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Operating at the fringes of the audio world, binaural recordings have continued to maintain a hardcore group of advocates. Creating a convincing three-dimensional surround effect using only a two-channel source, binaural technology is especially impressive with headphones.

This past month, John Sunier, host of the excellent PBS radio program Audiophile Audition, has brought high-quality (for the internet, anyway) samples of binaural recordings to his website at www.binaural.com.

These files offer an opportunity for anyone with a set of headphones and a stereo soundcard to get a taste of the effect. There are several examples available for download, and instructions on how to set up your system for optimum playback. Sunier points out that the MPEG compression used for the website samples (which are quite impressive) does not interfere with the results.

According to Sunier's website, binaural sound has been with us for over 100 years: "It was first used in transmission of opera from the stage of the Paris Opera House in 1881. Inventor Clement Ader used pairs of carbon telephone transmitters across the stage, mixed down to two separate telephone lines going to the homes of subscribers. They had to have two telephones and put the receivers from each one to their ears.

"In the 1920s there were experimental binaural radio broadcasts using a pair of frequencies, with listeners tuning in on a pair of crystal sets. At the 1939 World's Fair, the binaural dummy head 'Oscar' was a major attraction, with people lining up to don headphones and experience what was happening in the room in which Oscar was placed."

These days, binaural recordings are created using a "dummy head" with two specially calibrated microphones placed in its "ears." This head "hears" what we would hear in the room, and sends the two separate channels of audio to the recorder, where they are kept discrete with no further mixing required.

The technique preserves what is known as the HRTF, or Head Related Transfer Function, the process of how we localize sounds in space. From Sunier's website: "The ridges of the pinnae, as well as the other features of the head and shoulders, act as multiple frequency-selective band-pass filters tuned to the azimuth and elevation of every sound in our environment. The minute shifts in frequency response, phase, and sound level give the brain the data to localize the sounds. Without HRTFs, our ancestors would have all been eaten up by predators and we might not be here today!"

With the extra storage capacity of DVD-Audio on the horizon, Sunier hopes that music labels will consider releasing binaural versions of live recordings alongside the traditional stereo mix on a single DVD. "People in the computer industry are excited about binaural sound right now. Microsoft's new OS will even support a special 'headphone' listening mode that should prove successful for games and special applications."

Regarding concern that a binaural recording is sonically inferior to a traditional two-channel mix, Sunier states, "There are a lot of misconceptions about binaural recordings. It is simply not true that a binaural track played back on a conventional set of speakers will sound inferior. There is no degradation."

For listening to binaural recordings, Sunier recommends a good set of phase- and frequency-coherent headphones such as the AKG 1000, Grado, or Sennheiser 'phones, or Sony's top-of-the-line CD3000. He feels that the popular Sony V6 headphone doesn't work for some reason, prompting complaints from folks who use them.

Sunier's site also offers a list of binaural recordings for sale, with over 125 titles available to date, including 30 recent additions. Also featured is a complete FAQ (frequently asked question) page on the process, and scores of links to related resources.

If internet downloads are not your style but you still want to hear the technique, Sunier will be producing a binaural special for Audiophile Audition between February 10 and March 1. The program will air on over 120 public radio stations around the country---check the Audiophile Audition website, or call (800) 934-0442 for stations and times in your area.