Back in 2010 I received an email from a firm I had never heard of before, who had the name aptX. After a dinner at one of the tallest restaurants in Las Vegas I had a handle on what AptX was, but certainly not what it would become...
The aptX audio coding algorithm was created back in 1980 at the Queen's University in Belfast, Ireland. The original work was focused on bit-rate deduction for data streams over ISDN telephone lines, and later in the radio broadcasts. The first practical application of aptX for Bluetooth devices came in 2011 with the Galaxy Tab 7.0 Plus. Since then, AptX has been employed by more than 430 consumer electronic brands in their portable and Bluetooth-enabled devices.
Bluetooth, in its native form, is not really capable of supporting high sample/bit-rate audio streams. The first generation, 1.0, had a theoretical maximum throughput rate of 1Mbps, Bluetooth 2.x basic rate has a theoretical maximum rate of 3 Mbps. By the time Bluetooth reached 4.x the theoretical maximum allowed using Subband coding (SBC) was 328 Kbps, but the audio quality using this codec was still less than the best MP3.
But there are ways to improve Bluetooth audio. First is Advanced Audio Distribution Profile (A2DP). This profile relies on AVDTP and GAVDP. It includes mandatory support for the low-complexity SBC codec, and supports optionally MPEG-1 Part 3/MPEG-2 Part 3 (MP2 and MP3), MPEG-2 Part 7/MPEG-4 Part 3 (AAC and HE-AAC), and ATRAC, and manufacturer-defined codecs, such as aptX. Using A2DP portable device makers can add better quality audio codecs, which is exactly what they have done.
aptX comes in two varieties, aptX and aptX HD. aptX can transmit 16-bit/44.1kHz audio with a compression ratio of 4:1 at 352kpbs, while aptX HD can transmit 24-bit/48kHz audio with a "gentle" compression ratio of 4:1 at 576kpbs. While still not technically not "high resolution," this rate does allow for Redbook CD sound quality to fit through the Bluetooth "pipe."
Given aptX's superiority at fitting uncompressed music through a Bluetooth connection, you would think that every Bluetooth audio device would employ aptX or aptX HD, but they don't. Some manufacturers have their own proprietary data compression systems, such as Sony's LDAC, which has three different connection modes for transferring data. LDAC's "Connection" mode connects at 330 kbps, which is slightly slower than the SBC codec. Its "Normal" mode ups the rate to 660 kbps, the best mode, "Priority," is capable of sending data at a blazing 990 kbps, which is significantly higher than the aptX or aptX HD and will support 96/24 files.
Like all connection schemes that have a sender and a reciever, aptX requires the codec to be supported by both the sending device and the receiving device to work. If one of the components in your reproduction chain, be it your source device, headphones, or speakers, don't support aptX, they'll most likely default back to A2DP with its lower level of sound quality.
The takeaway from all this is simple. If you are looking into wireless headphones, and you want the best sound quality currently possible, look for ones that use aptX, aptX HD, or if Sony is your brand, the LDAC codecs. Do not, under any circumstances, (well maybe if they are being given away) accept a headphone or Bluetooth music playback device that doesn't have something better than plain-vanilla A2DP or earlier versions of Bluetooth. You have plenty of options. The aptX site has a list, seventeen pages long, of headphone options as well as three pages of portable players and twelve pages of phones. If you can't find a source device and headphones from those lists, you just haven't looked very hard...