Low-complexity bandwidth-enhanced target generation

Abstract

An encoder, a computer program, a computer program product, and a method implemented in an encoder (210, 1108A, 1108B). The method includes receiving (1203) a full-band input frame. The method includes interpolating (620, 1205) the full-band input frame toward an intermediate frame. The method includes performing (630, 1207) a spectral inversion of the intermediate frame to produce a spectrally-reversed intermediate frame. The method includes interpolating (640, 1209) the interpolated spectrally-reversed intermediate frame to match a sampling frequency of the low-pass filter and decimation process. The method includes performing (650, 1211) low-pass filtering and decimation of the spectrally-reversed spectrum to produce a bandwidth-extended (BWE) target signal.

Description

[Technical Field]

[0001] The present disclosure relates generally to communications, and more particularly to communication methods and associated devices and nodes that support wireless communications for voice and audio coding. [Background technology]

[0002] Most existing communication systems operate on limited audio bandwidths. Due to limitations in landline telephony systems, most voice services are limited to transmitting only the lower end of the frequency spectrum and only in a single mono channel. While lower-bandwidth mono signals are sufficient for most conversations, there is a desire to increase bandwidth and spatial reproduction to improve intelligibility and realism. While the capacity of communication networks continues to increase, limiting the required bandwidth per communication channel remains a major concern. In mobile networks, smaller transmission bandwidth for each call results in lower power consumption in both mobile devices and base stations. This translates into energy and cost savings for mobile operators, and end users experience extended battery life and increased talk time. Furthermore, as less bandwidth is consumed per user, mobile networks can serve a larger number of users in parallel.

[0003] A characteristic of the human auditory system is that perception is frequency dependent. In particular, human hearing becomes less accurate at higher frequencies. This has inspired the so-called bandwidth extension (BWE) technique, in which high-frequency bands are reconstructed from low-frequency bands using only a small amount of additional information.

[0004] Traditional BWE uses a representation of the spectral envelope of an extended high-band signal and a modified version of the low-band signal to reproduce the signal's spectral fine structure. When the high-band envelope is represented by a filter, the fine structure signal is often called the excitation signal. An accurate representation of the high-band envelope is perceptually more important than the fine structure. Therefore, available resources, expressed in bits, are spent on the envelope representation, while the fine structure is typically reconstructed from the coded low-band signal without additional side information. Furthermore, the temporal shape of the high-band can be adjusted using the temporal envelope. The basic concept of BWE is illustrated in Figure 1, which is described in more detail below in the detailed description of various embodiments.

[0005] In a typical stereo recording, channel pairs exhibit a high degree of similarity, or correlation. State-of-the-art stereo coding methods exploit this correlation by employing parametric coding, in which a single channel is coded at high quality and complemented with a parametric description that enables the reconstruction of the full stereo image. The process of reducing a channel pair to a single channel is often called downmixing, and the resulting channel is the downmix channel. Downmix procedures typically attempt to preserve energy by aligning the inter-channel time difference (ITD) and inter-channel phase difference (IPD) before mixing the channels. To maintain energy balance in the input signal, the inter-channel level difference (ILD) is also measured. The ITD, IPD, and ILD can then be coded and used in an inverse upmix procedure when reconstructing the stereo channel pair at the decoder. While the above parameters describe the correlated components of a channel pair, stereo channel pairs also typically contain uncorrelated components that cannot be reconstructed from the downmix. This component can be expressed as the inter-channel coherence parameter (ICC). The uncorrelated components can be artificially synthesized in a stereo decoder by running the decoded downmix channels through a decorrelator filter whose purpose is to create a signal with low correlation with the decoded downmix. The strength of the decorrelated components is then controlled by ICC parameters. The same principle applies to multichannel audio representations such as 5.1 and 7.1.4, as well as spatial audio representations such as Ambisonics or spatial audio object coding. The number of channels is reduced by exploiting the correlation between channels and bundling the reduced channel set with metadata or parameters for channel reconstruction or spatial audio rendering in the decoder.

[0006] To facilitate stereo or spatial audio signal reproduction at low bit rates, BWE techniques can be used in combination with parametric methods of spatial reconstruction, in which case a downmix is ​​also produced for the BWE target bands. Summary of the Invention

[0007] Currently, there are one or more challenges: target generation from the frequency domain is computationally complex. In a downmix encoder that operates in several modes, one solution is to inject zeros instead of synthesizing targets when operating in a mode where BWE is not used, but this can lead to zeros in the target frame when switching to a mode that uses BWE and back. This leads to energy loss and transition artifacts when going to a mode that uses BWE.

[0008] Some aspects of the present disclosure and their embodiments may provide solutions to these or other problems. According to some embodiments, a band-limited BWE target signal is extracted from a full-band target signal by low-complexity operations consisting of linear interpolation, spectral inversion, linear interpolation, and low-pass filtering and decimation.

[0009] According to some embodiments, a method in an encoder includes receiving a full-band input frame. The method further includes interpolating the full-band input frame toward an intermediate frame. The method further includes performing spectral inversion of the intermediate frame to produce a spectrally-reversed intermediate frame. The method further includes interpolating the spectrally-reversed intermediate frame to match a sampling frequency of a low-pass filter and decimation process. The method further includes performing low-pass filtering and decimation of the interpolated spectrally-reversed intermediate frame to produce a bandwidth-extended (BWE) target signal.

[0010] Similar encoders, computer programs, and computer program products are provided.

[0011] Some embodiments may provide one or more of the following technical advantages: Various embodiments may provide a target BWE signal with no additional delay and low computational complexity.

