AptX HD – truly high-quality sound without wires. The best sound over Bluetooth: we tell you what aptX, aptX HD and LDAC are
AptX HD Bluetooth: what is it and how to get it? July 8th, 2017
The aptX HD protocol is designed to provide Hi-Res audio transmission over Bluetooth. Here you will find everything you need to know about it and how to use it.
One piece of wisdom we've learned along the way is that many people are willing to sacrifice sound quality for convenience. Take wireless headphones, for example. They can rarely compete with good wired ones, but they are much more convenient.
However, some time ago the pendulum swung towards higher quality. The most striking examples of this trend can be considered the revival of vinyl (this is where we are not talking about convenience at all), as well as the growing popularity of Hi-Res audio. So, is there a way to combine usability and sound quality?
Developers from Qualcomm are confident of this. Earlier this year, they introduced the aptX HD codec, which allows you to wirelessly stream music in 24-bit Hi-Res audio format. Thus, Bluetooth-enabled devices (such as portable speakers) can theoretically sound much better.
What's good about aptX HD? How to get it and what devices support it? Now we'll find out.
What is aptX Bluetooth?
To understand what aptX HD is, you first need to remember the “classic” aptX. This is an audio encoding algorithm created in the 80s and widely used by film producers and radio stations. Today, aptX is closely related to Bluetooth, which is found on many computers, smartphones, AV receivers and other consumer electronic devices.
The main advantage of aptX is its ability to transmit a full-bandwidth music signal in near-CD quality (16 bit/44.1 kHz). This is "close" quality, not true CD quality, as aptX uses compression to reduce latency due to encoding and transmission. Classic aptX uses 4:1 compression and the data transfer rate is 352 kbps.
What is aptX HD?
Now let's move directly to aptX HD. It's essentially aptX, redesigned and improved to deliver higher quality music.
Its development was stimulated by the growing popularity of Hi-Res audio; it supports formats up to 24 bit/48 kHz, the compression ratio remains the same (4:1), and the data transfer rate has increased to 576 kbps.
How the sound quality will be comparable to transmitting a Hi-Res signal via cable remains to be seen; however, Qualcomm proudly waves the "better than CD" flag.
What do you need to evaluate aptX HD?
There's a lot that goes into using aptX HD. First of all, you will need the right equipment. We are talking about the CSR8675 Bluetooth audio system on a chip.
It not only supports full 24-bit audio, but also provides better digital signal processing than its predecessors. Qualcomm promises improved signal-to-noise ratio through encoding and decoding and reduced distortion, especially in the 10-20 kHz range.
The need for a specialized chipset means that to use aptX HD you will have to acquire compatible devices: there are no options for firmware updates. There are no prospects for any “rescaling” of the audio signal.
But you don’t have to worry about backward compatibility: devices with aptX HD will support all headphones and smartphones with “classic” aptX.
What devices support aptX HD?
The LG G5 puts a premium on sound quality with a modular design that includes an external DAC
The aptX HD codec was announced in January 2016. It will be used in Android smartphones and tablets, as well as portable media players.
The first smartphone to support aptX HD was the LG G5 released last year. It was followed by its brothers - G6 and V20.
In addition to them, aptX HD technology is also supported by high-end smartphones - Vertu Constellation Octane and Luna TG-L900S - which can hardly be called widespread.
Among manufacturers of portable music players, Astell & Kern has become the most ardent fan of aptX HD. The new codec is supported by its AK380, AK320, AK300 and AK70 players, as well as the XB10 amplifier/DAC.
The first attempt to get high-quality audio output wirelessly. No DIY. Details under the cut.
I recently set out to play music in my car from my phone through the head unit. It is assumed that the PG has an Aux input and power somewhere nearby. I have both ports in the armrest. Using a wired connection is no longer comme il faut: a bunch of wires and restrictions on placing the phone. Regular Bluetooth doesn't work either: the sound quality is like coming from a neighbor's kitchen through a ventilation vent. A more detailed Internet search revealed the first potential contender. Bluetooth with aptx support. Aptx uses the SBC codec, which is quite good in its essence.
