Signal generation system and signal generation method

Abstract

To provide an improved efficient scheme for cross-product high frequency reconstruction (HFR), in which a novel frequency component QΩ+rΩ0 is generated on the basis of existing components Ω and Ω+Ω0.SOLUTION: The present invention performs harmonic transposition of a block scheme, in which the time block of a complex subband sample is processed along with a common phase correction. The superposition of a plurality of corrected samples brings about an effect advantageous for limiting an unnecessary intermodulation product, thereby making it possible to use a coarse frequency resolution and / or a low oversampling degree. The present invention in one embodiment uses a window function that is suitable for combined use with an improved cross-product HFR of the block scheme. The hardware embodiment of the present invention has an analysis filter bank (101), a subband processing unit (102) that is set by control data (104), and a composition filter bank (103).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an audio source coding system that uses a harmonic transposition method for high-frequency reconstruction (HFR) in a digital effects processor, such as an exciter that introduces induced harmonic distortion into the luminance of the processed signal, and a time stretcher or time expander that extends the signal duration while preserving the spectral content. [Background technology]

[0002] In the patent document 1, the concept of transposition is described as a method for constructing high frequency bands from low frequency bands of an audio signal. The use of this concept in audio coding can save a significant bit rate. In the case of an audio coding system based on HFR, a narrow bandwidth signal is fed to a core waveform coder, and the higher frequencies are reconstructed using very low bit rate additional side information (information describing the target spectrum waveform on the decoder side) and transposition. At low bit rates, the bandwidth of the core coding signal is narrow, and it is becoming increasingly important to reconstruct a perceptually pleasant high band. The harmonic transposition disclosed in the patent document 1 works very well for complex music signals in the situation of low cross over frequency. The principle of harmonic transposition or harmonic transposition is to transpose a sine wave of frequency ω to a sine wave of frequency Q. φ The aim is to map or correspond to a sine wave of ω, Q φ>1 is an integer that determines the transposition order. In contrast, HFR based on single sideband modulation (SSB) maps a sine wave of frequency ω to a sine wave of frequency ω+Δω, where Δω is a constant frequency deviation or shift. For low bandwidth core signals, SSB transposition can cause unpleasant ringing artifacts.

[0003] To achieve the best possible audio quality, modern high-quality HFR methods use complex modulation frequency banks with a large degree of oversampling and a very fine frequency resolution to obtain the required audio quality. The fine resolution is necessary to avoid unwanted intermodulation distortions arising from nonlinearities in the synthesis of sine waves. For sufficiently narrow subbands, high-quality methods aim to have at most one sine wave in each subband. A large degree of oversampling in time is necessary to avoid aliasing distortions, and some oversampling in frequency is also necessary to avoid pre-echoes of transient signals. The obvious drawback is that this leads to a very heavy computational burden.

[0004] Another common drawback associated with harmonic transposition becomes apparent in the case of signals with a pronounced periodic structure. Such signals are superpositions of harmonics with frequencies Ω, 2Ω, 3Ω, ..., where Ω is the fundamental frequency. φ In the case of harmonic transposition where φ Ω, 2Q φ Ω, 3Q φ Ω, ... and Q φ >1, they are a part of the complete set of harmonics that you want. From the point of view of the resulting audio quality, the fundamental frequency of the transposition, Q φIt is common to perceive a "ghost" pitch corresponding to Ω. Harmonic transposition often introduces a "metallic" sounding character into the encoded and decoded audio signal.

[0005] In US Pat. No. 6,399,433, which is incorporated by reference in this application, the cross products method is improved to address the problem of ghost pitches occurring in the case of high-quality transposition. A nonlinear subband correction is supplemented with a nonlinear combination of at least two different analysis subbands by transmitting full or partial information about the fundamental frequency values ​​of the dominant harmonic parts of the transposed signal with high fidelity. As a result, the missing parts are reconstructed in the transposed output, but at the expense of considerable computational costs. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above-mentioned drawbacks of existing available HFR schemes, it is an object of the present invention to provide an improved and more efficient cross-product HFR scheme, in particular a method that allows for superior audio reproduction with less computational burden compared to existing schemes.

[0007] The present invention aims to alleviate or eliminate at least one of the above problems by the inventions described in the claims. [Means for solving the problem]

[0008] The signal processing system according to the disclosed invention comprises: 1. A signal generation system for generating a time-warped and / or frequency-transposed signal from an input signal, comprising: an analysis filter bank for deriving Y analysis subband signals from the input signal, each of the Y analysis subband signals having a plurality of complex analysis samples having a phase and an amplitude, where Y≧1; a subband processor for generating a synthesis subband signal from the Y analysis subband signals using a subband transposition factor Q and a subband stretch factor S; a synthesis filter bank for generating the time-warped and / or frequency-transposed signals from the synthesis subband signals; wherein at least one of Q and S is greater than 1, and the subband processing unit includes a block extraction unit, a nonlinear frame processing unit, and an overlap addition unit; The block extraction unit i) generating Y frames from L input samples, each of said frames being derived from a plurality of complex analysis samples of an analysis subband signal, said frames having a length of L (L>1); ii) generating a frame of input samples by applying a block hop size of h samples to the plurality of complex analysis samples before generating a subsequent frame of L input samples; The non-linear frame processor generates a frame of processed samples based on the Y corresponding frames of input samples generated by the block extractor by determining a phase and amplitude of each processed sample of the frame, and for at least one processed sample: i) the phase of the processed sample is based on a phase of a corresponding input sample in each of the Y frames of input samples; ii) the amplitudes of the processed samples are based on the phases of corresponding input samples in each of the Y frames of input samples; the overlap-add unit generating the composite subband signal by overlapping and adding samples of a series of frames of processed samples; The signal generating system is a signal generating system that operates at least when Y=2. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 illustrates the principle of subband block based harmonic transposition. [Diagram 2] FIG. 2 is a diagram showing nonlinear subband block processing for one subband input. [Diagram 3] FIG. 1 is a diagram showing nonlinear subband block processing for two subband inputs. [Figure 4] FIG. 13 illustrates the operation of harmonic transposition based on improved cross-product subband blocks. [Diagram 5] FIG. 1 illustrates an application example of subband block-based transposition using several orders of transposition in an improved HFR audio coder. [Figure 6] FIG. 1 shows an application of multi-order subband block based transposition using a 64-band QMF analysis filter bank. [Figure 7] FIG. 13 is a diagram for explaining the results of using the disclosed subband block based transposition method. [Figure 8] FIG. 13 is a diagram for explaining the results of using the disclosed subband block based transposition method. [Figure 9] 3 is a diagram showing in detail the nonlinear processing unit (including a pre-normalization unit and a multiplication unit) shown in FIG. 2 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Summary of the Invention> A signal generating system according to a first embodiment of the disclosed invention comprises: 1. A signal generation system for generating a time-warped and / or frequency-transposed signal from an input signal, comprising: an analysis filter bank for deriving Y analysis subband signals from the input signal, each of the Y analysis subband signals having a plurality of complex analysis samples having a phase and an amplitude, where Y≧1; a subband processor for generating a synthesis subband signal from the Y analysis subband signals using a subband transposition factor Q and a subband stretch factor S; a synthesis filter bank for generating the time-warped and / or frequency-transposed signals from the synthesis subband signals; wherein at least one of Q and S is greater than 1, and the subband processing unit includes a block extraction unit, a nonlinear frame processing unit, and an overlap addition unit; The block extraction unit i) generating Y frames from L input samples, each of said frames being derived from a plurality of complex analysis samples of an analysis subband signal, said frames having a length of L (L>1); ii) generating a frame of input samples by applying a block hop size of h samples to the plurality of complex analysis samples before generating a subsequent frame of L input samples; The non-linear frame processor generates a frame of processed samples based on the Y corresponding frames of input samples generated by the block extractor by determining a phase and amplitude of each processed sample of the frame, and for at least one processed sample: i) the phase of the processed sample is based on a phase of a corresponding input sample in each of the Y frames of input samples; ii) the amplitudes of the processed samples are based on the phases of corresponding input samples in each of the Y frames of input samples; the overlap-add unit generating the composite subband signal by overlapping and adding samples of a series of frames of processed samples; The signal generating system is a signal generating system that operates at least when Y=2.