[0012] The accompanying drawings, which are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this application, illustrate several non-limiting embodiments of the inventive concepts. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graphical illustration of the basic concept of Bandwidth Extension (BWE). [Figure 2] FIG. 1 is a block diagram illustrating a stereo encoder and decoder system. [Figure 3] FIG. 2 is a block diagram illustrating a downmix encoder according to some embodiments. [Figure 4] FIG. 2 is a block diagram illustrating a downmix decoder according to some embodiments. [Figure 5] FIG. 1 is a block diagram illustrating a BWE target extractor, according to some embodiments. [Figure 6] 10 is a flowchart illustrating the operation of an encoder, according to some embodiments. [Figure 7] 1A-1H are exemplary sample images and target bands according to some embodiments. [Figure 8] FIG. 10 is a graphical illustration of interpolation, according to some embodiments. [Figure 9] FIG. 2 is a block diagram of an encoder according to some embodiments. [Figure 10] FIG. 2 is a block diagram of a decoder according to some embodiments. [Figure 11] FIG. 1 is a block diagram of a virtualized environment, according to some embodiments. [Figure 12] 10 is a flowchart illustrating the operation of an encoder, according to some embodiments. [Figure 13] 10 is a flowchart illustrating the operation of an encoder, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0014] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Examples of embodiments of the inventive concepts are shown, and the embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art. However, the inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concepts to those skilled in the art. It should also be noted that these embodiments are not mutually exclusive. It may be implicitly assumed that a component from one embodiment is present / used in another embodiment.

[0015] As previously shown, a target BWE signal is provided with no additional delay and low computational complexity.

[0016] In one exemplary embodiment of the present disclosure, the embodiment operates in a stereo encoder of the stereo encoder and decoder system outlined in Figure 2. The stereo encoder 210 processes the input left and right channel signals in segments called frames. The stereo analysis and downmix block 212 performs parameter analysis and produces a downmix. For a given frame m, the input channels may be written as follows: TIFF2025528549000002.tif10170, where n=0,1,2,...,N denotes the number of samples in frame m, and N is the input sampling frequency f inputis the length of frame m in σ. In the following description, it is assumed that the frames are extracted by overlap in the encoder so that the decoder can reconstruct the stereo signal using an overlap-add strategy. This means that the analysis frame length N a This means that w(n) is generally larger than the input frame length N. The input signals on the left and right channels are windowed with a suitable windowing function w(n) and transformed into the DFT (Discrete Fourier Transform) domain. TIFF2025528549000003.tif29170It should be noted that other frequency domain representations may be used here, such as a QMF (quadrature mirror filter) filter bank, a hybrid QMF filter bank, or an odd DFT (ODFT) representation composed of MDCT (modified discrete cosine transform) and MDST (modified discrete sine transform) transform components.

[0017] For parametric analysis, the frequency spectrum is divided into bands b, where each band is a range of frequency coefficients k=k start(b) ...k end(b) , b=0,1,2,...N bands -1 where N bands indicates the total number of bands. The band limits are generally set to reflect the resolution of human hearing, which implies narrow bands for low frequencies and wider bands for high frequencies. Note that different band resolutions can be used for different parameters.

[0018] The signal is then analyzed in a parameter analysis block to extract ITD, IPD, and ILD parameters. Furthermore, channel coherence may be analyzed and ICC parameters may be derived. These parameters are encoded by a parameter encoder 218, added to a bitstream, and stored or transmitted to a decoder. Optionally, a stereo residual bitstream may be produced by a residual encoder 216, added to a bitstream, and stored or transmitted to a decoder.

[0019] Before creating the downmix channels, it may be beneficial to compensate for ITD and IPD to reduce cancellation and maximize the energy of the downmix. ITD compensation can be implemented in the time domain before frequency conversion or in the frequency domain, but essentially involves performing a time shift on one or both channels to eliminate ITD. Phase matching can be implemented in different ways, but the goal is to match the phase so that cancellation is minimized. This ensures maximum energy in the downmix. ITD and IPD adjustment can be performed in frequency bands or over the entire frequency spectrum, and should preferably be performed using quantized ITD and IPD parameters to ensure that the correction can be reversed at the decoder stage. The various embodiments described herein are independent of the implementation of IPD and ITD parameter analysis and compensation. Here, the ITD and IPD adjusted channels are shown below. TIFF2025528549000004.tif10170

[0020] Downmix signal X M (m,k) are encoded by the downmix encoder 214 and stored or transmitted to a decoder. This encoding can be done in the frequency domain, but this encoding can also be done in the time domain. In the case of a time-domain downmix encoder, a DFT synthesis stage generates the downmix signal x M It is required to create at least one time-domain version of (m,n), which is fed to the downmix encoder. If the downmix encoder operates on several frequency bands of the downmix signal, several DFT syntheses can be performed to generate the time-domain signal of the required band.

[0021] The downmix encoder 214 is described in more detail in FIG. 3. The downmix encoder 214 may include at least two encoding modes 310, where at least one of the encoding modes 310 operates on at least two frequency bands using a low-band encoder 312 and a BWE encoder 314. The encoding mode may be selected, for example, using signal analysis to select the most appropriate mode, or the encoding mode may be selected by running all possible modes and selecting the mode that gives the best performance for the current frame m. The low-band encoder 312 generates a low-band downmix signal x M,LO The BWE encoder 314 receives the delay-adjusted high-band downmix signal x' (m,n) from the BWE target signal buffer 316 and encodes the representation of this frequency band. M,HI (m,n) is received. The buffer allows for alignment of the analysis frames to give the desired analysis length and alignment, and compensates for any possible delay from the BWE process. Typically, a BWE encoder also uses parameters from a low-band encoder, such as a low-band excitation signal in a low-band ACELP (Algebraic Code Excited Linear Prediction) encoder.

[0022] During the encoding mode 310, the BWE target buffer 316 receives the highband downmix signal x generated by the DFT synthesis. M,HI (m,n). In the encoding mode 320, the full-band downmix signal x M(m,n) is used as input to the full-band encoder 322. The full-band signal is also applied to a low-complexity BWE target signal extractor 324. An alternative to extracting the BWE target signal is to run a DFT synthesis to create the target signal, as when mode 310 is used. However, this solution can be computationally complex. Another solution can be to skip target signal generation when mode 320 is used and populate buffer 316 with zeros. This would incur additional complexity of mostly zeros, but the buffer may partially contain zeros when the next frame is encoded using mode 310. This can lead to energy loss in the BWE domain during the transition to mode 310, which negatively impacts performance.

