In this post about wireless headphones, we are going to try to clear up concerns in relation to their operation, mainly for all those who try to understand something beyond its simple use to listen to music.
This is something very interesting that helps us to have more information when buying a wireless headset and know what to take into account.
In the same way, we are going to talk about a feature that several models of headphones today include in order to provide better practicality in everyday use: wireless headphone technology called Bluetooth.
In recent times, wireless technology in headphones gained a significant following thanks to smartphones that lost the P2 (3.5mm) input for the headphones. At the same time, there was a greater popularization of the most affordable headphones from Chinese companies, which is why today it is simpler to buy a Bluetooth headset.
In today’s market, we find more than one type of wireless headphone technology, although the most popular and efficient today is Bluetooth. Due to this, we will analyze below what Bluetooth technology is, how it works and how it is applied in the audio of our headphones.
How Bluetooth Technology Works
Bluetooth wireless technology uses radio waves to connect different types of gadgets such as laptops, smartphones, and tablets.
Bluetooth makes use of radio frequencies, more specifically the 2.45 GHz frequency, and as this frequency band is widely used, it is a requirement to ensure in some way that Bluetooth does not suffer interference and that it does not produce them either. For which, they took advantage of the communication by FH-CDMA (Frequency Hopping – Code Division Multiple Access), which allows the moderation of the interference indices, dividing the frequency into 79 channels (or 23, subject to each country).
Differences between Bluetooth 4.2 and 5.0
The first thing we notice in Bluetooth 5 is that the range was optimized. While version 4.2 has a range of up to 50 meters in an open environment and up to 10 meters in an indoor environment (with walls), version 5 manages to provide a range of up to 200 meters in an open area and up to 40 meters in a closed environment.
This increase in range potential is due to the fact that Bluetooth 5 provides a changing transmission speed. It manages to use 4 levels of data transmission and is regulated according to the requirements of the gadget being used.
You can automatically switch between the following transmission speeds: 2 Mbps, 1 Mbps, 500 kbps, and 125 kbps. The lower the data rate, the greater the distance reached in data transmission.
For example, smartwatches do not need to send a large amount of data and consequently accept a transmission speed of 125 kbps, providing a range of up to 200 meters in an open environment. However, when a large continuous stream of data such as 1 Mbps or 2 Mbps is required as is the case with wireless headphones, for example, the range is greatly reduced. But do not worry, Bluetooth 5 will allow you to walk quietly throughout your house without great losses depending on the kind of Bluetooth you use (which is different from the Bluetooth version).
The second feature that stands out in Bluetooth 5 is battery saving. It manages to standby for a longer time and consume less power than its past generation (4.2). This is made possible by the enhancement of Bluetooth Low Energy (BLE) technology that was introduced in Bluetooth 4.0. It was created thinking about applications that require low data transfer (less than 1 Mbps) and for that, it uses the GFSK (Gaussian Frequency-Shift Keying) modulation system.
Finally, another feature that draws attention to version 5 of Bluetooth is the ability to transmit data in a single packet. In Bluetooth 4 this rate is 31 bytes per packet, while in Bluetooth 5 this value increases to 255 bytes per packet.
How to use Bluetooth 5.0 on technology devices
You will need a smartphone, tablet, notebook or other devices that support Bluetooth 5.0 and a headset that supports that version of Bluetooth. Both devices must be compatible with the technology to be really used, otherwise, the mobile will use an older Bluetooth version.
Bluetooth classes
To make it possible to adjust Bluetooth to the most varied types of devices and purposes, the maximum range of the technology has been divided into four classes:
Class 1: Maximum power 100 mW (milliwatts) range up to 100 meters;
Class 2: Maximum power of 2.5 mW, range up to 10 meters;
Class 3: Maximum power of 1 mW, range up to 1 meter;
Class 4: Maximum power of 0.5 mW, range of up to 50 centimetres.
Bluetooth profiles
Bluetooth profiles are protocols that define what functions can be performed by devices that have Bluetooth.
There are currently around 40 different profiles, but some of these are found more frequently on devices that have this technology. The most relevant Bluetooth profiles for us will be presented below:
Advanced Audio Distribution Profile (A2DP)
This profile is responsible for transmitting audio from one Bluetooth device to another. It is used by all Bluetooth headphones and speakers today. Before the creation of this profile, Bluetooth audio was very grainy and only headsets were used for phone calls. The Bluetooth modules that support the A2DP profile have in them a set of audio codecs that can be executed according to the hardware capabilities. These codecs are designed to balance the needs for power use, audio processing, and sufficient data rates according to what is required.
Headset Profile (HSP)
This profile provides the ability to stream audio through the microphone to answer calls, and adjust the sound volume level. It is used together with the A2DP profile to be able to transmit the audio of the voices.
