Hearing is believing.
In 1881, Clement Ader set pairs of telephone transmitters across the Paris Opera House stage and fed the mixed-down signals to subscribers through two phone lines. When his subscribers held a telephone to each ear, they experienced the birth of binaural sound. Used to locate enemy planes during World War I, in radio broadcasts during the 1920s and at the 1939 World's Fair, binaural sound continues to be used today in self-help programs, nature recordings and some music.
Binaural
Binaural is defined as the perception of sound with both ears, and this type of sound is recorded to maximize this perception. Just as 3D stereographs can make 2D images look 3D, binaural recordings create a lifelike 3D soundstage that puts you in the action. They do this by recording sounds in an approximation of how your ears hear them, which is done by mounting omnidirectional mics in the ear canals of a dummy head. This dummy head accurately simulates a human head, with the same separation between its ears and the same ear structure. Binaural recordings use two channels just like stereo, but the channels aren't mixed. What the left mic hears only goes to your left ear, and the right mic's sounds only go to your right ear. The result is a 360-degree soundstage with each sound's source accurately placed inside it. You hear sounds like you would in the real world, not mixed like stereo recordings.
Transaural
While binaural recordings can only be experienced through headphones, transaural recordings are just as effective through speakers as they are through headphones. The reason is crosstalk. Headphones only allow each ear to hear sounds that were recorded by its mic, but speakers spread the sound so each ear picks up sounds recorded by the other ear's mic. This confuses your brain and prevents it from identifying the location of sounds in a recording. To get around this, a pair of speakers is placed at a 30-degree angle on each side of a center point. By sending an out-of-phase signal from each channel's output to the in-phase signal of the other channel, crosstalk is canceled; the out-of-phase signal is an inverted copy of the in-phase signal, and when the two combine, they cancel each other out. These out-of-phase signals are also time-delayed to match the distance between your ears. The result is a greatly expanded soundstage, where you can experience binaural sound without your headphones.
Holophonics
Just as the difference between stereo and binaural is like the difference between 2D and 3D, the difference between binaural and holophonics is like the difference between a 3D image and a hologram. Holophonics is an amazing breakthrough that takes binaural audio to the next level. Hugo Zuccarelli invented holophonics by applying the light interference patterns that create holograms to the world of sound. Zuccarelli believes when our ears process sounds, they add a reference signal. This reference signal creates an interference pattern that pinpoints sound locations on a 3D soundstage. Holophonic recordings are made with a miked dummy head, but an inaudible reference signal is mixed in to create an interference pattern. The result is a more realistic sonic presentation: Sounds move above, behind, in front of and beneath you with so much clarity you may find yourself turning in their direction.
Tags: difference between, binaural sound, dummy head, reference signal, binaural recordings, hear sounds
