Bluetooth problems Part 4
AptX is a popular marketing codec
Often times, in a new market, it is not the one who came up with the best solution that becomes the leader, but the one who came up with their solution first. This was the Apt-X codec, which was developed by Professor Stephen Smith of Britain’s Queen’s University in the 1980s for fast transmission of high-quality sound to various laptops and generally for fast recording. high-quality audio. Subsequently, the rights to the then Apt-X were bought by CSR, which made the codec wireless in 2009 and renamed it AptX. Well, in 2015, Qualcomm bought this company, which now owns the rights to AptX and voluntarily sells it to everyone.
The main idea behind AptX is to offer audio CDs with almost original quality. In fact, we see a 4: 1 compression, that is, the bitrate was up to 352 kbps at 16 bits and 44.1 kHz. Therefore, we are not talking about “almost” here: the maximum lossless compression does not exceed 2: 1, so data is still lost when transmitting sound using AptX. But how strong? We will talk about this below.
Since AptX is a purely mathematical codec that always covers the entire audio range up to 22 kHz; it seems like it should be better compared to the SBC, which often turns off the high frequencies. In fact, sadly, this is not the case. The basic principle of this codec is quantization, that is, the allocation of a certain number of bits for each subband: for example, 8 bits are used to transmit sound from 0 to 5500 Hz, from 5500 to 11000 Hz – 4 bits, 11000 to 16500 Hz and 16500 to 22000 Hz are 2 bits.
