JP5255699B2 - Apparatus and method for generating bandwidth extension signal - Google Patents

Description

The present invention relates to audio signal processing, and more particularly, to an apparatus and method for generating a bandwidth extension signal from an input signal, and a method and apparatus for generating a bandwidth reduction signal based on the input signal and the audio signal.

Perceptual adaptive coding of audio signals, that is, coding that reduces the effective data rate for efficient storage and transmission of audio signals, has been widely accepted in many fields. For example, many encoding algorithms such as MPEG-1 / 2-layer 3 (MP3) and MPEG-4-AAC (Advanced Audio Coding) are known. However, the encoding used for this degrades subjective audio quality, especially when operated at the lowest bit rate, and such quality degradation is due to bandwidth limitations of the audio signal to be transmitted. This is mainly caused by the encoder side.

In such a situation, Patent Document 1 discloses a method in which the audio signal is band-limited on the encoder side and only the low frequency band of the audio signal is encoded using a high-quality audio encoder (core encoder). Is disclosed. However, the high frequency band is very coarse, i.e. characterized by a parameter set that reproduces the spectral envelope of the high frequency band. On the decoder side, the high frequency band is then synthesized. For this purpose, a harmonic transposition is used, in which the low frequency band of the decoded audio signal is supplied to the filter bank. The low frequency band filter bank channel is connected or “patched” to the high frequency band filter bank channel. Envelope adjustment is performed on each patched bandpass signal. A synthesis filter bank belonging to a special analysis filter bank receives the bandpass signal of the audio signal in the low frequency band and the envelope adjusted bandpass signal of the low frequency band, and these signals are harmonically patched to the high frequency band. The output signal of the synthesis filter bank is an audio signal that is expanded compared to its original bandwidth. The original band is that transmitted by the core encoder operating at a very low data rate from the encoder side to the decoder side. In particular, filter bank computation and patch processing in the filter bank domain may require high computing capabilities.

Instead, the method of reducing the complexity for expanding the bandwidth of the band-limited audio signal approximates the information lost due to the band limitation. Therefore, the copying operation of the low-frequency signal portion (LF) is changed to the high-frequency region (HF). ). Such a method is disclosed in Non-Patent Documents 1 to 4 and Patent Document 2.

In these methods, harmonic transposition is not performed and a continuous bandpass signal in the low frequency band is introduced into a continuous filter bank channel in the high frequency band. By this method, a rough approximation of the high frequency band of the audio signal is achieved. In the next stage, this coarse approximation of this signal is assimilated to the original signal by post processing using control information obtained from the original signal. Here, as described in the MPEG-4 High Efficiency Advanced Audio Coding (HE-AAC) standard, for example, scale factors are used to apply spectral envelopes and inverse filtering, and for lost harmonics A scale factor is used to add a tonal adaptive noise floor and to supplement the sinusoidal signal portion.

Apart from the above, the next method uses a phase vocoder for bandwidth expansion. When applying a phase vocoder for spectral broadening, the frequency lines will be further away from each other. If a gap is present in the spectrum, for example by quantization, the gap is further increased by expansion. In energy adaptation, the lines left in the spectrum will receive too much energy compared to the individual lines in the original signal.

FIG. 13 shows a schematic diagram of bandwidth extension 1300 using a phase vocoder. In this example, two patches 1312, 1314 are added to the low frequency band 1302 of the signal. The upper cutoff frequency 1320, also called the so-called crossover frequency, of the signal is the lower limit frequency of the adjacent patch 1312, and twice the crossover frequency is the upper cutoff frequency of the adjacent patch 1312 and the lower side of the next patch 1314. Cut-off frequency. The phase vocoder obtains the adjacent patch 1312 by doubling the frequency of the frequency line of the low frequency band 1302 of the signal, and triples the frequency of the frequency line of the low frequency band 1302 of the signal to obtain the next patch 1314. get. Therefore, the spectral density of the adjacent patch 1312 is ½ of the spectral density of the low frequency band 1302 of the signal, and the spectral density of the next patch 1314 is １ ／ of the spectral density of the low frequency band 1302 of the signal. .

