By Mario Machaieie 
Lossless audio over Bluetooth? It used to be a pipe dream. Now, according to Qualcomm, it’s a reality. Over the last few weeks and months, I’ve been listening to music through three sets of true wireless IEMs, all supporting Qualcomm’s latest flavour of aptX: aptX Lossless. This, in theory, adds the lossless handling of CD-quality (but not hi-res) audio to the Bluetooth headphone experience. Those TW IEMs are the Denon Perl Pro, the Bose QC Ultra and the Sennheiser Momentum True Wireless 4. Plug ’em in yr ears, hit play and let the good times roll?
Not so fast.
Before the advent of aptX Lossless, all Bluetooth audio codecs were lossy — they discarded audio data to fit the digital signal inside Bluetooth’s narrow data pipe. According to Qualcomm, over 1Mbps is required to carry CD-quality signals from smartphone (‘source’) to headphone (‘sink’) without audio data loss. The closest we could previously get was LDAC’s 990kbps. Close, but no cigar.
But there was – and still is – a gotcha. According to Sony, LDAC doesn’t always operate at 990kbps. When faced with Bluetooth congestion or a weaker Bluetooth signal, the source will drop LDAC’s transmission rate to 660kbps. In worst-case scenarios, it’ll step down to 330kbps, only scaling up again as conditions improve. In other words, the source device dynamically adjusts LDAC’s bitrate according to environmental conditions. Remember this — we’ll be coming back to it.
Qualcomm asserts that its aptX Lossless codec operates at between 1.1 and 1.2Mbps. However, a true wireless earphone manufacturer told me that Qualcomm has gone beyond the Bluetooth specification (overseen by the Bluetooth SIG) to get there: “the BT radio is configured/operated outside the BT SIG specification; it is proprietary to Qualcomm, and specified as part of their Snapdragon Sound certification.”
website reads similarly: “The Denon Perl Pro supports Snapdragon Sound with aptX Lossless.”
However, we don’t see Qualcomm explicitly applying the same “aptX Lossless” terminology to the Bose QC Ultra. We only see “aptX Adaptive”. Odd. Clicking over to Bose’s press release from last year and we breathe easy again: “Both the QuietComfort Ultra Headphones and QuietComfort Ultra Earbuds feature Snapdragon Sound™ Technology Suite, enabling support for the latest Qualcomm® aptX Adaptive codec for audio streaming — including lossless and low latency capabilities.”
Does each of these True Wireless IEMs sound better with an aptX Lossless-loaded smartphone – like the Sony Xperia 1 V and Asus Zenfone 10 – than they do with a Google Pixel 7 Pro whose Bluetooth support only extends to AAC, aptX, aptX HD and LDAC?
In short, yes, but barely. More on that in a moment.
What of Bluetooth power users wanting to get their kicks from seeing the presence of aptX Lossless on their Sony or Asus (but not Google or Apple or Samsung) smartphone? This is where things get interesting confusing.
Pairing the Bose with the Sony Xperia 1 V, Bose’s Music app doesn’t tell us which codec is in play. The Sony phone’s Bluetooth connection notification bubbles and Bluetooth setting panel say aptX Adaptive. Ditto the Developer Options panel. aptX Lossless doesn’t get a mention. Cutting over to the Asus Zenfone 10, we see the same talk of aptX Adaptive (and not aptX Lossless) but with the addition of a Snapdragon Sound pop-up window.
It’s a similar story when pairing the Denon Perl Pro to the Asus or Sony. Both phones’ notification bubbles, Bluetooth connection panels and Developer Options say aptX Adaptive. The Denon Headphones app reads “aptX Adaptive HQ 48kHz”. Where is aptX Lossless?
Sennheiser gives us a strip of daylight. The Sony/Asus notification bubbles, Bluetooth setting panes and Developer Options panels read aptX Adaptive but the Smart Control app reads aptX Lossless…but only when playing from Tidal and Apple Music. Plexamp as a playback app pushes it back to aptX Adaptive. Could this be related to Android’s 48kHz sample rate conversion around which Tidal’s streams travel but Plexamp’s do not? I don’t know. What I do know is that we are deep into the weeds.
It was the majority absence of aptX Lossless confirmation across all three TW IEM models that (Bose aside) had me ask questions of their manufacturers.
One company representative told me that “aptX Adaptive is a different codec from aptX Lossless” but that aptX Lossless has priority over the always lossy aptX Adaptive when both are present in the smartphone and headphone.
