2018 Bluetooth Audio Codec Comparison Guide Part1: SBC & aptX

When Apple sidelined the 3.5-mm jack with the launch of last year’s iPhone 7, it looked like a bold move. But despite pockets of outrage over another clear case of planned obsolescence, it was a clear indication that the future of mobile audio is going to be wireless. The trend has officially begun with Google also abandoning the headphone jack with the launch of Pixel 2. Let’s face it, sound quality is not usually a priority for cell-phone manufacturers because it’s just not in demand from the majority of consumers. But the average phone’s 3.5 mm headphone jack was never built for sound quality. It’s a fact that has created a market for portable DAC/amplifiers, like the Oppo HA-2 SE, they use your phone’s raw digital output for an upgraded sonic experience for serious listeners that have invested in a good pair of headphones. The 3.5-mm headphone jack was never going to be missed by anyone with a serious headphone hi-fi obsession.

Cell phone makers claim that abandoning the headphone jack is necessary to save space for other, more important features inside our ever-narrowing phones. Cell phone companies are less forthcoming about the more important reason for dumping the headphone jack, planned obsolescence. There just isn’t much profit anymore in the kinds of bottom-of-the-line earbuds and headphones that satisfy the listening needs of 90% of consumers. Since the sun has long since set on the market for wired headphones, wireless turned out to be a great way to get consumers to buy something they don’t necessarily really need.

So far, it’s worked! June of 2016, when it was still only a rumor that Apple would drop the headphone jack on its upcoming iPhone 7, was the month sales revenue for wireless headphones topped wired headphones for the first time. Wireless claimed 54% of headphone dollar-sales, despite netting only 17% of unit-sales. This proved consumers are willing to pay a premium for wireless. Timing couldn’t have been more perfect for Apple to officially announce iPhone 7 in September, 2016 and substantiate rumors of the headphone jack’s demise.

Now you have the perfect excuse to buy those wireless headphones you’ve been thinking about, because sooner or later, you’ll have no choice. And let’s face it, once you’ve tasted the convenience of wireless you won’t want to go back to plugging earbuds into your phone like it was an iPod from 2003. If you’ve waited this long to go wireless, 2018 may be the perfect year to buy yourself a good pair of wireless headphones because a slew of new products have arrived with new options for enhanced wireless audio fidelity.

The latest Bluetooth codecs including aptX HD and LDAC are ushering in a new era of wireless hi-fi possibilities. But, navigating the minefield of compatibility in new wireless audio standards can be confusing, so lets separate some of the marketing hype from real-world results.

2018 - Peak Audio-Quality for Bluetooth

It’s difficult to believe it’s been almost a decade since I first wrote what has become a cliche when reviewing wireless audio: “Wireless sound quality has really come a long way since the bad old days of early Bluetooth A2DP.” In the early days, back when Bluetooth first started transmitting stereo sound, its primary goal wasn’t audio quality. Bluetooth sought to be an energy-efficient platform that’s perfect for portable, battery powered devices. But with new high-bit codecs, Bluetooth sound quality is changing for the better.

How far back does Bluetooth go? It might surprise you to know that the Bluetooth name dates way back to the Vikings, seriously. It was named after a 10th century Scandinavian king, Harald Gormsson, nicknamed “Bluetooth” for a blueish or black tooth. The Bluetooth symbol is an amalgamation of the runic characters that comprise the old king’s name.

Understanding the Audio Codecs: SBC, AAC, aptX and LDAC

To understand wireless audio, we must first understand the codec - the word is a blend of code/decode. So, it’s software that encodes and then decodes a digital data stream, in this case the digital data is audio. It’s important to note that whatever codec you wish to use, your transmitter (phone, Bluetooth transmitter etc.) must be compatible to the same codec as the receiver (headphones or wireless speaker, Bluetooth receiver etc.). So, if you got a fancy new set of headphones that feature “aptX HD”, you will need a phone that can transmit aptX HD before you’re able to hear aptX HD-quality audio from those headphones - and this is where it gets confusing.

