Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3-D stereo sound sensation for the listener of actually being in the room with the performers or instruments.
This effect is often created using a technique known as “dummy head recording”, wherein a mannequin head is outfitted with a microphone in each ear. Binaural recording is intended for replay using headphones and will not translate properly over stereo speakers. This idea of a three dimensional or “internal” form of sound has also translated into useful advancement of technology in multiple things such as stethoscopes creating “in-head” acoustics and IMAX movies being able to create a three dimensional acoustic experience.
The term “binaural” has frequently been confused as a synonym for the word “stereo”, and this is partially due to a large amount of misuse in the mid-1950s by the recording industry, as a marketing buzzword. Conventional stereo recordings do not factor in natural ear spacing or “head shadow” of the head and ears, since these things happen naturally as a person listens, generating their own ITDs (interaural time differences) and ILDs (interaural level differences). Because loudspeaker-crosstalk of conventional stereo interferes with binaural reproduction, either headphones are required, or crosstalk cancellation of signals intended for loudspeakers such as Ambiophonics. For listening using conventional speaker-stereo, or mp3 players, a pinna-less dummy head may be preferable for quasi-binaural recording, such as the sphere microphone or Ambiophone. As a general rule, for true binaural results, an audio recording and reproduction system chain, from microphone to listener’s brain, should contain one and only one set of pinnae (preferably the listener’s own) and one head-shadow.
Binaural beats, or binaural tones, are auditory processing artifacts, or apparent sounds, caused by specific physical stimuli. This effect was discovered in 1839 by Heinrich Wilhelm Dove and earned greater public awareness in the late 20th century based on claims coming from the alternative medicine community that binaural beats could help induce relaxation, meditation, creativity and other desirable mental states. The effect on the brainwaves depends on the difference in frequencies of each tone: for example, if 300 Hz was played in one ear and 310 in the other, then the binaural beat would have a frequency of 10 Hz.
The brain produces a phenomenon resulting in low-frequency pulsations in the amplitude and sound localization of a perceived sound when two tones at slightly different frequencies are presented separately, one to each of a subject’s ears, using stereo headphones. A beating tone will be perceived, as if the two tones mixed naturally, out of the brain. The frequencies of the tones must be below 1,000 hertz for the beating to be noticeable. The difference between the two frequencies must be small (less than or equal to 30 Hz) for the effect to occur; otherwise, the two tones will be heard separately, and no beat will be perceived.
Binaural beats are of interest to neurophysiologists investigating the sense of hearing.
Binaural beats reportedly influence the brain in more subtle ways through the entrainment of brainwave and provide other health benefits such as control over pain
How we hear
To understand hearing loss, it helps to understand how hearing works. Your ear is an amazing organ that can perceive sounds from barely audible to very loud and can pinpoint the direction of a sound source to an amazing degree of accuracy
The human ear consists of three parts:
The outer ear
includes the visible part of the ear (pinna) and the ear canal. Sound waves in the air, collected by the pinna travel down the ear canal to the eardrum (tympanic membrane). The sound waves set the eardrum into vibration.
The middle ear
is an air-filled cavity separated from the outer ear by the eardrum. The middle ear contains the three smallest bones in the human body, the ossicles. These bones vibrate along with the eardrum and convert sound waves into mechanical energy.
The inner ear
contains the cochlea, which is a snaillike organ filled with fluid and contains thousands of tiny nerve fibers. The mechanical action of theossicles creates movement in the fluid and stimulates the nerve fibers.
The nerve fibers then send electrical impulses along the auditory nerve to the brain, which interprets these impulses as sound.