Classifications

• • 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
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K15/00—Acoustics not otherwise provided for
  • G10K15/08—Arrangements for producing a reverberation or echo sound
  • G10K15/12—Arrangements for producing a reverberation or echo sound using electronic time-delay networks
• • 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

• the present invention provides for systems and methods for the input of an audio soundfield signal and the creation of a reverberant acoustic equivalent soundfield signal.
• Multi-channel audio signals are used to store or transport a listening experience, for an end listener, that may include the impression of a very complex acoustic scene.
• the multi-channel signals may carry the information that describes the acoustic scene using a number of common conventions including, but not limited to, the following:
• Discrete Speaker Channels The audio scene may have been rendered in some way, to form speaker channels which, when played back on the appropriate arrangement of loudspeakers, create the illusion of the desired acoustic scene.
• Examples of Discrete Speaker Formats include stereo, 5.1 or 7.1 speaker signals, as used in many sound formats today.
• the audio scene may be represented as one or more object audio channels which, when rendered by the listener's playback equipment, can re-create the acoustic scene.
• each audio object will be accompanied by metadata (implicit or explicit) that is used by the renderer to pan the object to the appropriate "location" in the listener's playback environment.
• Audio Object Formats include Dolby Atmos (Trade Mark), which is used in the carriage of rich sound-tracks on Blu-Ray Disc and other motion picture delivery formats.
• the audio scene may be represented by a Soundfield Format - a set of two or more audio signals that collectively contain one or more audio objects with the spatial location of each object "encoded" in the Spatial Format in the form of panning gains.
• Soundfield Formats include Ambisonics, and Higher Order Ambisonics (both of which are well known in the art). Example systems are described in Gerzon, M.A., Periphony: With-Height Sound Reproduction. J. Audio Eng. Soc, 1973. 21(1): p. 2-10, and 3D Sound Field Recording with Higher Order Ambisonics-Objective Measurements and Validation of Spherical Microphone S Bertet, J Daniel, S Moreau - Audio Engineering Society Convention 120, 2006
• a method for creating an output soundfield signal from an input soundfield signal including the steps of: (a) forming at least one delayed signals from the input soundfield signal, (b) for each of the delayed signals, creating an acoustically transformed delayed signal, by an acoustic transformation process, and (c) combining together the acoustically transformed delayed signals and the input soundfield signal to produce the output soundfield signal
• the acoustic transformation process utilises a multi-channel matrix mixer.
• the multi-channel matrix mixer can be formed by combining one or more spatial operations, including a spatial rotation operation.
• the multi-channel matrix mixer can be formed by combining one or more spatial operations, including a spatial mirror operation.
• the multi-channel matrix mixer can be formed by combining one or more spatial operations, including a directional gain operation.
• the multi-channel matrix mixer can be formed by combining one or more spatial operations, including a directional permutation operation.
• the acoustic transformation process preferably can include frequency-dependant filtering.
• each simulated echo can comprise a delayed and rotated copy of the input sound field signal.
• each simulated echo preferably can include substantially the same delay.
• the alternative direction of arrival can comprise a geometric transformation of the first direction of arrival.
• a system for processing of soundfield signals to simulate the presence of reverberance including: an input unit for the input of a soundfield encoded signal; a tapped delay line for interconnected to the input unit and providing a series of tapped delays of the soundfield encoded signal; a series of acoustic transformation units interconnected to the output taps of the tapped delay line, for applying an acoustic transformation to the output taps to produce transformed delayed outputs; and a combining unit for combining the transformed delayed outputs into an output soundfield signal.
• the acoustic transformation units can include: a multi channel matrix multiplier for applying a geometric transformation to an output tap to produce a geometric transformed output; and a series of linear audio filters applied to each channel of the geometric transformed output.
• Fig. 1 illustrates schematically an audio object, at direction ⁇ /) m , and an echo at direction ⁇ ' .