Main device, with cat. I was going to broadcast music - this is my note 3 phone. Versions with a Snapdargon processor support Aptx. All that remains is to make a choice in favor of a specific box model. The choice in Chinese stores is very large, but in the end it all comes down to 2-3 basic models from 1-2 manufacturers. I decided to choose an unbranded model with Spdif output. Nothing was known about the built-in DAC, so I suggested an alternative use for this box: output sound at home through a receiver using spdif.
The approach was correct, but, as it turned out, I still underestimated the quality of the “piping” and the components themselves, which is why the sound did not live up to expectations. Details below.
Aptx Bluetooth 4.0 music receiver
Let's start with the fact that the box came to me dead. For which I charged the manufacturer half the price.
Further troubleshooting revealed that only the power supply unit was dead.
Complete audio wires are discarded. They only tie up the roach for drying, worse than in the food photos below. 
The device started up with half a kick, but the first limitation immediately became clear. Contrary to the seller/manufacturer's claims, the device only supports one connection at a time. The declared AVRCP is also meaningless here: there are no buttons on the device and therefore there is nothing to control.
Now about the sound. This is where the potential of the device was revealed. Finally it sounded better than from the toilet tank, but still worse than even the radio on my GU.
At first I made a mistake on the built-in DAC, and therefore, on the second attempt, I connected the box at home via spdif to a proven receiver. But alas, the sound is just as lousy. The only remaining untested component was the phone itself. The difficulty with checking also lies in the fact that using standard software methods it is impossible to determine in any way which codec is used. The only option is to watch logcat. I tried it. The log is empty. I started digging and came to the conclusion that in my custom kernel (Ultimate kernel v70) the log is simply disabled. Installed an alternative custom kernel (AEL Kernel v7.12). I look at the logs - aptx is being initialized.
12-31 13:46:07.165 D/CODEC_IF(10758): codec_if_open: opening libbt-codec_aptx.so... 12-31 13:46:23.515 D/CODEC_IF(10758): codec_if_open: opening libbt-codec_aptx.so. ..
Finally, I decided to turn on the box again. And lo and behold! She started playing! It would seem that aptx is only firmware modules (aptx is only available in touchwiz-based kernels. In CM, AOSP, etc. aptx is not licensed) and nothing should depend on the kernel. But in my case, the whole catch was in the kernel.
Testing the sound.
Here we first need to make a retreat. Above, as commentators noted, I incorrectly described the codecs. SBC is a standard codec for the A2DP profile, it is required for implementation in all Bluetooth devices with A2DP. SBC is lossy encoding, maximum bitrate 345kbps. Aptx is a proprietary codec from CSR, but it also encodes with compression. The bitrate is only slightly higher than the maximum bitrate in SBC. But this is a completely different coding. all details are described. The most important conclusion is that the presence of the aptx nameplate guarantees you at least a codec bitrate no worse than mp3-320. CSR can also give comparable parameters, but no one can guarantee that your bluetooth device supports high bitrates. The check here will be even more non-trivial than with aptx.
It is quite possible that, as some commentators have noted, it is enough to buy only a good branded bluetooth without aptx. But this is ultimately a lottery. My parents have a Samsung microsystem with bluetooth. I tried to play music through my old SGS9000 - the sound was worse than from a radio. In addition, the concept of “good” sound is different for everyone, and the only objective comparison parameter in this case can only be the actual bitrate of the codec.
Moreover, my initial tests were apparently done with the SBC codec. The sound was terrible and I could not determine the actual bitrate. Although a good module is used. And again it is unclear: either the phone does not support high bitrate on the SBC, or the Bluetooth receiver.
Actually, sound via aptx.
Firstly, the output signal level with aptx is for some reason 2 times higher than without it. The most important difference between the aptx codec and the SBC is its wide dynamic range. Those. high frequencies are clearly distinguishable and musical instruments are easy to read. Low ones - first of all, they just appeared. And secondly, they are deep and dynamic. Subjectively comparing in the car: the sound has become no worse than radio stations without dynamic compression (Orpheus, for example). The sound is somewhat worse than mp3-320 through the built-in flash drive reader: less detail and stereo stage. And the sound is still much worse than CD.