By concentrating the energy of the band (patch) on only a few frequency lines, a substantial change in sound quality that is different from the original signal is brought about. The energy in the band (frequency line) that previously existed more is concentrated in a smaller number of remaining bands.

Non-Patent Documents 5 to 8 and Patent Document 3 disclose phase vocoders and some application examples thereof.

One technique for filling the gap is disclosed in Patent Document 4. It includes a method and apparatus for enhancing a source coding system that utilizes high frequency reconstruction. This application presents the problem of insufficient noise content in the reconstructed high frequency band with adaptive noise-floor addition. Although it may be possible to fill the gap by adding noise, the audio quality or subjective quality may not be improved sufficiently.

WO9857436 US Pat. No. 5,455,888 US Pat. No. 6,549,884 WO00 / 45379

M. Dietz, L. Liljeryd, K. Kjorling and 0. Kunz, “Spectral Band Replication, a novel approach in audio coding” in 112th AES Convention, Munich, May 2002 S. Meltzer, R. Bohm and F. Henn, “SBR enhanced audio codecs for digitalbroadcasting such as“ Digital Radio Mondiale (DRM) ”112th AES Convention, Munich, May 2002 T. Ziegler, A. Ehret, P. Ekstrand and M. Lutzky, “Enhancing mp3 withSBR: Features and Capabilities of the new mp3PRO Algorithm” in 112th AESConvention, Munich, May 2002 International Standard ISO / IEC 14496-3: 2001 / FPDAM l, “BandwidthExtension,” ISO / IEC, 2002 Frederik Nagel and Sascha Disch, “A Harmonic Bandwidth Extension Method for Audio odecs” ICASSP’09 M. Puckette. “Phase-locked Vocoder” IEEE ASSP Conference on Applications of Signal Processing to Audio and Acoustics, Mohonk 1995. Robel, A. “Transient detection and preservation in the phase vocoder; citeseer.ist.psu.edu/679246.html” Laroche L., Dolson M .: “Improved phase vocoder timescale modification of audio”, IEEE Trans. Speech and Audio Processing, Vol. 7, No. 3, pp. 323-332

It is an object of the present invention to provide a concept of bandwidth extension of an audio signal that improves the subjective quality of the bandwidth extended signal.

The object can be achieved by a device according to claims 1 and 11, an audio signal according to claim 14, and a method according to claims 15 and 16.

One embodiment of the present invention provides an apparatus for generating a bandwidth extension signal from an input signal. The input signal is represented by first resolution data for the first band and second resolution data for the second band, and the second resolution is lower than the first resolution. The apparatus comprises a patch generator and a combiner. The patch generator generates a first patch from a first band of the input signal according to a first patch algorithm, and generates a second patch from the first band of the input signal according to a second patch algorithm. . The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm. The combiner combines the first patch, the second patch, and the first band of the input signal to obtain the bandwidth extension signal. The apparatus for generating a bandwidth extension signal scales the input signal according to a first patch algorithm and a second patch algorithm such that the bandwidth extension signal satisfies a spectral envelope criterion, or a first patch And the second patch.

Some embodiments according to the present invention have a low spectral density (for example, the patch has more gaps compared to the low frequency band of the input signal) in order to extend the bandwidth of the input signal. The core of a patch with a high spectral density (which means, for example, that the patch has little or no gap compared to the low frequency band of the input signal) Is based on the idea. Since both patches are generated based on the input signal, the extension of the input signal to the low frequency band may provide a good approximation of the original audio signal. In addition, the first and second patches can be scaled before generation (by scaling the input signal) or after to meet the spectral envelope criteria. This is because the spectral envelope of the original audio signal should be considered for the reconstruction of the high frequency band of the input signal. In this way, the subjective quality or audio quality of the bandwidth extension signal will be greatly improved.