[0023] In the decoder 220, the stereo parameters are decoded by the parameter decoder 228, and optionally a reconstructed residual signal is produced by the residual decoder 226. The downmix decoder 224 is configured to decode and reconstruct the downmix signal encoded by the downmix encoder 214. As shown in FIG. 4, the downmix decoder comprises at least a decoding mode 420 having a full-band decoder 422 and a decoding mode 410 having a low-band decoder 412 and a BWE decoder 414. Similar to the encoder, the BWE decoder may use parameters from the low-band decoder, such as the low-band excitation signal of an ACELP decoder. The output of the decoding mode used for the current frame is a reconstructed downmix. The reconstructed downmix, the reconstructed stereo parameters, and optionally the reconstructed residual signal are fed to the stereo upmixer 222 to produce a reconstructed stereo signal.

[0024] An efficient implementation of the BWE target extractor 324 can be seen in Figure 5 and can follow the steps outlined in Figure 6. If the BWE operates on several different target bands, an optional initial step 610 can be performed by an intermediate length determiner 510 to determine the intermediate length of the interpolated signal. The intermediate length is determined by determining the input sampling frequency f such that the upper limit of the target band matches the Nyquist frequency in the interpolated frame. input The target bandwidth is determined by rescaling the length of the input frame N at lo ,f hi ), then the intermediate sampling frequency f inter teeth, f inter =2f hi and the intermediate length N inter teeth, The file is TIFF2025528549000005.tif11170.

[0025] The different target bands may depend on the bandwidth of the lower band encoder. If the lower band encoder uses a lower bandwidth, the start of the BWE target band should coincide with the end of the lower band bandwidth. Generally, the BWE target band is extracted to have a small overlap with the lower band encoder bandwidth to ensure a smooth frequency transition between the encoded bands.

[0026] In step 620, the interpolator 520 calculates the intermediate frame x inter Full-band input frame x to (m,n) M Perform (m,n) interpolation. Length N=640 and f input An example input frame with a sampling frequency of .times. ...

[0027] The interpolator may use linear interpolation, as shown in Figure 8. The sample points are assumed to be connected by a straight line, and the resampling uses the sample points that intersect that line. In general, the linear interpolation function that stretches or compresses a frame of length N1 to a frame of length N2 is given by: for i = 0, 1, ..., N2 It can be written as TIFF2025528549000006.tif20170, where The file is TIFF2025528549000007.tif26170.

[0028] x int The first two lines of the equation for (i) handle the case on the edge of a frame, where the new sampling point is extrapolated from the two last points of the frame or the two first points of the frame. Index offset i offset handles the case where N2>N1, and the first sample point in the decompressed frame will be below i=0 and the last sample point will be above i=N1-1. In some cases, a displacement is desired, denoted here as ∈. In one embodiment, ∈ is It can be specified according to TIFF2025528549000008.tif11170.

[0029] Linear interpolation provides cheap resampling at the expense of high aliasing. Some weak low-pass filtering is incorporated with linear interpolation. However, aliasing is limited if the resampling is not too large. Furthermore, the BWE target signal is not directly encoded but is used only for spectral shaping, temporal shaping, and energy measurement. For this reason, the BWE target signal is less sensitive to aliasing. Note that other variants of low-complexity interpolation may also be used.

[0030] The result of the interpolation step 620 is shown in FIG. 7C, where N inter= 560, where the upper limit of the target band corresponds to the Nyquist frequency in FIG. 7D. In step 630, the spectral inverter 530 performs spectral inversion of the intermediate frame. This can be implemented by changing the sign of every second sample. TIFF2025528549000009.tif13170

[0031] Alternatively, a spectral inversion equivalent for this purpose is It can be obtained using TIFF2025528549000010.tif13170.

[0032] The result of the spectral inversion is shown in Figure 7E, and the inverted spectrum is in Figure 7F. In step 640, the interpolator 540 adjusts the frame length to match the sampling frequency in step 650, where the low-pass filter and decimator 550 performs low-pass filtering and decimation to create the BWE target signal. Here, the decimator performs decimation by 2, which gives an output sampling frequency that is half the input sampling frequency. The low-pass filter has a cutoff frequency in the middle of the spectrum. In the example shown in Figure 7, the low-pass filter and decimator is f dec = 32kHz, which means This gives the decimated frame length of TIFF2025528549000011.tif10170, which in the example shown is N dec = 640. After this interpolation, the decimator frame x dec(m,n) is shown in FIG. 7G. In the frequency spectrum shown in FIG. 7H, the target band is now aligned in the lower half of the spectrum. This is the frequency band that the low-pass filter and decimator 550 then extracts to provide the extracted BWE target signal. Note that the spectrum of the BWE target signal is now inverted. When the BWE encoder operates on the inverted frequency spectrum, the target signal is ready to be provided to the BWE target buffer 316. If the spectrum needs to be inverted, spectral inversion can be performed as previously described by changing the sign of every second sample.

[0033] The downmix encoder outputs the coded representation from the downmix encoding mode into a downmix bitstream, which is then spliced ​​with the bitstream of the parameter encoder 218. Optionally, a stereo residual bitstream can be produced by the residual encoder 216. The bitstream components of the active modules are spliced ​​into a composite bitstream that is stored or transmitted to a decoder.

[0034] As previously explained, in the decoder 220, the stereo parameters are decoded by the parameter decoder 228 and, optionally, a reconstructed residual signal is produced by the residual decoder 226. The downmix decoder 224 is configured to decode and reconstruct the downmix signal encoded by the downmix encoder 214. The output of the active decoding mode is a reconstructed downmix. The reconstructed downmix, the reconstructed stereo parameters, and the optionally reconstructed residual signal are fed to the stereo upmixer 222 to produce a reconstructed stereo signal.

[0035] Before describing operations from the perspective of the encoder 210, FIG. 9 is a block diagram illustrating elements of the encoder 210 configured to encode audio frames, according to various embodiments herein. As shown, the encoder 210 may include a network interface circuit 905 (also referred to as a network interface) configured to provide communication with other devices / entities / functions / etc. The encoder 210 may also include a processing circuit 901 (also referred to as a processor and processor circuit) coupled to the network interface circuit 905, and a memory circuit 903 (also referred to as a memory) coupled to the processing circuit. The memory circuit 903 may include computer-readable program code that, when executed by the processing circuit 901, causes the processing circuit to perform operations according to embodiments disclosed herein.