Handsfree Profile (HFP)
This profile gives the Bluetooth device the ability to make hands-free audio calls in cars or smartphones. Add features such as accepting, rejecting or ending a call without needing to touch, for example, on the mobile phone to execute the command.
Audio / Video (A / V) Remote Control Profile (AVRCP)
This profile allows the user to control the music or sound of the Bluetooth device by performing functions such as play/pause, forward / backwards; beyond controlling the volume. It is generally used in conjunction with the A2DP profile to enable sound transmission and control.
Audio codecs
The codec determines how Bluetooth will transmit data from the source to the headphones. Encodes and decodes digital audio data in a specific format. Thinking of an ideal situation, the data is transmitted through a high fidelity signal at the specified minimum bit rate. This will use less band while maintaining good playback quality, better distance capacity, and better headphone battery life.
Before we begin, it is important to say that to get the quality of the desired codec, both the source and the headphones must have support for that codec. Furthermore, it is also necessary to know the meaning of some terms to make it easier to read about the codecs below.
Basic codec terms
- Sample rate (Hz): is the number of data points per second in an audio file. You need two samples to accurately capture any frequency, so the audio is sampled at least twice the limits of human hearing (approximately 20 kHz). The sampling frequency of the CD is 44,100 Hz, which means that with every second of sound, 44,100 measurements of the signal’s voltage variation are taken. In this way, the higher the sampling frequency, the more accurate the representation of the signal. A higher sample rate means a larger file size.
-  Bit depth (-bit): is the number of bits saved for each audio sample. A sample represented by only one bit could receive only two values: “0” or “1”. On the other hand, a representation with 3 bits could receive 8 different values ​​(23 = 8): 000, 001, 010, 100, 110, 101, 011, 111. A CD has a resolution of 16 bits, which allows a binary resolution with 65,534 (216) values. A higher bit depth records a signal more accurately. A higher bit depth multiplies the file size.
- Bit rate per second (kbps): generally measured in kbps or Mbps. That’s the amount of audio data transferred per second, in our case via Bluetooth.
SBC codec (Low-complexity sub-band codec)
The simplest existing codec is the Low Complexity Subband Codec (SBC). It is present in all Bluetooth devices that have the A2DP profile, being a universal codec. Its transfer rates reach up to 345 kbps, enough to play compressed MP3 files. So in case you want high-fidelity audio, don’t expect too much from this codec.
AAC (Advanced audio coding) codec
The AAC codec was developed by Bell Labs, Fraunhofer Institute, Dolby Labs, Sony, and Nokia. It is the standard format for iPhone, iPod, iPad, Nintendo DSi, Nintendo 3DS and PlayStation 3. It is compatible with PlayStation Vita, Nintendo Wii, Sony Walkman, Android and BlackBerry.
The codec can provide a data transfer rate of up to 250 kbps. But despite having slightly lower performance, AAC is widely praised among compression algorithms and is considered a breakthrough over the SBC codec.
Apple has chosen to adopt the AAC codec for all its devices, in addition to the SBC codec, which is a requirement to have the Bluetooth A2DP profile. Apple Music streams with AAC natively, making it the best choice for an AAC or ALAC file library. For best results, you should pay attention not to use your iPhone to stream other compressed audio formats. The compressed files in MP3 or Ogg Vorbis format Spotify must be decoded by the iPhone and then encoded in AAC before they are transmitted to the headphones.
AptX codecs
The aptX codecs were developed by Qualcomm with the aim of offering a quality that was close to that of a CD, offering a rate of 16bits / 48KHz with a data transfer rate of up to 352 kbps. Even in this way, aptX still adds lossy file compression, compromising the final sound quality.
The aptX HD was created specifically to obtain higher resolution audio and fewer losses than the first version. It is a codec capable of reaching a speed of 24bits / 48kHz in LPCM (Linear Pulse Code Modulation) with a data transfer rate of up to 576 kbps. This already provides significant gain compared to aptX or SBC in terms of sound quality.
To decrease audio latency in Bluetooth headphones, aptX Low Latency was created, thus enhancing gaming and video experiences. It is a codec that has a latency of fewer than 40 milliseconds with a data throughput of up to 420 kbps.
And finally, to improve the battery consumption of the headphones, Qualcomm has developed the aptX Adaptive codec that changes the data transfer speeds according to what the file that is being played requires. This codec supports a data transfer rate of up to 420 kbps.