In some embodiments of the invention, the first patch algorithm is a harmonic patch algorithm. In other words, the first patch is generated so as to include only a frequency that is an integral multiple of the frequency of the first band of the input signal. On the other hand, the second patch algorithm may be a mixed patch algorithm. This means that even if the second patch is generated so as to include, for example, a frequency that is an integer multiple of the frequency of the first band of the input signal and a frequency that is not an integer multiple of the frequency of the first band of the input signal. Means good. Therefore, the spectral density of the second patch is higher than the spectral density of the first patch. By combining the first patch and the second patch, the missing frequency line of the first patch may be filled by the frequency line of the second patch. In this way, the harmonic bandwidth extension gap according to the first patch algorithm is filled by the second patch, and the audio quality of the bandwidth extension signal is significantly improved.

Some embodiments of the invention relate to an apparatus for generating a bandwidth reduction signal based on an input signal. The apparatus comprises a spectral envelope data determiner, a patch scaling control data generator, and an output interface. The spectrum envelope data determiner determines spectrum envelope data based on a high frequency band of an input signal. The patch scaling control data generator is configured to scale the bandwidth reduction signal at the decoder or by the decoder so that the bandwidth extension signal generated by the decoder meets the spectral envelope criterion. Patch scaling control data for scaling the patch is generated. The spectral envelope criterion is based on spectral envelope data. A first patch is generated from the low frequency band of the bandwidth reduction signal according to a first patch algorithm, and a second patch is generated from the low frequency band of the bandwidth reduction signal according to a second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm. The output interface combines the low frequency band of the input signal, spectrum envelope data, and power scaling control data to obtain the bandwidth reduction signal. Further, the output interface provides the bandwidth reduction signal for transmission or storage.

Some further embodiments according to the invention relate to an audio signal comprising a first band and a second band. The first band is represented by first resolution data, and the second band is represented by second resolution data. The second resolution is lower than the first resolution. The second resolution data is for scaling the audio signal at the decoder such that the spectral envelope data of the second band and the bandwidth extension signal generated by the decoder meet the spectral envelope criteria, or the decoder Is based on the second band patch scaling control data for scaling the first patch and the second patch. The spectral envelope criterion is based on the spectral envelope data. The first patch is generated from the first band of the audio signal according to the first patch algorithm, and the second patch is generated from the first band of the audio signal according to the second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. It is the schematic of the produced | generated 1st patch. It is the schematic of the produced | generated 1st and 2nd patch. FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. It is the schematic of the cut-out sine wave input signal. It is the schematic of a half wave rectified sine wave input signal. FIG. 3 is a schematic diagram of a sine wave input signal that has been cut and full-wave rectified. FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. It is the schematic of the filter bank structure of a phase vocoder. FIG. 5b is a detailed view of one filter in FIG. 5a. FIG. 5b is a schematic diagram illustrating the operation of an amplitude (magnitude) signal and a frequency signal in one filter channel in FIG. 5a. It is a figure which shows schematically the structure of the conversion operation in a certain phase vocoder. FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. FIG. 2 is a block diagram of an apparatus for generating a bandwidth extension signal from an input signal. FIG. 2 is a block diagram of an apparatus for providing a bandwidth reduction signal based on an input signal. 3 is a flowchart of a method for generating a bandwidth extension signal from an input signal. 3 is a flowchart of a method for providing a bandwidth reduction signal based on an input signal. FIG. 2 is a schematic diagram of a known bandwidth extension algorithm.

In the following, in order to avoid duplication in the description of the embodiments, the same reference numerals are used for objects and functional parts having the same or similar functional characteristics, and those descriptions regarding the drawings are also applied to other drawings. Applied.

