Ambiophonics
Encyclopedia
Ambiophonics is a method in the public domain that employs digital signal processing (DSP) and two loudspeakers directly in front of the listener in order to improve reproduction of stereophonic and 5.1 surround sound
for music, movies, and games in home theaters, gaming PCs, workstations, or studio monitoring applications. First implemented using mechanical means in 1986 [1][2], today a number of hardware and VST plug-in makers offer Ambiophonic DSP [3]. Ambiophonics eliminates crosstalk inherent in the conventional “stereo triangle” speaker placement, and thereby generates a speaker-binaural soundfield that emulates headphone-binaural
, and creates for the listener improved perception of “reality” of recorded auditory scenes. A second speaker pair can be added in back in order to enable 360° surround sound reproduction. Additional surround speakers may be used for hall ambience, including height, if desired.
ing that distorts timbre
of central voices, and creating false “early reflections” due to the delay of sound reaching the opposite ear. In addition, auditory images are bounded between left (L) and right (R) speakers, usually positioned at ±30° with respect to the listener, thereby including 60°, only 1/6 of the horizontal circle, with the listener at the center. Human hearing can locate sound from directions not only in a 360° circle, but a full sphere.
Ambiophonics eliminates speaker crosstalk and its deleterious effects. Using ambiophonics, auditory images can extend in theory all the way to the sides, at ±90° left and right and including the front hemi-circle of 180°, depending on listening acoustics and to what degree the recording has captured the interaural level differences (ILD) and the interaural time differences (ITD) that characterize two-eared human hearing. Most existing two channel discs (LPs as well as CDs) include ILD and ITD data that cannot be reproduced by the stereo loudspeaker “triangle” due to inherent crosstalk. When reproduced using ambiophonics, such existing recordings’ true qualities are revealed, with natural solo voices and wider images, up to 150° in practice.
It is also possible to make new recordings using binaurally-based main microphones, such as an ambiophone,[3] which is optimized for Ambiophonic reproduction (stereo-compatible) since it captures and preserves the same ILD and ITD that one would experience with one’s own ears at the recording session. Along with life-like spatial qualities, more correct timbre (tone color) of sounds is preserved. Use of ORTF
, Jecklin Disk
, and sphere microphones without pinna (outer ear) can produce similar results. (Note that microphone techniques such as these that are binaural-based but without pinna also produce compatible results using conventional speaker-stereo, 5.1 surround, and mp3 players.)
Bob Carver
of Carver Corporation built filtering to attempt to pre-subtract anti-crosstalk in the analogue Carver C4000 Control Console in 1981. He called this Sonic holography.
An early hardware attempt to compensate for loudspeaker-ear crosstalk was to apply a little out-of-phase left channel to a separate driver in the right speaker cabinet, and vice-versa. This was invented and marketed in 1982 by Matthew Polk, founder of Polk Audio
, as true stereo in his SDA-SRS, SDA1 and SDA2 series speakers. Although the theory is questionable, the results were well-received.
On the early 1980s, Arnold Klayman of Hughes Aircraft
devised a way to use a HRTF
to add depth to a stereo image, calling it Sound Retrieval System
. The development was later spun-off as SRS Labs
.
In 1991, Roland Corporation
launched Roland Sound Space, a system that created a 3D sound-space using stereo speakers. It worked better for some listeners than others.
Ambiophonics is an amalgam of new research and previously known psychoacoustic principles and binaural technologies. This knowledge has enabled audio recording and reproduction that approaches the realistic soundfield at the ears of the listener that is comparable to what one would perceive in a concert hall, movie scene, or game environment. This level of high-fidelity was not realizable until human hearing and acoustics principles were thoroughly researched, and affordable PCs with sufficient processing speed became available. At the Casa Della Musica at the University of Parma, Italy, or at the listening lab at Filmaker Technology, Pennsylvania USA, ambiophonics, ambisonics, stereophonics, 5.1 2D surround, and hybrid full-sphere 3D systems can be compared for the abilities of these methods to convey the spatiality and tone color of real perception. Developers have provided many scientific papers and downloadable tools for implementing ambiophonics free of charge for personal use.[4]
, and using digital signal processing
(DSP) such as free RACE (Recursive Ambiophonic Crosstalk Elimination) or similar software,[5] ambiophonic reproduction is able to generate wide auditory images from most ordinary CDs/LPs/DVDs or MP3s of music, movies, or games and, depending upon the recording, restore the life-like localization, spatiality, and tone color they have captured. For most test subjects, results are dramatic, suggesting that Ambiophonics has the potential to revitalize interest in high-fidelity sound reproduction, both in stereo and surround.
