So you are having a nice coffee at your favorite coffee shop. Coffee makers are loud and noise. There’s also people. So it’s time to deploy your Bluetooth headset!
Nowadays Bluetooth is the king of music transmission between devices, and especially since the popularization of smartphones has been implanted as a standard in multitude of audio components.
When we want to transmit music from the mobile or the computer to a portable speaker, a wireless headset, an AV receiver or the car equipment, it is a very good solution. But the question that always arises is does Bluetooth make the original sound quality worse?
Audio codecs on Bluetooth
The A2DP profile for transmitting and controlling music in Bluetooth gives a theoretical speed of 721 kbps in optimal connectivity conditions, leaving less than 400 kbps to transmit music. Therefore, bluetooth could not transmit music with CD quality in real time as this requires at least 1411 kbps of speed.
So prior to transmitting music, Bluetooth needs to reduce the size of the audio using a compression codec, and the default incorporate all Bluetooth-A2DP devices is the SBC .
SBC, the default codec
The SBC or Low Complexity Subband Coding applies a perceptual- like algorithm to the music before it is transmitted, which removes the supposedly imperceptibledetails in a similar way as MP3 does . Therefore, it is a codec with loss of quality.
SBC will not only reduce the size and produce losses in the music that we transmit from a lossless file like a FLAC, ALAC or WAV, but if we transmit a previously encoded file with losses like MP3, AAC, WMA, etc., the codec SBC will increase the loss of quality that these formats already have.
In conclusion, Bluetooth with its default SBC codec always reduces the quality of origin of the music, whatever its format.
However, the Bluetooth A2DP profile allows the use of other codecs as long as both the sending and the receiving device are explicitly compatible , which is not easy since most manufacturers only include the default codec.
APTx, the best codec available
Today another codec of higher quality is being popularized among the high-end devices , the APTX codec . Its purpose is to overcome the quality offered by the SBC codec and transmit the highest quality possible by the bluetooth channel.
Due to limitations of Bluetooth, the maximum speed at which APTX can transmit is 352 kbps, which still makes it necessary to remove some information in case the original file comes from CD resolution or higher. Therefore APTX is also a lossy codec, although this time very optimized.
Its superiority to SBC is due to its use of an ADPCM algorithm, which is based on the predictability of the musical signal over time , instead of eliminating parts of the information that are considered imperceptible, as do the perceptual algorithms like SBC , MP3 or AAC.
This type of compression technology has been used in professional transmissions since the 1990s, and the advantage is that it allows a similar quality perception of the CD, with a minimum reduction of the dynamic range to 92 dBs instead of the theoretical 96 dBs Of the CD. Nothing to do with artifacts, metallic sound or auditory fatigue of other formats.
Another advantage, is that when APTX is going to transmit a Bluetooth source file that was already compressed with losses like MP3, AAC, etc … there is hardly any additional losses. This transcoding process is practically transparent.
Today to get the best quality with Bluetooth is to choose components that incorporate the APTX codec, already present in a multitude of high-end devices . Unfortunately it is still a lossy codec, but I think it deserves to be taken into account, since if the file we transmit is a FLAC, ALAC or WAV, the resulting quality will be higher than the best of MP3s, and as their Developers , virtually indistinguishable from a CD .
And alternatives to Bluetooth …
If in any case we want to have a medium of transmission that by itself does not imply any loss in the transmission of music and also allows to transmit formats of resolution higher than the CD, certainly today the alternative at home is the connection by Wifi, such as DLNA or Apple AirPlay.
But the handicap is that there are still no portable headphones or car radios with the possibility of connecting directly to the mobile by Wifi-Direct. Therefore, Bluetooth is still the wireless option for outdoor, and if it can be with the APTX codec better than better!