What is binaural recording?
What we hear is determined by the way that sound is transmitted around the head, the position of the ears, the shape of the ears, and the shape of our ear canals. Binaural recordings achieve realistic three-dimensional audio by using microphones in a configuration that approximates the characteristics of the human head. So called dummy head microphones have been designed with the same shape and acoustic characteristics of a human head in order to achieve what’s know as binaural recording. Sounds can be located around, above and below the head. When played on speakers, the effect is not so great due to crosstalk from the speakers. With headphones, each ear can only hear the sound recorded on that side of the head, while speakers spread the sound, and spill the sound meant for the left ear to the right ear, and vice versa. This seriously muddies the three-dimensional imaging.
When listening to a binaural recording with headphones, you experience a sense of being positioned within an acoustic space. It’s a technique that can immerse your listener in the amazing sounds of everyday life, cars passing as pedestrians wait for the crosswalk signal to change, monks chanting inside a temple, the ￼busy activity at lunchtime in a city square, etc. Binaural recording don’t always work well on conventional stereo speakers unless you turn the speakers in and sit between them, otherwise you don’t experience the sound localization you’d get with headphones. On the other hand, when processed with a surround matrix decoder, binaural recording provides excellent surround channel sound.
Four examples of binaural recordings
- The Missing Voice: Case Study B (Janet Cardiff, 1999), you can download the entire audio walk from Soundcloud.
- A Large Slow River (Janet Cardiff, 2000)
- A Short Binaural Thunderstorm Recorded with the Neumann KU-81i by thefritzfiles, YouTube
- Taipei Market Walk-Through by Matthew Lien, YouTube
Two professional binaural recording options
Professional dummy head microphones with a polar response pattern resembling human hearing are available, however, they are quite expensive. The Neumann KU 100 sells for $8,000. This microphone has two tiny omnidirectional condensers mics mounted at the position of the ear drums with special equalization to correct for the double traversal of the ear canal (first in recording and again in playback). This preserves what are called the Head Related Transfer Functions or HRTFs. These devices provide an efficient approach to binaural audio recording with very low noise along with three-dimensional imagery and field perception.
When recording in windy conditions, you’ll need to use a custom windscreen made for this microphone.
A less expensive option for binaural recording is the 3Dio Space Pro II microphone ($2,000). This system combines a pair of matched DPA 4060 microphone capsules mounted at the opening of ear canals. They are suitable for both studio recording and field recording as well. The microphone provides balanced stereo XLR outputs that support phantom power. The microphone also sports a stereo mini-jack output that is powered by an internal 9V battery.
Under windy conditions you’ll need to use a pair of Windy Ear Muffs made specifically for this microphone.
Two low-budget pseudo-binaural recording options
There’s a low-budget indie media maker’s alternative for creating binaural recordings that may not be quite as good as using a dummy head, however, it is far more affordable with surprisingly good results. A reasonably good binaural effect can be achieved by clipping lavaliere microphones to the left and right side of a pair of headphones or a baseball cap (if you’re monitoring with earbuds) for what may be called pseudo-binaural recording.
This approach takes advantage of the acoustic characteristics of your head and the separation of the microphones resembles the separation of your ears, however, it does not take advantage of the shape of your ear lobes or ear canal. In spite of this limitation, your listener will experience much of the binaural recording effect at a fraction of the cost. In addition, with this technique you can be far more inconspicuous while recording.
A versatile and affordable option for a pair of lavaliere microphones is the Giant Squid Audio Lab stereo omnidirectional microphone, a pair of electret condenser microphones terminating in a 3.5mm stereo mini-plug that works with plug-in power. Combined with a pair of headphones or tight-fitting earbuds for monitoring, you’re all set to go.
Another affordable option is the Roland CS-10EM. This all-in-one design combines ear buds for monitoring combined with electret condenser microphones you wear in your ears that place the microphones in a better position. The device terminates on two 3.5mm stereo mini-plug, one for the mic, the other for the monitors. This provides a all-in-one solution for binaural recording and monitoring and includes foam windscreens.
Since the phase changes introduced by the shape of the ear lobes contributes to the spatial perception of sound, these will sound a little better than the approach described above, yet still not quite as good as using a professional dummy head but again, they will provide surprisingly good results (here are always tradeoffs).
There are two major differences you’ll notice between professional microphones and consumer products. The first is the level of background noise inherent in the microphone. Professionals are willing to pay more for the lower noise floor. And second, professional gear sports balanced connections with XLR connectors because balanced lines (which use two conductors for the signal and one for the ground with special circuitry on each end to filter out noise) are much less susceptible to noise from sources of electromagnetic radiation. I often encounter noise problems with consumer gear that I don’t encounter when using my professional gear.
Some gaffer tape (never use duct tape or other sticky tapes on production gear) may be needed to dress the cable to avoid cable rustling sounds. Surgical tape should be used when taping cables to skin, since gaffer tape does not adhere to skin very well.
When working in windy conditions, a lavaliere windjammer will be necessary. The foam windscreens are only effective in very light wind. Lavaliere windjammers are essential for outdoor shooting and should be paired with any lavaliere microphone you have in your location sound recording kit.