• Fig. 2 is a schematic block diagram of a tapped delay line.
• Fig. 3 is a schematic block diagram of an echo processor.
• Fig. 4 is a schematic block diagram of an echo processor with direction-dependant filtering.
• Fig. 5 illustrates an alternative form of an echo processor.
• the preferred embodiments provide for a system and method which, given that an input soundfield signal contains audio components that are encoded with different directions of arrival, produces an output soundfield signal that will contain simulated echoes, such that each simulated echo will have a direction of arrival that is a function of the direction of arrival of the original audio component as it appeared in the input signal.
• the output soundfield signal thereby provides for reverberance and other simulated audio effects.
• N -channel Soundfield Format is often defined by it's panning function, P N (0) .
• G— ⁇ ⁇ ( ⁇ ) where G is an [N X l] column vector of gain values, and defines the spatial location of the object, i.e:
• a set of M objects (represented by the M audio signals ⁇ ⁇ ) , o 2 (t) , ⁇ , o M (t) ) can be encoded into a N -channel Spatial Format signal X N (t) as per Equation 2 below (where object m is "located" at the position defined by (f ) m )
• the signal X N (t) can be referred to as an Anechoic Mixture of the audio objects.
• any sound emitted by the audio object will reach the listener via multiple paths.
• This phenomenon is well known in the art, and the resulting sound, received at the listening position, is said to be reverberant.
• the number of acoustic paths, formed by the propagation of sound from the object and reflected off acoustic surfaces to reach the listener, may be infinite, but a reasonably close estimate of the sound received at the listening position may be formed by considering a finite number ( E ) of echoes.
• Fig. 2 illustrates an example of reverberance, where the sound from audio object m , 20, is received at the listening position from direction ⁇ ⁇ , along with one echo (echo e ) being received at the listening position from direction ⁇ ⁇ ' e .
• d m e the delay (in samples) of echo e from object m (7)
• Equation 2 shows how an N -channel soundfield signal, X N (t) , may be created by combining M audio objects, based on the assumption that each audio object has a location ( ⁇ ⁇ ) and an audio signal ( o m (t) ). [0036] It is possible to devise a more complex acoustic soundfield signal,
• R N (t) X N (t) + Y N (t) , intended to contain all of the M audio objects, combined together in a way that includes a simulation of an acoustic space (by including E echoes for each object). This is shown in Equation 10 below:
• R N (t) X N (t) + Y N (t) (9)
• the signal Y N (t) can be referred to as the Reverberant Mixture of the audio objects.
• the complete acoustic-simulation is created by summing together the Anechoic Mixture, X N (t) , and the Reverberant Mixture, Y N (t) .
• Equation 10 the terminology [o m ®h me ](t) is used to indicate the convolution of the object audio signal o m (t) with the impulse response h me (t), and hence [ m ®h me ](t— ⁇ ) indicates the convolved signal with an additional delay of d me samples (where F s is the sample frequency).
• Equation 11 may be written in terms of the frequency domain equation in Equation 12 below:
• the N -channel soundfield signal format is defined by the panning function, ⁇ ( ) .
• Equation 14 tells us that, if we wish to apply a 3x3 matrix transformation, A , to the ( , y, z) coordinates of an object location, prior to the computation of the panning function, we can instead achieve this transformation as a 4 x 4 matrix operation, applied to the panning-gain vector, after the computation of the panning function.
• Equation 14 The result shown in in Equation 14 can be applied to Equation 2, in order to manipulate the location of all objects in audio scene, as per Equation 17 below.
• a transformed soundfield signal, X N ' (t) is created from X N (t) , achieving the same result that would have occured if all of the objects had their ( , y, z) locations modified by the 3x3 matrix A .
• Rotation The locations of all objects within a soundfield can be rotated around the listening position.
• the manipulation of the (x, y, z) coordinates of each object may be defined in terms of a 3x3 matrix, A , and the manipulation of the 4-channel soundfield signal may be carried out according to Equation 17.