Additionally, ambiophonics provides for the optional use of concert-hall or other ambience impulse response
convolution to generate hall ambience signals for virtually any number and any placement of surround speakers.[6][7] But ambiophonics is not for theaters, auditoriums, or any large groups. Ambiophonics can usually accommodate more than one listener since one can move back and forth along the line bisecting the speakers. Precisely because of the higher level of envelopment along this line, the loss of realism when one moves away from the center line is more dramatic in the case of Ambiophonics than stereo. The listening area can be enlarged with ambience convolution, whereby surround speakers mimic the contributions of concert-hall walls.
Ambiophonics methods can be implemented in ordinary laptops, PCs, soundcards, hi-fi amplifiers, and even modest loudspeakers with consistent phase response, especially in any crossover regions. Neither true-binaural (dummy head with pinna) recordings nor head tracking are required, as with headphone-binaural listening. Commercial products now implement ambiophonics DSP, although tools for use on PCs are also available online.[4]
/SACD
recordings can be reproduced using just four speakers (a center speaker is obviated in ambiophonic layouts). Allowing for the human hearing “cone of confusion” at each side, a full 360° degree circle of perceived sound localization has been measured within ±5° of actual source azimuth, reproducing life-like spatial envelopment and timbre (contributed by accurate directional provenance of early reflections) of multi-channel music, movies, and game content.[3][8][9]
Especially in the case of stereo content where ambience has been purposely reduced (because a natural level coming from front 60°-only is perceived as too much), additional signals for surround speakers can be produced using a measured hall impulse response, convolved in a PC with the two front channel signals. For full ambiophonic replay, one PC can provide the DSP for 4-channel crosstalk-cancellation and four or more (up to 16 depending on the PC) surround speakers.[10]
The development of ambiophonics is the work of several researchers and companies including Ralph Glasgal, founder of the Ambiophonic Institute; Dr. Angelo Farina, University of Parma; Robin Miller, Filmaker Technology; Waves Audio; Dr. Roger West, Soundlab; Dr. Radomir Bozovic, TacT Audio; and Prof. Edgar Choueiri
, Princeton University.
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...
for music, movies, and games in home theaters, gaming PCs, workstations, or studio monitoring applications. First implemented using mechanical means in 1986 [1][2], today a number of hardware and VST plug-in makers offer Ambiophonic DSP [3]. Ambiophonics eliminates crosstalk inherent in the conventional “stereo triangle” speaker placement, and thereby generates a speaker-binaural soundfield that emulates headphone-binaural
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...
, and creates for the listener improved perception of “reality” of recorded auditory scenes. A second speaker pair can be added in back in order to enable 360° surround sound reproduction. Additional surround speakers may be used for hall ambience, including height, if desired.
Ambiophonics, stereophonics, and human hearing
In stereophonics, the reproduced sound is distorted by crosstalk, where signals from either speaker reach not only the intended ear, but the opposite ear, causing comb filterComb filter
In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb....
ing that distorts timbre
Timbre
In music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
of central voices, and creating false “early reflections” due to the delay of sound reaching the opposite ear. In addition, auditory images are bounded between left (L) and right (R) speakers, usually positioned at ±30° with respect to the listener, thereby including 60°, only 1/6 of the horizontal circle, with the listener at the center. Human hearing can locate sound from directions not only in a 360° circle, but a full sphere.
Ambiophonics eliminates speaker crosstalk and its deleterious effects. Using ambiophonics, auditory images can extend in theory all the way to the sides, at ±90° left and right and including the front hemi-circle of 180°, depending on listening acoustics and to what degree the recording has captured the interaural level differences (ILD) and the interaural time differences (ITD) that characterize two-eared human hearing. Most existing two channel discs (LPs as well as CDs) include ILD and ITD data that cannot be reproduced by the stereo loudspeaker “triangle” due to inherent crosstalk. When reproduced using ambiophonics, such existing recordings’ true qualities are revealed, with natural solo voices and wider images, up to 150° in practice.