[0011] A signal generating method according to a second embodiment of the disclosed invention includes: 1. A method for generating a time-warped and / or frequency-transposed signal from an input signal, comprising the steps of: deriving Y (Y≧2) analysis subband signals from the input signal, each of the analysis subband signals having a plurality of complex analysis samples having a phase and an amplitude; forming Y frames of L input samples, each frame being extracted from said plurality of complex analysis samples of an analysis subband signal, said frames having a length of L; applying a block hop size of h samples to the plurality of analysis samples prior to deriving a subsequent frame of L input samples to generate a sequence of frames of input samples; generating frames of processed samples by determining a phase and an amplitude for each processed sample of the frame based on Y corresponding frames of input samples, wherein for at least one processed frame, i) a phase of the processed sample is based on each of the phases of a corresponding input sample in each of the Y frames of input samples, and ii) an amplitude of the processed sample is based on each of the amplitudes of a corresponding input sample in each of the Y frames of input samples; determining a composite subband signal by overlappingly adding samples in a sequence of frames of processed samples; generating said time warped and / or frequency transposed signals from said composite subband signals; The signal generating method includes the steps of:

[0012] In this case, Y is any integer greater than 1. The signal generation system according to the first embodiment performs the above method at least for the case Y=2.

[0013] A third embodiment of the disclosed invention is a computer program or software having software instructions for causing a programmable computer to carry out the signal generation method according to the second embodiment.

[0014] A fourth embodiment of the disclosed invention is a storage medium (or data carrier) storing software instructions for causing a programmable computer to carry out the signal generation method according to the second embodiment.

[0015] The invention is based on the realization that the general concept of cross-product enhanced HFR gives excellent results when data is arranged and processed in blocks of complex subband samples. In particular, it allows a frame-by-frame phase offset to be applied to the samples. It also allows amplitude or magnitude adjustment, which has similar benefits. The cross-product enhanced HFR embodiment of the invention performs subband block-based harmonic transposition, which significantly reduces inter-modulation. Thus, filter banks with coarser frequency resolution and / or less oversampling (e.g. QMF filter banks) can be used while maintaining good output quality. In the case of subband block-based processing, time blocks of complex subband samples are processed with a common phase correction value, and the superposition of multiple corrected samples forming the output subband samples has the effect of reducing inter-modulation products that would otherwise occur when the input subband signal consists of multiple sine waves. Block-based transposition requires a much lighter computational burden than high-resolution transposers, and can achieve nearly the same high quality for many signals.

[0016] For the sake of convenience, it should be noted that in the embodiment, Y≧2, and the nonlinear processor uses as input Y “corresponding” frames of input samples, meaning that the frames are synchronous or nearly synchronous. For example, the samples in each frame relate to time intervals that have a lot of temporal overlap (or overlap or overlap) between the frames. The word “corresponding” is used to indicate that they are synchronous or approximately so. Furthermore, the word “frame” may be used interchangeably with “block”. Thus, the “block hop size” may be equal to or less than the frame length (adjusted for downsampling, if downsampling is performed), meaning that the input samples may belong to more than one frame. By determining the phase and amplitude based on the phase and amplitude of all Y corresponding frames of input samples, the system does not need to generate all processed samples in a frame; without departing from the invention, the system may generate the phase and / or amplitude of some processed samples based on a smaller number of corresponding input samples or based on only one sample.

[0017] In one embodiment, the analysis filter bank is a quadrature mirror filter (QMF) bank or pseudo-QMF bank with any number of taps and points. It may be, for example, a 64-point QMF bank. The analysis filter bank may be selected from the class of windowed discrete Fourier transform or wavelet transform. Advantageously, the synthesis filter bank matches the analysis filter bank with an inverse QMF bank, an inverse pseudo-QMF bank, etc. It is noted that such filters may have a relatively coarse frequency resolution and / or a relatively low degree of oversampling. Unlike the prior art, the present invention can be realized using such relatively simple components without suffering from degradation of the output, such that embodiments of the present invention exhibit better economy than the prior art.

[0018] In one embodiment, one or more of the following holds for the analysis filter bank: ●Analysis time progression width is Δt A is; ●Analysis frequency interval is Δf A is; ● The analysis filter bank has N>1 analysis subbands, where the analysis subbands are specified by analysis subband indices, n=0,...,N-1; - Analysis subbands are associated with frequency bands of the input signal.

[0019] In one embodiment, one or more of the following holds for the synthesis filter bank: ● The composite time progression width is Δt s is; ●The synthetic frequency interval is Δf s is; ● The synthesis filter bank has M>1 synthesis subbands, where the synthesis subbands are specified by synthesis subband indices m=0,...,M-1; The synthesis subband is associated with a time stretched signal and / or a frequency transposed signal.

[0020] In one embodiment, a non-linear processing unit is applied to two input frames (Y=2) to generate one frame constituting the processed frame, and the subband processing unit includes a cross processing control unit that generates cross processing control data. By clarifying the qualitative and / or quantitative nature of the subband processing, the invention can be made more flexible and applicable. The control data specifies (e.g., specified by index) subbands that differ on the frequency axis by the fundamental frequency of the input signal. In other words, the indices specifying the subbands may differ by an integer number that approximates the ratio of such fundamental frequency divided by the analysis frequency interval. This results in a psychologically pleasing audio output, since the new spectral components generated by the harmonic transposition are comparable to naturally occurring harmonics.