[0036] According to other embodiments, the processing circuit 901 may be defined to include memory such that a separate memory circuit is not required. As described herein, the operations of the encoder 210 may be performed by the processing circuit 901 and / or the network interface circuit 905. For example, the processing circuit 901 may control the network interface 905 to send communications to the decoder 220 and / or receive communications through the network interface 905 from one or more other network nodes / entities / servers, such as other encoder nodes, depository servers, etc. Moreover, modules may be stored in the memory 903, and these modules may provide instructions such that, when the instructions of the modules are executed by the processing circuit 901, the processing circuit 901 performs respective operations.

[0037] 10 is a block diagram illustrating elements of a decoder 220 configured to decode audio frames, in accordance with some embodiments of the inventive concept. As shown, the decoder 220 may include a network interface circuit 1005 (also referred to as a network interface) configured to provide communication with other devices / entities / functions, etc. The decoder 220 may also include a processing circuit 1001 (also referred to as a processor or processor circuit) coupled to the network interface circuit 1005, and a memory circuit 1003 (also referred to as a memory) coupled to the processing circuit. The memory circuit 1003 may include computer-readable program code that, when executed by the processing circuit 1001, causes the processing circuit to perform operations according to embodiments disclosed herein.

[0038] According to other embodiments, the processing circuit 1001 may be defined to include memory such that a separate memory circuit is not required. As described herein, the operations of the decoder 220 may be performed by the processor 1001 and / or the network interface 1005. For example, the processing circuit 1001 may control the network interface circuit 1005 to receive communications from the encoder 210. Moreover, modules may be stored in the memory 1003, and these modules may provide instructions such that, when the instructions of the modules are executed by the processing circuit 1001, the processing circuit 1001 performs respective operations.

[0039] In some embodiments, various operations of the encoder 210 and / or decoder 220 may be distributed across various components. Figure 11 is a block diagram illustrating a virtualization environment 1100 in which functionality implemented by some embodiments may be virtualized. In this context, virtualizing means creating a virtual version of an apparatus or device, such as an encoder and / or decoder, which may include virtualizing a hardware platform, storage devices, and networking resources. Virtualization, as used herein, may apply to any device described herein, or components thereof, and relates to implementations in which at least a portion of functionality is implemented as one or more virtual components. Some or all of the functionality described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1100 hosted by one or more hardware nodes, such as encoders, decoders, network nodes, UEs, and hardware computing devices operating as core network nodes.

[0040] An application 1102 (which may alternatively be referred to as a software instance, a virtual appliance, a network function, a virtual node, a virtual network function, etc.) is run in the virtualized environment 1100 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0041] Hardware 1204 includes processing circuitry, memory that stores software and / or instructions executable by the hardware processing circuitry, and / or other hardware devices described herein, such as network interfaces, input / output interfaces, etc. Software is executed by the processing circuitry to instantiate one or more virtualization layers 1106 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1108A and 1108B (one or more of which may be referred to generically as VMs 1108), and / or implement any of the functions, features, and / or benefits described with respect to some embodiments described herein. Virtualization layer 1106 may present to VMs 1108 a virtual operating platform that appears to be networking hardware.

[0042] The VMs 1108 may comprise virtual processing, virtual memory, virtual networking or interfaces, and virtual storage, and may be run by a corresponding virtualization layer 1106. Different embodiments of the virtual appliance 1102 instance may be implemented on one or more of the VMs 1108, and the implementation may be done in different ways. Hardware virtualization is referred to in some contexts as network functions virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry-standard high-volume server hardware, physical switches, and physical storage, which may be located in data centers and customer premises equipment.

[0043] In the context of NFV, a VM 1108 may be a software implementation of a physical machine that runs programs as if those programs were running on a physical, non-virtualized machine. Each VM 1108 and the portion of the hardware 1104 on which it runs, whether hardware dedicated to that VM and / or hardware shared by that VM with other VMs, form a separate virtual network element. Further, in the context of NFV, a virtual network function is responsible for handling a particular network function running in one or more VMs 1108 on the hardware 1104 and corresponds to the application 1102.

[0044] The hardware 1104 may be implemented in a standalone network node with general or specific components. The hardware 1104 may implement some functions via virtualization. Alternatively, the hardware 1104 may be part of a larger cluster of hardware (e.g., as in a data center or CPE) where many hardware nodes cooperate and are managed via a management and orchestration 1110 that, among other things, oversees the lifecycle management of the application 1102. In some embodiments, the hardware 1104 is coupled to one or more radio units, each including one or more transmitters and one or more receivers, which may be coupled to one or more antennas. The radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with virtual components to provide a virtual node with wireless capabilities, such as a wireless access node or base station. In some embodiments, some signaling may be provided using a control system 1112, which may alternatively be used for communication between the hardware nodes and the radio units.

[0045] The operation of the encoder 210 (implemented using the structure of the block diagram of FIG. 9) will now be described with reference to the flowchart of FIG. 12, in accordance with some embodiments of the inventive concepts. For example, modules may be stored in memory 903 of FIG. 9, and these modules may provide instructions such that, when the instructions of the modules are executed by the respective encoder processing circuitry 901, the encoder 210 performs the respective operations of the flowchart.

[0046] 12, in block 1201, the encoder 210 determines the intermediate length of the intermediate frame. In some embodiments, the encoder 210 increases the input sampling frequency f until the upper limit of the target band matches the Nyquist frequency during the intermediate frame. input The intermediate length is determined by rescaling the length N of the input frame in

[0047] In some of these embodiments, the encoder 210 Determine the mid-length according to TIFF2025528549000012.tif11170, Here, the target bandwidth is limited (f lo ,f hi ) when f inter =2f hi and N inter is the intermediate length, N is the length of the input frame, and f inter is the intermediate sampling frequency.

[0048] In block 1203, the encoder 210 receives a full-band input frame. For example, in some embodiments, the encoder 210 receives the full-band input frame by receiving a full-band downmix signal generated by Discrete Fourier Transform (DFT) synthesis, as described above.

