved Bluetooth', but regardless of your level of enthusiasm for sound quality I think you'd be very pleased with the results.

January 26, 2017 | 10:28 AM - Posted by Penteract (not verified)

Nice article Sebastian, thanks!

I'd be interested in your thoughts (an article) on MQA should you get the chance and have the desire to write about it.

January 26, 2017 | 11:39 AM - Posted by Sebastian Peak

Thanks! MQA is an interesting idea, but there are some big questions about it - even though audiophile magazines such as Stereophile and The Absolute Sound have praised it. But TAS for example has also said a particular $945 USB cable  "revealed an even larger and more dimensional spatial perspective" (the full 'review' is in their 2016 buyer's guide). MQA can certainly be questioned, as it operates in rather mysterious ways that are not fully explained. While not an independant souce, as they sell their own ADC/DAC products (which are very highly respected, by the way), it's interesting nonetheless to read what Benchmark has to say about MQA.

January 26, 2017 | 11:31 PM - Posted by Penteract (not verified)

Hans Beekhuyzen did a YouTube video that explained MQA well, I think. Sounds like an interesting methodology - and one he claims reduces jitter to an almost insignificant level.

Whether or not its something that will improve the listening experience for most people - I really doubt it, most people don't hear the kind of faults in sound reproduction he does.

Tidal (and I think a couple of others) have started streaming MQA music. As I understand it there is a software-level implementation which allows for some benefit even if you don't have a DAC with the technology built in. Of course a lot of their music files are just converted files from lower quality methodologies, and no improvement in compression or streaming can correct the work of a heavy-handed "sound engineer" that's stomped all over the music (as in the loudness problem you mentioned), which I think is a bigger problem than whatever compression type is used.

The hardware certification process is a serious issue. Schiit has said they won't use MQA because it means letting the parties responsible for the qualification a look into their proprietary hardware - and of course there will be licensing fees passed on to the customer. They might re-evaluate if it becomes wide-spread, but right now they have no plans to implement it.

Anyhoo, as you well know discussions about sound quality tend to degrade into trash-talking and are of no educational value. Personally I like to hear from a variety of sources about products and technologies. I respect your opinion, which is why I'd like your treatment on the subject. :)

January 26, 2017 | 10:33 AM - Posted by willmore

ADPCM in this day and age? That was outdated decades ago. It was popular because it was fairly simple to implement and gave reasonable compression. But that was in the 1980's!

Now, we have vastly more DSP embedded in all of our devices and ADPCM is not a good choice.

But, I'm sure Qualcomm has it pattened up and down, so of course they'll push it to broad adoption.

January 26, 2017 | 10:59 AM - Posted by Sebastian Peak

It's not outdated at all, and it used professionally for good reason. The focus of the article was its advantage in situations where we don't have the bandwidth for lossless compression, which still requires far more than the ~328-345 Kbps available with via Bluetooth, for example, what other method would you suggest to prevent the signal loss of psychoacoustic auditory masking such as SBC? Re-compression is a major problem using this technique, and can only be mitigated if you listen exclusively to uncompressed/lossless files.

Qualcomm purchased it in 2015 from CSR, and it has been an industry standard in compression since the 1990's. No professional application is going to use frequency-domain compression. Now that we have the bandwidth for PCM tracks with Blu-ray, I understand that it seems redundant for that use-case - however, aptX was never used for the home version of even the DTS sound system it was integrated with for commercial theater sound as AAC became the standard for DVD soundtracks. It is a pro-level form of compression that is now being implemented in consumer Bluetooth devices, and that's all.

You mention DSPs, and while a proprietary solution could certainly either be 'baked-in' to an SoC, how would it be transmitted without a proprietary connection? Bluetooth's limitations are what they are. Sony, for example, offers a very high quality wireless solution (LDAC) with their digital Walkman players, but it requires the use of - again - proprietary wireless technology only found in select Sony headphones and those compatible players. Without an alternative wireless connection, no DSP is going to circumvent the bandwidth limitation of Bluetooth.

And speaking of DSPs, now that Qualcomm owns aptX audio, it won't be long until Snapdragon processors can offer the tech in their audio DSP, which means that more and more smartphones going forward could potentially offer an aptX Bluetooth connection with compatible headphones (and the number of available, compatible headphones will obviously increase). Apple chose not to include aptX with the current iPhone, which means you are stuck using AirPods for the best wireless sound. Again, proprietary tech, and only one option on the market.

As aptX audio is actually gaining traction in hi-fi audio with some of the best wireless headphones and speakers adopting it, I again call to question the assertion that it is "outdated" technology.

January 26, 2017 | 05:09 PM - Posted by willmore

ADPCM and the variant known as AptX are quite old. The most recent commercial use of AptX was in 2007. ADPCM *was* popular in the late 80's and early 90's because it could be used to encode FM radio quality audio. I know this because *I was there doing it* commercially. We used ADPCM because it was the best sounding CODEC that could run in real time on DSP chips available to us. That changed in the early/mid 90's when other CODECs became practical because of the increased power of PCs and of DSPs.

