System and method for generating high frequency component of signal

Abstract

To mitigate the increase of different kinds of transposition orders and associated calculation processing loads.SOLUTION: A system for generating a high frequency component of a signal from a low frequency component of the signal comprises: an analysis filter bank for providing a set of analysis subband signals, which set includes at least two analysis subband signals, from the low frequency component of the signal, the analysis filter bank having a frequency resolution of Δf; a nonlinear processing unit for determining a set of synthesis subband signals from the set of analysis subband signals using a transposition order P, the set of synthesis subband signals comprising a portion of the set of analysis subband signals phase shifted by an amount derived from the transposition order P; and a synthesis filter bank for generating the high frequency component of the signal from the set of synthesis subband signals, the synthesis filter bank having a frequency resolution of FΔf, with F being a resolution factor. The transposition order P is different from the resolution factor F.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an audio coding system that utilizes harmonic transposition for high-frequency reconstruction (HFR), a digital effect processor such as a so-called exciter where the generation of harmonic distortion adds brightness to the processed signal, etc. In particular, the present application relates to a simple method for high-frequency reconstruction.

Background Art

[0002] In Patent Document 1 (WO98 / 57436), the concept of transposition has been established as a method of reconstructing a high-frequency band from a low-frequency band of an audio signal. By using this concept in audio coding, a fairly significant bitrate reduction effect can be obtained. In the case of an audio coding system using HFR, a low-bandwidth signal referred to as a low-frequency component of the signal is given to a core waveform coder, and very low-bitrate additional side information and signal transposition that describe the target spectral shape of the high-frequency components on the decoder side are utilized to regenerate the high frequencies referred to as the high-frequency components of the signal. In the case of a low bitrate, since the bandwidth of the coded signal of the core (i.e., the low-band signal or low-frequency component) is narrow, it becomes increasingly important to regenerate a high-band signal (i.e., the high-frequency component) with perceptually pleasant characteristics. The harmonic transposition defined in Patent Document 1 (WO98 / 57436) functions well for complex music content in the situation of a low crossover frequency, that is, in the situation where the upper limit frequency of the low-band signal is low. The principle of harmonic transposition is to map or associate a sine wave of frequency ω to a sine wave of frequency Tω, where T > 1 is an integer specifying the degree of transposition (i.e., the transposition degree). In contrast, HFR using single-sideband reshift (SSB) maps a sine wave of frequency ω to a sine wave of frequency ω + Δω, where Δω is a constant frequency shift amount. In the case of a low-bandwidth core signal (i.e., a low-band signal with a low upper limit frequency), SSB transposition typically causes an annoying resonant artifact, which is a drawback when compared with harmonic transposition.

[0003] To achieve improved audio quality and synthesize the bandwidth required for the high-band signal, the harmonic HFR method typically uses several degrees of transposition. To perform a plurality of transpositions with various transposition orders, conventional methods require a plurality of filter banks in the analysis stage, the synthesis stage, or both. Typically, a different filter bank is required for each different transposition order. When a core waveform coder operates at a sampling rate lower than the sampling rate of the final output signal, typically there is an additional requirement to convert the core signal to the sampling rate of the output signal, and such upsampling of the core signal is usually done by adding yet another filter bank. Therefore, as the number of different types of transposition orders increases, the computational processing burden becomes extremely heavy.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem of the embodiment is to at least reduce the conventional problem that the computational processing burden becomes extremely heavy as the number of different types of transposition orders increases.

Means for Solving the Problems

[0006] A system according to an embodiment is a system configured to generate high-frequency components of a signal from low-frequency components of the signal, an analysis filter bank configured to provide a group of analysis sub-band signals from the low-frequency components of the signal, the group of analysis sub-band signals including at least two analysis sub-band signals, and A non-linear processing unit configured to determine a group of synthesized sub-band signals from the group of analyzed sub-band signals, wherein the n-th synthesized sub-band signal in the group of synthesized sub-band signals is determined from the k-th analyzed sub-band signal and the (k + 1)-th analyzed sub-band signal in the group of analyzed sub-band signals, and the phase of the n-th synthesized sub-band signal is determined as the sum of the phase of the k-th analyzed sub-band signal scaled by a first integer phase multiplier and the phase of the (k + 1)-th analyzed sub-band signal scaled by a second integer phase multiplier, and the first and second integer phase multipliers are different, the non-linear processing unit, A synthesis filter bank configured to generate a high-frequency component of the signal based on the group of synthesized sub-band signals, A system having the above.

Brief Description of the Drawings

[0007]

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DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention provides a method for reducing the complexity of the harmonic HFR method by making a pair of an analysis filter bank group and a synthesis filter bank group shareable by several harmonic transposers, or by one or more harmonic transposers and an upsampler. The proposed frequency-domain transposition involves mapping a non-linearly modified subband signal from an analysis filter bank to a selected subband of a synthesis filter bank. The non-linear processing on the subband signal includes phase multiplication that increases by several times. Further, the present invention provides several forms for reducing the complexity of the HFR system.

[0009] As one embodiment, a system for generating a high-frequency component of a signal from a low-frequency component of the signal is described. This system has an analysis filter bank that provides a group of analysis subband signals typically including at least two analysis subband signals from the low-frequency component of the signal. The synthesis filter bank has a frequency resolution of Δf and L A analysis subbands, where L A > 1, and the index k of the analysis subband is k = 0,..., L A-1 . In particular, the analysis filter bank provides a group of complex analysis subband signals having samples of magnitude and samples of phase.

[0010] This system further has a non - linear processing unit that determines a group of synthesized sub - band signals from a group of analyzed sub - band signals using a certain transposition order P. The group of synthesized sub - band signals typically has a portion of the group of analyzed sub - band signals whose phase is shifted by an amount derived from the transposition order P. In other words, the group of synthesized sub - band signals is determined based on a portion of the group of analyzed sub - band signals whose phase is shifted by an amount derived from the transposition order P. The phase shift of the analyzed sub - band signals may be performed by multiplying the phase samples of the analyzed sub - band signals by an amount derived from the transposition factor P. In that case, the group of synthesized sub - band signals corresponds to a part or subset of the group of analyzed sub - band signals, and the amount derived from the transposition order is multiplied to the phase of the sub - band samples. In particular, the amount derived from the transposition order may be a fraction of the transposition order.

[0011] This system has a synthesis filter bank with a frequency resolution of FΔf that generates high - frequency components of a signal from a group of synthesized sub - band signals. F is a resolution factor where F≥1, and the synthesis filter bank has L S synthesized sub - bands, where L S >1, and the index n of the synthesized sub - bands is n = 0,..., L S −1. The transposition order P is different from the resolution factor F. The analysis filter bank uses an analysis time width (analysis time stride) Δt A and the synthesis filter bank uses a synthesis time width (synthesis time stride) Δt S The analysis time width Δt A and the synthesis time width Δt S may be equal.

[0012] Based on the analysis sub-band signals belonging to a group of analysis sub-band signals whose phases are shifted by the transposition order P, or based on a pair of analysis sub-band signals among a group of synthesis sub-band signals, the non-linear processing unit determines the synthesis sub-band signals of a group of sub-band signals. The first member of the pair of sub-band signals has a phase shifted by a factor P', and the second member of the pair of sub-band signals has a phase shifted by a factor P", where P'+P" = P. The above processing may be performed on the samples of the synthesis and analysis sub-band signals. In other words, the samples of the analysis sub-band signals may be determined based on the samples of the analysis sub-band signals whose phases are shifted by the transposition order P, or based on the sample pairs from the corresponding pairs of analysis sub-band signals. The first sample in the sample pair is phase-shifted by a factor P' only, and the second sample in the sample pair is phase-shifted by a factor P" only.

[0013] The non-linear processing unit determines the n-th synthesis sub-band signal among a group of synthesis sub-band signals from the combination of the k-th analysis sub-band signal and the adjacent (k + 1)-th analysis sub-band signal among a group of analysis sub-band signals. In particular, the non-linear processing unit determines the phase of the n-th synthesis sub-band signal as the sum of the phase shift of the k-th analysis sub-band signal and the phase shift of the (k + 1)-th analysis sub-band signal. Alternatively or additionally, the non-linear processing unit determines the magnitude of the n-th synthesis sub-band signal as the product of the magnitude in the exponential representation of the k-th analysis sub-band signal and the magnitude in the exponential representation of the (k + 1)-th analysis sub-band signal.

[0014] The analysis sub-band index k of the analysis sub-band signal contributing to the synthesis sub-band together with the synthesis sub-band index n may be given by an integer obtained by truncating (F / P)n. The remainder r in the truncation process is given by (F / P)n - k. In this case, the non-linear processing unit may determine the phase of the n-th synthesis sub-band signal as the sum of the phase of the k-th analysis sub-band signal shifted by P(1 - r) and the phase of the (k + 1)-th analysis sub-band signal shifted by P(r). In particular, the non-linear processing unit may determine the phase of the n-th synthesis sub-band signal as the sum of the phase of the k-th analysis sub-band signal multiplied by P(1 - r) and the phase of the adjacent (k + 1)-th analysis sub-band signal multiplied by P(r). Alternatively or additionally, the non-linear processing unit may determine the magnitude of the n-th synthesis sub-band signal as the product of the (1 - r)-th power of the magnitude in the exponential representation of the k-th analysis sub-band signal and the r-th power of the magnitude in the exponential representation of the (k + 1)-th analysis sub-band signal.

[0015] In one embodiment, the analysis filter bank and the synthesis filter bank may be set at integer multiple positions, the center frequency of the analysis sub-band may be given by kΔf, and the center frequency of the synthesis sub-band may be given by nFΔf. In another embodiment, the analysis filter bank and the synthesis filter bank may be set at half-integer multiple positions, the center frequency of the analysis sub-band may be given by (k + (1 / 2))Δf, the center frequency of the synthesis sub-band may be given by (n + (1 / 2))FΔf, and the difference between the transposition order P and the resolution factor F may be even.

[0016] As another embodiment, a system for generating high-frequency components of a signal from low-frequency components of the signal is described. This system has an analysis filter bank that provides a group of analysis sub-band signals including at least two analysis sub-band signals from the low-frequency components of the signal.

[0017] This system has a first non - linear processing unit that determines a first set of synthesized sub - band signals from a set of analyzed sub - band signals using a first transposition order P1. The first set of synthesized sub - band signals is determined based on a portion of the set of analyzed sub - band signals whose phase is shifted by an amount derived from the first transposition order P1. This system has a second non - linear processing unit that determines a second set of synthesized sub - band signals from a set of analyzed sub - band signals using a second transposition order P2. The second set of synthesized sub - band signals is determined based on a portion of the set of analyzed sub - band signals whose phase is shifted by an amount derived from the second transposition order P2, and the first transposition order P1 and the second transposition order P2 are different. The first and second non - linear processing units may be constructed according to any of the features and forms described in this application.

[0018] This system combines the first and second sets of synthesized sub - band signals to generate a combined set of synthesized sub - band signals. Such combination may be performed, for example, by combining (e.g., adding and / or averaging) the synthesized sub - band signals in the first and second sets corresponding to the same frequency range. In other words, the combining unit is constructed to overlay the synthesized sub - band signals in the first and second sets of synthesized sub - band signals corresponding to overlapping frequency ranges. Further, this system may include a synthesis filter bank that generates high - frequency components of the signal from the combined set of synthesized sub - band signals.