[0049] In block 1205, the encoder 210 interpolates the full-band input frame towards the intermediate frame. In some embodiments, the encoder 210 interpolates the full-band input frame by interpolating the full-band input frame using linear interpolation.

[0050] In some embodiments using linear interpolation, the encoder 210 calculates, for i=0, 1, ..., N2, Use linear interpolation to stretch or compress a frame of length N1 to a frame of length N2 according to TIFF2025528549000013.tif20170, where: TIFF2025528549000014.tif26170, x int (i) is the interpolated sample value at point i, x(0) is the sample point in the source vector x at the first point 0, x(1) is the sample point in the source vector x at the second point 1, and i frac is the fractional point at which the source vector x is to be estimated, and i offset is the offset and ∈ is the displacement. As explained before, the offset i offset is N2 <bold> >< / bold> N1, and handles the case where the first sample point in the decompressed frame falls below i=0 and the last sample point exceeds i=N1-1.

[0051] In some of these embodiments, ∈ is It is specified according to TIFF2025528549000015.tif11170.

[0052] Other displacements may be used.

[0053] In block 1207, the encoder 210 performs spectral inversion of the intermediate frame to produce a spectrally reversed intermediate frame. Perform spectral inversion according to TIFF2025528549000016.tif13170.

[0054] In some other embodiments, the encoder 210 Perform spectral inversion according to TIFF2025528549000017.tif13170.

[0055] In block 1209, the encoder 210 interpolates the spectrally reversed intermediate frames to match the sampling frequency of the low-pass filter and decimation process. In block 1211, the encoder 210 performs low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames to produce a bandwidth extension (BWE) target signal.

[0056] 13, the encoder 210 selects the low-pass filtering cutoff frequency to be substantially near the center of the spectrum, as shown in block 1301. In block 1303, the encoder 210 performs low-pass filtering and decimation of the inverted spectrum to produce the BWE target signal by performing low-pass filtering and decimation to match the BWE target signal in the lower half of the spectrum.

[0057] In some of these embodiments, the encoder 210 Determine the decimator frame length according to TIFF2025528549000018.tif10170, where N dec is the decimator frame length, and N inter is the intermediate length, and f dec is the operating frequency of the decimator, and f inter is the frequency of the intermediate frame.

[0058] 12, in block 1213, the encoder 210 inputs the BWE target signal to the BWE encoder 314 via the BWE target buffer 316, the BWE encoder 314 and the BWE target buffer 316 being part of the encoder 210 operating on at least two frequency bands. In one embodiment, the BWE encoder 314 and the BWE target buffer 316 are part of the downmix encoder 214. The downmix encoder 214 of the encoder 210, in some embodiments, has at least two encoding modes, at least one of which has the BWE encoder 314.

[0059] In some of these embodiments, the encoder 210 operates on the downmix signal in a parametric stereo encoder.

[0060] Various operations from the flowchart of Figure 12 may be optional with respect to some embodiments of the communications device and related methods. With respect to the method of exemplary embodiment 1 (described below), for example, the operations of blocks 1201 and 1213 of Figure 12 may be optional.

[0061] While the computing devices (e.g., encoders, decoders, UEs, network nodes) described herein may include the depicted combinations of hardware components, other embodiments may comprise computing devices with different combinations of components. It should be understood that these computing devices may comprise any suitable combination of hardware and / or software required to perform the tasks, features, functions, and methods disclosed herein. The determining, calculating, obtaining, or similar operations described herein may be performed by processing circuitry, which may process information by, for example, transforming the obtained information to other information, comparing the obtained or transformed information to information stored in the network node, and / or performing one or more operations based on the obtained or transformed information and as a result of the processing making a decision. Moreover, while components are illustrated as a single box located within a larger box or nested within multiple boxes, in reality the computing device may comprise multiple different physical components that make up the single depicted component, and functionality may be partitioned among the separate components. For example, a communications interface may be configured to include any of the components described herein, and / or the functionality of those components may be partitioned between the processing circuitry and the communications interface. In another example, non-computationally intensive functionality of any of such components may be implemented in software or firmware, and computationally intensive functionality may be implemented in hardware.

[0062] In some embodiments, some or all of the functionality described herein may be provided by a processing circuit executing instructions stored in a memory, which in some embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuit without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hardwired manner. In any of these particular embodiments, the processing circuit may be configured to perform the described functionality, regardless of whether or not it executes instructions stored on a non-transitory computer-readable storage medium. Benefits provided by such functionality are not limited to the processing circuit alone or to other components of the computing device, but are enjoyed by the computing device as a whole and / or by end users and wireless networks generally.

