Bluetooth audio is gaining a lot of followers today. The disappearance of the mini-jack ports for headphones on some smartphones, such as the iPhone, has led to audio companies producing high quality wireless devices. Among bluetooth audio technology, the Qualcomm aptX code is in a privileged place.

Bluetooth codecs What is a Bluetooth codec?

The word codec, when we talk about wireless audio, means the software’s method for encoding a stream of audio information that is sent wirelessly between two devices. In other words, it is the process by which zeros and ones, of binary digital data, acquire format. It serves to transmit stereo audio through a source device, such as a telephone, a computer, television etc …, to a receiver, such as wireless speakers or headphones.
Different codecs send the audio information using different formats, they can also introduce their own compression technologies to maintain a balance between the sound quality and the information package of the audio files. Compression may sound like something negative for lovers of high quality audio, but it is necessary if we are going to send heavy files wirelessly.

This means that the variants between the bluetooth codecs are compatible with different audio devices, in addition to providing different connection and sound qualities. All bluetooth devices support the standardized SBC (Low Complexity Subband Coding) codec, but SBC implementations have varied in quality throughout the history of this technology. To offer greater consistency to users of bluetooth products, several companies have developed their own bluetooth codecs, and then offer the license to other producing houses. AAC is one of these formats, the successor of MP3, used by Apple and others. Sony has its LDAC codec and Qualcomm offers aptX.
bluetooth codecs

AptX, SBC and AAC codecs, which one is the best?

The codecs are coding algorithms that compress audio to handle sound packets and thus achieve fast wireless transmission. The effectiveness of the codec determines the quality of the audio information that will be sent. The SBC code is the standard algorithm for most bluetooth devices. However, this codec has a relatively high latency and can be somewhat noisy. The three main codecs, which most users will encounter, are SBC, AAC and aptX:

SBC

It is the code found in most wireless devices and with which all bluetooth headphones have the A2DP (Advance Distribution Profile) profile. It is capable of transmitting up to 328kbps with sample rates of 44.1 Khz. It provides very decent quality audio and does not require much processing. However, audio may be inconsistent in some situations. This is notable especially when using cheap bluetooth transmitters.

AAC

Similar to SBC but provides better sound quality. This codec is very popular thanks to the Apple iTunes platform. As against, we must mention that it is not very comfortable to find it in headphones.
aptX

Ideal for demanding audio applications as it encodes audio more efficiently and accepts more information than the SBC. It has additional variations, such as aptX (LL) and aptX (HD), which dramatically reduce latency in the wireless connection and improve sound quality. However, it is somewhat limiting because both the transmitter and the receiver must have the aptX capability for this codec to work.
Since from Culturasonora we do not have a reliable means to measure the AAC and LDAC formats wirelessly, we have compared the SBC and aptX codes using them with Plantronics Backbeat Pro 2 headphones:

AptX and SBC sound quality

We perceive that the standard SBC codec works well for most audio applications. It is not particularly loud, although in the signal-to-noise ratio, the aptX has a greater range of optimal loudness. The audio differences are subtle with respect to aptX, but they can be notable for expert and critical ears. The resulting measurements, however, both for the frequency response and for the harmonic distortion, are very similar between the aptX and SBS codecs.

Bluetooth codec latency

Latency, or delay in wireless sound reproduction, is the aspect where the aptX codec separates. The SBS connection has about 100 ms of delay, which is notable when watching videos and can ruin certain gaming experiences. On the other hand. CSR developed the low-latency aptX code to fix these connection problems. The aptX improves the performance of the SBC, but it is the aptX-LL that has a greater impact on the results. The aptX-LL codec was excellent when we tested it by watching some movies and using some games. This makes the BackbeatPro2 and other headphones that have this technology, ideal options for these activities.
Based on our tests, we have noticed that codecs have a greater impact on latency than on sound quality. The aptX codec has subtle improvements in sound quality, but the differences are less noticeable than the improved speed at the time of audio playback via bluetooth.

AptX codec, why should we use it?

The SBC codec is configured to work with small bitrates, such as 200kbps, which does not offer the best sound quality. In theory, the SBC codec can operate with bitrates of up to 345 kbps, and the introduction of A2DP audio profiles allows wireless transfers of audio formats such as MPEG and ATRAC. However, support for these formats is optional and varies between headphones or wireless speakers.

The aptX codec, on the other hand, offers a better signal-to-noise radio in important frequency ranges, as well as better performance when it comes to delays in the Bluetooth connection. This codec exists, in part, to provide guaranteed quality audio in all products compatible with this format. AptX audio transfers are made with a 352 kbps / 16-bit 44.1 kHz bitrate. This means a 4: 1 compression compared to lossless files, and includes enough information to wirelessly carry files equivalent to the best MP3 formats. In terms of smartphones, the aptX standard codec is found in a large number of devices as well as the improved aptX HD, which has appeared on new wireless devices.

Another interesting aspect of the aptX codec is that it uses a technique called ADPCM (Adaptive Differential Pulse-Code Modulation). Essentially, it divides the audio frequency spectrum into four bands, each with its own bit depth and signal to noise ratio. In addition, this technology is superior to SBC when sending audio that has already been compressed via Bluetooth, such as MP3 audio files. The aptX codec has, as we said, a better signal to noise ratio than the SBC, about 5kHz more capacity, so we can better perceive the fine details of voices and instruments when we listen via an aptX codec, if our material Source has a good quality.

The Qualcomm codec also has a faster conversion speed than the algorithms used by the SBC and can transfer audio packets more efficiently. This means that it handles lower latency, an important factor for wireless audio when watching movies or playing with our favorite consoles. Qualcomm’s low latency technology handles a delay in the 40 ms region, although this may increase to about 150 ms in older codecs. The SBC is measured with a delay of 100 ms and can increase to 150 ms. The AD2P varies between 40 and 150 ms, depending on the conversion requirements.