EP1275272B1 - Prise de son ambiant multi-canal et techniques de reproduction qui preservent les harmoniques spatiales en trois dimensions - Google Patents

Prise de son ambiant multi-canal et techniques de reproduction qui preservent les harmoniques spatiales en trois dimensions Download PDF

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EP1275272B1
EP1275272B1 EP00970687A EP00970687A EP1275272B1 EP 1275272 B1 EP1275272 B1 EP 1275272B1 EP 00970687 A EP00970687 A EP 00970687A EP 00970687 A EP00970687 A EP 00970687A EP 1275272 B1 EP1275272 B1 EP 1275272B1
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Prior art keywords
speakers
signals
sound
sound field
harmonics
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EP1275272A1 (fr
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James A. Moorer
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S Aqua Semiconductor LLC
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SNK Tech Investments LLC
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
    • H04S3/02—Systems employing more than two channels, e.g. quadraphonic of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2400/00—Details of stereophonic systems covered by H04S but not provided for in its groups
    • H04S2400/15—Aspects of sound capture and related signal processing for recording or reproduction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
    • H04S2420/11—Application of ambisonics in stereophonic audio systems

Definitions

  • This invention relates generally to the art of electronic sound transmission, recording and reproduction, and, more specifically, to improvements in surround sound techniques.
  • Stereo (two channel) recording and playback through spatially separated loud speakers significantly improved the realism of the reproduced sound, when compared to earlier monaural (one channel) sound reproduction.
  • the audio signals have been encoded in the two channels in a manner to drive four or more loud speakers positioned to surround the listener. This surround sound has further added to the realism of the reproduced sound.
  • Multi-channel (three or more channel) recording is used for the sound tracks of most movies, which provides some spectacular audio effects in theaters that are suitably equipped with a sound system that includes loud speakers positioned around its walls to surround the audience.
  • WO 92/15180 discloses a system comprising a matrix for converting a first plurality of signals intended to feed a first plurality of loud speakers in a stereophonic arrangement into a second greater plurality of loud speaker feed signals suitable for feeding a second plurality of loud speakers in a second stereophonic arrangement. This conversion is conducted in a manner that is said to substantially preserve the width of the reproduced sound stage and that is said to substantially preserve or improve the sound localisation qualities of the created phantom sound images for listeners across a broad listening area.
  • WO 00/19415 discloses a recording and mixing method for three-dimensional audible rendering of multiple sound sources.
  • Directional panning and mixing of sounds is performed in a multi-channel encoding format.
  • Multi-channel encoded signal is converted into signals for play back over headphones or loudspeaker arrangements.
  • the decoders used for this conversion can be adapted to a number of geometric layouts of the loud speakers.
  • US 5,757,927 A discloses a surround sound apparatus wherein a decoder, which is preferably an Ambisonic decoder, decodes directionally encoded audio signals for reproduction via a loudspeaker layout over a listening area wherein the signals are decoded by a matrix.
  • the coefficients of the decoding matrix are such that at a predetermined listening position, the reproduced velocity vector direction and the reproduced energy vector position directions are substantially equal to each other and substantially independent of frequency in a broad audio frequency range.
  • a method of processing a sound field for reproduction of the sound field over a given frequency range through a surround sound system having a plurality of at least four channels individually feeding one of at least four speakers comprises acquiring multiple signals of the sound field, and directing the acquired sound field signals into individual ones of the plurality of channels with a set of relative gains for the entire frequency range that is determined by solving a relationship that (1) includes selected positions of the speakers around a listening area not constrained to a regular geometric, coplanar pattern and (2) substantially preserves individual ones of a plurality of three dimensional spatial harmonics of the sound field.
  • a sound field reproduced from the speakers arranged in said selected positions substantially reproduces the plurality of three dimensional spatial harmonics of the acquired sound field.
  • a system having an input to receive at least four audio signals of an original sound field that are intended to be reproduced by respective ones of at least four speakers at certain assumed positions surrounding a listening area and outputs to drive at least four speakers at certain actual positions different from the assumed positions.
  • the system comprises an input that accepts information, including declination and azimuth, of the speaker certain actual positions, and an electronically implemented matrix responsive to inputted actual speaker position information, including declination and azimuth, and to the assumed speaker positions to provide from the input signals other signals to the outputs which drive the speakers to reproduce the sound field with a number of three dimensional spatial harmonics that individually match substantially individual ones of the same number of three dimensional spatial harmonics in the original sound field.
  • a sound system having an input to receive audio signals of an original three dimensional sound field and output to drive at least four loud speakers at certain actual positions surrounding a listening area to reproduce the sound field.
  • the system comprises an input that accepts information of the speaker actual positions, and an electronically implemented matrix responsive to inputted information of the actual speaker positions and input signals to provide signals to the outputs which drive the speakers to reproduce the sound field with a number of three dimensional spatial harmonics that individually match substantially corresponding ones of the same number of three dimensional spatial harmonics in the original sound field.
  • An audio field is acquired and reproduced by multiple signals through four or more loud speakers positioned to surround a listening area, the signals being processed in a manner that reproduces substantially exactly a specified number of spatial harmonics of the acquired audio field with practically any specific arrangement of the speakers around the listening area. This adds to the realism of the sound reproduction without any particular constraint being imposed upon the positions of the loud speakers.