[0019] As another embodiment, a system for generating high-frequency components of a signal from low-frequency components of the signal is described. This system has an analysis filter bank with a frequency resolution of Δf. The analysis filter bank provides a group of analysis subband signals from the low-frequency components of the signal. This system has a non-linear processing unit that determines an intermediate group of synthesis subband signals having a frequency resolution of PΔf from the group of analysis subband signals using a certain transposition order P. The intermediate group of synthesis subband signals includes portions of the group of analysis subband signals whose phases are shifted by the transposition order P. In particular, the non-linear processing unit multiplies the phase of the complex analysis subband signal by the transposition order. It should be noted that the transposition order P may be, for example, the transposition order P or P1 or P2 as described above.

[0020] The non-linear processing unit interpolates one or more intermediate synthesis subband signals and determines a synthesis subband signal of a group of synthesis subband signals having a frequency resolution of FΔf. F is a resolution factor and F≧1. In one embodiment, two or more intermediate synthesis subband signals are interpolated. The transposition order P may be different from the frequency resolution F.

[0021] This system has a synthesis filter bank with a frequency resolution of FΔf. The synthesis filter bank generates high-frequency components of the signal from the group of synthesis subband signals.

[0022] The system described in the present application further has a core decoder that converts an encoded bitstream into a low-frequency component of a signal, and the core decoder may be based on any of the encoding schemes of Dolby E, Dolby Digital, AAA, and HE-AAC. The present system has a multi-channel analysis quadrature mirror filter (QMF) bank, and the QMF bank converts a high-frequency component and / or a low-frequency component into a plurality of QMF sub-band signals, and / or the present system has a high-frequency reconstruction processing module that modifies the QMF sub-band signals, and / or the present system has a synthesis QMF bank that generates a modified high-frequency component from the modified QMF sub-band signals. The present system has a downsampling unit that decreases the sampling rate of the low-frequency component of the signal upstream of the analysis filter bank and outputs the low-frequency component at the decreased sampling rate.

[0023] As another embodiment, a system is described that generates a high-frequency component of a signal at a second sampling frequency from a low-frequency component of the signal at a first sampling frequency. In particular, the signal including the low-frequency component and the high-frequency component may be at the second sampling frequency. The second sampling frequency is R times the first sampling frequency, where R ≥ 1. The present system has a harmonic transposer of order T that generates a modulated high-frequency component from the low-frequency component, and the modulated high-frequency component is determined based on a spectral portion of the low-frequency component transposed to a frequency range T times higher. The modulated high-frequency component is the product of the first sampling frequency multiplied by a factor S, where T > 1 and S ≤ R. In other words, the modulated high-frequency component may be at a sampling frequency lower than the second sampling frequency. In particular, the modulated high-frequency component may be sampled critically (or in a form close to critical).

[0024] This system has a QMF bank that associates (maps) modulated high-frequency components to at least one of X QMF sub-bands that are multiples of S, and provides at least one QMF sub-band signal; and / or a high-frequency reconstruction module that modifies the at least one QMF sub-band signal (e.g., QMF sub-band signals scaled by one or more); and / or a synthesis QMF bank that generates high-frequency components from the modified at least one QMF sub-band signal.

[0025] The harmonic transposer comprises any of the above features and is constructed to perform any of the methods described in this application. In particular, the harmonic transposer has an analysis filter bank that provides a group of analysis sub-band signals from the low-frequency components of a signal. The harmonic transposer has a non-linear processing unit with a transposition order of T that determines a group of synthesis sub-band signals from the group of analysis sub-band signals by changing the phases of the group of analysis sub-band signals. As described above, changing the phase includes multiplying the phases of the complex samples of the analysis sub-band signals. The harmonic transposer has a synthesis filter bank that generates the modulated high-frequency components of the signal from the group of synthesis sub-band signals.

[0026] The low-frequency component has a bandwidth that is B. The harmonic transposer generates a group of composite sub-band signals within a frequency range of (T-1)*B to T*B. In that case, the harmonic transposer modulates a group of composite sub-band signals to a baseband centered near zero frequency to generate a modulated high-frequency component. Such modulation may be performed by high-pass filtering a time-domain signal generated from a group of sub-band signals including a group of composite sub-band signals and modulating and / or time-sampling the filtered time-domain signal. Alternatively or additionally, such modulation may be performed by directly generating a modulated time-domain signal from a group of composite sub-band signals. This may be performed using a composite filter bank smaller than the normal size. Assuming that the composite filter bank has a normal size of L and the frequency range of (T-1)*B to T*B corresponds to composite sub-band indices of k0 to k1, the composite sub-band signals may be mapped to sub-band indices of 0 to k1-k0 in a composite filter bank of size k1-k0 (<L), that is, the composite filter bank has a size of k1-k0 that is narrower than L.

[0027] The system further has downsampling means upstream of the harmonic transposer, and the downlink sampling means provides a low-frequency component critically (or in a way close to critical) downsampled by a first sampling frequency divided by a downsampling factor Q from the low-frequency component of the signal. In this case, various sampling frequencies in the system may be divided by the downsampling factor Q. In particular, the modulated high-frequency component may be the first sampling frequency multiplied by a factor S and divided by the downsampling factor Q. X, which is the size of the analysis QMF bank, may be S / Q.

[0028] As another embodiment, a method for generating high-frequency components of a signal from low-frequency components of the signal is also described. The method includes providing a set of analysis sub-band signals including at least two analysis sub-band signals from the low-frequency components of the signal using an analysis filter bank having a frequency resolution of Δf. The method further includes determining a set of synthesis sub-band signals from the set of analysis sub-band signals using a certain transposition order P. The set of synthesis sub-band signals is determined based on a portion of the set of analysis sub-band signals whose phase is shifted by an amount derived from the transposition order P. Further, the method includes generating the high-frequency components of the signal from the set of synthesis sub-band signals using a synthesis filter bank having a frequency resolution of FΔf. In this case, F≥1, F is a resolution factor, and the transposition order P is different from the resolution factor F.

[0029] As another embodiment, a method for generating high-frequency components of a signal from low-frequency components of the signal is also described. The method includes providing a set of analysis sub-band signals including at least two analysis sub-band signals from the low-frequency components of the signal. The method includes determining a first set of synthesis sub-band signals from the set of analysis sub-band signals using a first transposition order P1. The first set of synthesis sub-band signals is determined based on a portion of the set of analysis sub-band signals whose phase is shifted by an amount derived from the first transposition order P1. Further, the method includes determining a second set of synthesis sub-band signals from the set of analysis sub-band signals using a second transposition order P2. The second set of synthesis sub-band signals is determined based on a portion of the set of analysis sub-band signals whose phase is shifted by an amount derived from the second transposition order P2. The first transposition order P1 and the second transposition order P2 are different. The first and second sets of synthesis sub-band signals are combined to generate a combined set of synthesis sub-band signals, and the high-frequency components of the signal are generated from the combined set of synthesis sub-band signals.

[0030] As another embodiment, a method for generating high-frequency components of a signal from low-frequency components of the signal is also described. This method includes providing an analysis sub-band signal having a frequency resolution of Δf from the low-frequency components of the signal. The method further includes determining an intermediate set of synthesized sub-band signals having a frequency resolution of PΔf from a set of analysis sub-band signals using a certain transposition order P. The intermediate set of synthesized sub-band signals includes a portion of the set of analysis sub-band signals phase-shifted by the transposition order P. One or more of the intermediate synthesized sub-band signals are interpolated to determine a synthesized sub-band signal of a set of synthesized sub-band signals having a frequency resolution of FΔf. F is a resolution factor and F≥1. The transposition order P may be different from the frequency resolution F. The high-frequency components of the signal are generated from the set of synthesized sub-band signals.

[0031] As yet another embodiment, a method for generating high-frequency components of a signal at a second sampling frequency from low-frequency components of the signal at a first sampling frequency is also described. The second sampling frequency is R times the first sampling frequency and R≥1. The method includes generating a modulated high-frequency component from the low-frequency components by performing a harmonic transposition of order T. The modulated high-frequency component is determined based on a portion of the low-frequency components transposed to a frequency range T times higher, and the modulated high-frequency component is the first sampling frequency multiplied by a factor S, where T>1 and S<R.

[0032] As another embodiment, a set-top box for decoding a received signal including at least a signal is also described. The set-top box has a system for generating high-frequency components of the signal from low-frequency components of the signal. The system includes any of the forms and / or features described in this application.

[0033] As another form, a software program is also described. When executed on a computer device, the software program causes a processor to execute any of the forms and methods described in this application.

[0034] In yet another form, a storage medium is also described. The storage medium stores a software program, which, when executed on a computer device, causes a processor to execute the features of any of the forms and methods described in the present application.

[0035] In another form, a computer program product is also described. The computer program product has instructions that, when executed on a computer device, cause the computer to execute any of the forms and methods described in the present application.

[0036] It should be noted that the multiple examples and embodiments described in the present application may be arbitrarily combined. In particular, it should be noted that the examples and forms described in relation to the system may be applied to the corresponding methods, and vice versa. Furthermore, it should be noted that the disclosure of the present application also includes combinations of claims other than the combinations of claims explicitly shown as dependent claims (i.e., the claims and their technical features may be combined in any order and in any form).

Examples

[0037] Hereinafter, examples that do not limit the scope of the present invention will be described with reference to the accompanying drawings.

[0038] The examples described below merely illustrate the principle of the present invention that performs efficiently synthesized harmonic transposition. It will be understood that variations and modifications to the forms and specific detailed examples described will be apparent to those skilled in the art. Therefore, it should be noted that the present invention is defined only by the appended claims and not by the specific details presented by the following description and description.

[0039] FIG. 1 shows an example of the processing of a first-order frequency-domain (FD) harmonic transposer 100. In its basic form, a T-th order harmonic transposer is, in theory, a device that shifts all the signal components of an input signal to a frequency T times higher. To perform such processing in the frequency domain, an analysis filter bank (or conversion unit) 101 converts the input signal from the time domain to the frequency domain and outputs complex subbands or subband signals referred to as analysis subbands or analysis subband signals. The analysis subband signals are provided to a non-linear processing unit 102, which modifies or adjusts the phase and / or amplitude according to the selected transposition order T. Typically, the non-linear processing unit outputs a number of subband signals equal to the number of input subband signals, i.e., the number of analysis subband signals. However, in the case of an advanced non-linear processing unit, it may be desirable to output a number of subband signals different from the number of input subband signals. In particular, two subband signals may be processed by the non-linear processing unit to generate one output subband signal. This will be described in detail below. The modified subbands or subband signals referred to as synthesis subbands or synthesis subband signals are provided to a synthesis filter bank 103 (conversion unit), which converts the subband signals from the frequency domain to the time domain and outputs a time-domain signal on which the transposition processing has been performed.

[0040] Typically, each of the filter banks has a physical frequency resolution expressed in Hertz and a time stride parameter expressed in seconds. These two parameters (i.e., the frequency resolution and the time stride) define the discrete-time parameters of the filter bank at the selected sampling rate. By selecting the physical time stride parameters of the analysis and synthesis filter banks to match (i.e., the time stride parameter measured in units of time, e.g., seconds), the output signal of the transposer 100 will have the same sampling rate as the input signal. Further, by omitting the non-linear processing unit 102, a complete reconstruction of the input signal at the output is achieved. This requires careful design of the analysis and synthesis filter banks. On the other hand, if the output sampling rate is selected to be different from the input sampling rate, a sampling rate conversion is performed. This mode of operation is necessary, for example, when applying signal transposition where the desired output bandwidth is greater than half of the input sampling rate, i.e., when the desired output bandwidth exceeds the Nyquist frequency of the input signal.