[0021] According to a further improvement to the above embodiment, the (input) analysis and (output) synthesis subband indexes are selected to satisfy the following formula (16), where the parameter σ makes it applicable to both odd-numbered and even-numbered stored filter banks. If the subband indexes are specified as an approximate solution (e.g., least square error) to formula (16), the new spectral components obtained by harmonic transposition will be comparable to the series of natural harmonics. Thus, HFR provides a faithful reconstruction of the original signal with the high frequency components removed.

[0022] According to a further improvement to the above embodiment, a method is provided for selecting the parameter r appearing in equation (16) and representing the order of the cross-product transposition. For a given output subband index m, each value of the transposition order r is calculated by multiplying the two analysis subband indexes n 1 , n 2 A further improved embodiment evaluates the magnitudes or amplitudes of the two subbands for a number of choices of r and selects the value that maximizes the smaller of the amplitudes of the two analysis subbands. This method of selecting the index makes it possible to eliminate the need to restore a number of amplitudes by amplifying weaker components of the input signal (which would result in poor output quality). In this respect, the magnitudes or amplitudes of the subbands may be calculated in a manner known per se, for example by taking the square root of the squares of the input samples forming a frame (block) or part of a frame. The magnitudes or amplitudes of the subbands may be calculated as the amplitude of a central or near-central sample in the frame. Such a calculation easily yields a suitable amplitude measure.

[0023] According to a further improvement to the above embodiment, the analysis subband receives contributions from harmonic transposition instances according to both direct processing and cross-product-based processing. In this respect, a criterion is applied that determines whether a particular possibility of regenerating missing parts by cross-product-based processing is used or not. For example, the improvement may be formed to refrain from using one or more cross subband processing units if any of the following conditions (a)-(c) are met:

[0024] The condition (a) is the amplitude M S and the minimum amplitude value M of the optimal pair of cross source terms resulting in the composite subband. Cand the ratio is greater than a predetermined value q, The condition in (b) is that the synthesis subband receives a large contribution from the direct processing unit; The condition in (c) is the fundamental frequency Ω 0 is the spacing of the analysis filter bank Δf A It is something smaller.

[0025] In one embodiment, the invention may perform a downsampling or decimation of the input signal. Indeed, one or more of the frames of input samples may be determined by downsampling the complex analysis samples in the subbands, as performed by a block extractor.

[0026] According to a further refinement of the above embodiment, the downsampling factor applied satisfies the following formula (15). The downsampling factors are not allowed to be all zero, which corresponds to a trivial or non-meaningful case. Formula (15) defines the downsampling factor D 1 and D. 2 , the subband stretch factor S, and the subband transposition factor Q. In addition, the phase coefficient T 1 and T 2 This ensures that the processed samples are in phase with other components of the input signal to which they are added.

[0027] In one embodiment, a window function is applied to the frames of samples to be processed before the frames are overlap-added. The windower applies a finite length window function to the frames of samples to be processed. Suitable window functions are defined in the appended claims.

[0028] The inventors have realized that cross-product methods of the type described in the patent application WO 2005 / 023363 are not perfectly suited for subband block-based processing schemes from the outset. Such methods may be applied satisfactorily to any subband sample of a block, but would introduce aliasing artifacts if extended directly to other samples in the block. For this reason, in one embodiment, a window function is applied that includes window samples that fit a substantially constant sequence (when weighted with a complex weight and shifted by a hop size). The hop size may be the product of the block hop size h and the subband stretch factor S. Using such a window function can significantly reduce aliasing artifacts. Alternatively or additionally, such a window function also reduces artifacts related to other quantities, such as phase rotation of the processed samples.

[0029] Preferably, the set of complex weights or weighting coefficients applied to evaluate the state for the windowed samples differ by a constant phase rotation angle. More preferably, the constant phase rotation angle is proportional to the fundamental frequency of the input signal. The phase rotation angle may be proportional to the order of the applied cross-product transposition and / or the difference in the downsampling factors and / or the analysis time advance. The phase rotation angle may be given, at least approximately, by equation (21).

[0030] The present invention, according to one embodiment, allows for cross-product enhanced harmonic transposition by varying the synthesis windowing depending on the fundamental frequency parameters.

[0031] In one embodiment, a series of frames of samples to be processed are added with a certain degree of overlap or overlap. To achieve the proper overlap, frames belonging to the processed samples are appropriately shifted by a hop size, which is the block size h upscaled or stretched by a subband stretch factor S. If the overlap of a series of frames belonging to the input samples was Lh, then the overlap of consecutive frames belonging to the processed samples will be S(Lh).

[0032] The system according to the present invention according to one embodiment can generate processed samples not only based on Y=2 input samples, but also based on Y=1 sample only. That is, the system can restore or regenerate missing parts not only by a cross-product scheme (e.g., equation (13) etc.) but also by a direct sub-band scheme (e.g., equations (5) and (11) etc.). Preferably, a controller controls the operation of the system, which control includes specifying which scheme should be used to restore a particular missing part.

[0033] A system according to a further improvement to the above embodiment generates a processed sample based on more than three samples (i.e., Y≧3). For example, the processed sample may be obtained by multiple harmonic transpositions based on cross products contributing to the processed sample, multiple direct subband processing, or a combination of cross product transposition and direct transposition. This method of applying the transposition method results in a powerful and versatile HFR. That is, the embodiment is operable to perform the method according to the second embodiment for Y=3, 4, 5, etc.

[0034] In one embodiment, the processed samples are determined as complex numbers having an amplitude, which is the average of the amplitude values ​​of the corresponding input samples. The average may be a (weighted) arithmetic mean, a (weighted) geometric mean or a (weighted) harmonic mean of two or more samples. For Y=2, the average is based on two complex input samples. Preferably, the amplitude of the processed samples is weighted geometric mean. More preferably, the geometric mean is weighted by parameters ρ and 1-ρ as shown in equation (13). In this case, the weighting parameter ρ of the geometric mean is a real number inversely proportional to the subband transposition factor Q. The parameter ρ may be inversely proportional to the warping factor S.

[0035] In one embodiment, the system determines a processed sample as a complex number having a phase, which is a linear combination of the phases of the corresponding input samples in the frame of input samples. In particular, the linear combination may be the phase associated with two input samples (Y=2). The linear combination of the two phases may use non-zero integer coefficients, the sum of which is equal to the warping factor S multiplied by the subband transposition factor Q. Alternatively, the phase obtained by such a linear combination may be further adjusted by a constant phase correction parameter. The phase of the processed sample may be given by Equation (13):

[0036] In one embodiment, the block extractor (or a corresponding step in the method according to the invention) may interpolate two or more analysis samples in the analysis subband signal to obtain one input sample to be comprised in a frame (block). Such an interpolation allows downmixing of the input signal by a non-integer factor. The interpolated analysis samples may or may not be consecutive.

