No Headphone Jack? The Case for Bluetooth Headphones

Rajeev Agarwal

Founder, Que Acoustics

Ever since Bluetooth headphones have been around there has been a debate about their sound quality. This subject has been discussed and written about exhaustively, here I offer one more perspective.

Convenience? But I’m an audiophile

Most purists and audiophiles scoff at wireless devices and some strongly believe that they will never be ‘good enough’. I started out firmly in this camp after first listening to a Bluetooth headset a few years ago. It didn’t help that many early models sounded poor, not because they were Bluetooth, but because of poor acoustic design. After having listened to a number of different models over the last couple of years I have become a believer. You could say I have been bitten by the wireless bug. Of course, their extreme convenience also makes a very compelling case for wireless headphones. Having worked with wireless audio (Wi-Fi and Airplay) for a number of years I understood it fairly well, but had never delved into Bluetooth. So I decided to take a closer look at it.

This article is not intended as a deep technical dive. Never the less, I think it is helpful to briefly review the relevant technical aspects that have a bearing on the discussion.

By the numbers

First, a quick refresher on the numbers. Although higher rate encoding is possible and is sometimes used for studio recordings, we’ll use the CD (compact disc) as our reference. Playing a stereo track from a CD at full bandwidth requires a bit rate of approximately 1,411 kb/s. This also means that a CD contains a vast amount of data, in fact each minute of music is encoded as more than 10 Mbytes of data. Of course, we carry most of our music these days as compressed files on smartphones, tablets or other devices. The most common formats are MP3 and its successor, AAC (Advanced Audio Coding). Both these formats reduce the data file size by discarding data that is not critical to audio reproduction. Depending upon the compression algorithm, many different bit rates are possible, some common ones being 96 kb/s, 128 kb/s, 192 kb/s 256 kb/s and 320 kb/s. Studies have shown that most listeners, even trained musicians, are unable to distinguish between music reproduced at 1,411 kb/s, 256 kb/s (AAC) or 320 kb/s (MP3). This, of course, is contentious and is vehemently refuted by the audio purists. But it does take sophisticated and expensive equipment under pristine listening conditions to detect any differences.

Bluetooth alphabet soup

Almost all Bluetooth audio devices support A2DP (advanced audio distribution profile) which was developed to allow stereo audio to be streamed over Bluetooth. A2DP specifies a number of different codecs that may be implemented but mandates one — Low Complexity SBC (sub-band coding). By requiring SBC, the Bluetooth standard ensures compatibility between any two devices that support A2DP. The low complexity implies that transmitters (and to a lesser extent receivers) do not require a high level of processing power (think low cost). Additional codecs that maybe implemented include MP3, AAC, ATRAC and aptX.

A word about aptX. This is a widely adopted proprietary codec (now owned by Qualcomm) that claims to deliver CD quality audio over Bluetooth. This claim is based upon the fact that aptX uses a compression algorithm that is said to be optimized for audio quality and can reproduce audio more faithfully than other compression methods. Of course, if the source material is an MP3 or AAC file, aptX won’t be able to improve upon the best playback you can achieve with the native file. Also, both ends of a Bluetooth stream (transmitter and receiver) must support aptX to benefit from it. Apple, for instance, does not support aptX. So if you are a user of any generation of iPhone or iPad, you do not have aptX.

The standard allows for the transmitter and receiver to use the highest bit rate codec they both support. In practice, most implementations revert to SBC, which can support bit rates up to 345 kb/s. Good implementations of SBC can adequately deliver MP3 and AAC streams up to 320 kb/s. Theoretically, aptX equipped devices may provide superior transport, but real evidence is hard to come by. Ideally, of course, we would want to play the native MP3 or AAC stream without any transcoding, either SBC or aptX. In the future, I hope, we will see more devices support native streaming over Bluetooth.

Summary

So what does all this mean in terms of Bluetooth sound quality? For those amongst us who consider anything less than CD quality (1,411 kb/s) to be unsatisfactory, Bluetooth is simply not good enough. Of course, this is also true of wired headphones if you are listening to MP3 or AAC music files from, say, your smartphone. So the question of whether Bluetooth headphones are as good as wired headphones is not as simple as it may first appear. It really depends on your listening conditions. For instance, if you were listening to an actual CD (or uncompressed audio) through decent playback equipment, one could argue that the wired system has an edge in terms of audio fidelity. On the other hand, if you are listening to music from your smartphone/music player/tablet/computer which is most likely to be MP3 or AAC files, a Bluetooth system is as good as a wired one. In fact, if MP3/AAC codecs are implemented so there is no transcoding, the music stream on Bluetooth headphones will be identical to the one on the wired headphones. Notwithstanding the superiority claims of aptX, even with SBC transcoding, a good Bluetooth implementation is able to carry the music stream with hardly any perceptible degradation.

Note: In addition to MP3 and AAC there are a number of other file formats that are also used for music. Full bandwidth CDs may be encoded as uncompressed WAV files. Another format in use is Ogg-Vorbis. There are also lossless compression formats, notably FLAC, ALAC and WMA lossless. We have restricted our discussion to MP3 and AAC since they are by far the most widely used audio file formats.

Conclusions

I have tried to examine the case for Bluetooth headphones in an objective manner and I think I can say that for most of us it is time to embrace Bluetooth as a legitimate conduit for high fidelity music. This is clearly the way forward, and I can imagine teenagers in the not too distant future being bemused when we tell them ‘we used to have headphones that needed to stay tethered to the playback devices’.

For most listening situations the differences in audio are barely detectable and pale into insignificance when weighed in by the convenience of wireless. Again, for most of us, the question of whether Bluetooth headphones are as good as wired ones is largely academic. After we cut through all the technical details, the A-B comparisons and the highly engineered tests using expensive equipment that can detect the minutest differences, the real question is this: Can we really enjoy high fidelity music in all its glory using a good set of Bluetooth headphones? I think the answer is a resounding YES.