FIG. 1 shows a block diagram of an apparatus 100 for generating a bandwidth extension signal 122 from an input signal 102 according to a first embodiment of the present invention. The input signal 102 has a first band expressed by the first resolution data and a second band expressed by the second resolution data, and the second resolution is lower than the first resolution. The apparatus 100 includes a patch generator 110 connected to a coupler 120. The patch generator 110 generates a first patch 112 from the first band of the input signal 102 according to the first patch algorithm, and generates a second patch 114 from the first band of the input signal according to the second patch algorithm. The spectral density of the second patch 114 generated according to the second patch algorithm is higher than the spectral density of the first patch 112 generated according to the first patch algorithm. The combiner 120 combines the first patch 112, the second patch 114, and the first band of the input signal 102 to obtain the bandwidth extension signal 122. Further, the apparatus 100 for generating the bandwidth extension signal 122 may scale the input signal 102 according to the first patch algorithm and the second patch algorithm such that the bandwidth extension signal 122 satisfies the spectral envelope criterion, or The first patch 112 and the second patch 114 are scaled.

Spectral density means, for example, the density of different frequencies or frequency lines within a certain frequency band. For example, a frequency band from 0 Hz to 10 kHz having a frequency part of 4 kHz and 8 kHz has a lower spectral density than a same frequency band having a frequency part of 2 kHz, 4 kHz, 6 kHz, 8 kHz, and 10 kHz. Since the spectral density of the first patch 112 is lower than that of the second patch, the first patch 112 includes a gap as compared to the second patch 114. Therefore, the second patch 114 can be used to fill these gaps. Since both patches are based on the first band of the input signal 102, both patches relate to the characteristics of the original signal corresponding to the input signal 102. Thus, the bandwidth extension signal 122 is a good approximation of the original signal, and the subjective quality or audio quality of the bandwidth extension signal 122 is significantly improved by using the above concept. In this way, more energy is distributed among the remaining lines, for example, unnatural sound can be prevented.

For example, the first patch algorithm may be a harmonic patch algorithm. Therefore, the patch generator 110 may generate the first patch 112 including only a frequency that is an integer multiple of the frequency of the first band of the input signal 102. While the harmonic bandwidth extension provides a good approximation of the tonal structure of the original signal, this patch algorithm will leave a gap between the harmonic frequencies. These gaps may be filled by the second patch. For example, when the second patch algorithm is a mixed patch algorithm, that is, the patch generator 110 not only has a frequency (harmonic frequency) that is an integer multiple of the frequency of the first band of the input signal 102, but also the input signal 102. This is a case where the second patch 114 including a frequency (non-harmonic frequency) that is not an integral multiple of the frequency of the first band is generated. Non-harmonic frequencies are used to fill the gaps in the first patch 112. It is also possible to couple the entire second patch 114 (including harmonic frequencies) to the first patch 112. In this example, by appropriately scaling the first patch 112 and / or the second patch 114, the expansion of the harmonic frequency by combining the harmonic frequency portions of the first patch 112 and the second patch 114 is considered.

The first patch 112 and the second patch 114 at least partially include the same frequency region. For example, the first patch 112 includes a frequency band ranging from 4 kHz to 8 kHz, and the second patch 114 includes a frequency band from 6 kHz to 10 kHz. In some embodiments according to the present invention, the lower cutoff frequency of the first patch is equal to the lower cutoff frequency of the second patch, and the upper cutoff frequency of the first patch 112 is the second patch 114. Equal to the upper cutoff frequency of. For example, both patches may include a frequency band ranging from 4 kHz to 8 kHz.

FIGS. 2 a and 2 b show examples of a first patch 112 according to the first patch algorithm 212 and a second patch 114 according to the second patch algorithm 214. For ease of explanation, FIG. 2 a shows only the first patch 112, and FIG. 2 b shows the first patch 112 and the corresponding second patch 114. FIG. 2 a shows an example 200 of a first band 202 of the input signal 102 and two first patches 112 generated according to a first patch algorithm 212. In this example, one patch has the same bandwidth as the first band 202 of the input signal 102. This bandwidth may be different. The upper cut-off frequency 220 of the first band 202 of the input signal 102 is shown as the “Xover” frequency (crossover frequency). In the embodiment shown in FIG. 2a, each patch starts at a frequency equal to a multiple of the crossover frequency Xover220. The frequency lines in the first patch 112 are integer multiples of the frequency lines of the first band 202 of the input signal 102 and can be generated, for example, by a phase vocoder. These first patches 112 include a gap corresponding to the lost frequency line as compared to the first band 202 of the input signal 102.

