Audio filter bank with decorrelation components

Abstract

A multiple-input, multiple-output audio processing is implemented as a linear system for use in an audio filter bank to convert a set of frequency domain input audio signals to a set of frequency domain output audio signals. A transfer function from one input to one output is defined as a frequency dependent gain function. In some implementations, the transfer function includes a direct component substantially defined as a frequency dependent gain and one or more decorrelated components having a frequency varying group phase response. The transfer function is formed by a set of sub-band functions, wherein each sub-band function is formed by a corresponding set of component transfer functions including a direct component and one or more decorrelated components.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is a divisional application of the invention patent application with application number 202080061556.5, application date September 2, 2020, and invention name “Audio filter group with decorrelation component”. The invention patent application claims priority to U.S. Provisional Patent Application No. 62 / 895,096 filed on September 3, 2019. The invention patent application and the U.S. Provisional Patent Application are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates generally to audio signal processing, and more particularly to audio signal processing that processes a set of one or more frequency-domain input audio signals to create a new set of one or more frequency-domain output audio signals. Background Art

[0004] In audio signal processing, a set of input audio signals is often converted into a new set of output audio signals, where the number of output audio signals can be the same as or greater than the number of input audio signals. For example, a surround sound system can convert two input audio signals (e.g., stereo audio signals) into five output audio signals using linear matrix operations. Linear matrix operations apply a matrix containing coefficients that can vary over time or frequency to the input audio signals. When the input audio signals have been subjected to a decorrelation process, linear matrix operations can also determine the covariance of the output audio signals. Summary of the Invention

[0005] A multi-input, multi-output audio process is implemented as a linear system for use in an audio filter bank to convert a set of frequency-domain input audio signals into a set of frequency-domain output audio signals. A transfer function from one input to one output is defined as a frequency-dependent gain function. In some implementations, the transfer function comprises a direct component, substantially defined as a frequency-dependent gain, and one or more decorrelated components having a frequency-varying group phase response. The transfer function is formed from a set of subband functions, where each subband function is formed from a set of corresponding component transfer functions comprising the direct component and one or more decorrelated components.

[0006] In some implementations, a method of converting a set of frequency-domain input audio signals into a set of frequency-domain output audio signals includes: calculating, using one or more processors, each frequency-domain output audio signal as a sum of filtered frequency-domain input audio signals, wherein each filter used to filter the frequency-domain input audio signal is characterized by a complex gain function over a corresponding sub-band frequency range of the frequency-domain input audio signal, wherein a contribution of the frequency-domain input audio signal to the frequency-domain output audio signal is determined by a composite frequency-domain gain vector, and the composite frequency-domain gain vector is obtained by: calculating, using the one or more processors, a set of component frequency-domain gain vectors, wherein at least one of the component frequency-domain gain vectors is a decorrelated component frequency-domain gain vector formed by enhancing the component frequency-domain gain vector with an additional component frequency-domain gain vector having a modified frequency response to create a decorrelation effect; and summing the component frequency-domain gain vectors using the one or more processors to form the composite frequency-domain gain vector.

[0007] In some implementations, the decorrelated component frequency-domain gain vector is formed by scaling the at least one of the component frequency-domain vectors by a component gain value.

[0008] In some implementations, one or more of the component frequency-domain gain vectors includes a phase response that varies over a sub-band frequency range, thereby providing a group delay that is substantially constant across the sub-band frequencies, and wherein the group delay is substantially constant if fluctuations in the group delay are sufficiently small to be not perceptually noticeable to a listener.

[0009] In some implementations, one or more of the component frequency-domain gain vectors includes a phase response that varies within the sub-band frequency range, thereby providing a group delay that varies within the sub-band frequency range to provide a decorrelation effect.

[0010] In some implementations, the decorrelated component frequency-domain gain vector is formed by multiplying the component frequency-domain gain vector by a decorrelation function.

[0011] In some implementations, an audio filter bank with decorrelated components includes: a converter configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals; and a linear mixer configured to convert the set of frequency-domain input audio signals into a set of frequency-domain output audio signals, wherein each frequency-domain output audio signal is a sum of filtered frequency-domain input audio signals, wherein each filter used to filter the frequency-domain input audio signal is characterized by a complex gain function over a corresponding sub-band frequency range of the frequency-domain input audio signal, and a contribution of the frequency-domain input audio signal to the frequency-domain output audio signal is determined by a complex frequency-domain gain vector.