  • Individual monaural sounds are mixed together in one embodiment by use of a matrix that, when making a recording or forming a sound transmission, angularly positions them, when reproduced through an assumed speaker arrangement around the listener, with improved realism.
  • a matrix that, when making a recording or forming a sound transmission, angularly positions them, when reproduced through an assumed speaker arrangement around the listener, with improved realism.
  • all of the channels are potentially involved in order to reproduce the sound with the desired spatial harmonics.
  • An example application is in the mastering of a recording of several musicians playing together. The sound of each instrument is first recorded separately and then mixed in a manner to position the sound around the listening area upon reproduction. By using all the channels to maintain spatial harmonics, the reproduced sound field is closer to that which exists in the room where the musicians are playing.
  • the multi-channel sound may be rematrixed at the home, theater or other location where being reproduced, in order to accommodate a different arrangement of speakers than was assumed when originally mastered.
  • the desired spatial harmonics are accurately reproduced with the different actual arrangement of speakers. This allows freedom of speaker placement, particularly important in the home which often imposes constraints on speaker placement, without losing the improved realism of the sound.
  • a sound field may initially be acquired with directional information by a use of multiple directional microphones. Either the microphone outputs, or spatial harmonic signals resulting from an initial partial matrixing of the microphone outputs, are recorded or transmitted to the listening location by separate channels in one embodiment. The transmitted signals can then be matrixed in the home or other listening location in a manner that takes into account the actual speaker locations, in order to reproduce the recorded sound field with some number of spatial harmonics that are matched to those of the recording location.
  • Spatial harmonics may be used in either two or three dimensions.
  • the audio wave front is reproduced by an arrangement of loud speakers that is largely coplanar, whether the initial recordings were based on two dimensional spatial harmonics or through projecting three dimensional harmonics on to the plane of the speakers.
  • one or more of the speakers is placed at a different elevation than this two dimensional plane.
  • the three dimensional sound field is acquired by a non-coplanar arrangement of the multiple directional microphones.
  • a person 11 is shown in Figure 1 to be at the middle of a listening area surrounded by loudspeakers SP1, SP2, SP3, SP4 and SP5 that are pointed to direct their sounds toward the center.
  • a system of angular coordinates is established for the purpose of the descriptions in this application.
  • the angular positions of the remaining speakers SP2 (front left), SP3 (rear left), SP4 (rear right) and SP5 (front right) are respectively ( ⁇ 2 , ⁇ 2 ), ( ⁇ 3 , ⁇ 3 ), ( ⁇ 4 , ⁇ 4 ), and ( ⁇ 5 , ⁇ 5 ) from that reference.
  • each of ⁇ 1 - ⁇ 5 is then 90° and these ⁇ s will not be explicitly expressed for the time being and are omitted from Figure 1 .
  • the elevation of one or more of the speakers above one or more of the other speakers is not required but may be done in order to accommodate a restricted space. The case of one or more of the ⁇ i ⁇ 90° is discussed below.
  • the sounds of the individual instruments will be positioned at different angles ⁇ 0 around the listening area during the mastering process.
  • the sound of each instrument is typically acquired by one or more microphones recorded monaurally on at least one separate channel. These monaural recordings serve as the sources of the sounds during the mastering process.
  • the mastering may be performed in real time from the separate instrument microphones.
  • Figures 2A-D are referenced to illustrate the concept of spatial frequencies.
  • Figure 2A shows the space surrounding the listening area of Figure 1 in terms of angular position. The five locations of each of the speakers SP1, SP2, SP3, SP4 and SP5 are shown, as is the desired location of the sound source 13.
  • the value a 0 thus represents the value of the spatial function's zero order.
  • FIG. 2B The spatial zero order is shown in Figure 2B , having an equal magnitude around entire space that rises and falls with the magnitude of the spatial impulse sound source 13.
  • Figure 2C shows a first order spatial function, being a maximum at the angle of the impulse 13 while having one complete cycle around the space.
  • a second order spatial function as illustrated in Figure 2D , has two complete cycles around the space.
  • the spatial impulse 13 is accurately represented by a large number of orders but the fact of only a few speakers being used places a limit upon the number of spatial harmonics that may be included in the reproduced sound field.
  • n is the number of harmonics desired to be reproduced
  • spatial harmonics zero through n of the reproduced sound field may be reproduced substantially exactly as exist in the original sound field.
  • the spatial harmonics which can be reproduced exactly are harmonics zero through n, where n is the highest whole integer that is equal to or less than one-half of one less than the number of speakers positioned around a listening area. Alternately, fewer than this maximum number of possible spatial harmonics may be chosen to be reproduced as in a particular system.
  • FIG 3 schematically shows certain functions of a sound console used to master multiple channel recordings.
  • five signals S1, S2, S3, S4, and S5 are being recorded in five separate channels of a suitable recording medium such as tape, likely in digital form. Each of these signals is to drive an individual loud speaker.
  • Two monaural sources 17 and 19 of sound are illustrated to be mixed into the recorded signals S1-S5.
  • the sources 17 and 19 can be, for example, either live or recorded signals of different musical instruments that are being blended together.
  • One or both of the sources 17 and 19 can also be synthetically generated or naturally recorded sound effects, voices and the like. In practice, there are usually far more than two such signals used to make a recording.
  • the individual signals may be added to the recording tracks one at a time or mixed together for simultaneous recording.