[0037] In one embodiment, the configuration of the subband processing may be controlled by control data provided by an external means for controlling the processing. The control data relates to the current acoustic characteristics of the input signal. For example, the system itself may have means for determining the current acoustic characteristics of the signal (e.g. the (dominant) fundamental frequency of the signal). The fundamental frequency knowledge serves as a criterion or guidance for selecting the analysis subbands from which the processing samples are taken. Preferably, the spacing of the analysis subbands is proportional to such fundamental frequency of the input signal. Alternatively, the control data is provided from outside the system and is preferably included in an encoding format suitable for communication as a bitstream over a digital communication network. In addition to the control data, such an encoding format may also include information about the low frequency components of the signal (e.g. the frequency components in part 701 of FIG. 7). However, from the viewpoint of economical use of bandwidth, it is preferred that the encoding format does not include complete information about the high frequency components (part 702 of FIG. 7) from which the high frequency components are reconstructed in the present invention. In particular, the present invention provides a decoding system having a control data receiver suitable for receiving such control data, which may be included in the received bitstream encoding the input signal or may be received as a separate signal or bitstream.

[0038] An embodiment provides a technique for efficient implementation of the operations performed in the method according to the invention. For that purpose, the hardware implementation comprises a pre-normalizer or pre-normalizer that rescales (rescales) the amplitude of the corresponding input stream in the part of the Y frame on which the frame of samples to be processed is based. After such rescaling, the processed samples can be calculated as (weighted) complex products of the rescaled or possibly unrescaled input samples. The input samples that appear as rescaled factors in the product do not usually have to appear as unrescaled factors. With the possible exception of the phase correction parameter θ, it is possible to calculate equation (13) as a product of (possibly rescaled) complex input samples. This is advantageous in terms of computational burden compared to treating the amplitude and phase of the processed samples separately.

[0039] In one embodiment, the system is set with Y=2, which has two block extractors working in parallel to form one frame of input samples.

[0040] In another embodiment, where Y≧3, the system comprises a number of subband processors, each of which determines an intermediate synthesis subband signal using different subband transposition factors and / or different subband stretch factors and / or a transition method based on cross-product or different from the direct one. The subband processors may be arranged in parallel and operate in parallel. In this embodiment, the system further comprises a synthesis unit arranged downstream of the subband processors and upstream of the synthesis filter bank. The synthesis unit synthesizes (e.g., by synthesizing together) the associated intermediate synthesis subband signals to generate a synthesis subband signal. As described above, the synthesized intermediate synthesis subbands may be obtained by both direct and cross-product based harmonic transposition. The system according to an embodiment may further comprise a core decoder for decoding the bitstream into the input signal. This forms an HFR processor arranged to apply the spectral band information, in particular by performing spectral shaping. The operation of the HFR processor may be controlled by information encoded in the bitstream.

[0041] An embodiment provides HFR of a multi-dimensional signal in a system reproducing an audio signal in a stereo format forming Z channels, e.g., left, right, center, surround, etc. In an embodiment processing an input signal with multiple channels, the warping factor S and transposition factor Q for each band may differ between channels, but are based on the same number of input samples as the processed samples for each channel. To this end, the embodiment comprises an analysis filterbank generating Y analog subband signals from each channel, a subband processing unit generating Z subband signals, and Z time warped and frequency transposed signals forming the output signal.

[0042] In variations on the above embodiments, the output signal may have a different number of output channels based on the analysis subband signals, for example, it may be desirable to allocate more computational resources to the HFR of acoustically prominent channels, e.g., multiple channels reproduced from an audio source in front of the listener may be surround or near surround channels.

[0043] It is to be expressly noted that the invention relates to all combinations of the above-described features, even if these are recited in different claims.

[0044] <Overview of the drawings> Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, which do not limit the scope and spirit of the present invention.

[0045] FIG. 1 shows the principle of subband block based harmonic transposition.

[0046] FIG. 2 shows the nonlinear subband block processing for one subband input.

[0047] FIG. 3 illustrates the nonlinear subband block processing for two subband inputs.

[0048] FIG. 4 illustrates the operation of harmonic transposition based on the cross product enhanced subband block.

[0049] FIG. 5 shows an application example of subband block based transposition using several orders of transposition in an improved HFR audio coder.

[0050] FIG. 6 shows an application of multi-order subband block based transposition using a 64-band QMF analysis filter bank.

[0051] FIG. 7 is a diagram for explaining the results of using the disclosed subband block based transposition method.

[0052] FIG. 8 is a diagram for explaining the results of using the disclosed subband block based transposition method.

[0053] FIG. 9 shows in detail the nonlinear processing section (including the pre-normalization section and the multiplication section) shown in FIG.

[0054] <Description of the Preferred Embodiments> The embodiments described below merely illustrate the principles of the present invention for improved cross-product subband block based harmonic transposition. It will be understood that variations and modifications to the apparatus, methods and specific details described herein will be apparent to those skilled in the art. It is therefore intended that the present invention be defined only by the appended claims and not by the specific details provided by the specification and drawings.

[0055] Fig. 1 is a diagram for explaining the working principle of subband block based transposition, time warping or time stretch or combined transposition and time warping. An input time domain signal is fed to an analysis filter bank 101, which provides a number of complex-valued subband signals. They are fed to a subband processing unit 102, whose operation is controlled by control data 104. Each output subband may be obtained by processing one input subband or two input subbands, or may be obtained as a superposition of several subbands so processed. The number of complex-valued output subbands is fed to a synthesis filter bank 103, which outputs a modified time domain signal. Optional control data 104 indicates the manner and parameters of the subband processing performed on the transposed signal. In the case of the improved cross-product transposition, the data includes information about the dominant fundamental frequency.

[0056] 2 is a diagram for explaining the operation of the nonlinear subband block processing in the case of one subband input. Using physical time warping and transposition target values ​​and physical parameters of the analysis filter bank 101 and the synthesis filter bank 103, the source subband index as well as the subband time warping and transposition parameters are derived for each target subband index. The objective of the subband block processing is to perform transposition, time warping or a combination of transposition and time warping corresponding to the complex-valued source subband signal to generate the target subband signal.

[0057] The block extractor 201 samples a finite number of frames from the input complex signal. The frames are defined by the input pointer position and the subband transposition factor. The frames are non-linearly processed by the processing unit 202 and then windowed by the windowing unit 213 with a finite possible variable length. The resulting samples are pre-added to the output samples in the overlap-adder 204, the output frame position being defined by the output pointer position. The input pointer is incremented by a fixed value and the output pointer is incremented by the fixed value multiplied by the subband stretch factor. This iteration of the process produces an output signal with a complex frequency transposed by the subband transposition position and a duration equal to the subband stretch factor multiplied by the input subband signal period, which duration is within the length of the synthesis window. The control signal 104 influences (controls) each of the three processing units 201, 202, 203.

