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.
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!)
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.
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.