by John Sunier
SO WHAT IS BINAURAL?
The binaural experience places the listener sonically where the sounds on the recording or broadcast originated, and requires no special equipment of any sort other than the binaural source and a pair of stereo headphones. The listener experiences sounds quite accurately localized in a complete 360-degree sphere- a true virtual audio environment. It does this via two tiny omnidirectional mikes placed at the entrance of the ear canals on a replica of a human head (“dummy head”). The two signals are kept entirely separate all the way from this artificial head mike system to the corresponding left and right drivers of the headphones worn by listeners.Though all modern binaural recordings are perfectly compatible for loudspeaker playback, in a normal stereo speaker setup you will lose the “you are there” binaural effect due to leakage of the sound cues intended for one ear into the other ear and vice versa.
Even sophisticated audiophiles are often confused about binaural due to the wrongful use of the term back in the l950’s by many who used Binaural and Stereo as synonyms for one another. Recording pioneer Emory Cook (if you were around then you’ll remember his twin-tracked early stereo LPs) was one of these. Yet in the notes provided with all RCA Victor two-track stereo open-reel tapes starting around 1956 was the following:
Stereophonic recording differs from Binaural (a term sometimes incorrectly applied to stereophonic records) in that the microphone placements are selected for loudspeaker reproduction. Binaural properly applies to a two-channel system designed for headphone reproduction. It thus requires the use of two channels fed by microphones spaced about seven inches apart (normal ear separation).
That definition just about tells the tale. All of us have noticed the tremendous difference between hearing a stereo recording on speakers and hearing it on headphones. Headphones seem to put a giant sonic magnifying glass on all aspects of the recording, including stereo separation. Many recordings sound like half the band or orchestra is in one studio with its signal feeding your left ear, and the other half in another studio with its signal feeding your right ear. The sounds seems to be localized at your two ears and totally inside your skull rather than happening outside your head. Some persons also image a central area of sounds in their skull, so that it feels like three little separated groups of musicians inside your head. The HeadRoom circuit was developed to minimize this effect when listening to standard stereo recordings.
The truth is that over 200 million stereo headphones having been sold in the past decade (way over 600 million if you include all the throw-away headphones bought by those airlines no longer giving passengers primitive plastic tubing). But the source material that nearly everyone is listening to on their headphones was never designed for listening on headphones, but for playing via loudspeakers! With speaker playback, the left channel sounds are meant to reach the right ear and visa versa. Producers of commercial recordings almost always monitor with speakers rather than headphones. Binaural keeps the left and right channels absolutely separated from the original dummy head (or your actual head) all the way to the listener’s headphones without mixing. This applies whether the medium is a recording, live, or a radio broadcast.
PROFESSIONAL MIKE SYSTEMS FOR BINAURAL
Commercial binaural recordings generally use one of two different expensive professional “dummy heads” (“Kunstkopf” in German). In fact, both come from Germany. The Neumann KU-81 or KU-100 head was probably used — often in conjunction with other mikes — on a CD or two in your collection. (Cost: about $6500.) The Aachen Head Acoustics system is more complex, with special equalization to achieve the most natural reproduction on both speakers and headphones. (Their current model is also used for precise acoustic measurement and runs about $29,000.) Some recording engineers feel either of these mikes is capable of making more natural and well-balanced ordinary stereo recordings for speaker playback than the best purist mike techniques. Of course, the full binaural effect is not present in speaker playback except with expensive specialized cross-cancellation electronics; which also force you to sit in a narrow “sweet spot” without the freedom of movement that headphones allow. However, any matrix surround processor using “ambience recovery” rather than “ambience synthesis” will give a better surround sound effect with binaural recordings than with most specially-encoded Dolby Surround CDs. Most Dolby Pro Logic decoders will suffice, though processes such as Circle Surround, Six Axes and EARS are even better. Just stay away from what colleague Dan Kumin calls “boingerizers” – those Hall/Stadium/Jazz Club processors that artificially generate reverberation (echo) to add to the original ambient signal on the recording.