• the locations of all objects within a soundfield may be mirrored about a plane that passes through the listening position.
• the manipulation of the (x, y, z) coordinates of each object may be defined in terms of a 3x3 matrix, A , and the manipulation of the 4-channel soundfield signal may be carried out according to Equation 17.
• Dominance A transformation of the 4-channel soundfield signal (known as the Lorentz transformation) may be applied by multiplying the 4 channels of the signal by the following 4 x 4 matrix:
• Echo Time Simplification It will be recalled that the original reverberation calculation (as per Equation 10) treats the reverberation for each object as a series of echoes, wherein for object m, echo e, has a time delay (relative to the direct-path) equal to d m e (so, the echo times are different for each object).
• a delay d k ' is defined to be the arrival time (relative to the direct sound) of echo k, and this delay is the same for every object (and hence, the echo delay, d k ' , is no longer dependant on the object identifier, m ).
• Echo Direction Simplification The original reverberation calculation (as per Equation 10) treats the reverberation for each object as a series of echoes, wherein for object m , echo e has a direction of arrival, ⁇ ⁇ ' e (so, the echo arrival directions are different for each object).
• Fig. 2 shows one method that may be used to achieve this, with the corresponding z - domain transfer function being shown in Equation 18 below:
• the processing chain 100 includes a Delay Line, 3, with K taps (and, in the following explanation, the variable k can be used to refer to a specific tap number, so that k € ⁇ 1 ,2,...,K ⁇ ).
• the input, 2, to the Delay Line 3 is the N -channel input signal, X N (t) .
• an N -channel delayed signal e.g. 5, is taken from the Delay Line, and processed via an acoustic transformation process, 200, to produce an acoustically transformed delayed signal, 6.
• the set of K acoustically transformed delayed signals are added together 7 to produce the output soundfield signal, 8.
• Fig. 3 illustrates one example form of implementation of an Echo Processor 200 which applies an acoustic transformation process.
• the input N -channel delayed signal 5 is processed, to produce the N -channel acoustically transformed delayed signal 6.
• two operations are performed by the acoustic transformation process, a multi-channel matrix mixer (represented by the N N matrix R k ) 11, and a linear time- invariant filter, H k (z) e.g. 12, applied to each of the N channels of the soundfield signal.
• a multi-channel matrix mixer represented by the N N matrix R k
• H k (z) linear time- invariant filter
• the intention of the acoustic transformation process is to create a simulation of the k' h acoustic echo according to the following operating principles: [0074] Echo Delay: The time delay of echo k is defined by use of the Delay Line so that input to the Delay Line 2 (of Fig. 2), is delayed by d k ' samples to give the input 5, to the k' h acoustic transformation process (referring to Figure 2).
• Equation 17 substitution A k in place of A in Equation 17.
• Echo Amplitude and Frequency Response The amplitude and frequency response of echo k are provided by the filter, H k (z) e.g. 12, applied to each of the N channels as per Fig. 3.
• Equation 20 defines the 4 x 4 matrix, BtoA that is the inverse of AtoB .
• R' and R" are arbitrary 3 x 3 rotation matrices.
• Equation 21 Equation 25
• EchoProcess k C k xH h ' xB k (25)
• a processing train for implementing the method of Equation 25 is also shown in Fig. 4, with the matrix processing Bk and Ck being separately implemented 21, 23.
• an acoustic transformation process can be implemented as a 4x4 matrix of arbitrary filter operations 200.
• the methods described above may also be combined with alternative reverberation processes, which may be known in the art, to produce a reverberant mixture that contains some echoes generated according to the above described methods, along with additional echoes and reverberation that are generated by the alternative methods.
• any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter.
• a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.
• exemplary is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment” is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.
• Coupled when used in the claims, should not be interpreted as being limited to direct connections only.
• the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other.
• the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.
• Coupled may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

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• 2016
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