First of all, here are a few hard facts to refresh your memory. Bluetooth is a standard for short-distance transmission of data via radio, which was developed back in the 1990s. Since its introduction, the technology has enabled wireless communication and data transfer between different devices. Similar to many other wireless devices, the data is transmitted via the ISM band (Industrial, Scientific and Medical band) between the 2.4 GHz and 2.48 GHz bands. This band was deliberately chosen to avoid the costs associated with licensing. We will discuss the effects of the selected frequency spectrum on the transmittable data volume and thus the available audio quality in more detail later in the article.
Since its introduction in 1999, the standard has gone through a number of versions. The aim has always been to meet the demands of the time. Particular attention was paid to improving the range and transmission speed while reducing power consumption. Thus, many changes were implemented in this direction, especially during the last big leap to Bluetooth 5.0. Already presented in 2019 by the Bluetooth Special Interest Group (SIG), since 2020, we are, as far as Bluetooth is concerned, in version 5.2. This version is based on a new codec called “Low Complexity Communications” (LC3). But back again – codec, what was that again?
Bluetooth codecs overview
Although we already briefly discussed this topic in the article mentioned at the beginning of this article, it seems to make sense for us to once again discuss exactly what we are talking about here, given the complexity of this topic. One of our readers rightly commented in the article that Bluetooth is a lossy standard and therefore has nothing to do with “high end”. But what does that mean exactly? When transmitting audio data from sender to receiver, the data size has a significant influence on the required bandwidth. Currently, as mentioned at the beginning, Bluetooth data transmission takes place over the ISM band with a bandwidth of 2.4 GHz and 2.48 GHz. The bandwidth can be imagined, figuratively explained, like the width of a highway. In our example, the traffic volume represents the file size. Just as traffic jams quickly occur on a highway that is too narrow when there is a lot of traffic, the same applies to the wireless transmission of music. Lossless audio formats such as WAV and AIFF have a higher sound quality, but at the same time they require significantly more memory than a lossy MP3 file, for example. If the uncompressed files were simply sent via Bluetooth as they are, a data jam would occur due to the large amount of data. This would result in stuttering and a general loss of sound quality, among other things. To prevent exactly this, various algorithms have been developed over the years that first encode the file to be transmitted by the sender into a compressed format and then decode it into a playable audio file by the receiver. During the encoding process, the data rate is reduced, which basically involves a loss of quality. It is important that both the sender and receiver support the same algorithm, known as a codec. Well-known codecs include SBC, AAC, aptX and LDAC.
SBC
As an integral part of the Advanced Audio Distribution Profile (A2DP), SBC was the first Bluetooth codec to be introduced. The energy-efficient codec has a variable bit rate, which makes it very flexible, but the output quality can, unfortunately be somewhat unpredictable at the same time. Theoretically, SBC allows bitrates up to 345 kBit/s at sample rates of maximum 48kHz at 16 bit. AAC is compatible with every Bluetooth capable device and is still used today. Especially when there are coupling problems when using other codecs. Since it is a public domain codec, its use in the context of Bluetooth is free of charge. Unfortunately, the codec is less suitable for gaming or streaming sessions due to high latency times.
AAC
AAC (Advanced Audio Coding) is also a lossy compression algorithm, although – as the name suggests – a better one than SBC. The name AAC actually refers to the type of audio that is played back after decoding. Compared to an MP3 file, AAC provides higher-quality audio at the same compression settings. AAC supports 44.1kHz/24-bit audio files and bitrates up to 320kbps; however, this comes at the price of significantly higher power consumption. In addition, the way it is encoded is a very aggressive form of psychoacoustic compression. By omitting areas within the music that would probably not be heard, AAC can reduce the amount of data. But unfortunately, the algorithm sometimes means well and cuts away too much here and there, resulting in a loss of detail. Even though AAC is more advanced than SBC, the codec unfortunately still doesn’t cut a perfect figure. Even though the codec is preset by default on all Apple devices, AAC is not owned by the Californian company. The codec is not in the public domain, which is why companies have to pay the patent holders to implement it in their technology. In addition, audio quality rises and falls extremely depending on the manufacturer. Generally, it can be said that iOS devices can handle the codec best. With other manufacturers, some worrying drops can already be seen from 14 kHz.