[0041] FIG. 2 shows an example of a multiple transposer system 200 including a plurality of harmonic transposers 201-1, ..., 201-P of different orders. An input signal on which transposition processing is performed is provided to a bank of P individual transposers 201-1, 201-2, ..., 201-P. The individual transposers 201-1, 201-2, ..., 201-P perform harmonic transposition of the input signal as described in connection with FIG. 1. Typically, each of the individual transposers 201-1, 201-2, ..., 201-P performs harmonic transposition of a different transposition order T. As an example, transposer 201-1 may perform transposition of order T = 1, transposer 201-2 may perform transposition of order T = 2, and transposer 201-P may perform transposition of order T = P. The results, i.e., the output signals from the individual transposers 201-1, 201-2, ..., 201-P, are added in a synthesizer, adder, or combiner 202 to generate an added transposer output.

[0042] It should be noted that each of the transposers 201-1, 201-2,..., 201-P requires an analysis and synthesis filter bank as shown in FIG. 1. Further, the individual transposers 201-1, 201-2,..., 201-P typically change the sampling rate of the input signal to be processed by different amounts. As an example, the sampling rate of the output signal of the transponder 201-1 is P times higher than the sampling rate of the input signal for the transponder 201-P. This is due to the bandwidth expansion factor P used in the transponder 201-P, that is, using a synthesis filter bank having P times more subchannels than the analysis filter bank. To do this, the sampling rate and the Nyquist frequency are increased by a factor of P. As a result, the individual time-domain signals need to be resampled in order to enable the synthesis of various output signals in the synthesis unit 202. Resampling of the time-domain signals can be performed on the input signal or the output signal for each of the individual transposers 201-1, 201-2,..., 201-P.

[0043] FIG. 3 shows a configuration example of a multiple harmonic transposer or multiple transposer system 300 that performs multiple transpositions using a common analysis filter bank. In the first stage of the design of the multiple transposer 300, the analysis filter banks (reference numeral 101 in FIG. 1) of all the transposers 201-1, 201-2, ..., 201-P are designed to be identical and replaceable with a single analysis filter bank 301 so that the individual transposers 201-1, 201-2, ..., 201-P of FIG. 2 can be designed. As a result, the time-domain input signal is converted into a single set of frequency-domain subband signals (i.e., a single set of analysis subband signals). These subband signals are provided to various non-linear processing units 302-1, 302-2, ..., 302-P for various transpositions. As described with respect to FIG. 1, the non-linear processing unit has a phase and / or amplitude correction unit for the subband signal, and this correction is different for different transpositions. Therefore, the differently corrected subband signals or subbands are respectively provided to different synthesis filter banks 303-1, 303-2, ..., 303-P corresponding to different non-linear processing units 302-1, 302-2, ..., 302-P. As a result, time-domain output signals subjected to different transpositions are obtained, and they are added in the synthesizer 304 to obtain an added transposer output.

[0044] It should be noted that when the synthesis filter banks 303-1, 303-2, ..., 303-P corresponding to various transposition orders operate at various sampling rates, for example, by using various bandwidth expansion degrees, the time-domain output signals of the various synthesis filter banks 303-1, 303-2, ..., 303-P need to be resampled variously in order to align the P output signals to the same time unit or time grid before being added in the synthesizer 304.

[0045] FIG. 4 shows a configuration example of a multi-harmonic transposer system 400 that utilizes multiple degrees of transposition using a common synthesis filter bank 404. In the first stage of the design of the multiple transposer 400, the individual transposers 201-1, 201-2, ..., 201-P of FIG. 2 are designed such that the synthesis filter banks of all transposers are identical and can be replaced by a single synthesis filter bank 404. As in the example shown in FIG. 3, it should be noted that the non-linear processing units 402-1, 402-2, ..., 402-P are different for each transposition degree. Further, the analysis filter banks 401-1, 401-2, ..., 401-P are different for different transposition degrees. Therefore, a group of P analysis filter banks 401-1, 401-2, ..., 401-P determines P groups of analysis sub-band signals. These P groups of analysis sub-band signals are given to the corresponding non-linear processing units 402-1, 402-2, ..., 402-P, which output P groups of modified sub-band signals. These P groups of sub-band signals are synthesized in the frequency domain in the synthesizer 403, and the synthesized group of sub-band signals is output as the input to a single synthesis filter bank 404. The synthesis of the signals in the synthesizer 403 includes giving differently processed sub-band signals to different sub-band ranges and / or overlapping the contributions of the sub-band signals to overlapping sub-band ranges. In other words, the various analysis sub-band signals processed at different transposition degrees cover overlapping frequency ranges. In that case, the individual contributions of the overlap are synthesized (i.e., added and / or averaged) by the synthesizer 403. The time-domain output signal of the multiple transposer 400 is obtained from the common synthesis filter bank 404. Similar to what was described above, when the analysis filter banks 401-1, 401-2, ..., 401-P operate at different sampling rates, the time-domain signal inputs to the various analysis filter banks 401-1, 401-2, ..., 401-P need to be resampled to align the output signals of the various non-linear processing units 402-1, 402-2, ..., 402-P to the same time unit.

[0046] FIG. 5 shows an example of a multi-harmonic transposer system 500 that has one common analysis filter bank 501 and one common synthesis filter bank 504 and performs a plurality of degrees of transposition. In this case, the individual transposers 201-1, 201-2, ..., 201-P of FIG. 2 are designed such that both the analysis filter bank and the synthesis filter bank of the P harmonic transposers are the same. If the conditions of the same analysis and synthesis filter banks for different P harmonic transposers match, the same filter banks can be replaced by one analysis filter bank 501 and one synthesis filter bank 504. The advanced non-linear processing units 502-1, 502-2, ..., 502-P output various contributing components to be synthesized in the synthesis unit 503, and the synthesis unit generates the synthesized input for the individual sub-bands of the synthesis filter bank 504. Similar to the multi-harmonic transposer 400 shown in FIG. 4, the synthesis of the signals in the synthesis unit 503 includes supplying the signals processed in different ways by the non-linear processing units 502-1, 502-2, ..., 502-P to various sub-band ranges, and superimposing the multiple contributing outputs on multiple overlapping sub-band ranges.

[0047] As described above, the non-linear processing unit 102 typically provides at the output a number of sub-bands corresponding to the number of sub-bands in the input. The non-linear processing unit 102 typically modifies the phase and / or amplitude of the sub-bands or sub-band signals according to the transposition order T used. As an example, the sub-bands in the input are converted to sub-bands at T times higher frequencies at the output, that is, the sub-bands (analysis sub-bands) in the range of [(k-(1 / 2))Δf, (k+(1 / 2))Δf] in the input to the non-linear processing unit 102 are converted to sub-bands (synthesis sub-bands) in the range of [(k-(1 / 2))TΔf, (k+(1 / 2))TΔf] at the output of the non-linear processing unit 102. Here, k is the sub-band index number, and Δf is the frequency resolution of the analysis filter bank. In order to be able to use the common analysis filter bank 501 and the common synthesis filter bank 504, one or more of the advanced processing units 502-1, 502-2,..., 502-P are configured to provide a number of output sub-bands different from the number of input sub-bands. In one embodiment, the number of input sub-bands to the advanced processing units 502-1, 502-2,..., 502-P is approximately F / T times the number of output sub-bands. Here, T is the transposition order of the advanced processing unit, and F is the filter bank resolution factor introduced in the following description.

[0048] Hereinafter, the principle of the advanced processing units 502-1, 502-2,..., 502-P regarding the non-linear processing units 502-1, 502-2,..., 502-P will be described. For this purpose, the following is assumed.

[0049] ● The analysis filter bank and the synthesis filter bank share the same physical time stride parameter Δt.

[0050] ● The analysis filter bank has a physical frequency resolution Δf.

[0051] ● The synthesis filter bank has a physical frequency resolution FΔf, where the resolution factor F is an integer greater than or equal to 1 (F ≧ 1).

[0052] Furthermore, the plurality of filter banks are prepared evenly or at integer multiples (evenly), that is, the sub-band at index 0 has its center near zero frequency, and it is assumed that the center frequency of the analysis filter bank is given by kΔf, and the analysis sub-band index k is k = 0, 1,..., L A -1, and L A is the number of sub-bands of the analysis filter bank. The center frequency of the synthesis filter bank is given by nFΔf, and the synthesis sub-band index n is n = 0, 1,..., L s -1, and L s is the number of sub-bands of the synthesis filter bank.

[0053] When performing a conventional transposition of degree T ≧ 1 as shown in FIG. 1, the resolution factor F is selected such that F = T, and the analysis sub-band k of the non-linear processing unit is mapped to the analysis sub-band with the same index n = k. The non-linear processing unit 102 typically multiplies the factor T to the phase of the sub-band or the sub-band signal, that is, for each sample of the sub-band of the filter bank, it can be written as follows: θ s (k) = Tθ A (k) (1) θ A (k) is the phase of the sample of the analysis sub-band k, and θ s (k) is the phase of the sample of the synthesis sub-band k. The magnitude or amplitude of the sample of the sub-band may be maintained without being modified, or may be increased or decreased by a certain gain factor. Since T is an integer, the processing of the formula (1) does not depend on the definition of the phase angle.

[0054] When the decomposition energy factor F is equal to the transposition order T (i.e., when F = T), the frequency resolution of the synthesis filter bank (i.e., FΔf) depends on the transposition order T. Therefore, in the analysis or synthesis processing stage, it is necessary to use different transposition orders T for different filter banks. This is because the transposition order T defines the degree of physical frequency resolution, that is, the degree of frequency resolution Δf of the analysis filter bank and the frequency resolution FΔf of the synthesis filter bank.

[0055] In order to be able to use a common analysis filter bank 501 and a common synthesis filter bank 504 for a plurality of different transposition orders T, it is proposed in the present application to set the frequency resolution of the synthesis filter bank to FΔf, that is, to make the frequency resolution of the synthesis filter bank 504 independent of the transposition order T. Therefore, when the decomposition energy factor F indicating the degree of physical frequency resolution of the analysis and synthesis filter banks does not need to follow the relational expression F = T, the problem becomes how to perform the transposition of order T.

[0056] As described above, according to the principle of the harmonic transposer, the input to the sub-band n of the synthesis filter bank with a center frequency of nFΔf is determined by the analysis sub-band at a center frequency (nFΔf / T) that is 1 / T times lower. The center frequency of the analysis sub-band can be specified as kΔf by using the analysis sub-band index k. The two expressions of the center frequency of the analysis sub-band index (i.e., nFΔf / T and kΔf) are equal (can be made to correspond). Considering that n is an integer, the rational number of the expression nF / T can be expressed as the sum of an integer analysis sub-band index k and the remainder r (r ∈ {0, 1 / T, 2 / T,..., (T - 1) / T}) as follows: nF / T = k + r (2) Therefore, it is guaranteed that the input to the synthesis sub - band for the synthesis sub - band index n is derived from the analysis sub - band or sub - band k of the index given by Equation (2) using a transposition of degree T. Since nF / T is a rational number, the remainder or residue r is not equal to a value of 0, and the value k + r is greater than the analysis sub - band index k and less than the analysis sub - band index k + 1. Therefore, the input to the synthesis sub - band for the synthesis sub - band index n is derived from the analysis sub - bands of the analysis sub - band indices k and k + 1 using a transposition of degree T, where k is given by Equation (2).