  • Figure 3 What is illustrated by Figure 3 is a technique of "positioning" the monaural sounds. That is, the apparent location of each of the sources 17 and 19 of sound when the recording is played back through a surround sound system, is set during the mastering process, as described above with respect to Figure 1 .
  • usual panning techniques of mastering consoles direct a monaural sound into only two of the recorded signals S1-S5 that feed the speakers on either side of the location desired for the sound, with relative amplitudes that determines the apparent position to the listener of the source of the sound. But this lacks certain realism.
  • each source of sound is fed into each of the five channels with relative gains being set to construct a set of signals that have a certain number of spatial harmonics, at least the zero and first harmonics, of a sound field emanating from that location.
  • One or more of the channels may still receive no portion of a particular signal but now because it is a result of preserving a given number of spatial harmonics, not because the signal is being artificially limited to only two of the channels.
  • the relative contributions of the source 17 signal to the five separate channels S1-S5 is indicated by respective variable gain amplifiers 21, 22, 23, 24 and 25. Respective gains g 1 , g 2 , g 3 , g 4 and g 5 of these amplifiers are set by control signals in circuits 27 from a control processor 29. Similarly, the sound signal of the source 19 is directed into each of the channels S1-S5 through respective amplifiers 31, 32, 33, 34 and 35. Respective gains g 1 ', g 2 ', g 3 ', g 4 ', and g 5 ' of the amplifiers 31-35 are also set by the control processor 29 through circuits 37. These sets of gains are calculated by the control processor 29 from inputs from a sound engineer through a control panel 45.
  • These inputs include angles ⁇ ( Figure 1 ) of the desired placement of the sounds from the sources 17 and 19 and an assumed set of speaker placement angles ⁇ 1 - ⁇ 5 . Calculated parameters may optionally also be provided through circuits 47 to be recorded. Respective individual outputs of the amplifiers. 21-25 are combined with those of the amplifiers 31-35 by respective summing nodes 39,40,41,42 and 43 to provide the five channel signals S1-S5. These signals S1-S5 are eventually reproduced through respective ones of the speakers SP1-SP5.
  • the control processor 29 includes a DSP (Digital Signal Processor) operating to solve simultaneous equations from the inputted information to calculate a set of relative gains for each of the monaural sound sources.
  • ⁇ 0 represents the angle of the desired apparent position of the sound
  • ⁇ i and ⁇ j represent the angular positions that correspond to placement of the loudspeakers for the individual channels with each of i and j having values of integers from 1 to the number of channels
  • m represents spatial harmonics that extend from 0 the number of harmonics being matched upon reproduction with those of the original sound field
  • N is the total number of channels
  • g i represents the relative gains of the individual channels with i extending from
  • the above linear equations may be expressed as the following matrix: 1 + 2 ⁇ cos ⁇ 0 - ⁇ 1 1 + 2 ⁇ cos ⁇ 0 - ⁇ 2 1 + 2 ⁇ cos ⁇ 0 - ⁇ 3 1 + 2 ⁇ cos ⁇ 0 - ⁇ 4 1 + 2 ⁇ cos ⁇ 0 - ⁇ 5 - 1 + 2 ⁇ cos ⁇ 1 - ⁇ 1 1 + 2 ⁇ cos ⁇ 2 - ⁇ 1 1 + 2 ⁇ cos ⁇ 3 - ⁇ 1 1 + 2 ⁇ cos ⁇ 4 - ⁇ 1 1 + 2 ⁇ cos ⁇ 5 - ⁇ 1 1 + 2 ⁇ cos ⁇ 1 - ⁇ 2 1 + 2 ⁇ cos ⁇ 3 - ⁇ 2 1 + 2 ⁇ cos ⁇ 4 - ⁇ 1 1 + 2 ⁇ cos ⁇ 5 - ⁇ 1 1 + 2 ⁇ cos ⁇ 1 - ⁇ 2 1 + 2 ⁇ cos ⁇
  • An alternate constraint which may be imposed on the solution of the general matrix is to require that a velocity vector (for frequencies below a transition frequency within a range of about 750-1500 Hz.) and a power vector (for frequencies above this transition) be substantially aligned.
  • a velocity vector for frequencies below a transition frequency within a range of about 750-1500 Hz.
  • a power vector for frequencies above this transition
  • the resulting signals S1-S5 can be played back from the recording 15 and individually drive one of the speakers SP1-SP5. If the speakers are located exactly in the angular positions ⁇ 1 - ⁇ 5 around the listener 11 that were assumed when calculating the relative gains of each sound source, or very close to those positions, then the locations of all the sound sources will appear to the listener to be exactly where the sound engineer intended them to be located. The zero, first and any higher order spatial harmonics included in these calculations will be faithfully reproduced.
  • the signals S1-S5 are rematrixed in the preferred embodiment by the listener's sound system in a manner illustrated in Figure 4 .
  • the sound channels S 1-SS played back from the recording 15 are, in a specific implementation, initially converted to spatial harmonic signals a 0 (zero harmonic), a 1 and b 1 (first harmonic) by a harmonic matrix 51.
  • the first harmonic signals a 1 and b 1 are orthogonal to each other.