Subband Coding - SBC

The default Bluetooth codec is Subband Coding (SBC). This is the codec that is usually blamed for the compressed sound quality that has often plagued the Bluetooth listening experience in the early days of Bluetooth audio. Like *all* the major Bluetooth codecs in use today, SBC is a lossy compression algorithm. This means that when it encodes music for playback, it literally drops pieces of music the algorithm deems low-priority, these are mostly sounds you can’t hear anyway because they’re masked by other sounds in the same frequency range at higher volume. This description of the SBC codec’s lossy compression algorithm makes it seem worse than it is in practice, and this is why the term “lossy” is often unnecessarily vilified. But, it’s certainly true that too much compression or compounded compression algorithms will often accumulate and result in a hollow or compromised sound experience.

On its own, the SBC codec is not a terrible lossy compression algo, it can provide suitable audio quality for most consumers, and it’s perfectly suited for lower quality, budget Bluetooth headphones. However, for truly discerning ears that have taken the time to store or stream high-quality music files for playback on hi-fi equipment capable of highly detailed audio quality, the limitations of SBC becomes apparent.

The priority of SBC doesn’t happen to audiophile quality sound, instead it’s designed to be efficient, using less data, less energy and low-latency. In other words, it’s never been SBC’s job to provide you with a high-end listening experience. Instead it’s designed to save bandwidth and the battery life of your wireless devices. SBC is capable of a respectable 328-kbps, that’s about the data-rate required of high-quality 320-bit MP3s. But that doesn’t mean streaming 320-bit MP3s via SBC will yield a pristine listening experience. On the contrary, both MP3 and SBC are lossy compression algorithms. Your MP3 files have already been compressed, uncompressed and then converted to another lossy compression algorithm (SBC) to travel wirelessly through Bluetooth. This is where we run headlong into compounded compression, a doubling of lossy compression algorithms. Compounded compression constitutes a significant compromise in audio quality when compared to listening to the same MP3 file over a pair of headphones that are hard-wired to your playback device.

To be perfectly honest, in real-world application using moderate to good quality wireless headphones, streaming 320-bit MP3s from your phone, you’d be hard-pressed to actually hear any discernible difference from the same source fully wired while bypassing Bluetooth SBC compression completely. But there is a difference, and higher-end headphones may illuminate SBC’s limitations.

SBC is the default Bluetooth codec. If both sides of any Bluetooth connection aren’t using a compatible alternative - you’re using SBC. While SBC is a lossy compression algorithm designed more for efficiency than hi-fi audio, things aren’t as bad as it seems. There are many more and much worse choke-points in the audio chain that could be downgrading your audio experience through Bluetooth namely, cheap headphones/earbuds or overly-compressed online streams or music files stored on your phone.

SBC Optimal Use: On-paper, the closest to hi-fi audio you can squeeze out SBC is the humble 320-bit MP3 or other compression algorithms that do not exceed SBC’s limit of 328-kbps. Although there is still that nagging matter of compounded compression you’ll get by having to transcode between two separate lossy compression algorithms such as MP3-to-SBC. These details may get under the skin of the more obsessive among us looking for the most pure audio experience possible. But, as soon as you start using lossless files, such as FLAC or lossless streams at 16-bit 44-kHz, like Tidal Hi-Fi, you’d be better served upgrading your codec from SBC.

To learn about advanced Bluetooth audio codecs like aptX and more, click over to Page 2 of the Bluetooth Audio Guide for 2018.

2018 Bluetooth Audio Codec Comparison Guide Part2: aptX HD, AAC & LDAC

aptX

SBC naturally takes a lot of abuse in marketing-copy from companies like Qualcomm, makers of premium-grade alternatives to SBC, like aptX and its new, more powerful aptX HD. For the majority of consumers looking for the convenience of wireless sound, gains in fidelity granted by aptX will be minimal or lost entirely to other chokepoints in the audio chain.

In scenarios where I’ve tested a pair of headphones with aptX (like the V-MODA Crossfade Wireless 2, for instance) and toggled between playback devices with/without aptX while using the same source files (FLAC 16/44) - the slight improvement aptX offered over SBC was not significant. Count me as calling a “maybe” there’s a difference, but I wouldn’t call it a clear step up in audio quality. Your mileage may vary and headphones specifically tuned with the aptX codec in mind may make a more substantial difference. But considering the difference in raw data-rate between SBC and aptX, it was never going to be a significant leap in sound quality.

Even if aptX alone doesn’t present a significant leap in audio quality, its arrival was a significant breakthrough for wireless headphone audio quality if only because it opened a door in demand for improved Bluetooth codecs. Headphone manufacturers willing to pay Qualcomm to license its aptX technology are making a clear statement that their product cares about wireless audio fidelity.