[0057] As a result of the above analysis, the advanced non - linear processing (advanced non - linear processing) performed in the non - linear processing units 502 - 1, 502 - 2,..., 502 - P generally involves considering two adjacent analysis sub - bands of indices k and k + 1 that give the output to the synthesis sub - band n. In the case of the transposition degree T, the phase adjustment performed by the non - linear processing units 502 - 1, 502 - 2,..., 502 - P may thus be determined by the following linear interpolation method: θ s (n)=T(1 - r)θ A (k)+Trθ A (k + 1)(3) Here, θ A (k) is the phase of the samples of the analysis sub - band k, θ A (k + 1) is the phase of the samples of the analysis sub - band k + 1, and θ s (k) is the phase of the samples of the synthesis sub - band n. That is, when the remainder r is close to 0, the value of k + r is close to k, and in that case, what mainly contributes to the phase of the samples of the synthesis sub - band is obtained from the phase of the samples of the analysis sub - band of sub - band k. On the other hand, when the remainder r is close to 1, the value of k + r is close to k + 1, and in that case, what mainly contributes to the phase of the samples of the synthesis sub - band is obtained from the phase of the samples of the analysis sub - band of sub - band k + 1. It should be noted that both the phase multiplication factors T(1 - r) and Tr are integers so that the phase adjustment of Equation (3) is clearly defined and does not depend on the definition of the phase angle.

[0058] Considering the size of the sub-band sample, the following geometric mean is selected to determine the size of the composite sub-band sample: a S (n)=a A (k) (1-r) a A (k + 1) r (4) a S (n) represents the size of the sample of the composite sub-band n, and a A (k) represents the size of the sample of the analysis sub-band, and a A (k + 1) represents the size of the sample of the analysis sub-band k + 1.

[0059] If the filter bank is prepared (oddly) at a position that is a half-integer multiple, the center frequency of the analysis filter bank is given by (k+(1 / 2))Δf, where k = 0, 1,..., L A -1, and the center frequency of the synthesis filter bank is given by (n+(1 / 2))FΔf, where n = 0, 1,..., L S -1, and the formula corresponding to the above formula (2) is derived by equating the center frequency (n+(1 / 2))FΔf / T of the synthesis filter bank after transposition and the center frequency (k+(1 / 2))Δf of the analysis filter bank. Considering the integer index k and the remainder r ∈ [0, 1], the following formula is derived for the filter bank at the half-integer multiple position: (n+(1 / 2))F / T = k + 1 / 2 + r (5) When T - F, that is, the difference between the transposition order and the resolution factor, is even, it can be seen that both T(1 - r) and Tr are integers, and the interpolation formulas of formulas (3) and (4) can be used.

[0060] Figure 5b shows how analysis sub-bands are associated with synthesis sub-bands. Figure 5b shows four mapping examples for four different transposition orders from T = 1 to T = 4. Each figure shows how a source bin 510 (i.e., an analysis sub-band) is mapped to a target bin 530 (i.e., a synthesis sub-band). For simplicity of illustration, it is assumed that the decomposition factor F is 1. In other words, Figure 5b shows how the analysis sub-band signal is mapped to the synthesis sub-band signal using equations (2) and (3). In the case of the illustrated example, with F = 1 and the maximum transposition order P = 4, the analysis / synthesis filter bank is set evenly at integer multiples.

[0061] In the case of the illustrated example, equation (2) can be written as n / T = k + r. Thus, for a transposition order T = 1, the analysis sub-band of index k is mapped to the corresponding synthesis sub-band n, and the remainder r is zero. This is shown in Figure 5b, where source bin 511 is one-to-one associated with target bin 531.

[0062] When the transposition order T = 2, the remainder r takes on the values 0 and 1 / 2, and the source bins are associated with multiple target bins. From the reverse perspective, it can be said that each of the target bins 532 and 535 receives contributions from at most two source bins. This is shown in Fig. 5b where the target bin 535 receives contributions from the source bins 512 and 515. However, the target bin 532 receives contributions only from the source bin 512. If the target bin 535 has an even index n (e.g., n = 10), Equation (2) shows that the target bin 532 receives contributions from the source bin 512 with index k = n / 2 (i.e., k = 5). In this case, the remainder r is zero, i.e., there is no contribution from the source bin 515 with index k + 1 (i.e., k + 1 = 6). For the target bin 535 with an odd index n (e.g., n = 11), the situation changes. In this case, Equation (2) shows that the target bin 535 receives contributions from the source bin 512 (index k = 5) and the source bin 515 (index k + 1 = 6). This is also the case for higher transposition orders T (e.g., T = 3 and T = 4 as shown in Fig. 5b).

[0063] For F = 2, Equation (2) can be written as 2n / T = k + r, and this case is shown in Fig. 5c. When the transposition order T = 2, the analysis sub - band with index k is mapped to the corresponding synthesis sub - band n, and the remainder r is always zero. This can be seen from the fact that the source bin 521 is mapped one - to - one to the target bin 514.

[0064] When the transposition order T = 3, the remainder r takes values of 0, 1 / 3, and 2 / 3, and the source bin is associated with multiple target bins. From the reverse perspective, it can be said that each of the target bins 542 and 545 receives contributions from at most two source bins. This is shown in Fig. 5c, where the target bin 545 receives contributions from the source bins 522 and 525. If the target bin 545 has, for example, an index n = 8, Equation (2) shows that k = 5 and r = 1 / 3, indicating that the target bin 545 receives contributions from the source bin 522 (index k = 5) and the source bin 525 (index k + 1 = 6). However, in the case of the target bin 546 with index n = 9, the remainder r becomes zero, and the target bin 546 receives contributions only from the source bin 525. This is also the case for higher transposition orders T (e.g., T = 4 as shown in Fig. 5c).

[0065] A further explanation of the advanced non-linear processing is as follows. The advanced non-linear processing can be understood as a combination of performing a transposition of a given order T and mapping the sub-band signal after the transposition to a frequency grid defined by a common synthesis filter bank (i.e., the frequency grid FΔf). To explain this interpretation, refer again to FIG. 5b or 5c. However, assume that the source bin 510 or 520 is a synthesis sub-band derived from the analysis sub-band using the transposition order T. These synthesis sub-bands have a frequency grid given by TΔf. To generate the synthesis sub-band in the predetermined frequency grid FΔf given by the target bin 530 or 540, the source bin 510 or 520 (i.e., the synthesis sub-band having the frequency grid TΔf) needs to be mapped to the predetermined frequency grid FΔf. This is done by interpolating one or more source bins 510 or 520 (i.e., the synthesis sub-band signals in the frequency grid TΔf) and determining the target bin 530 or 540 (i.e., the synthesis sub-band signals in the frequency grid FΔf). In the case of the preferred embodiment, linear interpolation is used, and the interpolation weight (weight coefficient) is proportional to the reciprocal of the difference between the center frequency of the target bin 530 or 540 and the corresponding source bin 510 or 520. As an example, the weight is 1 when the difference is zero, and the weight is 0 when the difference is TΔf.

[0066] In short, a non-linear processing method is described that enables the contribution of several analysis sub-bands to the synthesis sub-band by transposition to be determined. The non-linear processing method allows a single common analysis and synthesis sub-band filter bank to be used for various transposition orders, thereby significantly reducing the complex calculations of multiple harmonic transposers.

[0067] Hereinafter, some embodiments of a multi-harmonic transposer or a harmonic transposer system will be described. In a typical process in an audio source encoding / decoding system that uses high frequency reconstruction (HFR) such as spectral band replication (SBR) shown in Patent Document 1 (WO98 / 57436) etc. included in the references of the present application, a core decoder (i.e., a decoder for low frequency components of an audio signal) outputs a time domain signal to an HFR module or an HFR system (i.e., a module or a system that performs reconstruction of high frequency components of an audio signal). The low frequency component has a bandwidth narrower than half of the bandwidth of the original audio signal including the low frequency component and the high frequency component. Therefore, a time domain signal (time domain signal) including a low frequency component referred to as a low band signal (low band signal) may be sampled at half the sampling rate of the final output signal of the audio encoding / decoding system. In that case, the HFR module needs to efficiently resample (resample) the core signal (i.e., the low band signal) to twice the sampling frequency so as to assist in adding the core signal to the output signal. Therefore, the so-called bandwidth extension factor applied by the HFR module is equal to 2.

[0068] After generation of a high frequency component referred to as an HFR generated signal, the HFR generated signal is dynamically adjusted so as to match as much as possible the high frequency component of the original signal (i.e., the high frequency component of the originally encoded signal). This adjustment is typically performed by a so-called HFR processor that uses information on the transmission side. The transmission side information includes information on the spectral envelope of the high frequency component of the original signal, and the adjustment of the HFR generated signal includes adjustment of the spectral envelope of the HFR generated signal.

[0069] To perform the adjustment of the HFR generation signal according to the transmission - side information, the HFR generation signal is analyzed by a multi - channel Quadrature Mirror Filter (QMF) bank, and this multi - channel QMF bank provides the spectral QMF sub - band signals of the HFR generation signal. Then, the HFR processor performs the adjustment of the HFR generation signal in the spectral QMF sub - band signals obtained from the analysis QMF bank. Finally, the adjusted QMF sub - band signals are synthesized in the analysis QMF bank. To perform the change of the sampling frequency, for example, to double the sampling frequency from the sampling frequency of the low - band signal to the sampling frequency of the output signal of the audio encoding / decoding system, the number of analysis QMF banks may be different from the number of synthesis QMF banks. In one embodiment, the analysis QMF bank may generate 32 sub - band signals, and the synthesis QMF bank processor may process 64 QMF sub - bands, thereby providing a two - fold sampling frequency. It should be noted that typically, the analysis and / or synthesis filter banks of the transposer may generate hundreds of analysis and / or synthesis sub - bands and may provide a much higher frequency resolution than the QMF bank.

[0070] The HFR system 600 of FIG. 6 shows an example of a process for generating high-frequency components of a signal. The transmitted bitstream is received by a core decoder 601, and the core decoder provides the frequency components of the decoded output signal at a sampling frequency fs. The low-frequency components of the sampling frequency fs are input to individual respective transposers 602-1, ..., 602-P, and each individual transposer corresponds to an individual transposer with a transposition order T = 2, ..., P as shown in FIG. 1. The individual signals after transposition for T = 1, 2, ..., P are separately provided to specific instances of individual analysis QMF banks 603-1, ..., 603-P. Note that the low-frequency components are considered to be the transposition signals of order T = 1. Resampling of the core signal (i.e., resampling of the low-frequency components at the sampling frequency fs) is performed by filtering the low-frequency components using a downsampled QMF bank 603-1 (typically having 32 channels instead of 64 channels). As a result, 32 subband signals are generated, and each QMF subband signal has a sampling frequency fs / 32.

[0071] The influence on the signal by the transposition of order T = 2 at the sampling frequency fs is represented by a frequency diagram as shown in Fig. 12a. The frequency diagram 1210 shows the input signal to the transposer 602-2 with a bandwidth of B Hz. The input signal is divided (partitioned or segmented) into a plurality of analysis sub-band signals by an analysis filter bank. This is represented by the segmentation into the frequency band 1211. The analysis sub-band signals are shifted (transposed) to a frequency range T = 2 times higher, and the sampling frequency is doubled. The resulting frequency-domain signal is shown in the frequency diagram 1220, and the frequency diagram 1220 has the same frequency scale as the frequency diagram 1210 (one tick or one unit is the same). It can be seen that the sub-band 1211 has been transposed to the sub-band 1221. The process of transposition is indicated by the dashed arrow. Further, the periodic spectrum 1222 of the sub-band signal after transposition is shown in the frequency diagram 1220. Alternatively, the process of transposition may be shown as in the frequency diagram 1230, in which case the frequency axis is scaled, i.e., the transposition factor T = 2 is multiplied. In other words, the frequency diagram 1230 corresponds to the frequency diagram 1220 with a scale T = 2 times larger. Each of the sub-band signals 1231 has a bandwidth twice that of the segment 1211. This becomes the output signal of the transposer 602-2 having a sampling rate T = 2 times higher than the input signal (i.e., a sampling rate of 2fs), but the temporal duration of the signal remains unchanged.