[0058] FIG. 3 is a diagram for explaining the operation of the nonlinear subband block processing in the case of two subband inputs. Using the physical time warping and transposition target values ​​and the physical parameters of the analysis filter bank 101 and the synthesis filter bank 103, the source subband index as well as the subband time warping and transposition parameters are derived for each target subband index. If the nonlinear subband block processing is for generating missing parts by cross product addition, not only the settings of the processing units 301-1, 301-2, 302, 303 but also the values ​​of the two source band indexes depend on the output 403 of the cross processing control unit 404. The purpose of the subband block processing is to perform the corresponding transposition, time warping or combination of transposition and time warping for the two complex source subband signals to generate the target subband signal. The first block extractor 301-1 samples a finite time frame of samples from the first complex source band, and the second block extractor 301-2 samples a finite frame of samples from the second complex source band. The frames are defined by a common input pointer position and a subband transposition factor. The two frames go to a nonlinear processor 302, and are then windowed by a finite window length processor 303. The overlap adder 204 is the same as or similar to that shown in FIG. 2. This iteration of the process produces an output signal whose duration is the longer of the two subband signals (but not exceeding the length of the synthesis window) multiplied by the subband stretch factor. If the two input subband signals have the same frequency, the output signal will have a complex frequency transposed by the subband transition factor. If the two subband signals have different frequencies, the window processor 303 can be used to generate an output signal with a target frequency suitable for generating the missing part in the transposed signal.

[0059] FIG. 4 is a diagram for explaining the principle of transposition, time warping, or a combination of transposition and time warping based on the improved cross-product subband block. The direct sub-band processing unit 401 may be the one already described with reference to FIG. 2 (processing unit 202) or FIG. 3. The cross sub-band processing unit 402 performs non-linear sub-band block processing on the two sub-band inputs shown in FIG. 3, and the output target sub-band is summed with that from the direct sub-band processing unit 401 in the summation unit. The cross processing control data 403 is different for each input pointer position, and A selected list of target subband indices, A pair of source subband indices for each selected target subband index, and Finite length synthesis window The information includes at least information indicating the above.

[0060] The cross processing control unit 404 provides cross processing control data 403 based in part on control data 104 indicative of the plurality of complex subband signals and fundamental frequencies output from the analysis filter bank 101. The control data 104 also includes other signal dependent configuration parameters that affect the cross product processing.

[0061] The principles of the improved cross-product subband block based time warping and transposition are explained below with reference to Figs. 1-4 together with appropriate mathematical techniques.

[0062] The two main setup parameters for the Harmonic Transposer and / or Time Warping overall are: ·S φ : the desired physical time warping factor, and Q φ : the desired physical transposition factor It is.

[0063] The filter banks 101, 103 may be of any complex exponential modulated type such as QMF, windowed DFT or wavelet transform etc. The analysis filter bank 101 and synthesis filter bank 103 are stacked in even or odd bands during modulation and are defined from a larger range of prototype filters and / or windows. All these second order choices affect subsequent design details such as phase correction, subband mapping management etc., but the main system design parameters for subband processing are generally the following four filter bank parameters (all measured in physical units): Δt s / Δt A and Δf s / Δf A In the above quotient, Δt A is the subband sample time step or temporal stride of the analysis filter bank 101 (e.g., measured in seconds), Δf A is the subband frequency spacing of the analysis filter bank 101 (e.g., measured in Hertz [1 / s]), Δt s is the subband sample time step or temporal stride of the synthesis filter bank 103 (e.g., measured in seconds), Δf s is the subband frequency spacing of the synthesis filter bank 103 (eg, measured in Hertz [1 / s]).

[0064] Depending on the configuration of the subband processor 102, the following parameters should be calculated: S: Subband stretch factor. The subband stretch factor is applied to the subband processing unit 102 as a ratio of input and time samples, S φ This is to perform a global physical time warping of the time domain signal.

[0065] Q: Subband transposition factor. The subband transposition factor is applied to the subband processing unit 102 to produce a factor Q φ The objective of the present invention is to perform a global physical frequency transposition of a time domain signal by

[0066] The correspondence between source and target subband indices, where n denotes the index of the analysis subband entering the subband processing unit 102 and m denotes the index of the corresponding synthesis subband at the output of the subband processing unit 102.

[0067] To determine the subband stretch factor S, the input signal to the analysis subband of physical duration D is multiplied by the number of analysis subband samples at the input to the subband processing unit 102, D / Δt A Confirm that these correspond to D / Δt A The samples are then scaled by a subband processor 102 that applies a subband stretch factor S to the A At the output of the synthesis filter bank 103, these S·D / Δt A The samples are s ·S·D / Δt A This results in an output signal with a physical period of length S φ Therefore, the period of the time-domain output signal should correspond to a specific value of the physical time stretch factor S φ Since the time domain input signal should be stretched by:

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[0071] 2 for one source subband will now be described as a function of the subband processing parameters S and Q. Let x(k) be the input signal to the block extractor 201 and h be the stride, step size or step size of the input block. That is, x(k) is the complex analysis subband signal of the analysis subband with index n. The blocks extracted by the block extractor 201 are generally of the form L=R 1 +R 2 There is no loss as it is assumed to be sample defined.

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[0073] An interesting special case of formula (4) is R 1 =0 and R 2 = 1, and the extracted block consists of one sample, i.e., the block length L is L = 1.

[0074] In the case of a polar representation of a complex number z=|z|exp(j∠z), where |z| denotes the amplitude of the complex number and ∠z denotes the phase or phase angle of the complex number, the nonlinear processing unit 202 generating the output frame yl from the input frame xl is advantageously defined by a phase correction factor T=SQ according to the following formula:

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[0076] Equation (5) above shows that the phase of an output frame sample is determined by shifting or offsetting the phase of a corresponding input sample by a constant offset value. The constant offset value depends on a modification factor T, which itself depends on a subband stretch factor and / or a subband transposition factor. Furthermore, the constant offset value depends on the phase of a particular input frame sample among the input frames. This particular input frame sample is kept fixed in determining the phases of all the output frame samples of a given block. In the case of equation (5), the phase of the center sample of the input frame is used as the phase of the particular input frame sample.

[0077] The second line of equation (5) indicates that the amplitude of a sample of the output frame depends on the amplitude of a corresponding sample of the input frame. Furthermore, the amplitude of a sample of the output frame may depend on the amplitude of a particular input frame sample. The particular input frame sample may be used in determining the amplitudes of all the output frame samples. For equation (5), the center sample of the input frame is used as the particular input frame sample. In one embodiment, the amplitude of a sample of the output frame may correspond to the geometric mean of the amplitudes of the corresponding sample of the input frame and the particular input frame sample.

[0078] In the windowing unit 203, a window w of length L is applied to the output frame, resulting in the windowed output frame:

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[0081] If a complex sine wave is used as input to the subband processing unit 102, the analysis subband signal corresponds to the complex sine wave.