It is also possible to make new recordings using binaurally-based main microphones, such as an ambiophone,[3] which is optimized for Ambiophonic reproduction (stereo-compatible) since it captures and preserves the same ILD and ITD that one would experience with one’s own ears at the recording session. Along with life-like spatial qualities, more correct timbre (tone color) of sounds is preserved. Use of ORTF
ORTF stereo technique
The ORTF stereo microphone system is a microphone technique used to record stereo sound.It was devised around 1960 at the Office de Radiodiffusion Télévision Française at Radio France....
, Jecklin Disk
Jecklin Disk
A Jecklin Disk is a sound-absorbing disk placed between two microphones to create an acoustic "shadow" from one microphone to the other. The resulting two signals can possibly produce a pleasing stereo effect...
, and sphere microphones without pinna (outer ear) can produce similar results. (Note that microphone techniques such as these that are binaural-based but without pinna also produce compatible results using conventional speaker-stereo, 5.1 surround, and mp3 players.)
Roots & research
Around 1980, some miniature boom boxes had a switch for 'wide stereo' to compensate for reduced speaker separation. These subtracted a little Left signal from the Right channel and vice-versa, perhaps with some filtering and delay.Bob Carver
Bob Carver
Robert W. Carver is an American designer of audio equipment based in the Pacific Northwest.Educated as a physicist and engineer, he found an interest in audio equipment at a very young age. He applied his talent to produce numerous innovative high fidelity designs since the 1970s...
of Carver Corporation built filtering to attempt to pre-subtract anti-crosstalk in the analogue Carver C4000 Control Console in 1981. He called this Sonic holography.
An early hardware attempt to compensate for loudspeaker-ear crosstalk was to apply a little out-of-phase left channel to a separate driver in the right speaker cabinet, and vice-versa. This was invented and marketed in 1982 by Matthew Polk, founder of Polk Audio
Polk Audio
Polk Audio is a manufacturer of audio products best known for their home and automobile speakers. The company also produces a wide range of other audio products such as amplifiers and FM tuners. The company is headquartered in Baltimore, Maryland and in 2006, was acquired by Directed...
, as true stereo in his SDA-SRS, SDA1 and SDA2 series speakers. Although the theory is questionable, the results were well-received.
On the early 1980s, Arnold Klayman of Hughes Aircraft
Hughes Aircraft
Hughes Aircraft Company was a major American aerospace and defense contractor founded in 1932 by Howard Hughes in Culver City, California as a division of Hughes Tool Company...
devised a way to use a HRTF
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...
to add depth to a stereo image, calling it Sound Retrieval System
Sound Retrieval System
The Sound Retrieval System is a patented psychoacoustic 3D audio processing technology originally invented by Arnold Klayman in the early 1980s. The Sound Retrieval System (SRS) is a patented psychoacoustic 3D audio processing technology originally invented by Arnold Klayman in the early 1980s....
. The development was later spun-off as SRS Labs
SRS Labs
SRS Labs, Inc. , is a Santa Ana, California-based audio technology engineering company that specializes in audio enhancement solutions for wide variety of consumer electronic devices. Originally a part of Hughes Aircraft Company, the audio division developed the Sound Retrieval System technology,...
.
In 1991, Roland Corporation
Roland Corporation
is a Japanese manufacturer of electronic musical instruments, electronic equipment and software. It was founded by Ikutaro Kakehashi in Osaka on April 18, 1972, with ¥33 million in capital. In 2005 Roland's headquarters relocated to Hamamatsu in Shizuoka Prefecture. Today it has factories in Japan,...
launched Roland Sound Space, a system that created a 3D sound-space using stereo speakers. It worked better for some listeners than others.
Ambiophonics is an amalgam of new research and previously known psychoacoustic principles and binaural technologies. This knowledge has enabled audio recording and reproduction that approaches the realistic soundfield at the ears of the listener that is comparable to what one would perceive in a concert hall, movie scene, or game environment. This level of high-fidelity was not realizable until human hearing and acoustics principles were thoroughly researched, and affordable PCs with sufficient processing speed became available. At the Casa Della Musica at the University of Parma, Italy, or at the listening lab at Filmaker Technology, Pennsylvania USA, ambiophonics, ambisonics, stereophonics, 5.1 2D surround, and hybrid full-sphere 3D systems can be compared for the abilities of these methods to convey the spatiality and tone color of real perception. Developers have provided many scientific papers and downloadable tools for implementing ambiophonics free of charge for personal use.[4]
Results & limitations
By repositioning speakers closer together to create a stereo dipoleStereo dipole
A Stereo dipole is a sound source in an Ambiophonic system, made by two closely spaced loudspeakers that ideally span 10-30 degrees. Thanks to the cross-talk cancellation method, a stereo dipole can render an acoustic stereo image nearly 180° wide or 360° ....