[0012] In some implementations, the composite frequency-domain gain vector is obtained by: calculating a set of component frequency-domain gain vectors, wherein at least one of the component frequency-domain gain vectors is a decorrelated component frequency-domain gain vector formed by enhancing the component frequency-domain gain vector with an additional component frequency-domain gain vector having a modified frequency response to create a decorrelation effect on the frequency-domain output audio signal; and summing the component frequency-domain gain vectors to form the composite frequency-domain gain vector.

[0013] In some implementations, the decorrelated component frequency-domain gain vector is formed by scaling the at least one of the component frequency-domain vectors by a component gain value.

[0014] In some implementations, one or more of the component frequency-domain gain vectors includes a phase response that varies over a sub-band frequency range, thereby providing a group delay that is substantially constant across the sub-band frequencies, and wherein the group delay is substantially constant if fluctuations in the group delay are sufficiently small to be not perceptually noticeable to a listener.

[0015] In some implementations, one or more of the component frequency-domain gain vectors includes a phase response that varies within the sub-band frequency range, thereby providing a group delay that varies within the sub-band frequency range to provide a decorrelation effect on the frequency-domain output audio signal.

[0016] In some implementations, the decorrelated component frequency-domain gain vector is formed by multiplying the component frequency-domain gain vector by a decorrelation function.

[0017] In some implementations, a filter bank-based audio system includes: a converter configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals; and a linear mixer configured to convert the set of frequency-domain input signals into a set of frequency-domain output signals, wherein the linear mixer includes weighting coefficients that provide a frequency-dependent gain function, the frequency-dependent gain function including a direct component defined as a frequency-dependent gain and one or more decorrelated components having a frequency-varying group phase response, and wherein the frequency-dependent gain is formed by a set of sub-band functions, wherein each sub-band function is formed by a set of corresponding component transfer functions including the direct component and the one or more decorrelated components.

[0018] Other implementations disclosed herein relate to systems, devices, and computer-readable media. Details of the disclosed implementations are set forth in the following drawings and description. Other features, objectives, and advantages will become apparent from the description, drawings, and claims.

[0019] Certain embodiments disclosed herein provide one or more of the following advantages: The disclosed implementation integrates decorrelation processing into an audio filter bank, thereby allowing the use of a single linear mixer to map an input audio signal to an output audio signal, resulting in lower latency compared to conventional audio filter banks that use multiple linear mixers to perform decorrelation processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the accompanying drawings, for ease of description, a specific configuration or order of schematic elements, such as those representing devices, units, instruction blocks, and data elements, is shown. However, those skilled in the art will appreciate that the specific order or configuration of schematic elements in the accompanying drawings is not intended to imply a specific processing order or sequence, or separate processing. Furthermore, the inclusion of a schematic component in a figure is not intended to imply that such element is required in all embodiments, or that in some implementations, the features represented by such element may not be included in or combined with other elements.

[0021] In addition, in the accompanying drawings, when connecting elements such as solid or dashed lines or arrows are used to illustrate a connection, relationship, or association between or among two or more other schematic elements, the absence of any such connecting element is not intended to imply that any connection, relationship, or association may not exist. In other words, some connections, relationships, or associations between elements are not shown in the accompanying drawings to avoid obscuring the present invention. In addition, for ease of illustration, a single connecting element is used to represent multiple connections, relationships, or associations between elements. For example, when a connecting element represents the communication of signals, data, or instructions, those skilled in the art will understand that this element represents one or more signal paths that may be required to achieve the communication.

[0022] Figure 1 Filtering a set of input audio signals using a filter array to produce a set of audio output signals is shown in accordance with one or more embodiments.

[0023] Figure 2 Desired frequency response curves according to one or more embodiments are shown.

[0024] Figure 3 A set of filter bank frequency responses is shown in accordance with one or more embodiments.

[0025] Figure 4 Shown are bandpass responses of typical component frequency-domain gain vectors in accordance with one or more embodiments.

[0026] Figure 5 The frequency response of a sub-band filter having a group delay that varies significantly with frequency is shown in accordance with one or more embodiments.

[0027] Figure 6A known method for mixing input signals using a direct mixing matrix and one or more decorrelating mixing matrices to create an output signal is shown in accordance with one or more embodiments.

[0028] Figure 7 is a flow chart of an exemplary process for converting a set of frequency-domain input audio signals into a set of frequency-domain output audio signals in accordance with one or more embodiments.