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[0086] Below, the explanation of the subband processing unit will be expanded so that it can be applied to the case of FIG. 3 where there are two subband inputs. (1) (k) is the input subband signal to the first block extraction unit 301-1, and x (2) Let (k) be the input subband signal to the second block extractor 301-2. Since each extractor can use a different downsampling factor, the extracted blocks are:

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[0089] Non-negative real parameter D 1 , D 2 , ρ, a non-negative integer parameter T 1 , T 2 and the definition of the synthesis window w depends on the desired mode of operation. If the same subband is presented to both inputs, then x (1) (k)=x (2) (k), D 1 =Q,D 2 =0, T 1 =1, T 2 Note that when =T-1, the processing for equations (12) and (13) reduces to equations (4) and (5) for the one-input case.

[0090] In one embodiment, the frequency spacing of the synthesis filter bank 103, Δf s and the frequency interval Δf of the analysis filter bank 101 AWhen the ratio of is different from the desired physical transposition factor Q, it is useful to determine the synthesis subband samples with index m from two analysis subbands with indices n and n+1, respectively. For a given index m, the corresponding index n is given by an integer value obtained by truncating the analysis index value n given by mathematical formula (3). For example, one analysis subband signal, such as the analysis subband signal corresponding to index n, is provided to the first block extractor 301-1, and the other analysis subband signal, such as the analysis subband signal corresponding to index n+1, is provided to the second block extractor 301-2. Based on these two analysis subband signals, the synthesis subband signal corresponding to index m is determined according to the above process. The manner in which the analysis subband signals adjacent to the two block extractors 301-1 and 301-2 are designated may be based on the remainder obtained when truncating the index values ​​in mathematical formula (3), i.e. based on the difference between the extracted index value given by mathematical formula (3) and the truncated integer value n obtained from mathematical formula (3). If the remainder is greater than 0.5, the analysis subband signal corresponding to index n may be assigned to the second block extractor 301-2, otherwise the analysis subband signal may be assigned to the first block extractor 301-1. For this operation mode, the parameters are designed such that the input subband signals share the same complex frequencies.

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[0093] The following describes a method for the cross processing control 404. Given an output subband index m, parameters r=1,...,Q φ -1 and fundamental frequency Ω 0 For 1 and n 2 can be approximated.

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[0095] With these definitions, the following holds:

[0096] p=Ω 0 / Δf A : the fundamental frequency measured in units of the frequency interval of the analysis filter bank, F=Δf s / Δf A : the quotient of the frequency spacing of the synthesis filter bank to the frequency spacing of the analysis filter bank, n f =[(m+σ)F-rp] / Q φ - σ: Real-valued target for integer-valued low source index.

[0097] A specific example of a useful approximation to equation (16) is 1 n f Let n be the integer closest to 2 n f +p is the closest integer to

[0098] If the fundamental frequency is smaller than the analysis filterbank spacing, ie, p<1, it is advantageous to cancel or offset the addition of the cross products.

[0099] As taught in the patent application WO 2005 / 023363, cross products should not be added to output subbands that already have a significantly larger contribution from the transposition without cross products. Furthermore, in at most one case, r=1,...,Q φ −1 should be contributed to the cross product output. Here, these rules may be implemented by performing the following three steps for each of the target output subband indexes m: 1. The amplitude of the candidate source subband |x (1) | and |x (2) For all r=1,...,Q, the minimum of | φ The maximum value M out of -1 C Calculate the source subband x (1) and x (2) is the index n in formula (16). 1 and n 2 It is given as follows.

[0100] 2. Index n ≒ (F / Q φ ) m (see Equation 3) together with the corresponding magnitude or amplitude Ms for the direct source term |x| obtained from the source subbands.

[0101] 3. Only if Mc>qMs above, M is selected at point 1 (step 1) above. C Select a cross term from the winning candidates for q, where q is a predefined threshold.

[0102] Variations of the above procedure are desirable depending on the specific system configuration parameters. One such variation is to change the fixed threshold value of point 3 (step 3) to M C / M S Another variation is to replace the maximization at point 1 (step 1) with a relaxed rule that depends on the quotient of Q φ A further variation is to extend the range beyond -1, for example to a finite list of candidate values ​​for the fundamental frequency measured in analysis frequency interval units p. Yet another variation is to use another quantity for the amplitude of the subbands, for example the amplitude of a fixed sample, the maximum amplitude, the average amplitude, l p The amplitude by norm etc. may be used.

[0103] n 1 and n 2 The list of target subbands m selected for addition to the cross product along with the value of 1 , D 2 , ρ, the phase rotation, a non-negative integer parameter T that appears in (13) 1 , T 2 , for the synthesis window w used in the cross subband processing unit 402. Using a sinusoidal model for the cross-product situation, we obtain the following source band signal:

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[0109] Target output subband index m and fundamental frequency Ω 0It should be noted that the above algorithm for calculating the cross-processing control data 403 based on input parameters such as are merely illustrative of the nature of the present invention and are not intended to limit the scope of the present invention. Variations of the present disclosure, such as alternative subband block processing methods that provide an output such signal (18) in response to an input signal (17), within the scope of the present invention are possible using the common general knowledge and everyday experience of those skilled in the art.

[0110] Figure 5 shows an example of applying subband block based transposition using any order of transposition in an improved HFR audio codec. The transmitted bitstream is received by a core decoder 501, which provides a low bandwidth decoded core signal at a sampling frequency of fs. The low bandwidth decoded core signal is resampled to an output sampling frequency of 2fs by a complex modulated 32 band QMF analysis bank 502, which is followed (via an HFR processing unit) by a 64 band QMF synthesis bank (inverse QMF, IQMF) 505. The two filter banks 502 and 505 have the same physical parameters Δt s = Δt A and Δf s = Δf A , and the HFR processor 504 passes unmodified low sub-bands corresponding to the low bandwidth core signal. With the spectral shaping and modification performed by the HFR processor 504, the high frequency components of the output signal are obtained by providing high frequency sub-bands of the 64QMF synthesis bank 505 together with the output bands from the multiple transposer processor 503. The multiple transposer processor 503 takes as input the decoded core signal and outputs a number of sub-band signals, which represent the 64QAM band analysis by superposition or summation of several transposed signal components. The objective or goal is to provide a 64QAM band analysis by superposition or summation of several transposed signal components, each of which can be decoded by an integer physical transposition (Q) without time warping of the core signal when the HFR processing is circumvented or bypassed. φ = 2, 3, ... and S φ=1). In an embodiment of the present invention, the transposer control signal 404 includes data indicative of the fundamental frequency. This data may be transmitted in the bitstream from the corresponding audio encoder (the decoder performs pitch detection) or may be obtained from a combination of transmitted and detected information.

[0111] FIG. 6 is a diagram for explaining the operation of multi-order subband block-based transposition using a single 64-band QMF analysis filter bank. φ = 2, 3, 4 are generated, given the domain of a 64-band QMF operating at an output sampling rate of 2fs.

