In acoustics

Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

, dummy head recording (also known as artificial head or Kunstkopf) is a method used to make binaural recording

Binaural recording

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...

s, that allow a listener wearing headphones

Headphones

Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...

 to perceive the directionality and the room acoustics

Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

 of single or multiple sources.

Human perception of the direction of a sound source is complex, and consists of:

1. Simple "left-right" information can be gained from relative level differences and time of arrival differences of the sound in each ear.
2. For percussive sounds, the impact of a shock wave can register perceptibly on the skin (typically the upper torso), with the earliest and strongest sensory stimulus coming from the regions of skin aligned perpendicular to the direction of the sound source.
3. The human head imprints frequency-dependent distortions of phase
   Phase (waves)
   Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
   
    and amplitude
   Amplitude
   Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
   
    on sound reaching the eardrums, that are frequency-dependent level differences and these distortion effects vary with the direction of the sound source (being caused by the geometry and sound-transmitting characteristics of the sinus
   Paranasal sinus
   Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...
   
    and throat cavities, eustachian tube
   Eustachian tube
   The Eustachian tube is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi...
   
   s, inner ear, external ears, and other hard and soft tissues in the head and upper body (see: head-related transfer function
   Head-related transfer function
   A head-related transfer function is a response that characterizes how an ear receives a sound from a point in space; a pair of HRTFs for two ears can be used to synthesize a binaural sound that seems to come from a particular point in space. Some consumer home entertainment products designed to...
   
   , "HRTF").

Conventional stereo recording only makes use of left-right information. Dummy head recording uses both left-right information and frequency-dependent distortions.

Methods

There are three main ways of making a recording that uses this last effect to encode directionality information:

1. dummy head recording uses an artificial model of a human head, built from selected acoustic materials to emulate the sound-transmitting characteristics of a real human head, with two microphone inserts embedded at the "eardrum" locations,
2. simulated dummy head recording processes a signal electronically to imprint the HRTF information associated with a specified direction, and
3. finally, a pair of specially-designed microphones can be worn by a volunteer, fitted inside their ears, to make use of actual intra-cranial acoustics.

Limitations

Because each person's pinnae are unique, and because the filtering they impose on sound directionality is learned by each person from early childhood, the use of pinnae during recording that are not the same as the ultimate listener may lead to perceptual confusion.

History

Historically, dummy head recordings have been associated with the use of a physical synthetic head, the "Kunstkopf". The "head" could be placed in a concert hall to make a live orchestral recording, or actors could stand around the head when recording their dialogue. The head could also be used to imprint positional information on prerecorded sound effects by playing sounds through a loudspeaker placed in a suitable position by the head, and rerecording the result (for instance, it might be desirable for birdsong or thunder to seem to be coming from above the listener; this would not be achievable using conventional methods).

In the 1990s, electronic devices were made commercially available that used DSP

Digital signal processing

Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...

 processing power to reproduce an HRTF digitally. These devices allowed the operator to use dials to adjust the apparent direction of sounds in real time. They were unusual and expensive, but allowed an operator to "position" pre-recorded special effects quickly and conveniently, and also to move sound sources dynamically. By manipulating the dials, the sound engineer could take a monophonic recording of a passing car and make it sound to the listener as if it were passing behind them in a particular direction. With a "physical" dummy head, this would have also required a rerecording booth, and either a single moving loudspeaker or an array of speakers and some sort of multiple panning or switching device.

As portable digital recorders (using DAT

Digital Audio Tape

Digital Audio Tape is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a compact audio cassette, using 4 mm magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. As...

 and minidisc

MiniDisc

The disc is permanently housed in a cartridge with a sliding door, similar to the casing of a 3.5" floppy disk. This shutter is opened automatically by a mechanism upon insertion. The audio discs can either be recordable or premastered. Recordable MiniDiscs use a magneto-optical system to record...

 formats) became more popular, a market also arose for miniature "in-ear" microphones such as the Sound Professionals

Sound Professionals

The Sound Professionals, Inc. is a manufacturer of professional and consumer microphones and audio electronics, primarily for portable audio recording. Created in 1997, they are one of a small number of manufacturers of binaural and other types of microphones for binaural recording...

 SP-TFB-2 that could be "worn" by the operator inside their own ears to make "dummy head" recordings. Since these devices look like personal stereo "earbuds", they can be worn unobtrusively and are especially useful for making "audience" recordings of concerts and other live events, or for recording "ambient" sounds (such as birdsong, or traffic noises, or crowd sounds) with a realistic three-dimensional soundfield, which can later be mixed in together with more conventional recordings. A convincing radio play scene with two characters talking in a railway station could then be created by recording the actors in the studio, using in-ear microphones to record ambient "railway station" noises, and then mixing the two together. The disadvantage of the "in-ear" method for recording important events is that the wearer cannot wear earphones to monitor the recording, cannot receive audible instructions (without these being recorded), and cannot turn or dip their head without affecting the recording. They also have to be careful not to cough or clear their throat while recording.

Another problem with "in-ear" recording is that the effectiveness of the effect depends partly on the degree of correspondence between the properties of the recordist's head and the head of the listener - although the recordings may sound compelling to the person who made them, there is currently no easy way to rate a particular person's head characteristics to assess their suitability as a "dummy head" recordist.

External links

• Sony
  Sony
  , commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
  
   Virtualphones Technology ; 5.1ch & 7.1ch > to >{convert}> (2ch Holophonic) headphone, (Sony Virtualphones) hardware.
• Kall Binaural Audio - a mobile recording studio dedicated to dummy head binaural audio