  • the processor 59 calculates these gains from the mastering parameters that have been recorded and played back with the sound tracks, primarily the assumed speaker angles ⁇ 1 , ⁇ 2 , ⁇ 3 , ⁇ 4 , and ⁇ 5 and corresponding actual speaker angles ⁇ 1 , ⁇ 2 , ⁇ 3 , ⁇ 4 , and ⁇ 5 that are provided to the control processor by the listener through a control panel 61.
  • the algorithm of the harmonic matrix 51 is illustrated by use of 15 variable gain amplifiers arranged in five sets of three each. Three of the amplifiers are connected to receive each of the sound signals S1-S5 being played back from the recording. Amplifiers 63, 64 and 65 receive the S 1 signal, amplifiers 67, 68 and 69 the S2 signal, and so on. An output from one amplifier of each of these five groups is connected with a summing node 81, having the a 0 output signal, an output from another amplifier of each of these five groups is connected with a summing node 83, having the a 1 output signal, and an output from the third amplifier of each group is connected to a third summing node 85, whose output is the b 1 signal.
  • the amplifiers 63, 67, 70, 73 and 76 have unity gain
  • the matrix 53 takes these signals and provides new signals S1', S2', S3', S4' and S5' to drive the speakers having unique positions surrounding a listening area.
  • the representation of the processing shown in Figure 4 includes 15 variable gain amplifiers 87-103 grouped with five amplifiers 87-91 receiving the signal a 0 , five amplifiers 92-97 receiving the signal a 1 , and five amplifiers 98-103 receiving the signal b 1 .
  • the output of a unique one of the amplifiers of each of these three groups provides an input to a summing node 105, the output of another of each of these groups provides an input to a summing node 107, and other amplifiers have their outputs connected to nodes 109, 111 and 113 in a similar manner, as shown.
  • a matrix expression of the above simultaneous equations for the actual speaker position angles ⁇ is as follows, where the condition of the second spatial harmonics equaling zero is also imposed: 1 + 2 ⁇ cos ⁇ 1 - ⁇ 1 1 + 2 ⁇ cos ⁇ 2 - ⁇ 1 1 + 2 ⁇ cos ⁇ 3 - ⁇ 1 1 + 2 ⁇ cos ⁇ 4 - ⁇ 1 1 + 2 ⁇ cos ⁇ 5 - ⁇ 1 1 + 2 ⁇ cos ⁇ 1 - ⁇ 2 1 + 2 ⁇ cos ⁇ 2 - ⁇ 2 1 + 2 ⁇ cos ⁇ 3 - ⁇ 2 1 + 2 ⁇ cos ⁇ 4 - ⁇ 2 1 + 2 ⁇ cos ⁇ 5 - ⁇ 2 1 + 2 ⁇ cos ⁇ 1 - ⁇ 3 1 + 2 ⁇ cos ⁇ 2 - ⁇ 3 1 + 2 ⁇ cos ⁇ 4 - ⁇ 2 1 + 2 ⁇ cos ⁇ 5 - ⁇ 2 1 + 2 ⁇ co
  • FIG. 3 and 4 The description with respect to Figures 3 and 4 has been directed primarily to mastering a three-dimensional sound field, or at least contribute to one, from individual monaural sound sources.
  • FIG 5 a technique is illustrated for mastering a recording or sound transmission from signals that represent a sound field in three dimensions.
  • Three microphones 121, 123 and 125 are of a type and positioned with respect to the sound field to produce audio signals m 1 , m 2 and m 3 that contain information of the sound field that allows it to be reproduced in a set of surround sound speakers. Positioning such microphones in a symphony hall, for example, produces signals from which the acoustic effect may be reconstructed with realistic directionality.
  • these three signals can immediately be recorded or distributed by transmission in three channels.
  • the m 1 , m 2 and m 3 signals are then played back, processed and reproduced in the home, theater and/or other location.
  • the reproduction system includes a microphone matrix circuit 129 and a speaker matrix circuit 131 operated by a control processor 133 through respective circuits 135 and 137. This allows the microphone signals to be controlled and processed at the listening location in a way that optimizes, in order to accurately reproduce the original sound field with a specific unique arrangement of loud speakers around a listening area, the signals S1-S5 that are fed to the speakers.
  • the matrix 129 develops the zero and first spatial harmonic signals a 0 , a 1 and b 1 from the microphone signals m 1 m 2 and m 3 .
  • the speaker matrix 131 takes these signals and generates the individual speaker signals S1-S5 with the same algorithm as described for the matrix 53 of Figure 4 .
  • a control panel 139 allows the user at the listening location to specify the exact speaker locations for use by the matrix 131, and any other parameters required.
  • the arrangement of Figure 6 is very similar to that of Figure 5 , except that it differs in the signals that are recorded or transmitted.
  • the microphone matrixing 129 is performed at the sound originating location ( Figure 6 ) and the resulting spatial harmonics a 0 , a 1 , and b 1 of the sound field are recorded or transmitted at 127'.
  • a control processor 141 and control panel 143 are used at the mastering location.
  • a control processor 145 and control panel 147 are used at the listening location.
  • Each of the three microphone signals m 1 , m 2 and m 3 is an input to a bank of three variable gain amplifiers.
  • the signal m 1 is applied to amplifiers 151-153, the signal m 2 to amplifiers 154-156, and the signal m 3 to amplifiers 157-159.
  • One output of each bank of amplifiers is connected to a summing node that results in the zero spatial harmonic signal a 0 .