[0112] The multiplexer, synthesizer or merger 603 selects and synthesizes a related subband from one transposition factor branch among multiple QMF subbands provided to the HFR processor. φ The series of processes in the 64-band QMF synthesis unit 505 are φ = 1 (i.e. no stretching) with Q φ By identifying these three blocks along with 101, 102, and 103 in Figure 1, the physical transposition of Δt s / Δt A = 1 / 2 and F = Δf s / Δf A = 2, so that Δt A =64f s and Δf A =f s / 128. 602-Q φ The specific setting parameters for Q φ = 2, 3, 4 are discussed separately. For all cases, the analysis stride is chosen to be h = 1, and the normalized fundamental frequency parameter p = Ω 0 / Δf A =128Ω 0 / f sis assumed to be known.

[0113] First, Q φ Consider the case of T = 2. In this case, 602-2 must perform a subband stretch of S = 2, a subband transposition of Q = 1 (i.e., no stretching), and the correspondence between source n and target subband m is given by n = m for direct subband processing. During the process of cross-product addition, there is only one cross product to consider (i.e., r = 1) (see equation (15) above), and equation (20) becomes T 1 =T 2 =1 and D 1 +D 2 = 1. An example of a solution is D 1 =0 and D 2 = 1. For a direct processing synthesis window, R 1 =R 2 A rectangular window of length L=10 with R = 5 may be used to satisfy condition (10). 1 =R 2 A short L=2 tap window is used with h=1 to minimize the additional complexity of cross-product summation. And the beneficial effect of using long blocks for subband processing is most noticeable in the case of complex audio signals, where unwanted intermodulation terms are suppressed and the probability of such artifacts occurring in the case of dominant pitch is low. The L=2 tap window is the smallest possible to satisfy equation (10) since h=1 and S=2. However, the present invention can also satisfy equation (21). In that case, the parameters are defined as follows:

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[0115] Q φIn the case where r=3, the specification or operation of 602-3 according to equations (1)-(3) is to perform a subband expansion of S=2 and a subband transposition of Q=3 / 2, and the relationship between the target m subband and the source n subband for processing the direct terms is given by n≈2m / 3. There are two kinds of cross-product terms r=1,2, and equation (20) is simplified as follows:

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[0117] D 1 =0 and D 2 =3 / 2 (when r=1) D 1 =3 / 2 and D 2 =0 (when r=2) For direct processing synthesis windows, R 1 =R 2 A rectangular window of length L=8 may be used with R = 4. For the cross-processing synthesis window, R 1 =R 2 A short window of L=2 taps may be used with =1 to satisfy the following equation:

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[0119] Q φ For r = 4, the specification or operation of 602-4 according to equations (1)-(3) is to perform a subband expansion of S = 2 and a subband transposition of Q = 2, and the relationship between the target m subband and the source n subband for processing the direct terms is given by n ≈ 2m. There are three kinds of cross-product terms r = 1, 2, 3, and equation (20) is simplified as follows:

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[0121] D 1 =0 and D 2 =2 (when r=1) D 1 =0 and D 2 =1 (when r=2) D 1 =2 and D 2 =0 (for r=3) For direct processing compositing windows, R 1 =R 2 A rectangular window of length L=6 may be used with R = 3. For the cross-processing synthesis window, R 1 =R 2 A short window of L=2 taps may be used with =1 to satisfy the following equation:

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[0123] In each of the above examples where values ​​of r greater than 1 are applicable, options exist similar to the three-step procedure described above, for example equation (17).

[0124] Figure 7 shows the fundamental frequency Ω 0 7 shows the amplitude spectrum of a harmonic signal at 564.7 Hz. The low frequency part 701 of this signal is used as the input for several transposers. The purpose of the transposers is to generate a signal that is as close as possible to the high frequency part 702 of the input signal, so that the transmission of the high frequency part 702 is not necessary and so that the available bit rate can be used economically.

[0125] Figure 8 shows the amplitude spectrum of the output from a transposer having as input the low frequency portion 701 of the signal in Figure 7. Following the description in Figure 5, multiple transposers are constructed using a 64-band QMF filter bank with an input sampling frequency fs=14400Hz. However, for simplicity, we use two transposition orders Q φ Consider only =2,3. Three different spectra 801-803 represent the final output obtained using different settings of the cross-processing control data.

[0126] The spectrum 801 at the top shows the output spectrum obtained when all cross processing is cancelled and only direct subband processing 401 is performed. This is the case when the cross processing control data 404 receives p=0 (no pitch indication). φ The =2 transposition produces outputs in the range of 4 to 8 kHz, with a Q φ A transposition of =3 produces an output in the range of 8 to 12 kHz. As can be seen, the produced portions are far apart and the output deviates significantly from the (original) high frequency portion 702. Audible 2x and 3x "ghost pitch" artifacts appear in the resulting audio output.

[0127] In the middle spectrum 802, cross processing has been performed and pitch parameter p=5 is used (approximately 128 Ω 0A simple 2-tap synthesis window with w(0)=w(-1)=1, which satisfies equation (10) but with w(0)=w(-1)=1, is used for cross-subband processing. This is a direct combination of subband block-based processing and improved cross-product harmonic transposition. As shown, additional output signal components not present in 801 do not match the desired harmonic sequence. This shows that using the above procedure leads to insufficient audio quality to offset the effect of direct subband processing design with cross-product processing.

[0128] The spectrum 803 in the lower row shows an output spectrum similar to the spectrum 802 in the middle row, but with a Q φ α(iα)) is used, i.e., a two-tap window with w(0)=1 and w(-1)=exp(iα) satisfies equation (21) and uses the inventive feature that depends on the value of p. As can be seen, the synthesized output signal is a good match to the desired harmonic content 702.

[0129] FIG. 9 shows a portion of the nonlinear processing frame processor 202, which processes two input samples u 1 , u 2 and generates a processed sample (processed sample) w based on them, where the amplitude of the processed sample is given by the geometric mean of the amplitudes of the input samples and the phase of the processed sample is a linear combination of the phases of the input samples.

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[0131] Further embodiments of the present invention will be apparent to those skilled in the art upon reading the above description. Although the description and drawings show embodiments and examples, the present invention is not limited to those specific examples. Numerous modifications and variations are possible without departing from the scope of the present invention, which is defined by the appended claims.

