ByGoraud Mazanec 2019-10-15 56489
Let's take the example of a smartphone and a Bluetooth device. When the two devices are combined (by detection or grazing when an NFC chip is present), they present themselves to each other and list their respective capabilities.
As far as audio transmission is concerned, no less than 5 compression modes are possible. Their choice is (almost) never left to the user and it is the Bluetooth chips that determine the transmission mode to be used. If the radio frequency conditions allow it (low interference, proximity of the two devices, possible Bluetooth keyboards or mice connected to the source), the most qualitative mode is automatically chosen.
When conditions deteriorate (in public transport, for example, due to the proximity of other smartphones and Bluetooth headsets), transmitters and receivers adapt and change their communication methods seamlessly. The apt-X HD codec is then switched to the next lower quality codec.
Namely: when you listen to Spotify, Deezer, Qobuz, Google Music or Apple Music, the stream is automatically recompressed according to the codec chosen by the transmitter and receiver.
Many Bluetooth codecs coexist, the main ones being LDAC, Apt-X HD, Apt-X, AAC and SBC. These codecs make it easy to identify the maximum rate allowed when transmitting the Bluetooth signal and therefore the resulting audio quality. Here are the features of each of these Bluetooth codecs.
Currently, the most qualitative Bluetooth codec is the Sony LDAC. Its operation is based on the Bluetooth 4.0 standard so that a CD-quality audio file (16-bit / 44.1 kHz) can be transmitted without damage. A transmission up to 24 bits / 96 kHz is even possible, but with a minimum of compression.
For a long time remained the exclusive technology of the Japanese brand, only Sony devices could use it with each other. Fortunately, this codec has now been used by other brands for a few years. It can be found on many Bluetooth devices such as the Technics F70, Technics F50, Sony WH-1000XM3 headsets, as well as some personal music players such as the Shanling M0, Fiio M6, Shanling M2X or the Sony NW-ZX300.
Attention! As with any other Bluetooth codec, to enjoy LDAC audio transmission, the receiver (speaker, amp, etc.) and transmitter (computer, smartphone, tablet) must be LDAC compatible.
Now widely used, apt-X codecs offer high transmission quality, with a throughput of about 576 Kbits for apt-X HD and 350 Kbits for apt-X. The sound compression method is deteriorating (information is deleted), but the playback remains very good. Qualcomm, the company that developed the apt-X HD codec and markets the apt-X HD Bluetooth chips, evokes a quality close to the CD. Listening, we notice a rather pleasant ventilation and a wide frequency response.
If you own an iPhone, iPod touch or iPad, you will not be able to take advantage of the apt-X codec, Apple having chosen another Bluetooth controller supplier for its devices than Qualcomm (the only manufacturer to market apt-X chips). As a result, the impasse has so far been made on the apt-X. Apple has opted for AAC audio compression, which is also the format chosen for iTunes and Apple Music.
The qualitative differences with apt-X are very small, especially since if you listen to music with iTunes in AAC format, no re-compression is performed.
The Sub Band Codec (SBC) uses a compression algorithm comparable to Microsoft's WMA. When radio conditions are good, the data rate is 350 Kbits /sec with a correct listening quality. On the other hand, when the rate drops to 128 Kbps, audio artifacts are audible in the high frequencies. If you have ever had the impression that your Bluetooth headset was crackling, you didn't dream and the SBC codec is to blame.
If you are looking for a Bluetooth lossless transmission (without loss of information), you will need to choose LDAC-compatible devices such as an audiophile or Sony smartphone, as well as a Bluetooth headset, Bluetooth speaker or any other LDAC-compatible receiver device.
If you want to broaden the choice of compatible equipment, it is better to choose an apt-X or apt-X HD compatible source and broadcaster. For computers, Bluetooth apt-X HD transmitters are available in the form of USB micro keys. Many smartphones are (Samsung, Motorola, etc.), as well as the vast majority of audiophile players.
Finally, if after consulting your smartphone's manual you discover that it only has a Bluetooth SBC transmitter, be aware that some headphones and speakers have settings to force the smartphones to transmit music at a rate of 350 kBits / sec.
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