[0072] As shown in FIG. 6 and as described above, the output signal of each transposer 602-2 with a transposition order T = 2 has a sampling frequency of 2fs. In order to generate a QMF subband signal with a sampling frequency of fs / 32, an analysis QMF bank 603-2 having 64 channels should be used. Similarly, the output signal of each transposer 602-P with a transposition order T = P has a sampling frequency of Pfs. In order to generate a QMF subband signal at a sampling frequency of fs / 32, an analysis QMF bank 603-2 having 32P channels should be used. If the size (i.e., the number of channels of each of the analysis QMF banks 603-1,..., 603-P) is adapted to the signals resulting from the corresponding transposers 602-2,..., 602-P, the subband signals from all instances of the analysis QMF banks 603-1,..., 603-P have an equal sampling frequency. A group of QMF subband signals at a sampling frequency of fs / 32 is provided to the HFR processing module 604, and spectral adjustment of the high-frequency components is performed according to the transmission-side information. Finally, the adjusted subband signals are synthesized into a time-domain signal by a 64-channel inverse or synthesis QMF bank 605, whereby a signal decoded at a sampling frequency of 2fs from the QMF subband signals sampled at fs / 32 can be efficiently generated.

[0073] As described above, the transposer modules 602-2, ..., 602-P each generate time-domain signals at various sampling rates such as sampling rates 2fs, ..., Pfs. Resampling of the output signals of the transposer modules 602-2, ..., 602-P is performed by "inserting" or discarding subband channels in the subsequent corresponding QMF analysis banks 603-1, ..., 603-P. In other words, resampling of the output signals of the transposer modules 602-2, ..., 602-P may be performed by using different numbers of QMF subbands in the subsequent individual analysis QMF banks 603-1, ..., 603-P and the synthesis QMF bank 605. Therefore, the output QMF subband signals from the QMF banks 602-2, ..., 602-P need to be adapted to the 64 channels that are ultimately transmitted to the synthesis QMF bank 605. This adaptation or mapping is done by mapping or adding the 32 QMF subband signals from the 32-channel analysis QMF bank 603-1 to the first 32 channels (i.e., the 32 lower-frequency channels) of the synthesis or inverse QMF bank 605. In fact, this results in a filtered signal by upsampling the analysis QMF bank 603-1 by a factor of 2. All subband signals resulting from the 64-channel analysis QMF bank 603-2 may be directly mapped or added to the 64 channels of the inverse QMF bank 605. From the fact that the analysis QMF bank 603-2 is exactly the same size as the synthesis QMF bank 605, the individual signals after transposition are not resampled. The QMF banks 603-3, ..., 603-P have a number of output QMF subband signals that exceed 64 subband signals. In that case, the 64 channels on the low-frequency side may be mapped or added to the 64 channels of the synthesis QMF bank 605. The remaining channels on the high-frequency side may be discarded. As a result of the 32P-channel analysis QMF bank 603-P, the signal filtered by the QMF bank 603-P is downsampled by a factor of P / 2.Therefore, this resampling that depends on the transposition order P results in all transposition signals having the same sampling frequency.

[0074] In other words, even if the transposer modules 602-2, ..., 602-P generate time-domain signals with different sampling rates, it is desirable for the subband signals to have the same sampling rate when provided to the HFR processing module 604. This is achieved by using analysis QMF banks 603-3, ..., 603-P of different sizes, which are typically 32T, where T is the transposition factor or the order of transposition. Since the HFR processing module 604 and the synthesis QMF bank 605 typically process 64 subband signals (i.e., twice the size of the analysis QMF bank 603-1), all subband signals resulting from the analysis QMF banks 603-3, ..., 603-P with subband indices exceeding that number may be discarded. This is done because the output signals of the transposers 602-2, ..., 602-P virtually cover a frequency range exceeding the Nyquist frequency of the output signal. The remaining subband signals (i.e., the subband signals that map to the subbands of the synthesis QMF bank 605) may be added to generate frequency-overlapped (overlapped) transposition signals (see FIG. 12b described later), or alternatively synthesized to obtain non-overlapped transposition signals as shown in FIG. 12c (described later), for example. In the case of non-overlapped transposition signals, the transposer 602-T of order T (T = 2, ..., P) is typically assigned to a specific frequency range, and the transposer 602-T exclusively generates frequency components for that specific frequency range. In one embodiment, the dedicated (individual) frequency range of the transposer 602-T is [(T-1)B, TB], where B is the bandwidth of the input signal for the transposer 602-T. In that case, the combined subband signals of the transposer 602-T outside the individual frequency range are ignored or discarded. On the other hand, the transposer 602-T may generate frequency components that overlap with the frequency components of the other transposers 602-2, ..., 602-P. In that case, those overlapping frequency components are superimposed in the domain of the QMF subbands.

[0075] As described above, in a typical embodiment, the multiple transposers 602-2,..., 602-P are used to generate high-frequency components of the output signal of the HFR module 600. It is assumed that the input signals to the transposers 602-2,..., 602-P (i.e., the low-frequency components of the output signal) have a bandwidth of B Hz and a sampling rate of fs, and the output signal of the HFR module 600 has a sampling rate of 2fs. Thus, the high-frequency components may cover the frequency range [B, fs]. Each of the transposers 602-2,..., 602-P provides a contribution to the high-frequency components, and these contributions may or may not overlap. In FIG. 12b, overlapping contributions from various transposers 602-2,..., 602-P generate high-frequency components. Frequency diagram 1241 shows the low-frequency components (i.e., the input signals to the transposers 602-2,..., 602-P). Frequency diagram 1242 shows the output signal of the second-order transposer 602-2 including sub-bands in the frequency range [B, 2B], indicated by the hatched frequency range in the figure. The frequency range [0, B] generated by the transposer is typically ignored or discarded because that range is covered by the low-frequency input signal, which is indicated by the white frequency range in the figure. Frequency diagram 1243 shows the output signal of the third-order transposer 602-3 covering the frequency range [B, 3B], indicated by the hatched frequency range in the figure. Similarly, the transposer 602-P generates an output signal covering the frequency range [B, PB] shown in frequency diagram 1244. Finally, the output signals of the various transposers 602-2,..., 602-P and the low-frequency components are mapped to QMF sub-bands using the analysis QMF banks 603-1,..., 603-P, thereby generating a group of P QMF sub-bands. As can be seen from frequency diagram 1245, the QMF sub-band covering the frequency range [0, B] indicated by reference numeral 1246 has contributions only from the low-frequency components (i.e., the signals obtained from the first transposition).The QMF subbands covering the frequency range [B, 2B] shown by reference number 1247 receive contributions from the output signals with transposition orders T = 2, ..., P. The QMF subbands covering the frequency range [2B, 3B] shown by reference number 1248 receive contributions from the output signals with transposition orders T = 3, ..., P, and so on. The QMF subbands covering the frequency range [(P - 1)B, PB] shown by reference number 1249 receive contributions from the output signals with transposition order T = P.

[0076] In contrast, in FIG. 12c, the transposers 602-2, ..., 602-P are configured such that the frequency ranges of their respective output signals do not overlap. The frequency diagram 1251 shows the low-frequency components. The frequency diagram 1252 shows the output signal of the second-order transposer covering the frequency range [B, 2B]. The frequency diagram 1253 shows the output signal of the third-order transposer 602-3 covering the frequency range [2B, 3B], and the frequency diagram 1254 shows the output signal of the P-th order transposer 602-P covering the frequency range [(P-1)B, PB]. The signals of the low-frequency components and the output signals of the transposers 602-2, ..., 602-P are respectively supplied to the analysis QMF banks 603-1, ..., 603-P that provide P groups of QMF sub-bands. Typically, these QMF sub-bands do not have contributions from overlapping frequency ranges. This is shown in the frequency diagram 1255. The QMF sub-band covering the frequency range [0, B] indicated by the reference numeral 1256 receives only the contribution from the low-frequency components (signals from the first transposition). The QMF sub-band covering the frequency range [B, 2B] indicated by the reference numeral 1257 receives the contribution from the output signal of the transposer with the transposition order T = 2. The QMF sub-band covering the frequency range [2B, 3B] indicated by the reference numeral 1258 receives the contribution from the output signal of the transposer with the transposition order T = 3. The QMF sub-band covering the frequency range [(P-1)B, PB] indicated by the reference numeral 1259 receives the contribution from the output signal of the transposer with the transposition order T = P.

[0077] Figures 12b and 12c show an example where the output signals of transposers 602-2, ..., 602-P are completely overlapping and an example where the output signals of transposers 602-2, ..., 602-P are not completely overlapping. Note that examples where they are mixed with output signals having partial overlap are also possible. It should be noted that the two examples in Figures 12b and 12c show a system when the transposers 602-2, ..., 602-P are configured such that the frequency ranges of each output signal either overlap or do not overlap. This may be done by applying windowing in the spectral region of the transposer, for example by setting the selected subband signals to zero. An alternative is to generate a wideband signal (wideband signal) by synthesizing the subband signals obtained from the analysis QMF banks 603-1, ..., 603-P in an appropriate manner for both Figures 12b and 12c for the transposers 602-2, ..., 602-P and performing filtering of the transposed signals in the QMF subband region. For example, in the non-overlapping case, only one of the analysis QMF banks 603-1, ..., 603-P contributes to the subband signal given to the HFR processor 604 in each of the transposer output frequency ranges. In the overlapping case, multiple subband signals are added before being input to the HFR processor 604.

[0078] When all or part of the signals of the HFR system 600 are critically (proximally) sampled, as shown in FIGS. 7 and 13-16 for the HFR system 700, a more efficient embodiment than the system of FIG. 6 is obtained. This means that the output signal of the core decoder 701 and preferably other intermediate signals of the HFR system 700 (e.g., the output signals of the transposers 702-2,..., 702-P) are critically sampled. For example, the core decode signal at the output of the core decoder 701 is downsampled by a rational factor Q = M1 / M2, where M1 and M2 are appropriately selected integers. The downsampling factor Q is the largest factor that forces the input signal of bandwidth B to be critically sampled. At the same time, Q is selected such that the size (32 / Q) of the QMF bank 703-1 remains an integer. The downsampling by the rational factor Q is performed in the downsampler 706, generating an output signal at the sampling frequency fs / Q. To provide a critically sampled transposition signal, the transposers 702-2,..., 702-P preferably output only a portion of the associated transposition signal (i.e., the frequency range actually used by the HFR processor 704). The frequency range associated with the transponder 702-T of transposition order T may be the range [(T-1)B, TB] of the input signal having a bandwidth of B Hz in the non-overlapping case.

[0079] This means that the output from the downsampler 706 and the outputs from the transposers 702-2,..., 702-P are critically sampled. The output signal of the second-order transponder 702-2 has a sampling frequency fs / Q equal to the output signal of the downsampler 706. However, it should be noted that since the transponder 702-2 is designed to synthesize only an approximate transposition frequency range of B to 2B Hz, the signal from the second-order transponder 702-2 is, in fact, a high-pass signal with a bandwidth of fs / (2Q).

[0080] For higher-order transposers, such as the transposer 702-P, at least two situations can be considered. The first situation is when the transposition signals overlap, that is, the low-frequency side part of the P-th transposition signal overlaps with the frequency range of the (P - 1)-th transposition signal (see Fig. 12b). In this case, the output from the critically sampled transposer 702-P has a sampling frequency of Sfs / Q, where S = min(P - 1, 2Q - 1). When S = P - 1, the highest frequency of the P-th transposition signal is still lower than the Nyquist frequency of the output signal of the HFR system 700. When S = 2Q - 1, the bandwidth of the P-th transposition signal is limited by the Nyquist frequency fs of the output signal of the HFR system 700. That is, the sampling frequency of the output signal of the transposer 702-P is never greater than (2-(1 / Q))fs, which corresponds to a signal covering the frequency range from fs / (2Q) (the highest frequency of the low-frequency side signal) to the Nyquist frequency fs. Another situation is when the transposition signals do not overlap. In this case, S = 1, and the output signal of the inverse QMF bank 705 (i.e., the output signal of the HFR system 700) covers various non-overlapping frequency ranges, but all of the transposition signals have the same sampling frequency (see Fig. 12c).