A visible dropping of the jaw is the most frequent indication that someone who has put on headphones is hearing effective binaural for the very first time. Followed by exclamations of surprise, wonder and unbelievability. Binaural, rather than trying to bring the sounds into your listening room, takes you where the sounds originally occurred. You are aware of sounds 360 degrees around you not just right & left but forward & back and up & down! Someone whispering in one ear can make you jump, and a good rainstorm in binaural will have you opening your eyes (if they’re shut – which helps the impression) to make certain you’re not actually getting soaked!
In Binaural, the pinna or outer ears of the dummy head or head of the original recordist set up subtle interference patterns that locate the sounds around the head quite specifically in space. These are known technically as HRTFs – Head Related Transfer Functions – and have become central to current audio research directed toward achieving virtual audio effects with two or more loudspeakers that approach the realism of binaural with headphones. Computer gaming and virtual reality software are fertile fields for this sort of enveloping sound. Sounds coming from directly in front of us bounce off the rear part of the outer ear; sounds from below bounce off the top part of the ear. When a sound is directly in line with the left or right ear there is a straight shot into the ear canal, and this provides different directional information from the other approaches. The ear/brain combination works together closely in binaural hearing. Take for example “the cocktail party effect” – in which we “steer” our binaural hearing around a noisy room and focus it on the one person we want to hear, while minimizing the distraction of other voices.
The first experiment with binaural, way back in 1881, compared the effect to the popular stereoscopic views of the period. The inventor said of his binaural patent, “This double listening to sound produces the same effects on the ear that the stereoscope produces on the eye.” He set up a series of carbon telephone mikes in pairs (about 7 inches apart) along the edge of the stage of the Paris Opera. As the singers performed on stage, their voices were carried on twin pairs of telephone lines to a few subscribers homes who had two lines installed. They put the earpiece from one line to their left ear and the earpiece from the other to their right ear. Fortunately, a wide frequency response is not a requirement to convey the binaural effect, because the phone system of the time was surely quite primitive.
MORE RECENT BINAURAL ACTIVITY
There has been sporadic interest and activity in binaural since those early days late in the 19th century. In the middle 1920’s some radio stations in Connecticut and elsewhere broadcast experimentally on two different frequencies — feeding each transmitter separately from a left-ear and right-ear mike in a dummy head in the studio. Listeners were already listening on headsets for the most part, since primitive speakers were just coming into fashion. So this worked out well — they merely put one mono headset, tuned to the left-ear station, to one ear and put the other mono headset tuned to the second station, to their right ear. Some of the West German radio stations have devoted time to special binaural transmissions — often of radio dramas which they call “horspiel.” There has also been interest in Japan. “The Cabinet of Dr. Fritz” series of binaural radio dramas from ZBS Productions was carried for some years on public radio stations here in the U.S. Many of those same stations also carried my own weekly program, AUDIOPHILE AUDITION, on which I presented All Binaural Special broadcasts once per quarter for over 13 years.
In 1970 Stereo Review offered a binaural demonstration LP of music and sound effects which used a homemade dummy head known as the Blue Max. There have been many binaural recordings available in Germany, mainly of classical material and on LP. The disadvantage of employing either analog LP or cassette for binaural material is the noise problem. The surface noise or hiss that we have become accustomed to when listening via loudspeakers can become intolerable with headphones. The greater clarity via headphones makes extraneous noises in the source stand out and detracts from the total sonic experience of binaural. Add to that a peaky high end in some headphones that further points up surface noise and hiss compared to speaker reproduction.
As a result of this, the compact disc and other digital media such as MiniDisc and DAT have proven the perfect medium for binaural. The excellent signal-to-noise lets the listener concentrate on the sounds and begin to forget that he or she is actually listening to a recording – one just starts to take part in the original music or sound-making!