  • another one of the amplifier outputs of each bank is connected to a summing node 163, resulting in the first spatial harmonic signal a 1 .
  • outputs of the third amplifier of each bank are connected together in a summing node 165, providing first harmonic signal b 1 .
  • the gains of the amplifiers 151-159 are individually set by the control processor 133 or 141 ( Figures 5 or 6 ) through circuits 135. These gains define the transfer function of the microphone matrix 129.
  • the transfer function that is necessary depends upon the type and arrangement of the microphones 121, 123 and 125 being used.
  • Figure 8 illustrates one specific arrangement of microphones. They can be identical but need not be. No more than one of the microphones can be omni-directional. As a specific example, each is a pressure gradient type of microphone having a cardioid pattern. They are arranged in a Y-pattern with axes of their major sensitivities being directed outward in the directions of the arrows. The directions of the microphones 121 and 125 are positioned at an angle a on opposite sides of the directional axis of the other microphone 123.
  • the matrices are formed with parameters that include either expected or actual speaker locations. Few constraints are placed upon these speaker locations. Whatever they are, they are taken into account as parameters in the various algorithms. Improved realism is obtained without requiring specific speaker locations suggested by others to be necessary, such as use of diametrically opposed speaker pairs, speakers positioned at floor and ceiling corners of a rectangular room, other specific rectilinear arrangements, and the like. Rather, the processing of the present invention allows the speakers to first be placed where desired around a listening area, and those positions are then used as parameters in the signal processing to obtain signals that reproduce sound through those speakers with a specified number of spatial harmonics that are substantially exactly the same as those of the original audio wavefront.
  • the spatial harmonics being faithfully reproduced in the examples given above are the zero and first harmonics but higher harmonics may also be reproduced if there are enough speakers being used to do so. Further, the signal processing is the same for all frequencies being reproduced, a high quality system extending from a low of a few tens of Hertz to 20,000 Hz. or more. Separate processing of the signals in two frequency bands is not required.
  • the spherical harmonics are functions of two coordinates on the sphere, the angles ⁇ and ⁇ . These are shown in Figure 9 where a point on the surface of the sphere is represented by the pair ( ⁇ , ⁇ ). ⁇ is azimuth. Zero degrees is straight ahead. 90° is to the left. 180° is directly behind. ⁇ is declination (up and down). Zero degrees is directly overhead. 90° is the horizontal plane, and 180° is straight down. Note that the range of ⁇ is zero to 180°, whereas the range of ⁇ is zero to 360° (or -180° to 180°). In the discussion in two dimensions, the angular variable ⁇ has been suppressed and taken as equal to 90°. More generally, both angle are included.
  • Figures 1 and 8 can be considered either as a coplanar arrangement of the shown elements or a projection of the three dimensional situation onto a particular planar subspace.
  • ⁇ 0 ⁇ cos ⁇ 0 .
  • the gains to each of the speakers, g i are sought so that the resulting sound field around a point at the center corresponds to the desired sound field ( f 0 ( ⁇ , ⁇ ) above) as well as possible. These gains may be obtained by requiring the integrated square difference between the resulting sound field and the desired sound field be as small as possible.
  • BG S
  • G a column vector of the speaker gains:
  • G T g 1 ⁇ g N .
  • equation (19) is similar to the expansion in equation (16) for the unit impulse in a certain direction but for the term (-1) m .
  • the rank of the matrix B depends on how many terms of the expansion are retained. If the 0 th and 1 st terms are retained, the rank ofB will be 4. If one more term is taken, the rank will be 9. The rank of B also determines the minimum number of speakers required to match that many terms of the expansion.
  • any number of speakers may be used, but the system of equations will be under-determined if the number of speakers is not the perfect square number ( T +1) 2 corresponding to the T th order harmonics.
  • One way is to solve the system using the pseudo-inverse of the matrix B . This is equivalent to choosing the minimum-norm solution, and provides a perfectly acceptable solution.
  • Another way is to augment the system with equations that force some number of higher harmonics to zero.
  • Figures 3 and 4 illustrated the mastering and reconstruction process for a coplanar example of two monaural sources mixed into five signals which are then converted into the spatial harmonics through first order and finally matrixed into a modified set of signals.
  • any of these specific choices could be taken differently, although the choices of five signals being recording and five modified signals resulting as the output are convenient as a common multichannel arrangement is the 5.1 format of movie and home cinema soundtracks.
  • Alternative multichannel recording and reproduction methods for example that described in the co-pending U.S. patent application Ser. No. 09/505,556, filed February 17, 2000 , by James A. Moorer, entitled "CD Playback Augmentation" (granted as US 7,043,312 ).
  • control processor 59 must now calculate the gains form pairs of assumed speaker angles ( ⁇ i , ⁇ i ) and corresponding a pairs actual speaker angles ( ⁇ j , ⁇ j ) instead the just the respective azimuthal angles ⁇ i and ⁇ j , the ( ⁇ j , ⁇ j ) again being provided through a control panel 61.
  • one convenient choice for the three dimensional, non-coplanar case is to use six signals S1-S6 and also a modified set of six signals S1'-S6'.
  • non-coplanar speakers are required for the spherical harmonics just as at least three non-collinear speakers are required in the 2D case, since at least four non-coplanar points are needed to define a sphere and three non-collinear points define a circle in a plane.
