The Trifield process is a form of audio rendering in which a conventional two-channel signal is decoded (using Ambisonic principles) to an additional number of loudspeakers, typically three in the form of a Left-Centre-Right front stage. The technique provides significant additional image stability, especially when the listener is moving or off-axis.
It was developed by Dr Geoffrey Barton, a major figure in the "second wave" of original Ambisonics development, and Michael Gerzon. It should not be confused with a Yamaha system with a similar name.
Trifield also has applications in conventional surround mixing. There are several problems involved in mixing with an additional centre front channel for many engineers. The channel itself was originally designed for dialogue in matrix cinema surround systems and does not have a direct application in music mixing, where a 2-speaker stereo stage is generally, and traditionally, employed.
Many studio engineers with a background in conventional stereo music mixing find that simple panning of a source to the centre-front (CF) channel makes it fail to blend in with the stereo mix. However, if the CF channel is left silent, consumers may believe there is a fault with the disc or with their equipment. A way around this problem is offered by Trifield. The processor typically takes a 2-channel L-R signal and renders it for L-C-R, and no signals are sent to the CF except for those generated by the Trifield processor. Not only does CF content now blend with the mix: in addition, the resulting soundstage is more stable and listener-position independent, while the listener can confirm that something is actually emerging from their centre-front loudspeaker.
Gerzon, Michael A. (July–August 1992). "Optimum Reproduction Matrices for Multispeaker Stereo". Journal of the Audio Engineering Society. AES. 40 (7/8): 571–589.
A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summed to produce the combined output signals, which can then be broadcast, amplified through a sound reinforcement system or recorded.
Quadraphonic sound – equivalent to what is now called 4.0 surround sound – uses four audio channels in which speakers are positioned at the four corners of a listening space. The system allows for the reproduction of sound signals that are independent of one another.
Ambisonics is a full-sphere surround sound format: in addition to the horizontal plane, it covers sound sources above and below the listener.
Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener. Its first application was in movie theaters. Prior to surround sound, theater sound systems commonly had three screen channels of sound that played from three loudspeakers located in front of the audience. Surround sound adds one or more channels from loudspeakers to the side or behind the listener that are able to create the sensation of sound coming from any horizontal direction around the listener.
Matrix decoding is an audio technology where a small number of discrete audio channels are decoded into a larger number of channels on play back. The channels are generally, but not always, arranged for transmission or recording by an encoder, and decoded for playback by a decoder. The function is to allow multichannel audio, such as quadraphonic sound or surround sound to be encoded in a stereo signal, and thus played back as stereo on stereo equipment, and as surround on surround equipment – this is "compatible" multichannel audio.
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience. In many situations, a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage, typically by using electronic effects, such as reverb, as opposed to simply amplifying the sources unaltered.
3D audio effects are a group of sound effects that manipulate the sound produced by stereo speakers, surround-sound speakers, speaker-arrays, or headphones. This frequently involves the virtual placement of sound sources anywhere in three-dimensional space, including behind, above or below the listener.
Nimbus Records is a British record company based at Wyastone Leys, Ganarew, Herefordshire. They specialise in classical music recordings and were the first company in the UK to produce compact discs.
The Soundfield microphone is an audio microphone composed of four closely spaced subcardioid or cardioid (unidirectional) microphone capsules arranged in a tetrahedron. It was invented by Michael Gerzon and Peter Craven, and is a part of, but not exclusive to, Ambisonics, a surround sound technology. It can function as a mono, stereo or surround sound microphone, optionally including height information.
Ambisonic UHJ format is a development of the Ambisonic surround sound system designed to be compatible with mono and stereo media. It is a hierarchy of systems in which the recorded soundfield will be reproduced with a degree of accuracy that varies according to the available channels. Although UHJ permits the use of up to four channels, only the 2-channel variant is in current use. In Ambisonics, UHJ is also known as "C-Format".
This page focusses on decoding of classic first-order Ambisonics. Other relevant information is available on the Ambisonic reproduction systems page.
SQ Quadraphonic was a matrix 4-channel quadraphonic sound system for vinyl LP records. It was introduced by CBS Records in 1971. Many recordings using this technology were released on LP during the 1970s.
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, today a number of hardware and VST plug-in makers offer Ambiophonic DSP. Ambiophonics eliminates crosstalk inherent in the conventional stereo triangle speaker placement, and thereby generates a speaker-binaural soundfield that emulates headphone-binaural sound, 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.
In sound recording and reproduction, audio mixing is the process of optimizing and combining multitrack recordings into a final mono, stereo or surround sound product. In the process of combining the separate tracks, their relative levels are adjusted and balanced and various processes such as equalization and compression are commonly applied to individual tracks, groups of tracks, and the overall mix. In stereo and surround sound mixing, the placement of the tracks within the stereo field are adjusted and balanced. Audio mixing techniques and approaches vary widely and have a significant influence on the final product.
The sweet spot is a term used by audiophiles and recording engineers to describe the focal point between two speakers, where an individual is fully capable of hearing the stereo audio mix the way it was intended to be heard by the mixer. The sweet spot is the location which creates an equilateral triangle together with the stereo loudspeakers, the stereo triangle. In the case of surround sound, this is the focal point between four or more speakers, i.e., the location at which all wave fronts arrive simultaneously. In international recommendations the sweet spot is referred to as reference listening point.
In audio engineering, joint encoding refers to a joining of several channels of similar information during encoding in order to obtain higher quality, a smaller file size, or both.
A matrix mixer is an audio electronics device that routes multiple input audio signals to multiple outputs. It usually employs level controls such as potentiometers to determine how much of each input is going to each output, and it can incorporate simple on/off assignment buttons. The number of individual controls is at least the number of inputs multiplied by the number of outputs.
The design of speaker systems for Ambisonic playback is governed by several constraints:
The United Kingdom patent 394325 'Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems' is a fundamental work on stereophonic sound, written by Alan Blumlein in 1931 and published in 1933. The work exists only in the form of a patent and two accompanying memos addressed to Isaac Shoenberg. The text is exceptionally long for a patent of the period, having 70 numbered claims. It contains a brief summary of sound localization theory, a roadmap for introduction of surround sound in sound film and recording industry, and a description of Blumlein's inventions related to stereophony, notably the matrix processing of stereo signals, the Blumlein stereo microphone and the 45/45 mechanical recording system.
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