AptX is the latest trend for Bluetooth audio. But how does it “deliver pure wireless sound that doesn’t compromise on audio quality”?
When transmitting music over a Bluetooth connection, say between a phone and a Bluetooth speaker, the original music signal is compressed, transmitted to the destination device, and decompressed again to be played. The compression and decompression process is achieved via a codec. AptX is a codec that is optimized for delivering a full listening experience.
The standard Bluetooth codec is called (Low Complexity Subband Codec). SBC is designed to use as little processing power as possible, but it is not designed with perfect audio fidelity in mind.
It takes advantage of the fact that a loud sound at certain frequency will tend to mask quieter sounds in the same frequency band. It eliminates the quieter sound on the theory that its omission will be inaudible. The lower amplitude signals are removed and never reappear.
While human years can hear sounds up to 20 KHz, standard SBC rolls off above 16 KHz, so the treble usually sounds grainy and the signal-to-noise and harmonic distortion performance is poor.
For phone calls, SBC is perfectly fine. However for music, a lot of details get lost in the process, and that’s why if you compare a standard Bluetooth speaker and a wired speaker (of similar quality), you will notice that some small sounds, especially background sounds, are missing.
AptX relies primarily on ADPCM (Adaptive Differential Pulse Code Modulation). Instead of transmitting or storing complete audio samples, aptX starts with an audio signal, predicts what the signal will be next based on what it was before, then transmits only the difference between the original sample and the predicted sample. Unlike SBC which only looks at part of the music, aptX address the entire music sample.
SBC compression ratio can be anywhere from 7:1 to 12:1, but aptX runs at a fixed compression ratio of 4:1. Less compression means the output is closer to the original sound. Here is what happens when 32 pure equidistant tones are fed into both SBC (red) and aptX (Green).
In short, SBC have a lot more distortion than aptX, and the effect can be easily picked up by your ears.
At 354 kilobits per second, aptX almost doubles any typical SBC bitrate. The ability to address the entire music sample and passing more information (bits) to your speaker/headphone ensure you get a better sound.
Another advantage of aptX over SBC is low latency.
SBC is frame based, in which entire data frame (containing the core audio samples plus the information about how to unpack them) must be received and loaded into a memory buffer before it can be decoded. On the other hand, aptX is sample-based and the decoder can begin work as soon as it starts receiving samples, rather than wait for the rest of the data in the frame to arrive.
This is especially evident when you are watching a video or movie with Bluetooth connected sounds. Without aptX, the high latency can cause noticeable audio delay when watching a movie or film.
To Benefit from aptX
If you want the make the most out of your aptX enabled Bluetooth speaker or headphones:
- You need play music in HD quality. Most online streaming services (like Spotify) offer HD quality options. If you are playing MP3 files, this means the file bitrates should be more than 300 kbps. Usually a 3 and half minute song in HD quality can be as large as 10 MBs (a standard one is only 4 MBs)
- Both the music playing device and the speaker/headphone must support aptX. For example, you can pair the VAVA Voom with a Samsung Galaxy S6 or S7 to experience the rich listening experience.