[0063] Embodiment Embodiment 1. A method implemented in an encoder (210, 1108A, 1108B), the method comprising: receiving (1203) a full-band input frame; Interpolating (620, 1205) the full-band input frame towards an intermediate frame; performing (630, 1207) a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating the spectrally reversed intermediate frames (640, 1209) to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames (650, 1211) to produce a bandwidth extended (BWE) target signal; A method comprising: Embodiment 2. The method of embodiment 1, wherein interpolating the full-band input frame includes using linear interpolation in interpolating the full-band input frame. Embodiment 3. Using linear interpolation in interpolating the full-band input, for i=0, 1,..., N2, using linear interpolation to stretch or compress a frame of length N1 into a frame of length N2 according to TIFF2025528549000019.tif20170, wherein: TIFF2025528549000020.tif26170, x int (i) is the interpolated sample value at point i, x(0) is the sample point in the source vector x at the first point 0, x(1) is the sample point in the source vector x at the second point 1, and i offset 3. The method of embodiment 2, wherein x is an offset and ∈ is a displacement. Embodiment 4. ∈ is 4. The method of embodiment 3, as defined in accordance with TIFF2025528549000021.tif11170. Embodiment 5. The method according to any one of embodiments 1 to 4, wherein receiving the full-band input frame includes receiving a full-band downmix signal generated by Discrete Fourier Transform (DFT) synthesis. Embodiment 6. Performing spectral inversion of intermediate frames comprises: 6. The method of any one of embodiments 1 to 5, comprising performing spectral inversion according to TIFF2025528549000022.tif13170. Embodiment 7. Performing spectral inversion of intermediate frames comprises: 6. The method of any one of embodiments 1 to 5, comprising performing spectral inversion according to TIFF2025528549000023.tif13170. Embodiment 8. Determining the intermediate length of the intermediate frame (610, 1201) 8. The method of any one of embodiments 1 to 7, further comprising: Embodiment 9. Determining the intermediate length is performed by increasing the input sampling frequency f until the upper limit of the target band coincides with the Nyquist frequency during the intermediate frame. input 9. The method of embodiment 8, comprising rescaling the length N of the input frame in Embodiment 10. Determining the intermediate length comprises: determining an intermediate length according to TIFF2025528549000024.tif11170; Here, the target bandwidth is limited (f lo ,f hi ) when f inter =2f hi and N inter is the intermediate length, N is the length of the input frame, and f input 10. The method of claim 8 or 9, wherein: Embodiment 11. The method of any one of embodiments 1 to 10, further comprising selecting (1301) a cutoff frequency for low-pass filtering to be substantially near the center of the spectrum. Embodiment 12. The method of embodiment 11, wherein performing low-pass filtering and decimation of the inverted spectrum to create the BWE target signal includes performing low-pass filtering and decimation (1303) to match the BWE target signal in the lower half of the spectrum. Embodiment 13. The decimator frame length is Determined according to TIFF2025528549000025.tif10170, where N dec is the decimator frame length, and N inter is the intermediate length, and f dec is the operating frequency of the decimator, and f inter 13. The method of embodiment 12, wherein: is the frequency of the intermediate frame. Embodiment 14. The method of any one of embodiments 1 to 13, further comprising inputting (1213) a BWE target signal to a BWE encoder (314) via a BWE target buffer (316), wherein the BWE encoder (314) and the BWE target buffer (316) are part of an encoder (210, 1108A, 1108B) operating on at least two frequency bands. Embodiment 15. The method of embodiment 14, wherein the BWE encoder (314) and the BWE target buffer (316) are part of the downmix encoder (214) of the encoder (210, 1108A, 1108B). Embodiment 16. The method of embodiment 15, wherein the downmix encoder (214) of the encoder (210, 1108A, 1108B) has at least two encoding modes, and at least one of the at least two encoding modes has a BWE encoder (314). Embodiment 17. The method of embodiment 16, wherein the encoder (210, 1108A, 1108B) operates on the downmix signal in a parametric stereo encoder. Embodiment 18. An encoder (210, 1108A, 1108B), receiving (1203) a full-band input frame; Interpolating (620, 1205) the full-band input frame towards an intermediate frame; performing (630, 1207) a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating the spectrally reversed intermediate frames (640, 1209) to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames (650, 1211) to produce a bandwidth extended (BWE) target signal; and an encoder (210, 1108A, 1108B) adapted to: Embodiment 19. The encoder (210, 1108A, 1108B) of embodiment 18, wherein interpolating the full-band input frame includes using linear interpolation in interpolating the full-band input frame. Embodiment 20. Using linear interpolation in interpolating the full-band input, for i=0, 1,..., N2, using linear interpolation to stretch or compress a frame of length N1 into a frame of length N2 according to TIFF2025528549000026.tif20170, wherein: TIFF2025528549000027.tif26170, x int (i) is the interpolated sample value at point i, x(0) is the sample point in the source vector x at the first point 0, x(1) is the sample point in the source vector x at the second point 1, and i offset 20. An encoder (210, 1108A, 1108B) according to embodiment 19, wherein: is an offset and ∈ is a displacement. Embodiment 21. ∈ is An encoder (210, 1108A, 1108B) according to embodiment 20, defined in accordance with TIFF2025528549000028.tif11170. Embodiment 22. An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 21, wherein receiving a full-band input frame includes receiving a full-band downmix signal generated by discrete Fourier transform (DFT) synthesis. Embodiment 23. Performing spectral inversion of intermediate frames comprises: An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 22, comprising performing spectral inversion according to TIFF2025528549000029.tif13170. Embodiment 24. Performing spectral inversion of intermediate frames comprises: An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 22, comprising performing spectral inversion according to TIFF2025528549000030.tif13170. Embodiment 25. The encoder (210, 1108A, 1108B) Determining the intermediate length of the intermediate frame (610, 2201) An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 24, further adapted to perform the following: Embodiment 26. Determining the intermediate length is performed by increasing the input sampling frequency f until the upper limit of the target band coincides with the Nyquist frequency during the intermediate frame. input 26. An encoder (210, 1108A, 1108B) as recited in embodiment 25, comprising rescaling the length N of the input frame in Embodiment 27. Determining the intermediate length comprises: determining an intermediate length according to TIFF2025528549000031.tif11170; Here, the target bandwidth is limited (f lo ,f hi ) when f inter =2f hi and N inter is the intermediate length, N is the length of the input frame, and f input 27. An encoder (210, 1108A, 1108B) according to embodiment 25 or 26, wherein is an intermediate sampling frequency. Embodiment 28. An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 27, wherein the encoder (210, 1108A, 1108B) is further adapted to select (1301) a cutoff frequency for low-pass filtering to be substantially near the center of the spectrum. Embodiment 29. An encoder (210, 1108A, 1108B) as described in embodiment 28, wherein performing low-pass filtering and decimation of the inverted spectrum to create the BWE target signal includes performing low-pass filtering and decimation (1303) to match the BWE target signal in the lower half of the spectrum. Embodiment 30. The decimator frame length is Determined according to TIFF2025528549000032.tif10170, where N dec is the decimator frame length, and N inter is the intermediate length, and f dec is the operating frequency of the decimator, and f inter 30. The encoder (210, 1108A, 1108B) of embodiment 29, wherein is the frequency of the intermediate frame. Embodiment 31. An encoder (210, 1108A, 1108B) according to any one of embodiments 18 to 30, wherein the encoder (210, 1108A, 1108B) is further adapted to input (1213) a BWE target signal to the BWE encoder (314) via a BWE target buffer (316), and the BWE encoder (314) and the BWE target buffer (316) are part of an encoder (210, 1108A, 1108B) operating on at least two frequency bands. Embodiment 32. An encoder (210, 1108A, 1108B) according to embodiment 31, wherein the BWE encoder (314) and the BWE target buffer (316) are part of the downmix encoder (214) of the encoder (210, 1108A, 1108B). Embodiment 33. An encoder (210, 1108A, 1108B) according to embodiment 30, wherein the downmix encoder (214) of the encoder (210, 1108A, 1108B) has at least two encoding modes, and at least one of the at least two encoding modes has a BWE encoder (314). Embodiment 34. The encoder (210, 1108A, 1108B) according to embodiment 33, wherein the encoder (210, 1108A, 1108B) operates on the downmix signal in a parametric stereo encoder. Embodiment 35. An encoder (210, 1108A, 1108B), A processing circuit (901); a memory (903) coupled to the processing circuit; the memory includes instructions that, when executed by the processing circuitry, cause the encoder (210, 1108A, 1108B) to perform operations, the operations including: receiving (1203) a full-band input frame; interpolating (1205) full-band input frames toward intermediate frames; performing 1207 a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating 1209 the frequency-reversed intermediate frames to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames (1211) to produce a bandwidth extended (BWE) target signal; Including, encoders (210, 1108A, 1108B). Embodiment 36. An encoder (210, 1108A, 1108B) as described in embodiment 35, wherein the memory includes further instructions that, when executed by the processing circuit, cause the encoder (210, 1108A, 1108B) to perform the operations described in any one of embodiments 2 to 17. Embodiment 37. A computer program comprising program code to be executed by a processing circuit (903) of an encoder (210, 1108A, 1108B), the execution of which causes the encoder (210, 1108A, 1108B) to perform operations, the operations being: receiving (1203) a full-band input frame; interpolating (1205) full-band input frames toward intermediate frames; performing 1207 a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating the spectrally reversed intermediate frames (1209) to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames (1211) to produce a bandwidth extended (BWE) target signal; a computer program comprising: Embodiment 38. The computer program of embodiment 37, comprising further program code that, when executed by the processing circuit (903) of the encoder (210, 1108A, 1108B), causes the encoder (210, 1108A, 1108B) to perform a further operation described in any one of embodiments 2 to 17. Embodiment 39. A computer program product comprising a non-transitory computer-readable storage medium having program code to be executed by a processing circuit (903) of an encoder (210, 1008A, 1008B), the execution of which causes the encoder (210, 1108A, 1108B) to perform operations, the operations being: receiving (1203) a full-band input frame; interpolating (1205) full-band input frames toward intermediate frames; performing 1207 a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating the spectrally reversed intermediate frames (1209) to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames (1211) to produce a bandwidth extended (BWE) target signal; a computer program product, Embodiment 40. A computer program product as described in embodiment 39, wherein the non-transitory computer-readable storage medium includes further program code that, when executed by the processing circuit (903) of the encoder (210, 1008A, 1008B), causes the encoder (210, 1008A, 1008B) to perform further operations as described in any one of embodiments 2 to 17.