LDAC codec
Sony, in order to achieve the best sound quality in the Bluetooth headphone market, has created its own codec called LDAC. It has the ability to vary the bit rate according to the definition of the song and is capable of maintaining a speed of 96KHz / 24bits with a data transfer rate of up to 990 kbps. This data transfer speed is almost twice that of aptX HD and three times that of SBC. Fortunately, in the case of LDAC, it is possible to find non-Sony Bluetooth devices that support this codec. In this way, you will be able to obtain an audio quality superior to the aptX HD codec.
UAT codec
Hiby has recently developed its own codec, Ultra Audio Transmission (UAT), to overcome all the barriers of the existing ones, including Sony’s LDAC, and has managed to achieve a sampling rate of 192 kHz with a data transfer rate of 1200 kbps. There are still few devices compatible with this technology, but it is something surprising and that raises the quality that we have in our Bluetooth headphones even more.
How to use the best possible audio codec
Even in the case of Bluetooth 5.0, you will need a smartphone, tablet or laptop, and a headset that supports the desired codec (either aptX, LDAC or UAT). Both devices will need to be compatible with the technology to be really used, otherwise the mobile will use the SBC or AAC codec, which are inferior in terms of audio quality when compared to the other codecs mentioned.
Bluetooth does not support high-quality audio when the microphone is in use
When only the earphone is used to listen to some sound, the A2DP profile is activated and consequently, you are able to use codecs such as aptX HD, aptX Low Latency, LDAC, etc.
However, when you need the microphone, the Bluetooth profile will change to HSP (Headset Profile) or HFP (Handsfree Profile) and this will cause the audio quality to drop sharply because Bluetooth does not have enough bandwidth to maintain the audio quality and at the same time send data from the microphone.
This problem of lack of data transmission capacity can be improved with the use of Bluetooth 5.0 which has several improvements in terms of speed and data transmission capacity.
Apple W1 chip
Apple has a chip inside their headphones with a specific audio codec that can only be used on Apple devices. In case you do not have, for example, an iPhone and want to pair the AirPods on your Android smartphone, you will not get the same sound quality.
Also, if you have a better Bluetooth headset than Apple’s with support, for example, the LDAC or aptX HD codec, and you want to connect to an Apple device, it will unfortunately not be possible to benefit from these codecs. Your headset will use the SBC and AAC codecs which are simpler and low in quality compared to the other currently existing codecs.
Advantages and disadvantages of wired and wireless headphones
After all that has been talked about, you may have realized that Bluetooth technology in wireless headphones is by no means simple, requiring a lot of engineering and skill from both the source and the headphones themselves. All the development of Bluetooth versions and profiles, plus audio codecs, comes at a great cost.
In addition to having a cost in terms of technology built into the Bluetooth device, we still have the cost of the battery to keep the hardware working, the Bluetooth radio wave receiving antenna and the integrated chip with DAC and amplifier inserted inside the Bluetooth headphones. .
Unfortunately, this raises the price of a good wireless headset considerably. So do not fall into the mistake that cheap headphones of this type will offer you good quality since it is a challenge to balance the cost of Bluetooth technology with the sound quality of the headphones and with the quality of the materials used in the headset. manufacturing.
The Bluetooth headset, despite its high cost, makes it much easier to play sports by listening to music or a podcast, watching movies without disturbing others, or simply studying. All this without cables. However, if you prioritize sound quality above all else, it is interesting to consider the alternative of wired headphones over Bluetooth, since this technology has its limitations.
In terms of audio quality, regardless of the value, we still have some compression and degradation of the audio in headphones that work with Bluetooth technology compared to those with a cable. It also adds the audio latency problem that many wireless models, depending on the codec and the version of Bluetooth, still have.
In short, the wireless headphone market is constantly evolving and getting better and better. In the meantime, it will only be possible to obtain higher quality at a high cost, so it is important to weigh priorities.
In the future, the cost of the technology is likely to decrease, as well as an improvement in it. Meanwhile, you will hardly achieve the sound quality of a wired headphone. Just look at the headphones from the best manufacturers, none who intend to produce the best headphones in terms of quality are using Bluetooth technology. By contrast, all aspiring headphones have cables.
Does the device affect the quality of the Bluetooth audio?
If we were using the same audio codec, it will not affect the audio quality to use a different mobile phone (or laptop or tablet), model. This occurs because the function of the Bluetooth signal transmitting devices is only the transmission of the digital signal that has to be converted to the Analog signal so that the headset can emit sound.
Conversion of the transmitted digital signal (via an audio codec such as aptX HD or LDAC) and further amplification occurs within the Bluetooth headset, via an integrated circuit board that has a DAC and a system amplification.
That is if your smartphone has support for the aptX or LDAC codec and your Bluetooth headset has to support the same codec, the headset will sound the same even if you use another phone model (which also has support for the same codecs).