[0029] Figure 8 FIGURE 1 illustrates a method suitable for implementing a reference according to one or more embodiments. Figures 1 to 7 A block diagram of a system that describes the features and processes.

[0030] The same reference numbers used in the various drawings indicate similar elements. DETAILED DESCRIPTION

[0031] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the various described embodiments. Those skilled in the art will appreciate that the various described embodiments can be practiced without these specific details. In other instances, well-known methods, processes, components, and circuits have not been described in detail to avoid unnecessarily obscuring aspects of the embodiments. Several features are described below, each of which can be used independently of one another or in any combination with other features.

[0032] Nomenclature

[0033] As used herein, the term "including" and its variations will be interpreted as open-ended terms meaning "including, but not limited to." The term "or" will be interpreted as "and / or," unless the context clearly indicates otherwise. The term "based on" will be interpreted as "based at least in part on." The terms "an example implementation" and "example implementation" should be interpreted as "at least one example implementation." The term "another implementation" will be interpreted as "at least one other implementation." The terms "determined" and "determine" will be interpreted as obtaining, receiving, calculating, computing, estimating, predicting, or deriving. In addition, in the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0034] Systematic review

[0035] Figure 1A linear hybrid system 100 is shown in accordance with one or more embodiments, wherein a set of input audio signals is filtered to produce a set of audio output signals. System 100 may be implemented, for example, in an audio filter bank. The audio filter bank comprises an array of bandpass filters that separate the input audio signal into a plurality of frequency sub-bands of the input audio signal. In the example shown, linear hybrid system 100 comprises a set of filters 101 and a summer 102. N input signals (X1 ... X N ) are processed by the filter bank 101 and summed by the summer 102 to produce M output signals (Y1 . . . Y M ). The linear hybrid system 100 can be defined in terms of frequency domain input and frequency domain output signals as follows:

[0036]

[0037] According to formula [3], the frequency domain output audio signal Y m (f)(m∈[1…M]) is formed as the filtered frequency domain input audio signal X n (f) where the frequency domain input audio signal X n (f)(n∈[1…N]) for Y m The contribution of (f) is given by the composite frequency domain vector G according to the following formula m,n (f) determine:

[0038]

[0039] For the purposes of the following discussion, G(f) will be referred to as an exemplary composite frequency-domain gain vector, and this term should be understood to refer to the composite frequency-domain gain vector G used in equations [3] and [4]. m,n Any of (f).

[0040] Figure 2 , which is a graph showing the expected frequency response of a filter according to one or more embodiments. The expected frequency response of an exemplary composite frequency domain gain vector may be generated by a process of creating a smoothing function, such as Figure 2 As shown, the filter gain 20 as a function of frequency is defined according to a predefined set of control frequencies fc1, fc2, ... and corresponding component gain values w1, w2, ... For example, the gain 21 of the filter at frequency fc2 is set by the component gain value w2, as shown in FIG. Figure 2 As displayed. Figure 2 The frequency response shown in is achieved by a weighted sum of several predefined component frequency domain gain vectors.

[0041] Figure 3 1 shows a set of filter bank frequency responses according to one or more embodiments, wherein the response 300H of reference frequency band 2 is shown. 0,2(f). The frequency responses of these predefined component frequency domain gain vectors are hereinafter referred to as component frequency domain gain vectors H 0,b (f), b∈[1…B], where B is the number of frequency bands (e.g., in Figure 3 In the example of , B = 5), and each of the component frequency domain gain vectors has a time domain impulse response h 0,b (n) An alternative representation of the form

[0042] In an embodiment, the desired filter response (see Figure 2 ) can be formed by a weighted sum of the predefined filter bank responses. This can be expressed as a time domain or frequency domain summation:

[0043]

[0044] In some implementations, the set of component frequency-domain gain vectors is modified with an additional component frequency-domain gain vector H whose frequency response is modified to create a decorrelation effect. 0,b (f) Enhancement. The amplified component frequency domain gain vector group is referred to as the decorrelated component frequency domain gain vector in the following text, which is represented by the following nomenclature:

[0045] H l,b (f)b∈[1…B],l∈[0…L]. [6]

[0046] where B is the number of subbands and L is the number of decorrelation functions.