There is barely audible background noise at max volume. It is completely absent even when playing MP3. It should be noted that the box does not have galvanic isolation for power supply and therefore there may be interference. I haven’t tried it while driving yet, so I can’t say anything.
I won’t be able to test the sound via spdif in the near future, because the receiver is at my dacha and I won’t get there soon.
And finally, regarding media signals. If an SMS arrives on your phone, the sound via bluetooth is muted, but the sound of the SMS itself does not pass through.
Offal
Now let's look at the giblets of this box. Everything is easy to open: just pry off the bottom, which is attached only with latches. And this is what appears to our eyes.
Aptx is indeed present in the form of a chip. It is built in as a ready-made bluetooth module. For reference, such modules are .
Well, the DAC, as I expected, turned out to be the most primitive - it’s ancient. Aside from that, the largest chip is the transceiver for implementing spdif. There is another mysterious chip (medium in size), it is not marked in any way. It was not possible to remove the board from the reverse side, because It was planted too tightly and I was afraid of breaking it or cutting the bluetooth antenna (two thick conductors on the edge of the module). But it turned out that the OEM manufacturer of such boxes is .
It's up to you to buy or not. In my opinion, the device is definitely worth the money, but it has one significant drawback - for good sound you need a phone with APTX support. And these are just some Sony, HTC and Samsung Galaxy.
Another drawback is that you need to confirm the connection of the box every time, because... its power is turned off when the ignition is turned off.
I'm tired of headphones with a constantly coming off jack and a broken computer socket. I decided to give up wires and started looking at an FM headset, but based on the reviews I realized that my option was bluetooth.
However, there are also difficulties here.
An FM headset is essentially an FM receiver and transmitter. There is no encoding before transmission and no decoding of sound after reception, which means there is no lag between the sound and the picture on the monitor.
In the case of Bluetooth, a certain time passes between the transmission of audio in digital format and its reception + decoding to the level of sound vibrations. And the weaker the Bluetooth version, the greater the lag between the sound and the picture.
While studying the topic, I came across information about profiles and codecs supported by bluetooth versions. As it turned out, having the same set of supported profiles, Bluetooth gadgets from different manufacturers can behave differently in terms of audio lag from video. The whole point is in the codecs for encoding and decoding the stream.
Today, the most advanced, high-speed codec is the Aptx codec, implemented in CSR8645 chips.
Based on this chip, bluetooth modules CSR8645 with Aptx support are produced in China.
I ordered one for myself at a price of $5.2 with free delivery to our region at the time of purchase.
However, when I received the parcel I was very surprised - I ordered this one 
and got this: 
Those. The package contained the module I needed, but it came with an external two-channel amplifier at a price without it. 
I didn’t start an argument out of modesty), but they could have fired someone. Thank you for the mistake, although not cleverly.
Now let's talk about everything in order.
Technical characteristics of the bluetooth module:
1. Bluetooth version: 4.0
2. Supply voltage: DC3.6V-4.2V
3. Bluetooth protocols supported: HFP V1.6/ V1.2 A2DP/ AVRCP V1.4/ HSP V1.2
4. Working current: ≤30mA
5. Standby current:< 50uA
6. Temperature Range: -40~+80 Celsius
7. Transmission distance: >10m
8. Transmitter power: CLASS1/CLASS2/CLASS3, 9dbm (Max)
9. Frequency Range: 2.4GHz ~ 2.480GHz
10. External interface: PIO/ SPI/ I2S/ PCM/ USB
11. Audio codecs: AAC/ MP3/ SBC/ APTX
I looked into the datasheet and discovered several more very interesting functions:
1.Possibility of connecting two microphones
2. 5-band customizable equalizer
3. noise reduction of microphone inputs, including wind!!!
4.Voice recognition for hands-free function while answering a call
5. Connect two phones at the same time
6. possibility of programming
7. Attention: charge control of the lithium battery!!!
Thanks to its very modest dimensions (27*13.3 mm only for Bluetooth and 29*30.5 mm with an amplifier), the module can be installed almost anywhere.
Pin assignment: 
I can't say anything about programming. Allegedly, this requires some kind of specific programmer. But this function, like most consumers, is unlikely to be of interest to me.