Unfortunately, it still doesn’t really sound like high-end. So, the statement under our older article still stands, right? Especially in the last few years, the demand for Bluetooth devices has been growing. We at HiFi im Hinterhof have also had Bluetooth headphones in our range for a long time and just recently inaugurated our new wireless studio. In recent years, in line with the demand, a lot has already happened in terms of HiFi Bluetooth: What it is, we do not want to withhold from you. At the same time, we try to get a little closer to the answer to the question of whether Bluetooth can also “High End”.
aptX
If you have ever done any research on the topic yourself in the past, you inevitably did not get past aptX. When we talk about aptX, we are usually talking about a whole family of codecs that can be attributed to the company Qualcomm Technologie. The abbreviation aptX stands for “Audio Processing Technology”. By the way, the oldest version of aptX with the same name has been around longer than Bluetooth. But it was only with the release of Sennheiser’s first aptX-compatible Bluetooth headset in 2009 that aptX found its way into the headphone market as an alternative to SBC. AptX, just like SBC, is still used in a variety of wireless devices to this day. However, the data compression process of aptX is completely different from that of SBC and AAC. Instead of a psychoacoustic analysis of the audio material, Adaptive Differential Pulse Code Modulation (ADPCM) is used to reduce the bit rate. Instead of simply neglecting “unimportant” frequency ranges completely, an attempt is made to map the entirety of all frequencies in the file. HiFi? – we’ll see. Since the first version, Qualcomm launched a total of six more aptX versions until 2022: aptX Low Latency, Enhanced aptX, aptX Live, aptX HD as well as aptX Adaptive and aptX Lossless. For each version, the focus is on a specific challenge within the audio industry. For example, aptX Low Latency – the lowest bit rate codec in the aptX family – focuses on minimizing latency. Exciting especially for streaming applications and computer games, as well as audio and MIDI signals from musical instruments and controllers.
Nevertheless, we will only discuss aptX HD, aptX Adaptive and aptX Lossless in more detail here, since they play the most crucial roles in the context of high-fidelity music playback. The aptX HD codec was actually developed specifically for encoding audio files. In contrast to aptX LL, more latency is deliberately accepted here at the price of a higher bit rate of 576 kbps. Thus, high-resolution audio signals can be encoded and encoded with sampling rates of up to 48 kHz at a bit depth of 24 bits (better than CD quality). The audio quality of the encoding here comes close to the quality of the original with the same specifications, almost without loss. It also has a greater signal-to-noise ratio than aptX or aptx LL, for example.
AptX Adaptive combines the benefits of aptX LL and aptX HD into a single, highly efficient wonder codec. By automatically adjusting the bitrate to the type of content between 279 kbps and 420 kbps, both the low latency of aptX LL and the near-perfect audio quality of aptx HD can be achieved. AptX Adaptive supports high-resolution audio files up to 96 kHz at 24-bit. In addition, the codec is characterized by its backwards compatibility with aptX and aptX HD. In terms of sound quality, aptX Adaptive definitely seems to make demands towards the “high end”. Incidentally, Apple does not use aptX compatibility in its own products. The codec family is not license-free, but the price for the rights is simply insignificant, especially in view of Apple’s total revenue, so that it would be justified to reserve this flexible codec for the own customers.
LDAC
The same applies to LDAC, by the way. Of all the audio codecs discussed here, Sony‘s proprietary codec is currently the one with the best chance of answering the question of whether Bluetooth has something to do with “high end” or not with “yes”. But first take it easy – it’s not quite that simple. LDAC is able to stream with up to 990 kBit/s at full potential, whereby we are talking about audio files with a sampling rate of 96 kHz at 24 bit. That is definitely High-Res. However, as mentioned, only at full potential. Depending on the signal strength, LDAC jumps between fixed bitrates of 330, 660 and 990 kbps. This means that the available bit rate is automatically reduced as soon as interference occurs. In the best case, the bit rate is thus a good three times that of SBC and thus also the most audiophile. At the same time, it can also be worse than that of classic aptX, depending on the transmission situation. Nevertheless, LDAC is still more powerful than aptX HD even using the medium bit rate. Due to these enormous fluctuations, LDAC is unfortunately not an overly reliable codec. In addition to that, there are further requirements that unfortunately still make a fixed implementation in as many devices as possible difficult so far. First of all, a license agreement with Sony is required. This is probably the biggest obstacle for competing manufacturers in the same industries to get involved with this codec and at the same time optimize their own hardware for compatibility with LDAC. In addition, both the sending and the receiving device must be compatible with the codec and able to cope with the large bandwidth of the data.