[0081] The effects of the above sub-sampling or down-sampling on the output signal of the core decoder 701 with a bandwidth of B Hz are shown in FIGS. 13-16. FIG. 13 schematically shows the signal transition from the output of the core decoder 701 to the output of the transposer 702-2 with a transition order T = 2. The frequency diagram 1310 shows the output signal of the core decoder with a bandwidth of B Hz. This signal is critically down-sampled by the down-sampler 706. The down-sampling factor Q is a rational value that ensures that the analysis QMF band 703-1 has an integer value 32 / Q with respect to the sub-band. Further, the down-sampler 706 provides an output signal that is critically sampled (i.e., an output signal having a sampling frequency fs / Q) (as close as possible to twice the bandwidth of the core decode signal) (Q < fs / (2B)). Such a critically sampled signal is shown in the frequency diagram 1320. The critically sampled signal with a sampling frequency fs / Q is applied to the transposer 702-2 and segmented into a plurality of analysis sub-bands. Such a segmented signal is shown in the frequency diagram 1330. Next, non-linear processing is performed on the analysis sub-band signal, stretching the analysis sub-band signal to a frequency range T = 2 times higher and the sampling frequency to 2fs / Q. This is shown in the frequency diagram 1340 (alternatively, it may be shown as the frequency diagram 1330 with a scaled frequency axis). It should be noted that typically only a portion of the sub-bands that are transposed are considered in the HFR processing module 704. These related transposed sub-bands are shown in the frequency diagram 1340 as hatched sub-bands covering the frequency range [B, 2B]. Only the hatched sub-bands need to be considered in the transposer synthesis filter bank, so the related range is modulated down to the baseband and the signal is down-sampled to the sampling frequency fs / Q by a factor of 2.This is shown in the frequency diagram 1360, and it can be seen that the signal covering the frequency range [B, 2B] is modulated to the baseband range [0, B]. The fact that the modulated signal actually covers the higher frequency range [B, 2B] is indicated by the reference signs "B" and "2B".

[0082] It should be noted that the steps of the illustration of the transposition (frequency diagram 1340) and the subsequent modulation to the baseband (frequency diagram 1360) are for illustrative purposes only. Both of these processes may be performed by assigning the hatched subbands (frequency diagram 1340) to the composite subbands of a composite filter bank having half the number of subbands of the analysis filter bank. As a result of such a mapping process, an output signal is obtained as shown by the frequency diagram 1360 modulated to the baseband (centered near zero frequency). In the case of non-overlapping examples, the size of the composite filter bank is reduced compared to the analysis filter bank, and an achievable downsampling factor given by a ratio can be utilized, and that ratio is the ratio of the total frequency range [0, PB] covered by the output signal of the P-th transposer 703-P to the actual frequency range [(P-1)B, PB] covered by the output signal of the P-th transposer 703-P, that is, the factor P.

[0083] FIG. 14 schematically shows the signal transition from the output of the core decoder 702-1 to the output of the transposer 702-3 with a transition order T = 3 in the case of overlapping frequency ranges. The signal with bandwidth B shown in the frequency diagram 1410 is downsampled by a factor Q by the downsampler 706 to generate the signal shown in the frequency diagram 1420. The analysis subband shown in the frequency diagram 1430 is transposed to a subband with a frequency T = 3 times higher. The transposed subband is shown in the frequency diagram 1440, and the sampling rate is increased from fs / Q to 3fs / Q. As described with respect to FIG. 13, this may be represented on a scale with the frequency axis tripled. It can be seen that the frequency range of the third-order transposer 702-3 (i.e., the hatched frequency range [B, 3B]) overlaps with the frequency range of the second-order transposer 702-2. Similar to the case of FIG. 13, the hatched subband is given to a reduced-size synthesis filter bank, which generates a signal having only frequencies from the hatched frequencies. Then, the high-pass signal is down-converted to baseband using downsampling by a factor of 3 / 2. The critically sampled output signal of the transposer 703-2 having a sampling frequency of 2fs / Q is shown in the frequency diagram 1460.

[0084] Similar to the case of FIG. 13, it should be noted that the transposition process shown in the frequency diagram 1440 and the modulation process to the baseband shown in the frequency diagram 1460 are executed by mapping the subbands hatched in the frequency diagram 1440 to the composite subbands of the composite filter bank with a reduced size. In the case of overlapping examples, the size of the composite filter bank is reduced compared to the analysis filter bank, and an achievable downsampling factor given by a certain ratio can be utilized. The ratio is the ratio of the entire frequency range [0, PB] covered by the output signal of the P-th transposer 703-P to the actual frequency range [B, PB] covered by the output signal of the P-th transposer 703-P, that is, the factor P / (P - 1).

[0085] FIG. 15 schematically shows the signal transition from the output of the downsampler 706 to the output of the transposer 702-P with a transposition order T = P when the transposition frequency range does not overlap with the related frequency range of the lower-order transposer (T = P - 1), that is, [(P - 2)B, (P - 1)B]. As described with respect to FIG. 13, the downsampled signal shown in the frequency diagram 1530 is transposed by the transposer 702-P. The transposition subbands covering the related frequency range [(P - 1)B, PB] are shown as the hatched frequency range in the frequency diagram 1540. The subbands corresponding to the hatched frequency range are given to a composite filter of reduced size, thereby generating a signal including only the frequency range [(P - 1)B, PB]. Therefore, this high-pass signal is modulated to the baseband and downsampled using the factor P. As a result, the critically sampled output signal of the transposer 702-P shown in the frequency diagram 1560 is obtained. The output signal of the transposer 702-P has frequency components in the frequency range [(P - 1)B, PB]. This needs to be considered when mapping the transposer output to the QMF subbands for HFR processing.

[0086] FIG. 16 schematically shows the signal transition from the output of the downsampler 706 to the output of the transposer 702-P with transposition order T = P when the transposition frequency range overlaps with the associated frequency range of the lower-order transposers (T = 2, ..., P-1) (i.e., [B, (P-1)B]). Similar to the explanation regarding FIG. 14, the downsampled signal shown in the frequency diagram 1630 is transposed by the transposer 702-P. The transposition subband covering the frequency range [B, PB] is shown as the hatched frequency range in the frequency diagram 1640. Similar to the case of FIG. 14, it can be seen that the hatched subband covers frequencies lower than (P-1)B. Therefore, the hatched subband overlaps with the frequency ranges of the lower-order transposers 702-2, ..., 702-P-1. Further, due to the fact that the hatched subband covers a range higher than [(P-1)B, PB], only a reduced downsampling factor can be used. As described above, when the frequency range covered by the output signal of the P-th transposer 702-P is [B, (P-1)B], this downsampling factor becomes P / (P-1). As a result, a downsampled output signal of the transposer with a sampling frequency of (P-1)fs / Q is obtained.

[0087] As noted above, it should be noted that the intermediate signals in the transposer 702-P (i.e., in particular, the signals shown in the frequency diagrams 1340, 1440, 1540, 1640) are not the signals that physically appear in the HFR system shown in FIG. 7. These signals are shown only for the purpose of explanation and are shown as "virtual" signals in the transposer 702-P, indicating the effects of transposition and filtering during implicit downsampling.

[0088] As described above, it should be noted that the output signal from the core decoder 701 may be critically sampled in advance at the sampling rate fs / Q when input to the HFR module 700. This can be done, for example, using a synthesis transform size smaller than the normal size in the core decoder 701. In this case, due to the small synthesis transform and the obsolete downsampler used in the core decoder 701, the computational burden is reduced.

[0089] Another measurement for improving the efficiency of the HFR system is combined with the individual transporters 602-2, ..., 602-P of FIG. 6 according to any of the methods described with respect to FIGS. 3, 4 or 5. As an example, instead of the individual transporters 602-2, ..., 602-P for the various transposition orders T = 2, ..., P, a multiple transporter system 300, 400 or 500 may be used. A possible situation is shown in FIG. 8, where transporters with a transposition factor T of 2 or less are grouped together for the multiple transporter 802 and may be implemented according to any of the forms described with respect to FIGS. 3-5. The output from the multiple transporter 802 has a sampling frequency of 2fs (i.e., a sampling frequency twice as high as the sampling frequency of the input signal to the multiple transporter 802). The output signal of the multiple transporter 802 is filtered by a single analysis QMF bank 803-2 having 64 channels.

[0090] As described with reference to FIG. 6, resampling of the core signal (i.e., resampling of the output signal of the core decoder 801) may be performed by filtering the signal using a downsampling QMF bank 803-1 having only 32 channels. As a result, a group of QMF subband signals has QMF subband signals at a sampling frequency of fs / 32. Two of the group of QMF subband signals are provided to the HFR processing module 804, and finally, the adjusted QMF subband signals are synthesized into a time domain signal by the 64-channel synthesis QMF bank 805. In the example described, it should be noted that the multiple transposer 802 generates a transposed time domain signal at a transposition of twice the sampling rate fs. As described with reference to FIGS. 3, 4, and 5, this transposed time domain signal is the sum of a number of transposed signals with different transposition factors T, where T is greater than 1. The reason the multiple transposer 802 provides an output signal at a sampling frequency of 2fs is that the output signal of the multiple transposer 802 covers the high frequency range (i.e., the range up to [B, fs]) of the output signal of the HFR module 800, where B is the bandwidth of the low frequency components and fs is the Nyquist frequency of the output signal of the HFR module 800.

[0091] As described with reference to FIG. 7, the efficiency of the HFR system 800 can be increased by increasing the level (degree) of subsampling of the time-domain signal, i.e., preferably by providing a critically downsampled signal at the output of the core decoder and the output of the transposer, the efficiency of the HFR system 800 can be increased. This is shown in FIG. 9, where the output signal of the core decoder 901 is downsampled by the downsampling unit 906, resulting in a downsampled signal at the sampling frequency fs / Q. This signal is provided to the multiple transposer 902 and the analysis QMF bank 903-1. Since the output of the multiple transposer 902 is a combination of signals with transposition orders from T = 2 to P, the output of the multiple transposer 902 has a sampling frequency of Sfs / Q (where S = min(P - 1, 2Q - 1)). The transposed signal is provided to the analysis QMF bank 903-2 with a size of 32S / Q. Similar to the above case, two groups of QMF subband signals are processed in the HFR processor 904 and finally converted into a time-domain signal using the synthesis QMF bank 905.

[0092] In one embodiment, if the multiple transposer is constructed to notify an invariant copy of the core signal (i.e., an invariant copy of the output signal of the core decoder), the QMF bank that analyzes the core signal (i.e., the analysis QMF bank 803-1 in FIG. 8) may be omitted. In the case of the transposer terminology, this is equivalent to transposition using a transposition factor T = 1 (i.e., first-order transposition). When first-order transposition is added to the multiple transposer system 802 in FIG. 8, the block diagram of the HFR module 1000 modified in this way is shown in FIG. 10. As shown in FIG. 10, the signal decoded by the core decoder 1001 is simply used as an input to the multiple transposer 1002, i.e., the signal decoded by the core decoder 1001 is not given to any additional elements of the HFR module 1000. The multiple transposer 1002 is constructed such that its single output signal has a sampling frequency of 2fs. In other words, the multiple transposer 1002 generates a time-domain signal that is twice the sampling rate, and the time-domain signal is the sum of transposition signals with different transposition factors T, where T takes any value between 1 and P. This single output signal from the multiple transposer 1002 is analyzed by a 64-channel QMF bank 1003, and the QMF subband signals are then given to the HFR processing module 1004, which adjusts the QMF subband signals using the transmission-side information. The adjusted QMF subband signals are finally synthesized by a 64-channel synthesis QMF bank 1005.