  • the reason six speakers is a convenient choice is that it allows for four or five of the recorded or transmitted tracks on medium 15 to be mixed for a coplanar arrangement, with the remaining two or one tracks for speakers placed off the plane. This allows a listener without elevated speakers or without reproduction equipment for the spherical harmonics to access and use only the four or five coplanar tracks, while the remaining tracks are still available on the medium for the listener with full, three dimensional reproduction capabilities. This is similar to the situation described above in the 2D case where two channels can be used in a traditional stereo reproduction, but the additional channels are available for reproducing the sound field.
  • each of the six signals S1-S6 would feed four amplifiers in matrix 51, one for each of the four summing nodes corresponding to A 0 , A 1 , A 11 , and B 11 (or, more generally, four independent linear combinations of these) to produce theses four output in this example using the 0 th and 1 st order harmonics.
  • Matrix 53 now has six amplifiers for each of these four harmonics to produce the set of six modified signals S1'-S6'. Again, the declination as well as the azimuthal location of the actual speaker placements is now used. More generally, control panel 61 could also supply control processor 59 with radial information on any speakers not on the same spherical surface as the other speakers. The control processor 59 could then use this information matrix 53 to produce corresponding modified signals to compensate for any differing radii by introducing delay, compensation for wave front spreading, or both.
  • a standard directional microphone has a pickup pattern that can be expressed as the 0 th and 1 st spatial spherical harmonics.
  • the constant C is called the "directionality" of the microphone and is determined by the type of microphone.
  • C is one for an omni-directional microphone and is zero for a "figure-eight" microphone.
  • Intermediate values yield standard pickup patterns such as cardioid (1/2), hyper-cardioid (1/4), super-cardioid (3/8), and sub-cardioid (3/4).
  • the terms m 1 , ..., m M refer to M pressure-gradient microphones with principal axes at the angles ( ⁇ 1 , ⁇ 1 ), ..., ( ⁇ M , ⁇ M ).
  • Each row of this matrix is just the directional pattern of one of the microphones.
  • Four microphones unambiguously determine all the coefficients for the 0 th and 1 st order terms of the spherical harmonic expansion.
  • the angles of the microphones should be distinct (there should not be two microphones pointing in the same direction) and non-coplanar (since that would provide information only in one angular dimension and not two). In these cases, the matrix is well-conditioned and has an inverse.
  • each microphone is now specified by a pair of parameters, the angles ( ⁇ , ⁇ ) the principal axes, and each of the signals S1-S6 or S1'-S6' had a declination as well as an azimuthal angle.
  • the microphone matrix of Figure 7 will correspondingly now have four sets of four amplifiers.
  • one of the microphones may be placed at a different radius for practical reasons, in which case some delay or advance of the corresponding signal should be introduced. For example, if the rear-facing microphone m 2 of Figure 8 were displaced a ways to the rear, the recording advanced about 1ms for each foot of displacement to compensate for the difference in propagation time.
  • Equation (23) is valid for any set of four microphones, again assuming no more than one of them is omni-directional. By looking at this equation for two different sets of microphones, the directional pattern of the pickup can be changed by matrixing these four signals.
  • the starting point is equations (23) and (24) for two different sets of microphones and their corresponding matrix D.
  • the actual microphones and matrix will be indicated by the letters m and D, with the rematrixed, "virtual" quantities indicated by a tilde.
  • the matrix D ⁇ represents the directionality and angles of the "virtual" microphones. The result of this will be the sound that would have been recorded if the virtual microphones hand been present at the recording instead of the ones that were used.
  • This allows recordings to be made using a "generic" sound-field microphone and then later matrix them into any set of microphones. For instance, we might pick just the first two virtual microphones, m ⁇ 1 , and m ⁇ 2 , and use them as a stereo pair for a standard CD recording. m ⁇ 3 could then be added in for the sort of planar surround sound recording described above, with m ⁇ 4 used for the full three dimensional realization.
  • any non-degenerate transformation of these four microphone feeds can be used to create any other set of microphone feeds, or can be used to generate speaker feeds for any number of speakers (greater than 4) that can recreate exactly the 0 th and 1 st spatial harmonics of the original sound field.
  • the sound field microphone technique can be used to adjust the directional characteristics and angles of the microphones after the recording has been completed.
  • the microphones can be revised through simple matrix operations. Whether the material is intended to be released in multi-channel format or not, the recording of the third, rear-facing channel allows increased freedom in a stereo release, with the recording of a fourth, non-coplanar channel increasing freedom in both stereo and planar surround-sound.
  • the three or four channels of (preferably uncompressed) audio material respectively corresponding to the 2D and 3D sound field may be stored on the disk or other medium, and then rematrixed to stereo or surround in a simple manner.
  • equation (25) or its 2D reduction
  • two channels could store a suitable stereo mix
  • the third store a channel for a 2D surround mix
  • use the fourth channel for the 3D surround mix In addition to the audio, the matrix D ⁇ or its inverse is also stored on the medium.
  • the player For a stereo presentation, the player simply ignores the third and fourth channels of audio and plays the other two as the left and right feeds.
  • the inverse of the matrix D ⁇ is used to derive the 0-th and first 2D spatial harmonics from the first three channels. From the spatial harmonics, a matrix such as equation (8) or the planar projection of equation (17) is formed and the speaker feeds calculated.
  • the 3D harmonics are derived from D ⁇ using all four channels to form the matrix of equation (17) and calculate the speaker feeds.