, and using digital signal processing
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...
(DSP) such as free RACE (Recursive Ambiophonic Crosstalk Elimination) or similar software,[5] ambiophonic reproduction is able to generate wide auditory images from most ordinary CDs/LPs/DVDs or MP3s of music, movies, or games and, depending upon the recording, restore the life-like localization, spatiality, and tone color they have captured. For most test subjects, results are dramatic, suggesting that Ambiophonics has the potential to revitalize interest in high-fidelity sound reproduction, both in stereo and surround.
Additionally, ambiophonics provides for the optional use of concert-hall or other ambience impulse response
Impulse response
In signal processing, the impulse response, or impulse response function , of a dynamic system is its output when presented with a brief input signal, called an impulse. More generally, an impulse response refers to the reaction of any dynamic system in response to some external change...
convolution to generate hall ambience signals for virtually any number and any placement of surround speakers.[6][7] But ambiophonics is not for theaters, auditoriums, or any large groups. Ambiophonics can usually accommodate more than one listener since one can move back and forth along the line bisecting the speakers. Precisely because of the higher level of envelopment along this line, the loss of realism when one moves away from the center line is more dramatic in the case of Ambiophonics than stereo. The listening area can be enlarged with ambience convolution, whereby surround speakers mimic the contributions of concert-hall walls.
Ambiophonics methods can be implemented in ordinary laptops, PCs, soundcards, hi-fi amplifiers, and even modest loudspeakers with consistent phase response, especially in any crossover regions. Neither true-binaural (dummy head with pinna) recordings nor head tracking are required, as with headphone-binaural listening. Commercial products now implement ambiophonics DSP, although tools for use on PCs are also available online.[4]
Surround sound
In practice in its simplest two-speaker implementation, ambiophonic reproduction unlocks auditory cues for images of up to 150° horizontally (azimuth), depending on the binaural cues captured in existing stereo recordings. Multi-channel recordings made with ambiophone-like microphone arrays to make 5.1-compatible DVDDVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
/SACD
Super Audio CD
Super Audio CD is a high-resolution, read-only optical disc for audio storage. Sony and Philips Electronics jointly developed the technology, and publicized it in 1999. It is designated as the Scarlet Book standard. Sony and Philips previously collaborated to define the Compact Disc standard...
recordings can be reproduced using just four speakers (a center speaker is obviated in ambiophonic layouts). Allowing for the human hearing “cone of confusion” at each side, a full 360° degree circle of perceived sound localization has been measured within ±5° of actual source azimuth, reproducing life-like spatial envelopment and timbre (contributed by accurate directional provenance of early reflections) of multi-channel music, movies, and game content.[3][8][9]
Especially in the case of stereo content where ambience has been purposely reduced (because a natural level coming from front 60°-only is perceived as too much), additional signals for surround speakers can be produced using a measured hall impulse response, convolved in a PC with the two front channel signals. For full ambiophonic replay, one PC can provide the DSP for 4-channel crosstalk-cancellation and four or more (up to 16 depending on the PC) surround speakers.[10]
The development of ambiophonics is the work of several researchers and companies including Ralph Glasgal, founder of the Ambiophonic Institute; Dr. Angelo Farina, University of Parma; Robin Miller, Filmaker Technology; Waves Audio; Dr. Roger West, Soundlab; Dr. Radomir Bozovic, TacT Audio; and Prof. Edgar Choueiri
Edgar Choueiri
Edgar Y. Choueiri is a Lebanese American plasma physicist and currently President of the Lebanese Academy of Sciences. He is best known for clarifying the role of plasma instabilities in spacecraft electric thrusters , for conceiving and developing new spacecraft propulsion concepts and, more...
, Princeton University.
External links
- Sound Performance Lab (SPL) 'Vitalizer' stereo enhancer - hardware and software
- Behringer Edison Stereo enhancer hardware
- Fruity Stereo Shaper VSTVirtual Studio TechnologySteinberg's Virtual Studio Technology is an interface for integrating software audio synthesizer and effect plugins with audio editors and hard-disk recording systems. VST and similar technologies use digital signal processing to simulate traditional recording studio hardware with software...
Effect Plugin