I also couldn’t figure out the equalizer, but I believe that it exists - the manufacturer of the Cambridge Silicon Radio chip values its reputation. Most likely, the equalizer is activated by a certain combination of buttons, but even with the default settings the sound is simply excellent, and its settings can be done on the source (computer, phone, etc.)
The internal battery charge control circuit can provide a charging current of 200 mA; for higher currents, an external transistor is required with a connection according to the datasheet. When the battery voltage drops to 2.8 volts, the controller turns off the power.
The connection diagram for external components to implement a headset for a telephone is extremely simple: 
With the connection of LEDs, battery and control buttons, everything is very clear. There are some reservations about connecting headphones/speakers (hereinafter referred to as N/A) and microphones - each N/A is connected with two separate wires; ground wires cannot be combined, otherwise the excitation and background will be half-limited. At first glance, it is not very convenient, but there is good channel isolation and no interpenetration of signals from channel to channel. A D/N connection with a resistance of 16-32 Ohms is allowed.
Since electret microphones are now used, power is required for their operation, which is implemented by the output of the Mic Bias module.
In my case (Bluetooth module on the power amplifier board), all the necessary external components are already placed on the power amplifier board - LEDs with current-limiting resistors, external circuits of one microphone (if you need a second one, you will have to solder similar circuits directly to the Bluetooth module).
The package sent to me does not have a POWER button. The module is in sleep mode by default and to activate it, press and hold the PLAY button for a few seconds, after which the module turns on and connects to the signal source (another Bluetooth device).
Thus, only five buttons are needed for control - Play, Vol+, Vol-, Track+, Track-.
One pin of each button is connected to the corresponding pin on the board, and the second pin of each button is connected to the COM pin. In test mode, the wire soldered to the COM point simply connected with Play, Vol+, Vol-, Track+, Track-. The controls work great.
Pairing with a phone and current consumption in standby mode. 
What can I say about the stereo amplifier?
It is built on two single-channel audio amplifiers HT6872. Both channels are completely independent of each other. The speakers, already with a resistance of 4 ohms, are also connected each with their own pair of wires. This is convenient for using a module with an amplifier as a basis for Bluetooth headphones or speakers. In other cases, where the use of the total mass of two channels is required, additional circuit solutions will have to be used. Each channel develops a power of 3 watts.
It is possible to power a module with a power amplifier with a voltage of up to 6.5 Volts - there is a 7536 stabilizer on the amplifier board. The amplifier is powered from the input voltage (up to 6.5 Volts), and the bluetooth module is powered from the received 3.6 V.
There are also Bluetooth modules on sale with a different amplifier. It uses one microcircuit and requires three wires to connect the speakers.
The sound quality is simply excellent, I was very pleased with the low frequencies, the microphone is sensitive. At a distance of one meter from the microphone, the subscriber hears me perfectly. The communication range is about ten meters.
“On-the-knee” design and the results of measuring current consumption at maximum and average volume.
I apologize for the quality of the photo - the camera has died for a long time.
I'm planning to buy +128 Add to favorites I liked the review +73 +161Are you unhappy with the sound from your Bluetooth headphones? Perhaps the whole point is that your Android uses a “bad” SBC audio codec instead of the advanced LDAC, aptX, aptX HD, AAC?
More and more manufacturers are abandoning the 3.5 mm audio jack in favor of transmitting sound via Bluetooth, but such innovations are not always so useful! It's all about the codecs... and Android doesn't use the best one by default!
A little about Bluetooth audio codecs
SBC (Subband Coding) - this lossy codec is currently used in most cases of audio transmission over wireless headphones. The main problem with SBC is that the codec distorts the sound very much, more than MP3, so it is clearly not suitable for listening to high-quality audio material.
A.A.C.(Advanced Audio Coding) is also a lossy audio codec, but the sound quality is much higher than SBC.
aptX And aptX HD is an audio codec developed by Qualcomm, so it can be found almost only on devices with a Snapdragon processor. The aptX and aptX HD codec, unlike SBC and AAC, has virtually no loss, audio is compensated and transmitted via Bluetooth.