Claims

1. A method implemented in an encoder (210, 1108A, 1108B), said method comprising: receiving (1203) a full-band input frame; Interpolating (620, 1205) the full-band input frame towards an intermediate frame; performing (630, 1207) a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; Interpolating (640, 1209) said spectrally reversed intermediate frames to match the sampling frequency of the low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frame (650, 1211) to produce a bandwidth extension (BWE) target signal; A method comprising:

2. Intermediate length N of the intermediate frame ｉｎｔｅｒ Determining (610, 1201) The method of claim 1 further comprising:

3. Determining the intermediate length includes adjusting the input sampling frequency f until the upper limit of the target band coincides with the Nyquist frequency during the intermediate frame. ｉｎｐｕｔ 3. The method of claim 2, comprising rescaling the length N of the input frame in

4. determining the intermediate length determining the intermediate length according to Here, the target bandwidth is limited (f ｌｏ , f ｈｉ ) when f ｉｎｔｅｒ =2f ｈｉ and N ｉｎｔｅｒ is the intermediate length, N is the length of the input frame, and f ｉｎｐｕｔ 4. The method of claim 2, wherein is the intermediate sampling frequency.

5. The method of claim 1 , wherein interpolating the full-band input frame comprises using linear interpolation in interpolating the full-band input frame.

6. Using the linear interpolation in interpolating the full-band input frame is ２ Regarding According to the length N １ The frame of length N ２ using said linear interpolation to stretch or compress the image to a frame of and x ｉｎｔ (i) is the interpolated sample value at point i, x(0) is the sample point in source vector x at the first point 0, x(1) is the sample point in said source vector x at the second point 1, and i ｆｒａｃ is the fractional point at which the source vector x is to be estimated, and i ｏｆｆｓｅｔ The method of claim 5 , wherein ∈ is the offset and ∈ is the displacement.

7. ∈ is The method of claim 6 , wherein the method is defined according to

8. The method of claim 1 , wherein receiving the full-band input frames comprises receiving a full-band downmix signal generated by Discrete Fourier Transform (DFT) synthesis.

9. performing the inversion of the spectrum of the intermediate frame, performing the inversion of the spectrum according to Here, N ｉｎｔｅｒ The method of claim 1 , wherein is the length of the intermediate frame.

10. performing the inversion of the spectrum of the intermediate frame, performing the inversion of the spectrum according to Here, N ｉｎｔｅｒ The method of claim 1 , wherein is the length of the intermediate frame.

11. 11. The method of claim 1, further comprising selecting (1301) a cutoff frequency of the low-pass filtering to be substantially near the center of the spectrum.

12. 12. The method of claim 11 , wherein performing the low-pass filtering and decimation of the inverted spectrum to produce the BWE target signal comprises performing the low-pass filtering and decimation to match the BWE target signal in a lower half of the spectrum (1303).

13. The decimator frame length is is determined in accordance with Here, N ｄｅｃ is the decimator frame length, and N ｉｎｔｅｒ is the intermediate length, and f ｄｅｃ is the operating frequency of the decimator, and f ｉｎｔｅｒ The method of claim 12 , wherein is the frequency of the intermediate frames.