[0093] Similar to the downsampling described with reference to FIGS. 7 and 9, the efficiency of the HFR module 1000 can be improved by utilizing subsampling of the time-domain signal. Such an HFR module 1100 is shown in FIG. 11. The received bitstream is decoded by the core decoder 1101, which provides a time-domain signal at the sampling frequency fs. The time-domain output signal is downsampled by a factor Q using the downsampling section 1106. The signal downsampled at the sampling frequency fs / Q is provided to the multiple transposer 1102. The output from the multiple transposer 1102 has the sampling frequency Sfs / Q. However, since the transposed signal has the decoded and downsampled output signal from the core decoder 1101, the parameter S is selected as S = min(P, 2Q). The output signal of the multiple transposer 1102 is segmented into QMF subband signals using an analysis QMF bank 1103 having 32S / Q channels. The QMF subband signals are adjusted using the transmission-side information and then absorbed by the synthesis 64-channel QMF bank 1105.

[0094] As described above, the multiple transposers 802, 902, 1002, and 1102 shown in FIGS. 8 - 11 may be based on any of the configurations related to FIGS. 3 - 5. Further, although the arithmetic processing efficiency is inferior compared to the multiple transposer of FIGS. 3 - 5, the configuration of the transposer shown in FIG. 2 may be used. In the first preferred embodiment, the HFR module configurations shown in FIGS. 10 and 11 may be combined with the multiple transposer described with reference to FIG. 5. A specific example of mapping the analysis subbands of the transposer to the synthesis subbands of the transposer is shown in FIG. 5b. In the second preferred embodiment, the HFR module configurations shown in FIGS. 8 and 9 may be combined with the multiple transposer described with reference to FIG. 5. A specific example of mapping the transposer analysis subbands to the transposer synthesis subbands is shown in FIG. 5c.

[0095] In conjunction with the examples described with respect to FIGS. 7, 9, 11, 13 - 16, general configuration blocks of a maximally decimated or critically sampled transposer may be formed. Such a configuration block 170 is shown in FIG. 17. An input signal at a sampling frequency fs is first processed by a downsampler 171 by a factor Q and filtered by a transposer analysis filter bank 172. The analysis filter bank has a filter bank size or transform size of N a and a hop size or input signal stride of δ a samples. The subband signals are then processed by a non - linear processing unit 173 using a transposition factor T. The non - linear processing unit 173 performs any of the non - linear processing described in this application. In one embodiment, the non - linear processing described with respect to FIGS. 5, 5b, 5c may be performed in the non - linear processing unit 173. Finally, the subband signals are gathered (assembled, put together, created) in a transposer synthesis filter bank 174 into a time - domain signal at a sampling frequency Rfs, where R is the desired resampling factor. The synthesis filter bank has a filter bank size or transform size of N S and a hop size or input signal stride of δ S samples. The expansion factor W for the analysis filter bank 172, the non - linear processing unit 173, and the synthesis filter bank 174 is the ratio of the sampling frequency of the output signal from the synthesis filter bank to the input signal to the analysis filter bank, as given by the following equation.

[0096] W = Rf s / f s / Q = RQ (6) The filter bank or transform size N a and N s satisfy the following relationship.

[0097] N s =(W / T)N a (7) The hop size or signal stride δ a and δ S satisfy the following relationship.

[0098] δ S =Wδ a (8) The most decimated or critically sampled transposer configuration block 170 has an input signal to the analysis filter bank 172, an output from the synthesis filter bank 174, or both, and exclusively covers the spectral bandwidth for subsequent processing, such as the HFR processing unit 704 of FIG. 7. Critical sampling of the input signal is obtained by filtering the input signal in the downsampler 171 (possibly by modulating after decimation). In one embodiment, critical sampling of the output signal is achieved by mapping the subband signals to a synthesis filter bank 174 of a minimum required size and exclusively covering the subband channels relevant for subsequent processing, such as shown in equation (7). FIGS. 13-16 show the situation when the output from the synthesis filter bank exclusively covers the relevant spectral bandwidth and is most decimated.

[0099] The plurality of configuration blocks 170 are synthesized and configured such that a transposer system critically sampled at several transposition orders is obtained. In such a system, one or more modules 171-174 of the configuration block 170 may be shared among configuration blocks of different transposition orders. Typically, a system using a common analysis filter bank 301 as described in relation to FIG. 3 has an output signal maximally decimated from the synthesis filter banks 303-1, ..., 303-P, while the input signal to the common analysis filter bank 301 is maximally decimated with respect to the transposer configuration block 170 requiring the maximum input signal bandwidth. A system using a common synthesis filter bank 404 as described in relation to FIG. 4 may have a maximally decimated input signal to the analysis filter banks 401-1, ..., 401-P and a maximally decimated output signal from the common synthesis filter 404. The system described in relation to FIG. 2 preferably has both a maximally decimated input signal to the analysis filter bank and a maximally decimated output signal from the synthesis filter bank. In the case of this example, the configuration of the system may simply be a plurality of transposer configuration blocks 170 in parallel. As described in relation to FIG. 5, a system utilizing both a common analysis filter bank 501 and a common synthesis filter bank 504 typically has a maximally decimated output signal from the common synthesis filter bank 504, while the input signal to the common synthesis filter bank 501 may be maximally decimated with respect to the signal requiring the maximum input signal bandwidth for the transposition order. In the case of this system, the transposition factor T of Equation (7) is replaced by the factor F described in relation to FIGS. 5, 5b, and 5c. It should be noted that the adder sections 202 of FIG. 2 and 304 of FIG. 3 are constructed to process and synthesize the critically sampled subband signals from the synthesis filter banks of the transposer building blocks in the case of the above example.As an example, the addition unit has a QMF analysis filter bank following the means for synthesizing sub-band signals or time-domain resampling modulation means following the means for adding signals.

[0100] The present application has described a multiple transposition method and system that enable the use of a common analysis filter bank and a common synthesis filter bank. In order to enable the use of a common analysis and synthesis filter bank, an advanced non-linear processing method has been described, and mapping from a plurality of analysis sub-bands to synthesis sub-bands is performed. By using the common analysis filter bank and the common synthesis filter bank, the multiple transposition method is improved to reduce the computational processing burden compared to the conventional transposition method. In other words, by sharing pairs of analysis and synthesis filter banks for a number of harmonic transposers, or by combining one or more harmonic transposers with an upsampler, the computational burden in the harmonic HFR method is significantly reduced.

[0101] Furthermore, various forms of HFR modules that perform multiple transitions have also been described. In particular, a form of an HFR module with reduced complexity has been described, in which critically downsampled signals are processed. The methods and systems described may be used in various decoding devices such as, for example, multimedia receivers, video / audio set-top boxes, mobile devices, audio players, video players, and the like.

[0102] The methods and systems for transposition and / or high-frequency reconstruction described in this application may be implemented as software, firmware, and / or hardware. A certain component may be implemented, for example, as software operating on a digital signal processor or a microprocessor. Another component may be implemented, for example, as hardware and / or an application-specific integrated circuit. The signals used in the described methods and systems may be stored in a medium such as a random access memory or an optical storage medium. These information may be transmitted through a network (for example, including the Internet, etc.) such as a wireless network, a sanitary network, a wireless network, or a wired network. A typical device using the methods and systems described in this application is a portable electronic device or other consumer device that stores and / or uses audio signals. The present method and system may be used in a computer system (for example, an Internet web server) that stores and provides audio signals such as music signals for downloading.

[0103] Hereinafter, means according to embodiments will be exemplarily listed.

[0104] [Appended Claim 1] A system for generating a high-frequency component of a signal from a low-frequency component of the signal, an analysis filter bank having a frequency resolution of Δf that provides a group of analysis sub-band signals including at least two analysis sub-band signals from the low-frequency component of the signal; a non-linear processing unit that determines a group of synthesis sub-band signals from the group of analysis sub-band signals using a certain transposition order P, wherein the group of synthesis sub-band signals is determined based on a part of the group of analysis sub-band signals whose phase is shifted by an amount derived from the transposition order P. A synthesis filter bank having a frequency resolution of FΔf for generating high-frequency components of signals from the group of synthesis sub-band signals, where F is a resolution factor with F≧1, and the transposition order P is different from the resolution factor F, and the synthesis filter bank and a system having the same.

[0105] [Appended Claim 2] An analysis sub-band signal belonging to the group of analysis sub-band signals whose phase is shifted by the transposition order P, or A pair of analysis sub-band signals in the group of synthesis sub-band signals Based on this, the non-linear processing unit determines the synthesis sub-band signal of the group of sub-band signals. The first member of the pair of sub-band signals has a phase shifted by a factor P’, and the second member of the pair of sub-band signals has a phase shifted by a factor P”, where P’ + P” = P. The system according to Appended Claim 1.

[0106] [Appended Claim 3] The analysis filter bank has L A analysis sub-bands, where L A >1, and the index k of the analysis sub-band is k = 0,..., L A -1, and The synthesis filter bank has L S synthesis sub-bands, where L S >1, and the index n of the synthesis sub-band is n = 0,..., L S- -1. The system according to Appended Claim 1. [Appended Claim 4] The non-linear processing unit determines the nth synthesis sub-band signal in the group of synthesis sub-band signals from the kth analysis sub-band signal and the (k + 1)th analysis sub-band signal in the group of analysis sub-band signals. The system according to Appended Claim 3.

[0107] [Appended Claim 5] The non-linear processing unit Determine the phase of the n-th synthesized sub-band signal as the sum of the phase shift of the k-th analysis sub-band signal and the phase shift of the (k + 1)-th analysis sub-band signal, and / or The system according to claim 4, wherein the magnitude of the n-th synthesized sub-band signal is determined as the product of the magnitude in the exponential representation of the k-th analysis sub-band signal and the magnitude in the exponential representation of the (k + 1)-th analysis sub-band signal.

[0108] [Claim 6] The system according to claim 5, wherein the analysis sub-band index k of the analysis sub-band signal contributing to the synthesized sub-band, together with the synthesized sub-band index n, is given by an integer obtained by truncating (F / P)n, and the remainder r of (F / P)n is given by (F / P)n - k.

[0109] [Claim 7] The non-linear processing unit Determine the phase of the n-th synthesized sub-band signal as the sum of the phase of the k-th analysis sub-band signal multiplied by P(1 - r) and the phase of the (k + 1)-th analysis sub-band signal multiplied by P(r), and / or The system according to claim 6, wherein the magnitude of the n-th synthesized sub-band signal is determined as the product of the (1 - r)-th power of the magnitude in the exponential representation of the k-th analysis sub-band signal and the r-th power of the magnitude in the exponential representation of the (k + 1)-th analysis sub-band signal.

[0110] [Claim 8] The system according to any one of claims 1 - 7, wherein the analysis filter bank and the synthesis filter bank are set at integer multiples of positions, the center frequency of the analysis sub-band is given by kΔf, and the center frequency of the synthesis sub-band is given by nFΔf.

[0111] [Claim 9] The analysis filter bank and the synthesis filter bank are set at positions that are integer multiples of half, the center frequency of the analysis sub-band is given by (k + (1 / 2))Δf, and the center frequency of the synthesis sub-band is given by (n + (1 / 2))FΔf. The system according to any one of claims 1-7, wherein the difference between the transposition order P and the resolution factor F is an even number.