[0047] This enhanced set of component frequency-domain gain vectors can be used in a filterbank-based audio processing system to generate a composite frequency-domain gain vector by applying a modified form of Equation [5] as shown in Equation [7]:

[0048]

[0049] Figure 4 ] shows the bandpass response of a typical component frequency domain gain vector according to one or more embodiments. In the example shown, the component frequency domain gain vector H 0,b (f) has an amplitude response 401 that is generally dominant within a particular sub-band of the overall frequency range, and a group delay 402 that is substantially constant within the sub-band. When the filter is used to process an audio signal, the group delay is considered to be substantially constant if fluctuations in the group delay are small enough to be perceptually unnoticeable to a listener.

[0050] Figure 5 The frequency response of the sub-band filter with a group delay that varies significantly with frequency according to one or more embodiments is shown. The frequency response of the decorrelated component frequency domain gain vector (such as H l,b(f)(l≠0)) exhibits a group delay 502 that varies within the sub-band frequency range, and wherein the variation in group delay is such that the frequency domain gain vector H is de-correlated with the component l,b The input audio signal filtered by (f)(l≠0) is perceived as being equal to the input audio signal filtered by the component frequency domain gain vector H 0,b (f) Decorrelation of the filtered input audio signal.

[0051] It is known in the art how to create a frequency response with a varying group delay that varies over a wide frequency range for the purpose of creating a perceptual decorrelation effect. In one embodiment, the known decorrelation frequency response can be adjusted by applying the magnitude response 501 to form a decorrelation component frequency domain gain vector. In one embodiment, the known decorrelation function D l (f)(l∈[1…L]) is used to calculate a set of B decorrelated component frequency domain gain vectors:

[0052] H l,b (f) = D l x H 0,b (f)(b∈[1…B]). [8]

[0053] Figure 6 A system 600 is shown for mixing input signals to produce output signals using a direct mixing matrix and one or more decorrelating mixing matrices according to one or more embodiments. l (f)(l∈[1…L]), an N-channel input signal (X) is processed by system 600 to produce an M-channel output signal (Y). In this example, processing for one sub-band (e.g., band b) is shown, where an N-channel input 601 (X) is applied to a direct linear mixing matrix 602 (C) (e.g., an M×N matrix) to produce an M-channel direct signal 603. The N-channel input 601 is also processed by a linear mixer 610 (Q l )(For example, K L ×N matrix) to generate a set of K L Channel 611, which passes K L A decorrelation filter 612 (D l ) of a group, each decorrelation filter applies a frequency response D L (f) to produce K L Channel signal 613, K L The channel signal 613 is then mixed by a linear mixer 614 (P l )(For example, M×K L The M-channel direct signal 603 is remixed with the M-channel decorrelated component signal (e.g., decorrelated component signal (615)) to generate an M-channel output 602 (Y).

[0054] In this embodiment, by using a single set of weighting coefficients Replace the linear mixing matrix C, Q1...Q L and P1…P L The function is implemented Figure 6 According to one embodiment, and referring back to equation [4], the output channel Y m (f) may be generated by:

[0055]

[0056] Equation [9] can be implemented in a filter bank based audio processing system, where the number of filters is (L+1) x B, rather than the B filters used in the art. This expanded filter bank can be further viewed as the B filters known previously, with the addition of L x B filters corresponding to L different decorrelation functions.

[0057] In some embodiments, Equation [9] is implemented as an audio filter bank configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals X n (f) a converter (e.g., a fast Fourier transform), and a configuration to implement To input the set of frequency domain audio signals X n (f) Converted into a set of frequency domain output audio signals Y m (f) A linear mixer (performing a matrix multiplication operation) is provided. Each frequency-domain output audio signal is a sum of filtered frequency-domain input audio signals, and each filter used to filter the frequency-domain input audio signal is characterized by a complex gain function within a frequency range of a corresponding sub-band of the frequency-domain input audio signal. The contribution of the frequency-domain input audio signal to the frequency-domain output audio signal is determined by a complex frequency-domain gain vector.

[0058] In some embodiments, Equation [9] is implemented as an audio filter bank system comprising a filter configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals X n (f) a converter (e.g., a fast Fourier transform), and a configuration for implementing To input the set of frequency domain audio signals X n (f) Converted into a set of frequency domain output audio signals Y m (f) Linear mixer (software and hardware for performing sum of products). The linear mixer includes weighting coefficients (elements G) that provide a frequency-dependent gain function. m,n(f)), the frequency-dependent gain function comprises a direct component defined as a frequency-dependent gain and one or more decorrelated components having a frequency-varying group phase response. The frequency-dependent gain is formed by a set of subband functions, wherein each subband function is formed by a set of corresponding component transfer functions comprising a direct component and one or more decorrelated components.