LDAC- a recently developed audio codec by Sony, which should displace the established SBC codec. This audio codec performs low-loss compression. Since Android 8.0 Oreo, it has become part of the system, so LDAC will soon become standard for transmitting audio over wireless headphones and speakers.
If the headphones only support the SBC codec, then you won’t be able to enable the Bluetooth codec LDAC, aptX, aptX HD!
How to enable the required Bluetooth audio codec on Android?
First, you need to make sure that your headphones or speakers support a more advanced audio codec. You'll have to do a lot of digging on the Internet to figure out what codec they support.
The second condition must be that your Android is version 8.0 or newer.
In order to activate one of the listed codecs, you will need to activate the “Developer Menu”. How to do it? You can read about this in the article "". Or you can watch two videos.
On bare Android:
Once you're in the developer menu, scroll down the menu to "Bluetooth audio codec" and select it.
Select the required codec - LDAC, apt, aptX, AAC, SBC. 
Codec activated! 
You can reboot Android! The sound over wireless headphones should improve!
Do you still have questions? Write them in the comments, tell us what you did or vice versa!
That's all! Read more useful articles and instructions in the section. Stay with the site, it will be even more interesting!
Bluetooth is the wireless transmission of data between two devices over a short distance. This is done via radio waves (WPAN).
Few people know that the name Bluetooth technology comes from the name of the Danish king Harald Bluetooth (Harald Bluetooth I, 958 AD). It was he who reunited parts of Norway and Denmark. And the Bluetooth symbol itself represents the Scandinavian runes B and H.
So, to transfer music via Bluetooth, 3 factors are needed:
Sampling frequency(kHz): The higher the sampling frequency, the clearer the sound can be transmitted (closer to digital). Distortion in sound is reduced and the audible frequency range expands.
Sampling depth(bit): The higher the sampling depth, the higher the resolution of the music. Dynamics increase as the range between soft and loud sounds increases. In this way, it is possible to obtain more subtle sound levels and tonal nuances.
Data transfer rate(kbps): This is the connection speed at which in this case the music audio data is transferred from the device to the headphones. This, however, is not entirely true. More precisely, this value indicates the possible size of the transmitted amount of data at a certain point in time. The higher the data transfer rate with Bluetooth headphones, the more data (at the same time) the device can transfer. Thus, the audible sound is significantly improved. 
What do the abbreviations aptX, pptx HD and LDAC mean?
These abbreviations are intended to represent Bluetooth codecs and mainly describe various data transfer options. They differ in sampling frequency, sampling depth and transmission speed. Android 8.0 devices support these audio codecs and you can enjoy better audio quality.
atpX- This is the slowest option for wireless music transfer. This technology provides a maximum transfer rate of 352 kilobits per second at a sampling rate of 48 kHz and a sampling depth of 16 bits. The analog signal is read 48,000 times per second and stored with 16 bits. In principle, these are solid numbers. For comparison, a CD is read and stored with identical parameters. However, relatively slow transmission results in almost a 50% loss in sound quality. Thus, the sampling depth is only 8 bits, which is due to the resolution of the music.
AtpX HD also has a sampling rate of 48 kHz, but the digital signal is stored at 24 bits. The dynamic range is increased, resulting in higher sound quality. Using LPCM (Linear Pulse Code Modulation) results in lossless data transfer from analog to digital signal. The sound is therefore cleaner.
PCM is a modulation technique that converts an analog signal to a digital one. The CD receives the analog sound waves of recorded music.
Sony H.EAR in Wireless To what extent the bit rate is adapted in this codec simply to transmit better sound in headphones is not yet known.
Bluetooth codec Sony LDAC- The best and fastest of the three wireless audio options.
With data rates of less than 1 Mbit/s at a sampling rate (96 kHz) and a sampling depth of 24 bits, near CD quality is achieved.
Compatible Bluetooth Headphones
The modern market offers both in-ear headphones and regular headphones, e.g. Sony h. ear wireless MDREX750BT/B, LG Tone Active+ or PSB M4U 8. For a complete list of headphones that support wireless music listening, visit the aptX-HD website. Headphones Sony MDR-1000X and MDR-1ABT support LDAC.