Qualcomm says aptX was designed to bring “CD-like” quality over Bluetooth by delivering 16-bit/48kHz sampling of your source material and streaming streaming it over a Bluetooth connection with 352-kbps throughput. So, if you’re listening to high quality source files like FLAC at 16-bit/48kHz (a popular lossless compression algorithm) where both your phone and headphones are aptX compatible, you are listening in the best-case scenario for aptX and have reached the codec’s upper limitations. Even then, aptX does introduce lossy compression, so the sound quality will be slightly compromised in-so-far as FLAC does not introduce any loss whatsoever. When adopting aptX to your wireless listening experience it’s important to keep in mind, if either side of the wireless connection doesn’t feature aptX compatibility (or another alternative codec) your Bluetooth communication will default back to SBC.

A common complaint about most Android phones is that the phone initiates the aptX handshake without notice to the user. Sure, it’s an automated convenience, but the drawback is that it’s often not possible to find any settings to prove that your phone is using aptX, leaving the listener with no method of switching between aptX and SBC. The best you can do is check your phone’s codec compatibility list and trust that it’s using aptX where available. 

aptX Best Use: Qualcomm’s aptX codec can only be employed when both Bluetooth transmitter (phone) and receiver (headphones) are aptX-ready. Optimal aptX performance is engaged when your source files are encoded in a lossless format at 16-bit/44 or 48kHz, as this exceeds the capability of SBC. Because aptX is a lossy compression algorithm, compounded compression will occur when your music must be decoded from any other lossy compression algorithm such as MP3 or Ogg Vorbis (used by Spotify). But compounded compression is avoided when using lossless sources like Tidal’s Hi-Fi music stream or locally stored music in any lossless compression format (ie. FLAC)

Editorial Note about Online Music Streaming Services

Let’s take a for-instance, say your phone and headphones are both aptX-ready, but you’re streaming music from one of the many music services available, in this example I’ll use Spotify. If, in this scenario, you’re using Spotify’s “High Quality” setting, you’re streaming the equivalent of 160-kbps music files, using the Ogg Vorbis, a codec that uses a lossy compression algorithm. Spotify’s source stream is presenting a bottleneck in the audio-chain and gains from aptX are lost because the codec can’t add resolution. So, any difference in sound quality you may detect between SBC and aptX in that scenario, is simply the difference in how each of the respective codecs perform the job of lossy compression. But there are no on-paper gains in fidelity. We can only trust that the folks at Qualcomm built a better mousetrap than SBC. 

aptX HD

New products featuring the latest version of aptX are now hitting the market for 2018. This new breed of high-end wireless headphones will join Bowers & Wilkins flagship PX wireless noise cancelling headphones that were released late last year. Qualcomm created aptX HD specifically for high resolution audio sampled at 24-bit/48kHz in Linear Pulse Code Modulation (LPCM) through its data stream that is capable of 576-kbps. Now, that’s a significant on-paper gain from either aptX or SBC. Although your options for compatible hardware is presently limited, many more were announced at CES 2018.

Whether or not high resolution audio (24-bit/48kHz or higher) presents any audible gains over the CD-quality standard of 16-bit/44kHz is a controversial topic. We won’t weigh-in on that particular minefield here, but suffice it to say, if you’ve got it - why not at least try to hear it!

aptX HD Best Use: If you’ve got a collection of high-resolution audio files at 24/48 or subscribe to a music service capable of high resolution audio, aptx HD was made for you. The only high res subscription music service available in North America at this time is Tidal Hi-Fi Master, which streams Master Quality Audio (MQA) at 24-bit / 96kHz, but this level of resolution is only available through the Tidal desktop app and exceeds the capability of aptX HD.

LDAC

Tell me if you’ve heard this story before. A growing consumer electronics format gets competition from a proprietary Sony equivalent. For better or for worse, the story has lead to format wars in markets ranging from game consoles to video and high-resolution discs. The latest iteration of this recurring theme is Sony’s new high-resolution Bluetooth audio codec LDAC and can be found on Sony Xperia phones and select Sony headphones.