[0059] Example Process

[0060] Figure 7 is a flow chart of an exemplary process 700 for converting a set of frequency domain input audio signals into a set of frequency domain output audio signals according to one or more embodiments. Figure 8 The system 800 described is implemented.

[0061] The process 700 calculates each frequency-domain output audio signal as the sum of filtered frequency-domain input audio signals, each filtered frequency-domain input audio signal defining a complex gain function over a corresponding sub-band frequency range, wherein the contribution of the frequency-domain input audio signal to the frequency-domain output audio signal is determined by a complex frequency-domain gain vector (701).

[0062] Process 700 continues by obtaining a composite frequency-domain gain vector by calculating a set of component frequency-domain gain vectors (702). At least one of the component frequency-domain gain vectors is a decorrelated component frequency-domain gain vector formed by enhancing a component frequency-domain gain vector with an additional component frequency-domain gain vector having a modified frequency response to create a decorrelation effect.

[0063] Process 700 continues by summing the component frequency-domain gain vectors to form a composite frequency-domain gain vector ( 703 ).

[0064] Example system architecture

[0065] Figure 8 A block diagram illustrates an example system 800 suitable for implementing embodiments of the present disclosure. System 800 includes one or more server computers or any client device, including, but not limited to, call servers, user equipment, conference room systems, home theater systems, virtual reality (VR) devices, and immersive content ingestion devices. System 800 also includes any consumer device, including, but not limited to, smartphones, tablets, wearable computers, in-vehicle computers, gaming consoles, surround sound systems, kiosks, and the like.

[0066] As shown in the figure, the system 800 includes a central processing unit (CPU) 801, which is capable of executing various processes according to a program stored in, for example, a read-only memory (ROM) 802 or a program loaded from, for example, a storage unit 808 to a random access memory (RAM) 803. The RAM 803 also stores data required when the CPU 801 executes various processes, as needed. The CPU 801, ROM 802, and RAM 803 are connected to each other via a bus 804. An input / output (I / O) interface 805 is also connected to the bus 804.

[0067] The following components are connected to the I / O interface 805: an input unit 806, which may include a keyboard, a mouse, or the like; an output unit 807, which may include a display such as a liquid crystal display (LCD) and one or more speakers; a storage unit 808, which includes a hard disk or another suitable storage device; and a communication unit 809, which includes a network interface, such as a network card (e.g., wired or wireless).

[0068] In some implementations, input unit 806 includes one or more microphones at different locations (depending on the host device) capable of acquiring audio signals in various formats (eg, mono, stereo, spatial, immersive, and other suitable formats).

[0069] In some implementations, the output unit 807 includes a system with various numbers of speakers. The output unit 807 (depending on the capabilities of the host device) can present audio signals in various formats (e.g., mono, stereo, immersive, binaural, and other suitable formats).

[0070] The communication unit 809 is configured to communicate with other devices (e.g., via a network). The drive 810 is also connected to the I / O interface 805 as needed. A removable medium 811 (e.g., a magnetic disk, an optical disk, a magneto-optical disk, a flash drive, or another suitable removable medium) is mounted on the drive 810 so that a computer program read therefrom can be installed into the storage unit 808 as needed. Those skilled in the art will understand that although the system 800 is described as including the above components, in actual applications, some of these components may be added, removed, and / or replaced, and all such modifications or changes fall within the scope of the present disclosure.

[0071] According to exemplary embodiments of the present disclosure, the processes described above may be implemented as a computer software program or on a computer-readable storage medium. For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program comprising program code for executing the method. In such an embodiment, the computer program may be downloaded and installed from a network via the communication unit 809, and / or installed from a removable medium 811, such as in Figure 8 As shown in .

[0072] In general, various exemplary embodiments of the present invention may be implemented in hardware or dedicated circuits (e.g., control circuits), software, logic, or any combination thereof. For example, the units discussed above may be implemented by control circuits (e.g., Figure 8 The present disclosure may be executed by a CPU (in combination with other components of the present disclosure), and thus, the control circuitry may perform the actions described in the present disclosure. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device (e.g., control circuitry). Although various aspects of the exemplary embodiments of the present disclosure are shown and described as block diagrams, flow charts, or using some other graphical representations to illustrate and describe, it should be understood that, as non-limiting examples, the blocks, devices, systems, techniques, or methods described herein may be implemented in hardware, software, firmware, dedicated circuitry or logic, general-purpose hardware or controllers, or other computing devices, or some combination thereof.