14. 14. The method of claim 1, further comprising inputting (1213) the BWE target signal to a BWE encoder (314) via a BWE target buffer (316), wherein the BWE encoder (314) and the BWE target buffer (316) are part of an encoder (210, 1108A, 1108B) operating on at least two frequency bands.

15. The method of claim 14 , wherein the BWE encoder (314) and the BWE target buffer (316) are part of a downmix encoder (214) of the encoder (210, 1108A, 1108B).

16. 16. The method of claim 15, wherein the downmix encoder (214) of the encoder (210, 1108A, 1108B) comprises at least two encoding modes, and at least one of the at least two encoding modes comprises the BWE encoder (314).

17. The method of claim 16, wherein the encoder (210, 1108A, 1108B) operates on the downmix signal in a parametric stereo encoder.

18. An encoder (210, 1108A, 1108B) adapted to implement the method according to at least one of claims 1 to 17.

19. An encoder (210, 1108A, 1108B), A processing circuit (901); a memory (903) coupled to said processing circuit; wherein the memory includes instructions that, when executed by the processing circuitry, cause the encoder (210, 1108A, 1108B) to perform operations, the operations including: receiving a full-band input frame; interpolating the full-band input frames toward intermediate frames; performing a spectral inversion of the intermediate frame to produce a spectrally inverted intermediate frame; interpolating the spectrally reversed intermediate frames to match the sampling frequency of a low-pass filter and decimation process; performing low-pass filtering and decimation of the interpolated spectrally reversed intermediate frames to produce a bandwidth extended (BWE) target signal; an encoder (210, 1108A, 1108B) including:

20. The memory includes a memory for storing, when executed by the processing circuit, a signal to the encoder (210, 1108A, 1108B), Intermediate length N of the intermediate frame ｉｎｔｅｒ To determine 20. The encoder of claim 19, including instructions that cause operations to be performed further including:

21. Determining the intermediate length includes adjusting the input sampling frequency f until the upper limit of the target band coincides with the Nyquist frequency during the intermediate frame. ｉｎｐｕｔ 21. The encoder of claim 20, including rescaling the length N of the input frame in

22. determining the intermediate length determining the intermediate length according to Here, the target bandwidth is limited (f ｌｏ , f ｈｉ ) when f ｉｎｔｅｒ =2f ｈｉ and N ｉｎｔｅｒ is the intermediate length, N is the length of the input frame, and f ｉｎｐｕｔ 22. An encoder according to claim 20 or 21, wherein is the intermediate sampling frequency.

23. 23. The encoder of any one of claims 19 to 22, wherein interpolating the full-band input frame comprises using linear interpolation in interpolating the full-band input frame.

24. Using the linear interpolation in interpolating the full-band input frame is ２ Regarding According to the length N １ The frame of length N ２ using said linear interpolation to stretch or compress the image to a frame of and x ｉｎｔ (i) is the interpolated sample value at point i, x(0) is the sample point in source vector x at the first point 0, x(1) is the sample point in said source vector x at the second point 1, and i ｆｒａｃ is the fractional point at which the source vector x is to be estimated, and i ｏｆｆｓｅｔ 24. The encoder of claim 23, wherein is an offset and ε is a displacement.

25. ∈ is 25. The encoder of claim 24, defined according to:

26. 26. The encoder of claim 19, wherein receiving the full-band input frames comprises receiving a full-band downmix signal generated by Discrete Fourier Transform (DFT) synthesis.

27. performing the inversion of the spectrum of the intermediate frame, performing the inversion of the spectrum according to Here, N ｉｎｔｅｒ 27. An encoder according to any one of claims 19 to 26, wherein is the length of the intermediate frame.

28. performing the inversion of the spectrum of the intermediate frame, performing the inversion of the spectrum according to Here, N ｉｎｔｅｒ 28. An encoder according to any one of claims 19 to 27, wherein is the length of the intermediate frame.

29. The memory includes a memory for storing, when executed by the processing circuit, a signal to the encoder (210, 1108A, 1108B), selecting the cutoff frequency of said low-pass filtering to be substantially near the center of said spectrum; 29. An encoder according to any one of claims 19 to 28, including instructions to perform operations further comprising:

30. 30. The encoder of claim 29, wherein performing the low-pass filtering and decimation of the inverted spectrum to produce the BWE target signal comprises performing the low-pass filtering and decimation to match the BWE target signal in a lower half of the spectrum.

31. The decimator frame length is is determined in accordance with Here, N ｄｅｃ is the decimator frame length, and N ｉｎｔｅｒ is the intermediate length, and f ｄｅｃ is the operating frequency of the decimator, and f ｉｎｔｅｒ 31. The encoder of claim 30, wherein is the frequency of the intermediate frames.

32. The memory includes a memory for storing, when executed by the processing circuit, a signal to the encoder (210, 1108A, 1108B), inputting the BWE target signal to a BWE encoder (314) via a BWE target buffer (316); and wherein the BWE encoder (314) and the BWE target buffer (316) are part of an encoder (210, 1108A, 1108B) that operates on at least two frequency bands.

33. The encoder of claim 32, wherein the BWE encoder (314) and the BWE target buffer (316) are part of a downmix encoder (214) of the encoder (210, 1108A, 1108B).

34. 34. The encoder of claim 33, wherein the downmix encoder (214) of the encoder (210, 1108A, 1108B) has at least two encoding modes, and at least one of the at least two encoding modes has the BWE encoder (314).

35. 35. The encoder of claim 34, wherein the encoder (210, 1108A, 1108B) operates on a downmix signal in a parametric stereo encoder.

36. 18. A computer program comprising program code to be executed by a processing circuit (903) of an encoder (210, 1108A, 1108B), the execution of which causes the encoder (210, 1108A, 1108B) to perform the operations of at least one of claims 1 to 17.

37. 18. A computer program product comprising a non-transitory computer-readable storage medium having program code to be executed by a processing circuit (903) of an encoder (210, 1008A, 1008B), the execution of which causes the encoder (210, 1108A, 1108B) to perform the operations described in at least one of claims 1 to 17.

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