aptX audio compression codec technology completely overturns the listening experience of Bluetooth stereo, providing high-quality wireless audio for consumer electronic applications such as Bluetooth stereo headsets and various speakers. The aptX technology was originally used in radio broadcasting and was not introduced to Bluetooth applications until 4 years ago. Its application enables devices that support stereo Bluetooth A2DP connectivity to output CD-quality audio.
Although aptX technology overcomes the lower sound quality of Bluetooth audio, developers still need to address the latency of Bluetooth audio to develop high-quality wireless headsets and speakers for consumers who use mobile devices to watch movies or play games. Latency is the time it takes for an audio stream to travel from an audio source (smartphone, media player, computer, or console) to a wireless receiving device (speaker or headset).
Wearing a wireless headset When watching a movie on a tablet, the user does not want to experience a phenomenon in which the sound is out of sync with the picture; while on a wireless device, a game that involves shooting, explosion, and other intermittent accidents, the game player also wants Get an intuitive audio response. In order to achieve synchronization between sound and motion, the delay must be controlled within 40ms. Due to the delay time of traditional Bluetooth technology over 100ms, its performance can not achieve dialogue and real-time synchronization of the game. As a result, a variety of patent-based RF solutions (most of which require adapters) have emerged to fill the gap in this area, but few success stories have been made.
CSR's recently introduced low-latency aptX audio compression codec technology allows developers to easily resolve latency issues without the need for complex adapters. The new low-latency aptX audio compression codec technology not only provides lossless high-quality audio over Bluetooth, but also delivers low-latency output performance as low as 40ms. aptX breakthrough technology has many advantages, including:
â— Uses standards-based RF technology and is compatible with Bluetooth
â—Because Bluetooth is 100% compatible with smartphones, tablets and notebooks, there is no need to use adapters
â— Runs in existing chip design systems with simple software updates
Low latency audio compression codec technology problem
The key to this problem is the lead or lag of audio and video signals. According to the European Broadcasting Recommendation R37-2007, the time slot between the sound of the TV signal and the transmission of the image component is: "The sound should be no more than 40ms ahead of the image signal and the hysteresis should not be higher than 60ms." The Bluetooth transport layer uses the A2DP protocol supporting the standard SBC codec and the encoding algorithm based on psychoacoustic sensing technology. However, SBC and perceptual compression techniques use frame compression, and the overall delay time can be as high as 100ms to 500ms, which is mainly due to the following three factors:
1. Codec Delay: Each audio codec causes some internal delay before encoding and transmitting the data. Traditional codecs have detected codec delays of up to 50ms.
2. Transmission delay: The A2DP transport layer uses a packet structure. When engineers use SBC or perceptual-based frame to fill packets, there are two options: one is to put one frame into a large Bluetooth packet; the other is to break a frame into two Bluetooth packets. Adopting the first scheme will reduce the robustness of data transmission, while in the second scheme, the decoder can decode the decomposed frame only after receiving two Bluetooth packets, thus significantly increasing the transmission delay time.
3. The codec will not begin decoding until it has received the entire packet or frame.
In addition, due to its bit rate setting characteristics, the audio quality provided by SBC and perceptron-based codecs is highly variable. That is to say, even if multiple identical codecs are used, stable audio effects cannot be provided.
A2DP transmissions are not the best of both worlds. For low latency performance, the audio's robustness and sound quality will be reduced. As a result, many proprietary RF solutions have been introduced to meet consumer demand for wireless transmission.
aptX low latency technology
The sampling mode-based aptX codec has two major advantages over the A2DP codec: it provides an ultra-low codec delay of 1.9ms and, more importantly, no frame format. Therefore, during the decoding process, the aptX codec can efficiently fill the Bluetooth data packet without waiting, that is, once it receives the data packet, it starts the decoding process. In addition, aptX uses a fixed compression ratio algorithm that always provides the same bit rate during transmission, ensuring that each aptX-equipped product outputs the same sound quality.
aptX's unique set of features delivers professional audio performance and robustness while guaranteeing 40ms end-to-end latency. 40ms meets the standards set by the European Broadcasting Union (EBU) to achieve dialogue and action synchronization.
TV and games
Since the birth of the flat-panel TV, engineers have been working to narrow the TV frame, the main purpose is to better install the TV on the bedroom wall. However, the thinner the thin and light design is inversely proportional to its quality TV, sound proportional to the volume of their speakers, that is, the television, the sound quality worse. For the current 5mm flat panel TVs on the market, we offer two options based on low latency Bluetooth connectivity:
1. Manufacturers can make independent speakers, built aptX low-latency technology in the TV case and embed decoder in the speaker
2. TV purchasers can use the receiver to transmit signals from the linear output port to existing aptX-compatible stereo systems.
Games are also an increasing area of ​​application. While the traditional indoor game console market is still strong, the mobile gaming market has boomed. Modern operating systems enable all smartphones and tablets on the market to run 3D games, which will create hundreds of millions of potential users for the gaming market.
Players who wear Bluetooth headsets on the road to control the game absolutely don't want to encounter delays. They want the sounds heard through the headphones to keep pace with the game screens and controls. If the time between triggering the trigger and hearing the gunshot is more than 50ms, the delay will be more obvious, and the game will become less interesting.
aptX low latency technology and its low latency of 40ms ensure that gamers get the audio synchronization they need. In addition, aptX can also open a two-channel audio stream to pass back the signal from the headset to the game console, providing the game team with wireless voice chat and enhancing the gaming experience.
Headphones with built-in aptX can be used to play games, listen to high-quality music, hands-free calls and other applications to create a variety of wonderful experiences for users.
How to use aptX low latency technology
The two ends of the aptX low-latency technology connection are: compression/encoder/source and decompression/decoder/sink. It is suitable for various encoders based on Linux, Android Jelly Bean and Kit Kat, and is compatible with BlueZ and Bluedroid Bluetooth protocol stacks. Once the output signal is confirmed to be accurate, data integration can be completed within two business days.
On the decoder side, users can use CSR chips such as BC05MM and SR8670. Both flash-based chip components are compatible with Kalimba's onboard DSP. Users can then integrate aptX low-latency technology into the Kalimba DSP platform. In addition aptX, CSR rich chip can also provide various other functions, including high performance DAC and the ADC, capacitive touch, input / output (SPDIF, I2S, I2C and GPIO, etc.) and the like; if using CSR8670, also Bluetooth Smart connectivity is available.
What is your choice?
As explained at the beginning of this article, since the codec based on SBC and other frames has certain constraints in Bluetooth connection, the A/V industry has no choice but to choose other proprietary solutions. Given the successful resolution of latency issues by CSR technology, manufacturers can now consider Bluetooth connectivity in their ecosystem design, which is easy to use, cost-effective (chips and systems), and ensures that their products are never out of date.
Abandoning the private solution and choosing a standards-based approach will help manufacturers enjoy the R&D results of various Bluetooth semiconductor companies. The benefits include:
â— Accelerate the design process
â— Form economies of scale to ensure superior price
â— In addition to Bluetooth RF, you can enjoy a variety of other rich features, including onboard DSP, ADC, DAC and sample rate converter.
The Bluetooth standard has been adopted by a wide range of consumer electronics manufacturers, and sales of Bluetooth chips have exceeded 3 billion in the past decade. All smartphones, tablets and most feature phones and portable media players on the market are equipped with Bluetooth and are compatible with the A2DP protocol to provide wideband stereo audio. It allows users to listen to high-quality audio through wireless headphones and speakers without having to use an electronic dog while watching a smartphone to store video. This will be a huge business.
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