Despite the growth in the wireless headphones market, Bluetooth and ultra-high quality audio haven’t become synonymous terms, simply because the wireless standard is too slow and relies on compression to reduce the file size down to a manageable level. Qualcomm has announced a new Bluetooth codec for mobile, the CSR8675, which claims to support hi-res 24-bit Bluetooth audio, so perhaps these days are over.
The CSR8675 is an all in one solution for implementing high resolution, wireless audio into a smartphone, tablet, or other gadget. The chip features its own 120MHz DSP unit, integrated “high performance” stereo DACs and ADCs, two I2S channels to communicate with other codecs, Bluetooth 4.1 support, and there are even touch sensor and other IO pins.
Moving past all that developer stuff, the big lure for the audio enthusiasts out there is that the chip supports 24-bit inputs and outputs, going above the regular 16-bit CD quality, even over a Bluetooth connection. This should result in an improved signal-to-noise ratio and less distortion for a more detailed listening experience.
Unfortunately Qualcomm’s new Codec can’t do anything to address the speed limitation of Bluetooth and still requires compression to send audio over the air. Qualcomm stresses that it compresses audio files “without affecting the listening experience quality,” but that sounds subjective. The technique is based on further development of 16-bit aptX compression, known as aptX HD. Here’s an explanation, if you want to get technical.
Rather than psychoacoustic compression methods used with the MP3, aptX uses adaptive differential pulse-code modulation, which splits data up into multiple frequency bands and uses a variable quantization step (bit-depth) to save on bandwidth where possible. Qualcomm uses aptX HD with the CSR8675, which adds 2 additional bits of data in each of the four sub-bands compared with regular aptX, for an improved signal-to-noise ratio and less distortion than before.
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This is still a lossy compression technique and clearly plays a bit loose with the claims of true 24-bit audio, but you have to accept some trade-offs when using Bluetooth. One the plus side, aptX offers a fairly low latency connection to other supported Bluetooth devices, in the region of 40 milliseconds.
Remember, that to make use of all this Bluetooth audio technology, you will also need a compatible set of headphones or speakers at the other end that can decode the aptX HD compression algorithm. The aptX HD source has already been launched for Android devices and the CS8675 codec is immediately available. Qualcomm expects to see devices using its new chip appear over the course of 2016.