[0112] [Claim 10] The analysis filter bank uses an analysis time width Δt A and the synthesis filter bank uses a synthesis time width Δt S and the analysis time width Δt A and the synthesis time width Δt S are equal. The system according to any one of claims 1-9.

[0113] [Claim 11] The non-linear processing unit uses the transposition order P to determine a group of intermediate synthesis sub-band signals having a frequency resolution of PΔf from the group of analysis sub-band signals, and the group of intermediate synthesis sub-band signals is determined based on a part of the group of analysis sub-band signals whose phase is shifted by the transposition order P. The non-linear processing unit interpolates one or more intermediate synthesis sub-band signals and determines the synthesis sub-band signals of the group of synthesis sub-band signals having a frequency resolution of FΔf. The system according to claim 1.

[0114] [Claim 12] A system for generating high-frequency components of a signal from low-frequency components of the signal, an analysis filter bank that provides a group of analysis sub-band signals including at least two analysis sub-band signals from the low-frequency components of the signal, A first non-linear processing unit that determines a first set of synthesized sub-band signals from the set of analyzed sub-band signals using a first transposition order P1, wherein the first set of synthesized sub-band signals is determined based on a portion of the set of analyzed sub-band signals whose phase is shifted by an amount derived from the first transposition order P1, the first non-linear processing unit; A second non-linear processing unit that determines a second set of synthesized sub-band signals from the set of analyzed sub-band signals using a second transposition order P2, wherein the second set of synthesized sub-band signals is determined based on a portion of the set of analyzed sub-band signals whose phase is shifted by an amount derived from the second transposition order P2, and the first transposition order P1 and the second transposition order P2 are different, the second non-linear processing unit; A combining unit that combines the first and second sets of synthesized sub-band signals to generate a combined set of synthesized sub-band signals; A synthesis filter bank that generates the high-frequency component of the signal from the combined set of synthesized sub-band signals A system having the above.

[0115] [Appended Claim 13] The system according to appended claim 12, wherein the combining unit superimposes the synthesized sub-band signals belonging to the first and second sets of synthesized sub-band signals corresponding to overlapping frequency ranges.

[0116] [Appended Claim 14] A core decoder that converts an encoded bitstream into the low-frequency component of the signal, A QMF bank that converts the high-frequency component into a plurality of quadrature mirror filter (QMF) sub-band signals, A high-frequency reconstruction processing module that corrects the QMF sub-band signals, A synthesis QMF bank that generates a corrected high-frequency component from the corrected QMF sub-band signals The system according to appended claim 12 or 13, further having the above.

[0117] [Additional Item 15] The system according to Item 14, further comprising a downsampling unit that reduces the sampling rate of the low-frequency component of the signal on the upstream side of the analysis filter bank and outputs the low-frequency component at the reduced sampling rate.

[0118] [Additional Item 16] The system according to Item 14 or 15, wherein the core decoder is based on an encoding method that is any one of Dolby E, Dolby Digital, AAA, and HE-AAC.

[0119] [Additional Item 17] A system for generating a high-frequency component of a signal at a second sampling frequency that is R times the first sampling frequency from a low-frequency component of the signal at the first sampling frequency, a harmonic transposer for generating a modulated high-frequency component from the low-frequency component, wherein the modulated high-frequency component is determined based on a spectral portion of the low-frequency component transposed to a frequency range T times higher, and the modulated high-frequency component is the product of the first sampling frequency multiplied by a factor S, and R ≧ 1, T > 1, and S < R.

[0120] [Additional Item 18] a QMF bank that associates the modulated high-frequency component with at least one of X analysis quadrature mirror filter (QMF) sub-bands that are multiples of S to provide at least one QMF sub-band signal, a high-frequency reconstruction module for modifying the at least one QMF sub-band signal, and a synthesis QMF bank for generating the high-frequency component from the modified at least one QMF sub-band signal The system according to Item 17, further comprising.

[0121] [Additional Item 19] The harmonic transposer is An analysis filter bank that provides a group of analysis subband signals from the low-frequency component of the signal; A non-linear processing unit with a transposition order of T that determines a group of synthesis subband signals from the group of analysis subband signals by changing the phase of the group of analysis subband signals; A synthesis filter bank that generates a modulated high-frequency component of the signal from the group of synthesis subband signals The system according to claim 17 or 18, comprising:

[0122] [Claim 20] The low-frequency component has a bandwidth of B, The group of synthesis subband signals is within a frequency range of (T-1)*B to T*B, The harmonic transposer modulates the group of synthesis subband signals into a baseband centered near zero frequency and generates the modulated high-frequency component. The system according to claim 19.

[0123] [Claim 21] The system according to claim 20, wherein the harmonic transposer associates the group of subband signals with the subbands of the synthesis filter bank.

[0124] [Claim 22] The system according to any one of claims 17-21, wherein the harmonic transposer constitutes the system according to any one of claims 1-13.

[0125] [Claim 23] Further comprising downsampling means upstream of the harmonic transposer, the downlink sampling means providing a critically downsampled low-frequency component from the low-frequency component of the signal at the first sampling frequency divided by a downsampling factor Q; The modulated high-frequency component is the first sampling frequency multiplied by a factor S and divided by the downsampling factor Q; X is the system according to any one of appended claims 18 - 22, which is S / Q.

[0126] [Appended claim 24] A method for generating a high - frequency component of a signal from a low - frequency component of the signal, providing a group of analysis sub - band signals including at least two analysis sub - band signals from the low - frequency component of the signal using an analysis filter bank having a frequency resolution of Δf; determining a group of synthesis sub - band signals from the group of analysis sub - band signals using a certain transposition order P, wherein the group of synthesis sub - band signals is determined based on a part of the group of analysis sub - band signals whose phase is shifted by an amount derived from the transposition order P; generating the high - frequency component of the signal from the group of synthesis sub - band signals using a synthesis filter bank having a frequency resolution of FΔf, wherein F is F≧1 and is a resolution factor, and the transposition order P is different from the resolution factor F.

[0127] [Appended claim 25] A method for generating a high - frequency component of a signal from a low - frequency component of the signal, providing a group of analysis sub - band signals including at least two analysis sub - band signals from the low - frequency component of the signal; determining a first group of synthesis sub - band signals from the group of analysis sub - band signals using a first transposition order P1, wherein the first group of synthesis sub - band signals is determined based on a part of the group of analysis sub - band signals whose phase is shifted by an amount derived from the first transposition order P1; Determining a second set of synthesized sub-band signals from the set of analyzed sub-band signals using a second transposition order P2, wherein the second set of synthesized sub-band signals is determined based on a portion of the set of analyzed sub-band signals whose phase is shifted by an amount derived from the second transposition order P2, and wherein the first transposition order P1 and the second transposition order P2 are different; Combining the first and second sets of synthesized sub-band signals to generate a combined set of synthesized sub-band signals; Generating the high-frequency component of the signal from the combined set of synthesized sub-band signals; A method comprising the steps of.

[0128] [Appendix 26] A method for generating a high-frequency component of a signal at a second sampling frequency that is R times the first sampling frequency from a low-frequency component of the signal at the first sampling frequency, comprising: Generating a modulated high-frequency component from the low-frequency component by performing harmonic transposition of order T, wherein the modulated high-frequency component is determined based on a portion of the low-frequency component transposed to a frequency range T times higher, and wherein the modulated high-frequency component is the first sampling frequency multiplied by a factor S, and R ≧ 1, T > 1, and S < R.

[0129] [Appendix 27] A set-top box for decoding a received signal including at least a signal, The system according to any one of Appendices 1-23 for generating a high-frequency component of the signal from a low-frequency component of the signal. A set-top box having the system.

[0130] [Appendix 28] A software program for causing a processor of a computer device to execute the method according to any one of Appendices 24-26.

[0131] [Additional item 29] A storage medium storing a software program that causes a processor of a computer device to execute the method according to any one of additional items 24 to 26.

[0132] [Additional item 30] A computer program having instructions for causing a computer to execute the method according to any one of additional items 24 to 26.

Claims

1. A system configured to generate a high-frequency component of a signal from a low-frequency component of the signal, an analysis filter bank configured to provide a group of analysis sub-band signals from the low-frequency component of the signal, the group of analysis sub-band signals including at least two analysis sub-band signals, the analysis filter bank; a non-linear processing unit configured to determine a group of synthesis sub-band signals from the group of analysis sub-band signals, the non-linear processing unit being configured to determine an nth synthesis sub-band signal of the group of synthesis sub-band signals from a kth analysis sub-band signal and a (k + 1)th analysis sub-band signal of the group of analysis sub-band signals, a magnitude of the nth synthesis sub-band signal depending on a magnitude in an exponential representation of the kth analysis sub-band signal and a magnitude in an exponential representation of the (k + 1)th analysis sub-band signal, a sum of an exponential part of the magnitude in the exponential representation of the kth analysis sub-band signal and an exponential part of the magnitude in the exponential representation of the (k + 1)th analysis sub-band signal being equal to 1, and a phase of the nth synthesis sub-band signal depending on a transposition order T, the non-linear processing unit; a synthesis filter bank configured to generate the high-frequency component of the signal based on the group of synthesis sub-band signals; A system having the above components.

2. The analysis filter bank has L Ａ analysis sub-bands, where L Ａ > 1, and the index k of the analysis sub-band is k = 0, ..., L Ａ is -1, The synthesis filter bank has L Ｓ synthesis sub-bands, where L Ｓ > 1, and the index n of the synthesis sub-band is n = 0,..., L Ｓ - 1. The system according to claim 1.

3. The number L of the analysis sub-bands Ａ is equal to the number L of the synthesis sub-bands Ｓ of the system according to claim 2

4. The analysis filter bank has a frequency resolution of Δf, The synthesis filter bank has a frequency resolution of FΔf, where F is a resolution factor such that F ≥ 1. The system according to claim 1.

5. a core decoder configured to convert an encoded bitstream into the low-frequency component of the signal; an analysis quadrature mirror filter bank (QMF bank) configured to convert the high-frequency component into a plurality of QMF sub-band signals; a high-frequency reconstruction processing module configured to modify the QMF sub-band signals; a synthesis QMF bank configured to generate a modified high-frequency component from the modified QMF sub-band signals; The system according to claim 1, further having the above components.

6. A method for generating a high-frequency component of a signal from a low-frequency component of the signal, Providing a group of analysis sub-band signals from the low-frequency component of the signal, wherein the group of analysis sub-band signals includes at least two analysis sub-band signals; Determining a group of synthesis sub-band signals from the group of analysis sub-band signals, wherein the nth synthesis sub-band signal among the group of synthesis sub-band signals is determined from the kth analysis sub-band signal and the (k + 1)th analysis sub-band signal among the group of analysis sub-band signals, the magnitude of the nth synthesis sub-band signal depends on the magnitude in the exponential representation of the kth analysis sub-band signal and the magnitude in the exponential representation of the (k + 1)th analysis sub-band signal, the sum of the exponential parts of the magnitude in the exponential representation of the kth analysis sub-band signal and the magnitude in the exponential representation of the (k + 1)th analysis sub-band signal is equal to 1, and the phase of the nth synthesis sub-band signal depends on the transposition order T; Generating a high-frequency component of the signal based on the group of synthesis sub-band signals; A method having the above steps. **Claim 7** The group of analysis sub-band signals is generated from the low-frequency component using an analysis filter bank; The high-frequency component is generated from the group of synthesis sub-band signals using a synthesis filter bank. The method according to claim 6. **Claim 8** A software program configured to be executed by a processor, which, when executed by a computer device, causes the steps of the method according to claim 6 to be executed. **Claim 9** A storage medium including a software program configured to be executed by a processor, which, when executed by a computer device, causes the steps of the method according to claim 6 to be executed.

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