How does Bluetooth work, and should it be considered for serious critical listening?
Leslie Shapiro | Aperion Audio
Reprinted with permission from Aperion Audio.
Bluetooth has come a long way. It originated from a Danish king from the 10th century – Harald Blåtand, or as he’s known in English, Harold Bluetooth. Under his rule, fighting groups were united into what is today Norway, Sweden and Denmark. When a technology was developed that connected different products, industries, brands and technologies, the creators named it Bluetooth after the famous king.
In more modern times, Bluetooth technology has come a long way since it was first introduced as a low-bandwidth way to wirelessly transmit audio from a cell phone to a headset. It quickly transitioned into a hands-free way to integrate the phone into a car’s audio system. Shortly after that, people realized that they could also send music via this same wireless technology to speakers and headphones. How does Bluetooth work, and should it be considered for serious critical listening?
What Are The Bluetooth Formats, and What Does Each Mean For Sound Quality?
- SBC -
Bluetooth is a low-power transmission system that allows a device to send audio wirelessly over a short distance – initially, a range of 30 feet, but now up to 300 feet. For its initial applications in the car and for headsets, this distance was more than generous. SBC – Low Complexity Subband Coding – was the first technology used for Bluetooth. Since it was intended for phone audio, it uses a significant amount of data compression, similar to the compression used for MP3. It uses very little power for processing, making it ideal for the wireless headsets it was initially designed for. As phones developed and Bluetooth gained momentum, better iterations of SBC developed. However, as we’ll see throughout this discussion, all Bluetooth formats default to the lowest common denominator. In other words, if your new headset has the highest quality SBC but you pair it with a phone that has a low quality SBC, you’re going to end up decoding the audio at the lowest rate of either the source, or the playback.
- aptX -
One of the biggest shortcomings of SBC is that it adds an additional layer of data compression. If you’re starting out with an MP3 file that’s already severely data compressed, SBC compresses it even more. Enter aptX. While it’s still a form of data compression, it is a time-domain compression, instead of using the psycho-acoustics of MP3 data compression that removes data that the models think you won’t hear. aptX creates smaller files that are easily transmitted via Bluetooth, but they sound significantly better – the aptX developers claim it to be CD-like. This is especially important if you’re listening to higher resolution formats such as FLAC or WAV. Similarly to SBC, both the playback device and source have to have aptX or it will revert back to SBC. Another important consideration with aptX is that it doesn’t have the latency (delay) of other Bluetooth formats, making it ideal when used while synced to video.
- A2DP -
Both SBC and aptX apply an additional layer of data compression on material that is already data compressed. However, hidden in the Bluetooth standard is the Advanced Audio Distribution Profile. This states that additional codecs are supported, including MP3. So, instead of adding an additional layer of compression, MP3 can be transmitted without undergoing additional compression. As with the other two, this only applies if both devices – the transmitter and receiver – can support A2DP.
- Bluetooth 4.0 -
The latest version of Bluetooth is 4.0, and it has really bumped up the bandwidth. Version 2.1 had a throughput rate of just 2Mbps, while 3.0 and 4.0, in theory, are 26Mbps. This will let it handle not just audio streaming while supporting higher bit rates, but also potentially video streaming.
Possible Connectivity Issues To Be Aware Of.
While most devices will figure out how to connect without any input from the user, what other challenges will be faced as you try to set up a Bluetooth system in your own home? Here are two you should be aware of.
- Distance -
Bluetooth range continues to improve, but at best, it’s 300 feet. And that is under ideal circumstances. If you know you’re going to be pushing the limits, you should be sure to pick products that use Bluetooth 4.0, and perhaps use AC power. Products that require the use of high-power transmitters would eat up batteries, while products that can be plugged in have no problem with a larger signal, provided they use that power to enhance reception. Structural layout is important too. Setting devices 50 feet apart in a large room will be much less problematic than setting them 20 feet apart with a concrete wall in between. Since Bluetooth is a low-power signal, it has a hard time going through most solid materials.
- Ease of pairing and setup -
A Bluetooth system needs to connect the transmitter to the receiver. This process is known as pairing. Basically, it’s how to pick which Bluetooth devices are talking to each other at any given time. On a busy subway car, you want to make sure your phone is paired to your headphones, not your nearest fellow commuter’s phone. Some manufacturers make their devices a breeze to set up. Either a display screen or something as simple as a series of indication tones can make pairing simple. Some devices leave users guessing if they’re in pairing mode – these typically are systems that require a certain sequence of button presses. Most product reviews will mention how difficult or easy a system is to pair – pay attention to what’s been said.
Once you know how to connect, there are a few things you can do to ensure you get the best sound from your system.
Ways To Optimize Sound Quality From Bluetooth
- Specs to heed -
Try to get the best Bluetooth profile you can on both sides of the transmission chain. Try for Bluetooth 3.0 or better and aptX, especially if you’ll be pushing the limits. Most devices will indicate their range of transmission. This is usually relevant for the transmitter, but a high-powered receiver will also be advantageous. If you’ll be using the device on battery power, look for long playback times – or at least of a duration that will be useful for you. If you regularly spend 2 hours at the gym and your headphones will only play for 1.5 hours, you’re gonna be awfully bored for that last set of squats.
- Optimizing the source -
Bluetooth will never improve the quality of your sound source, and in the worst case scenario, it can severely decrease the quality. There’s no point in sending your high-resolution FLAC files over a Bluetooth system that can only use basic SBC coding. Conversely, if your source is low-res MP3, even the best Bluetooth transmission won’t improve it, but at least it won’t further degrade the signal.
- Optimizing playback -
Once you’ve transmitted the best possible Bluetooth signal, you want to make sure the playback device is the best possible. Get the best product that suites your situation. If you need a device that’s small and portable, get it. However, if the device is always going to reside in your living room, get the largest speakers you can afford with the most power supplying them.
It’s always best to take a realistic look at your needs. Sadly, to this day, a wired connection, or a USB connection will most likely give you better sound quality than Bluetooth. If you don’t need to be wireless, don’t bother with it. It’s convenient, looks cleaner, but it can degrade the signal. Will the degradation be noticeable? It depends on a variety of things: source quality, bitrate and the quality of the playback system. Even the best Bluetooth playback source with the highest resolution audio will be wasted on a tiny battery-powered, mono cheap speaker. Splurge on the speakers – that’s always going to be the most noticeable place for improvement.
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