I was also told that “aptX Adaptive has five quality levels: L1 (284kbps) -> L5 (620kbps)” and “aptX Lossless has five quality levels: L1 (242kbps) -> L5 (around 1Mbps)”. This could explain why I hear the soundstage on the Bose and Denon momentarily collapse to sound muffled in the top-end when on a busy street or at the airport. Assuming their presence in the connected headphone, a smartphone supporting aptX Adaptive and/or aptX Lossless will dynamically scale the bitrate according to environmental conditions, just like Sony’s LDAC. This scaling prevents playback interruptions.
But that still doesn’t explain why the Sony Xperia 1 V’s and Asus Zenfone 10’s notification bubbles, Bluetooth connection setting panels and Developer Options all read ‘aptX Adaptive’ instead of ‘aptX Lossless’, especially when the latter has priority.
A little more digging with another manufacturer revealed that “aptX lossless is an optional part of aptX adaptive. This is a bit confusing.”
It sure is.
I then asked if aptX Lossless was, in fact, the top rung on the aptX Adaptive ladder and was told that despite Qualcomm being vague about specifics, the system could be seen that way; that if aptX Lossless wasn’t possible due to environmental conditions, the connection would fall back to one of aptX Adaptive’s various lossy operational modes.
Another manufacturer confirmed that aptX Lossless did sit at the top of the aptX Adaptive tree. He elaborated: “aptX Lossless is part of the aptX Adaptive technology (Snapdragon Sound™ Technology)” and “the codec shown in the developer options and the app does not distinguish between different codecs within the Adaptive technology as recommended” but “the developer of the product can define more specifically what is presented”
Despite those words not coming from a Sennheiser representative, they led me to conclude that Sennheiser has elected to have its Smart Control app show aptX Lossless as a distinct qualitative tier within the aptX Adaptive set whilst other manufacturers’ apps do not make this distinction because Qualcomm recommends against it.
The upshot is that Sennheiser aside, we have no idea if aptX Lossless is in play or if Bluetooth congestion – or too much distance between smartphone and headphone – has caused the connection’s bitrate to step down to a lower level. That’s not good news for power users looking for visual confirmation of aptX Lossless and a little confusing for everyone else, but it is good news for anyone wanting to trust their ears.
I built a playlist of five songs on Tidal and Apple Music – The The, Snoop Dogg, Pixies, Monolake, Giant Sand – and took each TW IEM for a spin with the Sony, the Asus and the Pixel. With the Denon and the Sennheiser, I wouldn’t swear on aptX Lossless’s audible advantage being crystal clear, especially when out in the street. There might be a reason for this: the Bluetooth connection falls back to aptX with the Google phone because Denon and Sennheiser added aptX support (but not LDAC) to their flagship true wireless models.
The audible difference between the Sony/Asus phones and the Google phone is most pronounced with the Bose QC Ultra. We lose some top-end extension and air. This is (probably) because Bose’s fallback codec is AAC (and not aptX or LDAC). I find the step up from AAC to aptX Lossless sonically worthwhile but my jury is still out on the move from aptX to aptX Lossless – I hear a teaspoonful of extra detail, a few additional puffs of recording space air and perhaps a slightly wider headstage but those improvements are incremental. If it means moving away from IEMs or headphones you like already, I’d advise you to stay put. I say that not to throw shade over aptX Lossless’ audible prowess but to complement the effectiveness of lossy aptX flavours and Sony’s LDAC.
I hear far greater differences in sound quality between the TW IEMs themselves than between the codecs that run across their Bluetooth audio connections. In other words, the hardware matters more; much more. I will make a video about the Denon, the Bose and Sennheiser in ascending order of preference over the next few months. In this post, I wanted to walk readers through my investigations into aptX Lossless so I don’t bog down each video with talk of it. Because the bottom line is this: aptX Lossless is a) nice to have but it’s not essential and b) don’t expect your phone to tell you when it’s in action.
Most people won’t care which Bluetooth codec connects their smartphone to their headphones — but power users do. Those same power users will be drawn to aptX Lossless, especially when it appears pivotal to the promotional language used by headphone manufacturers and Qualcomm. They’ll want to hear it through their headphones and see it on their smartphone. My complaint, such that it is, is that aptX Lossless is (Sennheiser aside) hidden from view behind aptX Adaptive’s wall of dynamic bitrate scaling.
One final thought: to those wondering why we fuss over this stuff, consider the results of a YouTube Community poll conducted last month where 60% of 9000 respondents said that sound quality was the most important feature of a true wireless IEM.