YOU CAN DO IT YOURSELF
Their introduction to binaural makes a great impact on some listeners. Then when they learn how basically simple the recording process can be they are energised to make their very own binaural recordings. Some years ago consumer-level binaural mike systems were offered by Sennheiser, Sony and JVC, but have been long discontinued. Today several suppliers provide a variety of in-ear mike systems at a $70-$300 price range. They are usually paired with a DAT or MiniDisc portable recorder, though a good quality cassette recorder may also be used. [Editor: See the Commercial Links page for binaural resources.]
For such recording efforts, sounds in motion are especially effective in binaural, as well as sounds that are spatially separated. I have some binaural tapes of a symphony orchestral rehearsal, and for demo purposes, it must be admitted that feeling like you are sitting right on stage with the orchestra during the rehearsal, with music stands clanking, chairs squeaking, the conductor walking around to help some of the players with small problems, can sometimes be more exciting than hearing the final performance of the music. Sound effects such as a motorcycle or train passing by, take on a quantum step in “you are there” realism with binaural vs. the old-fashioned stereo demos of trains passing between your loudspeakers. Keep some of these tricks in mind when doing your own recording with binaural mike systems. For example, if you have a quartet of instruments or singers, have them perform in a circle around you instead of in a line in front of you! (I’m a nut on sax quartets and do they ever sound great recorded in this way!) Instead of sitting out in the front row of the audience to tape an early music ensemble, one recordist set up his dummy head with mics in a chair right in the middle of the group onstage – creating an effect as though the listener is one of the musicians performing! – most exciting early music recording I’ve every heard. The surrounding spatiality adds great interest to the music. Another recordist taped his taking an elevator, walking into the concert hall and settling in his seat at the beginning of a concert and then the reverse at the end to make it a more complete binaural experience for listeners. (Unfortunately, the elevator was totally silent, so he edited out that part.)
HEADPHONES FOR BINAURAL
While binaural can be heard with any stereo headphones down to the simplest $5 “ear-buds,” the better the phones, the more amazing the experience. I have found some of the Sony phones around the $100 price point to be good. (The Grado SR-80 at the same price is excellent.) I can’t vouch for current Sony models, but do stay away from the MDR-V6 (once recommended by Consumer Reports) because it destroys much of the binaural effect. Among the best under-$600 phones I have heard for binaural are the Sennheiser HD 600, SONY MDR-CD3000, AKG K-501, Beyer 990 Pro, Etymotic ER-4S, and Grado RS-1. (No special order intended in that list.) The K-500 has many of the qualities of AKG’s flagship K-1000 ($895) which I find the best all-around binaural phone due especially to its ability to help image the sounds outside one’s head. The Jecklin and Ergo headphones from Switzerland, at about the same price point, also offer this advantage. The Etymotic are basically test probes inserted deeply into the ear canals – just the opposite of the off-ear-driver phones. However, their fans rave about them for binaural, and with the tight seal to the eardrum bass reproduction equals the most monster subwoofer you could fit in a room! Extra-cost custom ear molds make the Etymotic more comfortable for extended wear.
The Grado RS-1 Reference phones and the Sennheiser HD 600 are also excellent and of interest to those who find the AKGs too bizarre with their little earspeakers suspended on either side of your head. Both the Grado and Sennheiser provide more deep bass than any other on or off -ear headphones I have heard. The Stax electrostatic earspeakers have been the standard for binaural for years. Their top-of-line Omega has a dedicated tubed amp and goes for over $4000 but is probably the best-sounding headphone ever. Don’t worry about the suitability to binaural of feature differences such as circumaural vs. on-ear, free field vs. diffuse field or electrostatic vs. dynamic. Even extended frequency response is not a prerequisite for successfully transmitting the full binaural effect. Phase accuracy and flat response within the frequency spectrum are the most important parameters. A trend showing the increased interest in headphones and binaural is dedicated high end headphone amps — HeadRoom, Melos, Grado, Music Hall, Musical Fidelity and others have them. AKG will introduce a new model soon. Some of the high end phones practically demand a good dedicated amp, and even a modest amp can upgrade the sonics of a more modest headphone.