aptX Lossless
With the introduction of aptX Lossless in September 2021, another player will appear in the field of high-end codecs and the possibility of lossless streaming via Bluetooth will come a bit closer again. With a data rate of up to more than 1 mBit/s, AptX Lossless promises the lossless transmission of data on CD quality. Higher resolutions with 24-bit and a sampling rate of 96 kHz can also be transmitted, but then not lossless, i.e. not as a bit-for-bit exact copy. The codec is based on aptX Adaptive and is accordingly also dynamic. The transmission rate can be scaled down to 140 kbps in case of a bad connection. According to Qualcomm, devices should automatically detect the most suitable transmission path depending on the content and connection quality, but this should also be manually selectable depending on the device. Either way, the use of the standard requires that the transmitter and receiver support the codec. Qualcomm has only made aptX Lossless available to a few companies so far. We will have to wait and see until the codec is actually used in devices.
HiFi & High End
At this point, however, a new question inevitably arises: Is HiFi the same as “High End”? HiFi is indeed a defined quality standard in audio technology, which is specified by EN 61305 and refers to the complete reproduction of the range audible by humans. However, this no longer plays a quality-determining role in the HiFi market. It is simply assumed from the outset that equipment in this sector meets, if not exceeds, these requirements. Which brings us to “high end.” This term can be interpreted in a number of ways, since there is no generally established definition of the term and it does not appear exclusively in the field of audio technology. On the one hand, in terms of audio technology, it refers to a component that stands out compared to others of a similar design and is therefore at the upper end of what is technically possible. It is therefore a very relative description, because after all, what might be called “high end” today can be yesterday’s news after just one year. On the other hand, the seal of approval can, cynically speaking, simply be used as a reason to sell one’s own products as expensively as possible. For our application of the term, however, we want to assume that this term in relation to Bluetooth audio is equivalent to what is possible in terms of data rates during transmission in wired applications. In a closed trial, i.e. Bluetooth with Bluetooth, the topic could otherwise be quickly closed. In this case, LDAC would be the “high end” of Bluetooth to some extent. But what efforts are there to put Bluetooth on a pedestal in terms of comparability to wired connections? Practically getting closer to the actual “high end”, i.e. the best that is technically possible in this field so far? In this respect, we would like to give a few perspectives in the following. This brings us back to Apple.
The future
In an interview with Gary Geaves, vice president of Apple’s Acoustics Team and head of the team that is largely responsible for Apple’s audio products, “What Hifi” magazine gives some exciting hints about what the future holds for Bluetooth. Despite all the intensive research that Geaves and his team have done, not least in the course of developing the Airpods, Aplle, like many other manufacturers before them, keeps pushing the limits of what Bluetooth allows today. Geaves refers to Bluetooth in this context as a “bottle-neck” that prevents qualitative leaps in terms of wireless headphone development. In and of itself, Apple could already implement innovative codecs in their products and thus counteract the problem, but at this point they act again in the usual appletypical way. Especially in view of their additional Lossless offer on Apple Music and the fact that they now exclusively sell wireless headphones, the manufacturer from Cupertino unnecessarily stands in its own way and that of its customers. Especially the highly praised codec LDAC could be a solution for Apple’s bottleneck problem. However, it looks like the customers will have to wait until the manufacturer has found a solution. Geaves and his team are currently putting a lot of resources into finding a solution to the problem. In the interview, he noted that there are tricks that offer the possibility to get more out of the Bluetooth technology than before. Specifically, he talks about Apple simply wanting more bandwidth. In itself, this sounds like a very exciting approach to us. More bandwidth would ultimately allow a higher bit rate and thus the transport of larger, uncompressed files. However, regarding Apple Music and ALAC (Apple Lossless Audio Codec) – Apple’s own lossless audio compression technology – the company’s website still says as of this writing: “Bluetooth signals do not support lossless audio.” We remain curious to see what will happen in this direction in the near future. Whether Apple implements aptX into their products, as many fans have long wished, or whether they follow their own plans instead remains to be seen. Apple has just always not been a fan of proprietary standards and equally not of licensing fees, so we would rule out the former alternative. Alternatively, a jump to Bluetooth 5.2 would be conceivable. This way, app users could benefit from the LC3 audio codec in the future. In fact, the introduction of Bluetooth with 6 GHz bandwidth also seems more and more realistic. Since December 1, 2021, the EU Commission has required its member states to open up the 6 GHz band from 5945 MHz to 6425 MHz for license-free services. Sooner or later, not only Apple would benefit from this, but all devices that communicate with Bluetooth.