[0132] The system and method disclosed in this application may be realized as software, firmware, hardware, or a combination thereof. All or some of the elements may be realized as software executed by a digital signal processor or a microprocessor, or as hardware or an application specific integrated circuit. Such software may be stored in a computer readable storage medium, and the storage medium includes computer readable media (or non-transient media), but the medium itself is a concept that includes communication media (transient media). As known to those skilled in the art, computer storage media includes volatile media, non-volatile media, removable media, non-removable media, etc., and is realized in any method or technique for storing information such as computer readable instructions, data structures, program modules, or other data. The computer storage medium may be, but is not limited to, RAM, ROM, EEPROM, flash memory, or other types of memory, CD-ROM, digital versatile disk (DVD) or other optical disk media, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and that can be accessed by a computer. In addition, those skilled in the art will appreciate that communication media may typically be embodied by computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or transmission medium and may include any information delivery mechanism. [Prior art documents] [Patent documents]

[0133] [Patent Document 1] WO 98 / 57436 [Patent Document 2] International Publication No. 2010 / 081892 [Patent Document 3] International Publication No. 2004 / 097794 [Patent Document 4] International Publication No. 2007 / 085275

[0134] (Appendix 1) 1. A signal generation system for generating a time-warped and / or frequency-transposed signal from an input signal, comprising: an analysis filter bank for deriving Y analysis subband signals from the input signal, each of the Y analysis subband signals having a plurality of complex analysis samples having a phase and an amplitude, where Y≧1; a subband processor for generating a synthesis subband signal from the Y analysis subband signals using a subband transposition factor Q and a subband stretch factor S; a synthesis filter bank for generating the time-warped and / or frequency-transposed signals from the synthesis subband signals; wherein at least one of Q and S is greater than 1, and the subband processing unit includes a block extraction unit, a nonlinear frame processing unit, and an overlap addition unit; The block extraction unit i) generating Y frames from L input samples, each of said frames being derived from a plurality of complex analysis samples of an analysis subband signal, said frames having a length of L (L>1); ii) generating a frame of input samples by applying a block hop size of h samples to the plurality of complex analysis samples before generating a subsequent frame of L input samples; The non-linear frame processor generates a frame of processed samples based on the Y corresponding frames of input samples generated by the block extractor by determining a phase and amplitude of each processed sample of the frame, and for at least one processed sample: i) the phase of the processed sample is based on a phase of a corresponding input sample in each of the Y frames of input samples; ii) the amplitudes of the processed samples are based on the phases of corresponding input samples in each of the Y frames of input samples; the overlap-add unit generating the composite subband signal by overlapping and adding samples of a series of frames of processed samples; A signal generating system, the signal generating system operating at least when Y=2. (Appendix 2) the analysis filter bank is one of a quadrature mirror filter bank, a windowed discrete Fourier transform or a wavelet transform; 2. The signal generation system of claim 1, wherein the synthesis filter bank is a corresponding inverse filter bank or transform. (Appendix 3) 3. The signal generation system of claim 2, wherein the analysis filter bank is a 64-point quadrature mirror filter bank and the synthesis filter bank is an inverse 64-point quadrature mirror filter bank. (Appendix 4) The analysis filter bank has an analysis time progression width Δt A applying to the input signal; The analysis filter bank has an analysis frequency interval Δf A Using n=0,...,N-1 is an analysis subband index, the analysis filter bank having N analysis subbands, an analysis subband among the N analysis subbands is associated with a frequency band of the input signal; The synthesis filter bank has a synthesis time progression width Δt s applying to the synthesis subband signal; The synthesis filter bank has a synthesis frequency interval Δf s Using m=0,...,M-1 is a synthesis subband index, the synthesis filter bank having M synthesis subbands, 4. A signal generation system according to any one of claims 1-3, wherein a synthesis subband among the M synthesis subbands is associated with a frequency band of the time-warped signal and / or the frequency-transposed signal. (Appendix 5) The subband processing unit is formed for Y=2 and further comprises a cross processing control unit, the cross processing control unit being arranged to control a fundamental frequency Ω of the input signal. 0 and the analysis frequency interval Δf A The subband indexes n associated with the analysis subband signals are different by an integer p that is an approximation of the ratio of 1 , n 2 5. The signal generation system of claim 4, further comprising: (Appendix 6) The subband processing unit is configured for Y=2 and further comprises a cross-processing control unit, the cross-processing control unit being configured to process the analysis subband signal and a subband index n associated with the analysis subband index m. 1 , n 2 wherein the subband indexes are related to an approximate solution of the following equation:

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Claims

1. 1. A system configured to generate a time-warped and / or frequency-transposed signal from an input signal, the system comprising one or more processing elements, the one or more processing elements comprising: deriving Y (Y≧1) analysis subband signals from the input signal, each analysis subband signal having a plurality of complex analysis samples each having a phase and an amplitude; generating synthesis subband signals from the Y analysis subband signals using a subband transposition factor Q and a subband stretch factor S, where at least one of Q and S is greater than 1; and generating the time-warped and / or frequency-transposed signal from the composite subband signal; and the system is capable of operating for at least Y=2, and the generating of the composite subband signal comprises: forming Y frames of L input samples, each frame extracted from the plurality of complex analysis samples of an analysis subband signal, L being a frame length greater than one, and at least one of the L input samples being derived by interpolating two or more of the plurality of complex analysis samples; applying a block hop size of h samples to the plurality of complex analysis samples prior to forming a subsequent frame of L input samples to generate a sequence of frames of input samples; generating a frame of processed samples based on Y corresponding frames of input samples by determining a phase and an amplitude of each of the processed samples of the frame, the phase and amplitude being determined, for at least one processed sample: i) the phases of the processed samples are based on a linear combination, with non-negative integer coefficients, of phases of corresponding input samples in each of the Y frames of input samples; and ii) the amplitudes of the processed samples are based on amplitudes of corresponding input samples in each of the Y frames of input samples; applying a window function to the frame of processed samples, the window function having a length corresponding to the frame length L; and determining said composite subband signal by overlapping and adding samples of a sequence of frames of processed samples; A system that performs the above.

2. 1. A method for generating a time-warped and / or frequency-transposed signal from an input signal, comprising the steps of: deriving Y (Y≧2) analysis subband signals from the input signal, each analysis subband signal having a plurality of complex analysis samples each having a phase and an amplitude; forming Y frames of L input samples, each frame extracted from the plurality of complex analysis samples of an analysis subband signal, L being a frame length greater than one, and at least one of the L input samples being derived by interpolating two or more of the plurality of complex analysis samples; applying a block hop size of h samples to the plurality of complex analysis samples prior to deriving a subsequent frame of L input samples to generate a sequence of frames of input samples; generating a frame of processed samples based on Y corresponding frames of input samples by determining a phase and an amplitude of each of the processed samples of the frame, the phase and amplitude being determined, for at least one processed sample: i) the phases of the processed samples are based on a linear combination, with non-negative integer coefficients, of phases of corresponding input samples in each of the Y frames of input samples; and ii) the amplitudes of the processed samples are based on amplitudes of corresponding input samples in each of the Y frames of input samples; determining a composite subband signal by applying a window function of length corresponding to the frame length L to the frame of processed samples and overlapping and adding samples of the sequence of windowed frames of processed samples; and generating the time-warped and / or frequency-transposed signal from the composite subband signal; The method according to claim 1,

3. A non-transitory data carrier storing computer readable instructions for carrying out the method of claim 2.

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