But this time the story is a little different than Sony simply exercising its consumer electronics and media privilege as both manufacturing giant and owner of half the world’s media. Instead of holding a death-grip on a proprietary platform as a Sony-exclusive, LDAC compatibility is now being licensed to other companies. One example is the RBH edition Prostereo H2. H2 Earphones are an excellent sounding set of wireless earbuds carrying a Swiss army knife of codecs that includes aptX, aptX HD and LDAC. Like all Bluetooth codecs, both phone and headphones must be compatible with the codec and this leads us to the best thing about LDAC - it’s going to be freely available to Android OEM phones.

In an unexpected twist, Sony has worked closely with Android to build LDAC right into the Android Open Source Project (AOSP) code of Android version 8.0 aka. Oreo. This means your next Android phone is very likely to include LDAC.

LDAC is a lossy compression algorithm that raises the bar with a throughput up to 990-kbps, nearly double that of aptX HD and triple SBC. LDAC is capable of a sample rate and bit-depth of 94-kHz at 24-bit. At the time of writing this article, it is literally the best wireless sound you can get for your lossless high-resolution audio library and comes close to matching the capability of Tidal Hi-Fi MQA.

LDAC Best Use: You guessed it! Both phone (transmitter) and headphones (receiver) must be LDAC compatible. You’ll probably see LDAC prominently displayed on the packaging for any compatible audio equipment and soon, just about any phone or tablet using Android 8, Oreo will also be compatible. You’ll acheive a near-perfect sonic replication of your high-resolution library of music files sampled at 94-kHz/24-bit. LDAC is of course a lossy compression algorithm, so your LDAC headphones won’t receive a bit-perfect copy of the music being decoded. But for today, it’s as good as it gets, and many claim that it’s better than human ears could possibly discern.

AAC Apple iOS

Unfortunately for Apple users, the aforementioned options for high-res wireless glory just isn’t for you. But, that’s not to say iOS users are left out in the cold when it comes Bluetooth audio. Apple introduces an interesting wrinkle in what might otherwise be a linear hierarchy of codecs-to-bitrates and demonstrates that higher bit-rates don’t necessarily result in better sound quality. Long story short, Apple’s simplicity and near-universal compatibility in codecs is its biggest strength.

Besides SBC, a requirement for the Bluetooth stereo A2DP spec, the iPhone is capable of streaming Apple’s preferred Advanced Audio Coding (AAC) codec. Apple keeps a tight rein on its software, so it’s no surprise iPhone codecs are limited to AAC or SBC. However, Macbook and iMac are aptX compatible, so maybe there’s future hope for additional codecs on iPhone.

The good news, is despite being slightly lower throughput, AAC is widely praised among lossy algorithms as a step up from SBC and there is a wide variety of compatible headphones. If you’re using a pair of AAC-compatible headphones, you’re theoretically getting no loss in audio quality from your stored AAC files (the iTunes standard) or streaming from the Apple Music service.

AAC Best Use: iPhone users will want a pair of headphones compatible with the AAC codec, then you want an AAC or Apple Lossless (ALAC) music library as your source. This will provide the cleanest sound quality possible, free from compounded compression your music would otherwise suffer.

Apple Music provides a native AAC stream, so it’s the next best thing to a library of AAC or ALAC files. For best results, you’ll need to pay attention that you don’t use your iPhone to stream any other lossy compression algorithms. Compression algorithms like MP3 or Spotify’s Ogg Vorbis will need to be decoded by the iPhone then encoded into another lossy algorithm (AAC) before being transmitted to your headphones.

Codecs and Bitrates Comparison

• AAC: 250 kbps
• SBC: 328 kbps
• aptX: 352 kbps
• aptX HD: 576 kbps
• LDAC: 990 kbps

Now You’re Ready for Fine Bluetooth Audio in 2018

The most important things to remember is your phone (transmitter) and receiver (headphones/speakers or Bluetooth receiver) must be compatible with the same Bluetooth codec to work. If they’re not compatible, they’re defaulting to SBC.

Generally, the bitrate between devices corresponds directly to the quality of audio you can expect. The higher the bitrate, the better possible audio quality. But it’s never that simple, because if you’re serious about sound, you also want to avoid making your phone transcode music files between different codecs, because this will result in compounded compression. So, it's usually better to get a clean transfer between lower-bit, but compatible codecs, than to have to transcode to a lossy codec from another, higher-bit lossy codec. Now, whether or not your ears can actually hear the difference in double blind a/b/x testing is up to you - the important thing is to have fun trying.

What codec are you streaming wirelessly with? Please share your experiences in the related forum thread below.