[0073] In addition, the various blocks shown in the flowcharts may be viewed as method steps, and / or operations resulting from the operation of computer program code, and / or a plurality of coupled logic circuit elements configured to perform the associated one or more functions. For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program containing program code configured to perform the method described above.

[0074] In the context of this disclosure, a machine / computer readable medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device. A machine / computer readable medium may be a machine / computer readable signal medium or a machine / computer readable storage medium. A machine / computer readable medium may be non-transitory and may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of machine / computer readable storage media would include: an electrical connection having one or more conductors; a portable computer disk; a hard disk; RAM; ROM; an erasable programmable read-only memory (EPROM or flash memory); optical fiber; a portable compact disc read-only memory (CD-ROM); an optical storage device; a magnetic storage device; or any suitable combination of the foregoing.

[0075] Any combination of one or more programming languages can be used to write a computer program code for performing the disclosed method. Such computer program codes can be provided to a general-purpose computer, a special-purpose computer, or a processor of other programmable data processing devices with a control circuit so that when executed by the processor of a computer or other programmable data processing device, the program code enables the function / operation specified in the flow chart and / or block diagram to be realized. The program code can be executed entirely on a computer, partially on a computer (as an independent software package), partially on a computer and partially on a remote computer, or entirely on a remote computer or server or dispersed across one or more remote computers and / or servers.

[0076] Although this document contains many specific implementation details, these details should not be considered as limitations on the scope of the claims, but rather as descriptions of features specific to a particular embodiment. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable subcombination. In addition, although features may be described above as working in a particular combination, or even initially claimed as such, in some cases, one or more features from the claimed combination may be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination. The logical flow depicted in the accompanying drawings does not necessarily require the specific order or sequential order shown to achieve the desired result. In addition, other steps may be provided, or steps may be eliminated from the described process, and other components may be added to or removed from the described system. Therefore, other embodiments are also within the scope of the following claims.

Claims

1. An audio filter bank having decorrelated components, comprising: a converter configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals; and a linear mixer configured to convert the set of frequency-domain input audio signals into a set of frequency-domain output audio signals, wherein each frequency-domain output audio signal is a combination of filtered frequency-domain input audio signals, wherein each filter for filtering the frequency-domain input audio signals is characterized by a complex gain function over a corresponding sub-band frequency range of the frequency-domain input audio signals, and wherein a contribution of the frequency-domain input audio signals to the frequency-domain output audio signals is determined by a complex frequency-domain gain vector, wherein the complex frequency-domain gain vector is obtained by the following operations: computing a set of component frequency-domain gain vectors, wherein at least one of the component frequency-domain gain vectors is a decorrelated component frequency-domain gain vector formed by augmenting the component frequency-domain gain vector with an additional component frequency-domain gain vector having a modified frequency response to create a decorrelation effect; and The component frequency-domain gain vectors are summed to form the composite frequency-domain gain vector.

2. The audio filterbank of claim 1, wherein the decorrelated component frequency-domain gain vector is formed by scaling the at least one of the component frequency-domain vectors by a component gain value.

3. An audio filter bank as described in any of claims 1-2, wherein one or more of the component frequency-domain gain vectors includes a phase response that varies within a sub-band frequency range, thereby providing a group delay that is substantially constant across the sub-band frequencies, and wherein the group delay is substantially constant if fluctuations in the group delay are sufficiently small to be perceptually unnoticeable to a listener.

4. An audio filter bank as claimed in any one of claims 1 to 3, wherein one or more of the component frequency-domain gain vectors comprises a phase response that varies within the sub-band frequency range, thereby providing a group delay that varies within the sub-band frequency range to provide a decorrelation effect on the frequency-domain output audio signal.

5. The audio filter bank of any one of claims 1 to 4, wherein the decorrelated component frequency-domain gain vector is formed by multiplying the component frequency-domain gain vector by a decorrelation function.

6. A filter bank-based audio system comprising: a converter configured to convert a set of time-domain input audio signals into a set of frequency-domain input audio signals; and A linear mixer configured to convert the set of frequency-domain input signals into a set of frequency-domain output signals, wherein the linear mixer includes weighting coefficients that provide a frequency-dependent gain function, the frequency-dependent gain function including a direct component defined as a frequency-dependent gain and one or more decorrelated components having a frequency-varying group phase response, and wherein the frequency-dependent gain is formed by a set of sub-band functions, wherein each sub-band function is formed by a set of corresponding component transfer functions including the direct component and the one or more decorrelated components.

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