SBC is a very simple CODEC but, at high bit rates, has way fewer artifacts than ADPCM until you get to very high bit rates. I might point out that AptX is not a strict time domain ADPCM--instead it is a subband filter and the resulting subbands are then predictively coded. At the bit rates used in BT, SBC does very little masking that you would be able to detect. The reason they do psychoaccoustical masking is *because you can't hear it*. SBC is perfectly fine for the application for which it's being used.

If I were to offere a different CODEC in its place, the last thing I would do would be to suggest something like AptX or any other ADPCM derived system. I'd suggest opus. It's low latency, very high quality at low bit rates, resistant to packet loss, and is very near lossless at reasonably low bit rates--rates well lower than what AptX needs. This lower bandwidth need could go into more FEC or on lowering the transmitted bit rate to increase the Eb/N0 of the RF link.

The bandwidth available on BT are signifigantly above what you need for near lossless audio. SBC and opus are both easily implemented on the DSPs that are *already* inside of our phones. Every little BT module *is* a DSP. That's host most modern RF processing is done. In the context of Qualcomm, every single one of their phone chips has a DSP built in that is well larger than needed for SBC or opus.

There is no need for a propriatary CODEC to solve this problem be it from Qualcomm or Sony.

ADPCM and AptX have as little place in this day and age as tube amps.

January 27, 2017 | 04:16 PM - Posted by Tucker Smith (not verified)

Tube amps are the shit, yo.

January 27, 2017 | 10:34 PM - Posted by willmore

They are, indeed, shit.

February 5, 2017 | 07:19 AM - Posted by Anonymous (not verified)

See you throw these big words around dude but you haven't even experienced the difference. If you had you wouldn't be arguing.

It sounds like it's plugged in. Period. And I'm an audiophile freak.

Normal Bluetooth sounds OK, but not good like this.

What's your deal anyway? Trying to defend your iPhone 7 or something lol

February 5, 2017 | 11:21 AM - Posted by willmore

Sebastian, is that you?

January 26, 2017 | 10:57 AM - Posted by DiaperDanDoodied

great article, learned a lot about the history of this tech. thanks~!

January 26, 2017 | 11:40 AM - Posted by Sebastian Peak

Thank you!

January 26, 2017 | 11:21 AM - Posted by Jann5s

Is there a relation with the Audio-Technika tech that was (i think) disclosed at CES?

[edit] I think, the answer is yes: [/edit]

January 26, 2017 | 11:40 AM - Posted by Sebastian Peak

Yep! AT is expanding wireless headphones and includes aptX audio support.

January 26, 2017 | 03:01 PM - Posted by David (not verified)

The problem is aptx is not supported on the platforms that matter: Pure Google (Nexus AOSP), iOS (iPhone / iPad), and Windows (without CSR Bluetooth dongles)

I'm not investing hundreds of dollars into headphones that won't be aptx-enabled on most of my devices.

February 5, 2017 | 07:13 AM - Posted by Anonymous (not verified)

30$ Bluetooth headphones on Amazon support it. In fact most all headphones support it. You can also clearly hear the difference. My old 200$ Android phone from 2 years ago supports it as well.

The only way it won't be supported is if your in the Apple ecosystem but then you don't care about quality anyway.

January 26, 2017 | 04:39 PM - Posted by Tucker Smith (not verified)

There's a nice budget audiophile niche this appeals to. A future iteration of that little 25w stereo tube amp with aptX/Bluetooth sold by Monoprice would be awesome plugged into nice full range driver speakers. Madisound sells a Fostek kit that's supposed to be Lights out. If Bluetooth audio was truly improved, hi fidelity audio would be a mainstream thing again.

The Monoprice amp:

The Madisound kit:

January 26, 2017 | 08:19 PM - Posted by Rudolfo (not verified)

Samsung has something called UHQ audio which is supposed to be better than aptx. Is it possible that you evaluate UHQ audio? I thoroughly enjoyed reading this one, thanks!

January 26, 2017 | 10:24 PM - Posted by James (not verified)

345Kbit is actually quite a bit for audio -- that's enough room for a 320Kbit MP3 or even something like Ogg Vorbis which is not wrapped up in a bunch of licensing BS. Not sure why they went with AptX instead. Hrmm

January 27, 2017 | 10:36 PM - Posted by willmore

Because Qualcomm bought CSR and CSR makes *all the BT chipsets* Well, a very large chunk of them that aren't in Qualcomm chipsits already.

January 28, 2017 | 04:22 AM - Posted by DAN TOMITC (not verified)

aptX audio why not in V20 lg ???

February 2, 2017 | 12:50 AM - Posted by Poppapete (not verified)

Been using Logitech G933 headphones and not happy all sorts of trouble even after a free replacement set. Bought sennheiser Momentum which support aptx and Telme2 Toslink to BTadapter attached to SPDIF MB port. I am amazed with the audio. Best I have ever had for wireless audio by far.

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