LC3
At this point in time, however, this still sounds a bit like dreams of the future. However, there are a few more rays of hope that seem a bit more tangible at this point. In the context of the different Bluetooth versions, we briefly discussed the underlying codec LC3 at the beginning of the article, in relation to the current Bluetooth version 5.2 and LE Audio. The Low Complexity Communications Codec replaces SBC as the new preset codec from Bluetooth 5.2 and thus heralds a new era of Bluetooth. As the biggest innovation, a versatile audio transfer with low energy requirements was integrated into the Bluetooth standard. Bluetooth LE Audio (BLE) was developed in close collaboration between Qualcomm Technologies and Bluetooth SIG and expands the application possibilities for Bluetooth in terms of both telephony and streaming. Among other things, it allows multiple playback devices to simultaneously obtain music from a single source. However, this version requires an update of the software as well as correspondingly optimized hardware. Unfortunately, only a few devices are equipped with the standard so far, so we will have to be patient for the time being.
Final Thoughts
Finally, we would of course, like to go back to the initial claim that Bluetooth has nothing to do with HiFi, let alone “High End.” As you now know, there are a variety of challenges that are posed to the transmission standard. Depending on the application and requirements, different approaches have been delivered over the years. Different algorithms, called codecs, sometimes allow for vanishingly low latencies, sometimes for transmission of up to more than 1 mBit/s. As far as “High End” is understood as a claim to correspond to the lossless transmission of audio data of a wired connection, as already explained, the reality turns out to be somewhat sobering, at least at this point in time. Codecs like aptx HD, aptx Lossless and LDAC allow the most faithful transmission to CD quality, but resolutions above that do not remain uncompressed under any circumstances. However, Bluetooth has developed considerably since the noisy beginnings today, and we by no means expect a standstill due to the high demand.
Even though we would not mind if Bluetooth audio operated losslessly in the future, we ask ourselves whether it is a decisive purchase or non-purchase criterion at this point, where it is not yet the case. Especially when it comes to Bluetooth headphones, a lot of other factors play a role. In view of the application situation, perhaps even more decisive ones. As a rule, Bluetooth headphones are used most on the go. Who, if not us, could better understand wanting to access high playback qualities on the go? But let’s be honest: There is little room for analytical listening sessions in hectic everyday life. Here, issues like noise-cancelling, handling and looks play a more important role in most cases. For immersing yourself in the multi-layered sounds of an orchestra, you can still use the wired headphones at home, while Bluetooth takes over the control, for example of the streamer. One thing is certain: the Bluetooth trend will not simply fade away in the coming years. The standard has always been future-oriented, and already we see serious efforts from various companies and manufacturers to bring it even further forward.
For those of you who already want to see what is possible with Bluetooth at the moment, we would like to recommend a very special Bluetooth headphone that can handle LDAC as well as many other codecs. The HiFiMAN Ananda BT theoretically only requires a source that is also compatible with the codec, and then there’s nothing standing in the way of high-fidelity, wireless music enjoyment. You are welcome to make a direct comparison and see for yourself how much the resolution-related differences really matter to you in terms of sound. We are curious to see what innovative ideas we can expect from Bluetooth in the near future. Unfortunately, we can’t promise you with absolute certainty that Bluetooth will one day be as loss-insensitive as a cable connection. But we can assure you that we will continue to keep you up to date with the latest products, not only in the field of Bluetooth, but with everything that makes the HiFi heart beat faster. Because even if Bluetooth may not yet have anything to do with “high end” — we certainly do.
