Not long ago, the CEO of Sennheiser, world-renowned creator of hi-fi headphones and in-ear monitors, predicted that the future of headphones would be in 3D. In fact, while the acoustic loudspeaker has evolved from stereo audio (2 speakers) to 3D surround sound (3 to 11 speakers), headphones, with their two ear cups, have remained inexorably associated with stereo audio. Since it wouldn’t be practical to add a third ear cup, producing 3D audio with headphones is a matter of finding the appropriate audio recording techniques and mixing techniques, as well as fitting headphone amplifiers and home theater receivers with highly efficient processors. Clarifications.
Advantages and disadvantages of using headphones to listen to 3D audio
First off, can a pair of headphones offer as good a listening experience as a loudspeaker? To find an answer to this question, we can consider two factors: the acoustic qualities of headphones and the intentions of the audio engineer.
As far as acoustic qualities go, headphones are superior to loudspeakers in a few areas. The first advantage headphones offer is the mechanical coupling of the drivers with the listener’s ears. Once in place, headphones emit sound toward and even directly into the listener’s ear, while loudspeakers “radiate” sound throughout the listening area, with profits and losses for the audio message. A second advantage comes from the fact that headphones, due to their compact size, necessarily employ very small drivers which are capable of covering the entire audio spectrum. As there is no need for an electronic filter (used to split frequencies between several drivers), the audio signal thus remains intact. For these reasons, headphones always offer a very clear listening experience, while loudspeakers are not always as reliable. Of course, we’re talking about quality headphones here.
All things considered, we can conclude that headphones offer a more realistic listening experience than loudspeakers. But realistic in which terms? By nature, music is made to be shared, and for this reason it is more often played through loudspeakers. Audio engineers, who have never lost sight of this fact, mix audio with loudspeakers in mind. In practice, all audio is mixed using a pair of reference loudspeakers, with two separate audio sources positioned several meters in front of the listener, and not on either side. A very different configuration than that associated with a pair of headphones.
When we listen to speakers, both of our ears hear the sound produced by each one, whereas with headphones, the audio message sent to one ear cannot be heard by the other. This is a significant difference.
With a pair of headphones, the depth of the soundstage is negligible, and in any case inferior to that offered by a pair of speakers positioned several meters in front of the listener. While headphones offer an intensely immersive listening experience, as gratifying as this may be, it remains completely unrealistic. But let’s be clear: it’s the mix, and not the headphones, that are at fault.
How is 3D sound produced for headphones?
It is perfectly possible to enjoy a 3D listening experience, in which the height, the width, and the depth of the soundstage are perceptible, with a pair of headphones. The solution involves creating two mixes during the production process, or even running two takes simultaneously: one for listening with speakers and another for listening with headphones. Using the recorded audio, a sophisticated mix relying on binaural technology is a simple solution to create a convincing 3D soundstage. Binaural sound involves sending the same audio signal over two channels, but with a slightly different tone (a few dozen Hertz) in order to allow the brain to pinpoint each sound. However, the increased production costs would be significant and it would thus be unreasonable to imagine that studio mixes of musical albums will be made for headphones. But if a practical solution can’t be found in the first stages of audio production, maybe one exists later on…
In fact, certain headphone amplifier manufacturers have been putting in long hours developing technologies which give the listener the impression of attending a live concert just by putting on a pair of headphones, all while using a mix created for loudspeakers. Meridian has developed Analog Spatial Processing (ASP) technology, which works by mixing the left and right channels to recreate the same listening conditions with headphones as with speakers (see the Meridian Prime Headphone Amplifier). Hafler, which specializes in creating headphone amplifiers for professional studios, proposes a Variable Focus mode on its Hafler HA15 and Hafler HA75 headphone amplifiers, which simulates a loudspeaker effect on headphones.
Smyth Research has chosen a much more sophisticated approach, adopted by the Smyth Realiser A8, which can create 3D sound for headphones with a stereo (2.0) or multichannel (5.1) signal by taking into account the movements of the listener’s head.
3D sound with headphones, Dolby style
Many of the latest home theater receivers integrate Dolby Headphones technology. Behind the name is a 3D audio spatialization effect which optimizes a stereo, 5.1, 7.1 or Dolby Atmos mix for headphones. Audio from 6 or 8 channels is positioned exactly as determined during the studio mixing process. By taking advantage of a very rich multichannel mix (DVD, Blu-ray, Netflix, etc.), Dolby Headphones technology is able to create a noteworthy 3D audio effect.
As binaural encoding software has been made available, it is possible to find binaural versions of some musical tracks online. Some internet users have created binaural files by remixing 5.1 versions of certain albums. Should you go looking for them, keep in mind that while you’ll find some on YouTube, the audio encoding used for the video platform (lossy compression) isn’t the best way to get a taste of 3D audio with a pair of headphones. What would be better is to hunt down versions in FLAC format, which pays much more respect to 3D audio spatialization.
Choosing a file format when using headphones to listen to 3D audio
All lossless audio file formats are compatible with 3D audio encoded in stereo format. The ALAC, FLAC, WAV and AIFF formats can all be used. On the other hand, lossy audio formats (MP3, AAC, Bluetooth aptX, etc.) are not fit for 3D audio playback, since the frequencies which are destroyed by compression are indispensable to 3D audio spatialization.
A note on 3D audio and loudspeakers
To enjoy 3D audio with loudspeakers, you’ll need a home theater receiver and at least 5 speakers. The ultimate solution would involve adding two more speakers to this setup, ideally installed in or on the ceiling, and using a receiver which handles Dolby Atmos. If having a low-profile system is your first priority, the Yamaha YSP-5600, Philips Fidelio B8, Sony HT-ST5000 and LG SJ9 soundbars are all convenient solutions which are compatible with Dolby Atmos. Lastly, Auro-3D technology, which competes with Dolby Atmos, is being used by more and more theaters, and it would thus be a good call to keep an eye out for an Auro-3D compatible home theater receiver and Blu-ray discs with an Auro 3D audio track…
This post is also available in: French