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Claims (28)

  1. Procédé de traitement d'un champ acoustique pour la reproduction du champ acoustique sur une gamme de fréquences donnée via un système de son d'ambiance ayant une pluralité d'au moins quatre canaux (S1' à S4') alimentant individuellement l'un d'au moins quatre haut-parleurs, comportant :
    l'acquisition de multiples signaux (S1 à S5) du champ acoustique, et
    l'acheminement des signaux de champ acoustique acquis (S1 à S5) dans des canaux individuels de la pluralité de canaux (S1' à S5') avec un ensemble de gains relatifs (21 à 25, 31 à 35, 63 à 78, 87 à 103) pour la gamme de fréquences complète qui est déterminé en résolvant une relation qui (1) inclut des positions sélectionnées des haut-parleurs autour d'une zone d'écoute non limitée à un motif géométrique, coplanaire régulier et (2) préserve sensiblement des harmoniques individuelles parmi une pluralité d'harmoniques spatiales tridimensionnelles du champ acoustique,
    moyennant quoi un champ acoustique reproduit à partir des haut-parleurs placés dans lesdites positions sélectionnées reproduit sensiblement la pluralité d'harmoniques spatiales tridimensionnelles du champ acoustique acquis.
  2. Procédé selon la revendication 1, dans lequel le nombre d'harmoniques spatiales tridimensionnelles qui sont sensiblement préservées, inclut uniquement des harmoniques d'ordre 0 et 1.
  3. Procédé selon la revendication 1, dans lequel le nombre d'harmoniques spatiales tridimensionnelles qui sont sensiblement préservées, inclut des harmoniques d'ordre 0 à n, où n est un entier inférieur ou égal à 1 moins la racine carrée du nombre de haut-parleurs.
  4. Procédé selon la revendication 1, 2 ou 3, dans lequel l'acquisition de multiples signaux du champ acoustique inclut l'acquisition de multiples signaux monophoniques (17, 19) de sons dont on souhaite qu'ils soient situés à des positions spécifiques autour de la zone d'écoute, et ladite relation inclut ces positions spécifiques, moyennant quoi le champ acoustique reproduit à partir des haut-parleurs inclut de plus les sons monophoniques auxdites positions spécifiques.
  5. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'acquisition de multiples signaux du champ acoustique inclut le positionnement de multiples microphones directionnels (121, 123, 125) dans le champ acoustique.
  6. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'ensemble de gains relatifs (21 à 25, 31 à 35, 63 à 78, 87 à 103) est déterminé au moins en partie par la relation qui inclut des positions supposées des haut-parleurs autour d'une certaine zone d'écoute.
  7. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel l'ensemble de gains relatifs (21 à 25, 31 à 35, 63 à 78, 87 à 103) est déterminé au moins en partie à un emplacement adjacent à la zone d'écoute par la relation qui inclut des positions réelles des haut-parleurs autour de la zone d'écoute.
  8. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'ensemble de gains relatifs (21 à 25, 31 à 35, 63 à 78, 87 à 103) est de plus déterminé par ce qui entraîne un alignement sensible des vecteurs de vitesse et de puissance.
  9. Procédé selon l'une quelconque des revendications 1 à 7, dans lequel l'ensemble de gains relatifs (21 à 25, 31 à 35, 63 à 78, 87 à 103) est de plus déterminé par ce qui entraîne une minimisation des harmoniques d'ordre 2 ou supérieur parmi ladite pluralité d'harmoniques spatiales tridimensionnelles.
  10. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel le système de son d'ambiance a exactement six canaux alimentant individuellement un haut-parleur différent parmi exactement six haut-parleurs.
  11. Procédé selon la revendication 10, dans lequel au moins un desdits exactement six haut-parleurs est positionné pour être non coplanaire avec les autres haut-parleurs parmi lesdits exactement six haut-parleurs.
  12. Procédé selon la revendication 1, dans lequel l'ensemble de gains relatifs (63 à 78, 87 à 103) est déterminé en résolvant une relation d'une déclinaison et d'un azimut de la position apparente désirée du son par rapport à un point et un ensemble de positions angulaires s'étendant autour dudit point qui correspondent à des positions attendues de haut-parleurs commandés par des signaux individuels parmi les multiples signaux de canaux, ladite relation étant résolue d'une manière qui préserve sensiblement des harmoniques tridimensionnelles au moins d'ordre 0 et 1 du son lorsqu'il est reproduit par des haut-parleurs aux positions attendues comme si le son monophonique était effectivement présent dans ladite position apparente.
  13. Procédé selon la revendication 12, dans lequel des haut-parleurs sont réellement positionnés avec au moins un desdits haut-parleurs ayant une position réelle différente de celle des positions attendues, et comportant de plus le calcul d'un ensemble modifié de gains relatifs (63 à 78, 87 à 103) pour commander les haut-parleurs en résolvant une seconde relation incluant les positions réelles des haut-parleurs et d'une manière qui préserve des valeurs individuelles d'harmoniques tridimensionnelles au moins d'ordre 0 et 1 du son lorsqu'il est reproduit par des haut-parleurs aux positions réelles comme si le son monophonique était réellement présent dans ladite position apparente.
  14. Procédé selon la revendication 12 ou 13, dans lequel l'ensemble de gains relatifs (63 à 78, 87 à 103) est de plus déterminé par ce qui entraîne un alignement sensible des vecteurs de vitesse et de puissance d'un champ acoustique reproduit par les haut-parleurs.
  15. Procédé selon la revendication 12 ou 13, dans lequel l'ensemble de gains relatifs (63 à 78, 87 à 103) est de plus déterminé par ce qui entraîne une minimisation des harmoniques spatiales tridimensionnelles d'ordre 2 et supérieur d'un champ acoustique reproduit par les haut-parleurs.
  16. Procédé selon la revendication 12 ou 13, dans lequel le nombre de canaux est d'exactement six.
  17. Procédé selon la revendication 15, dans lequel au moins une des positions attendues des haut-parleurs est non coplanaire avec les autres positions parmi les positions attendues des haut-parleurs.
  18. Procédé selon la revendication 1, dans lequel ledit acheminement des signaux de champ acoustique acquis dans des canaux individuels parmi la pluralité de canaux comporte le traitement de ladite pluralité de signaux électriques de manière à générer des signaux d'harmoniques spatiales tridimensionnelles au moins d'ordre 0 et 1 dudit champ acoustique, et le traitement des signaux d'harmoniques spatiales tridimensionnelles de manière à déterminer des gains relatifs (63 à 78, 87 à 103) de signaux acheminés jusqu'aux haut-parleurs individuels en résolvant une relation qui inclut des termes de positions réelles des haut-parleurs et, une fois résolue, préserve sensiblement les harmoniques tridimensionnelles au moins d'ordre 0 et 1 du champ acoustique reproduit par les haut-parleurs lorsqu'elles correspondent respectivement aux harmoniques tridimensionnelles d'ordre 0 et 1 du champs acoustique acquis.
  19. Procédé selon la revendication 18, lequel comporte de plus l'enregistrement et la lecture de la pluralité de signaux électriques représentatifs du champ acoustique.
  20. Procédé selon la revendication 18, lequel comporte de plus l'enregistrement et la lecture des signaux des harmoniques de champ acoustique.
  21. Procédé selon l'une quelconque des revendications 18 à 20, dans lequel le champ acoustique est reproduit par exactement six haut-parleurs.
  22. Procédé selon la revendication 19, dans lequel au moins un desdits exactement six haut-parleurs est positionné pour être non coplanaire avec les autres haut-parleurs parmi lesdits exactement six haut-parleurs.
  23. Système acoustique ayant une entrée pour recevoir des signaux audio (17, 19) d'un champ acoustique tridimensionnel d'origine, et une sortie (S1' à S5') pour commander au moins quatre haut-parleurs dans certaines positions réelles entourant une zone d'écoute, dans lequel les positions réelles ne sont pas limitées à un motif géométrique, coplanaire régulier, pour reproduire le champ acoustique, comportant :
    une entrée (61) qui accepte des informations des positions réelles des haut-parleurs, et
    une matrice mise en oeuvre électroniquement (S3) sensible à des informations appliquées en entrée du haut-parleur réel et des signaux d'entrée pour fournir des signaux (S1' à S5') aux sorties qui commandent les haut-parleurs pour reproduire le champ acoustique avec un nombre d'harmoniques spatiales tridimensionnelles qui correspondent individuellement à des harmoniques sensiblement correspondantes du même nombre d'harmoniques spatiales tridimensionnelles dans le champ acoustique d'origine.
  24. Système acoustique selon la revendication 23, dans lequel les signaux audio comportent au moins quatre signaux audio (S1 à S5) et dans lequel les informations des positions réelles de haut-parleurs incluent la déclinaison et l'azimut.
  25. Système acoustique selon la revendication 23 ou 24, dans lequel la matrice inclut en outre :
    une première partie (51) qui développe, à partir des informations sur les positions supposées des haut-parleurs et des signaux d'entrée, des signaux individuels correspondant au nombre d'harmoniques spatiales tridimensionnelles, et
    une seconde partie (S3) qui développe, à partir des signaux d'harmoniques spatiales tridimensionnelles et des informations sur les positions réelles des haut-parleurs, des signaux individuels (S1' à S5') pour les haut-parleurs réels.
  26. Système acoustique selon l'une quelconque des revendications 23 à 25, dans lequel le nombre d'harmoniques spatiales tridimensionnelles mises en correspondance inclut des harmoniques d'ordre 0 et 1.
  27. Système acoustique selon l'une quelconque des revendications 23 à 25, dans lequel le nombre d'harmoniques spatiales tridimensionnelles mises en correspondance inclut uniquement des harmoniques d'ordre 0 et 1.
  28. Système acoustique selon l'une quelconque des revendications 23 à 25, dans lequel le nombre de haut-parleurs dans les positions réelles de haut-parleurs inclut exactement six.
EP00970687A 2000-04-19 2000-10-06 Prise de son ambiant multi-canal et techniques de reproduction qui preservent les harmoniques spatiales en trois dimensions Expired - Lifetime EP1275272B1 (fr)

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US09/552,378 US6904152B1 (en) 1997-09-24 2000-04-19 Multi-channel surround sound mastering and reproduction techniques that preserve spatial harmonics in three dimensions
PCT/US2000/027851 WO2001082651A1 (fr) 2000-04-19 2000-10-06 Prise de son ambiant multi-canal et techniques de reproduction qui preservent les harmoniques spatiales en trois dimensions

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