FIG. 2 b shows a further embodiment 250 for two corresponding second patches 114. These patches are generated according to the second patch algorithm 214 and include harmonic and non-harmonic frequencies. Non-harmonic frequency lines can be used to fill the gap in the first patch 112. The frequency line of the second patch 114 can be generated by nonlinear distortion, for example.

In this method, the gap may not be filled arbitrarily, for example when filling the gap with noise. The gap is filled based on the first resolution data of the first band of the input signal and thus filled based on the original signal.

For example, the first band of the input signal 102 may correspond to the low frequency band of the original audio signal encoded with high resolution. Further, the second band of the input signal 102 may correspond to, for example, a high frequency band of the original audio signal, and one or more parameters such as spectral envelope data and noise data and / or lost low-resolution harmonics. It may be quantized by data. The original audio signal may be, for example, an audio signal recorded by a microphone before processing or encoding.

The scaling of the input signal according to the first patch algorithm and the second patch algorithm means that, for example, after the input signal is scaled once according to the first patch algorithm before the first patch is generated, it is then scaled. A first patch is generated based on the input signal, and after the input signal is scaled once according to the second patch algorithm before the second patch is generated, the second patch is then generated based on the scaled input signal. As a result, after combining the first patch, the second patch, and the first band of the input signal, the bandwidth extension signal satisfies the spectral envelope criterion. Instead, the first and second patches may be scaled after their generation so that the bandwidth extension signal meets the spectral envelope criteria. Scaling of the input signal according to the first and second patch algorithms combined with the scaling of the first and second patches is also possible.

The combiner 120 may be, for example, an adder, and the bandwidth extension signal 122 may be a weighted sum of the first band of the first patch 112, the second patch 114, and the input signal 102.

Satisfying the spectral envelope criterion means that, for example, the spectral envelope of the bandwidth extension signal is based on the spectral envelope data included in the input signal. The spectral envelope data may be generated by an encoder or may represent the second band of the original signal. Thus, the spectral envelope of the bandwidth extension signal is a good approximation of the spectral envelope of the original signal.

The apparatus 100 may comprise a core decoder for decoding the first band of the input signal 102.

Patch generator 110 and combiner 120 may be, for example, specially designed hardware, a part of a processor or microcontroller, or a computer program configured to be executed on a computer or microcontroller. The apparatus 100 may be part of a decoder or audio decoder.

FIG. 3a is a block diagram of an apparatus 300 for generating a bandwidth extension signal 122 from an input signal 102, according to one embodiment of the present invention. In this embodiment, the patch generator 110 includes a phase vocoder 310 for generating the first patch 112 and an amplitude clipper 320 for generating the second patch 114. The phase vocoder 310 and the amplitude cuter 320 are connected to the coupler 120. The phase vocoder 310 expands the first band of the input audio signal 102 to generate the first patch 112 including the harmonic frequency. In a non-linear processing step, the amplitude clipper 320 cuts the input signal 102 and generates a second patch 114 that includes harmonic and non-harmonic frequencies. Instead of amplitude cutout 320, a half-wave rectifier, full-wave rectifier, mixer or diode may be used in the secondary region of the characteristic curve to generate a non-harmonic frequency based on the input signal 102 by a non-linear processing step.

Figures 3b, 3c and 3d show examples of the input signal 102 that has been cut and / or rectified to produce non-harmonic frequencies. FIG. 3 b shows a schematic waveform 350 of the truncated sinusoidal input signal 102. By cutting the signal, a discontinuous point having a shape of a sharp change in the signal slope 380 is generated, and a harmonic part and a non-harmonic part having a higher frequency are generated.

Alternatively, FIG. 3 c shows a schematic waveform 360 of the half-wave rectified sinusoidal input signal 102, which also has a discontinuity point 380.

It is also possible to combine cutting and rectification. FIG. 3d shows a schematic waveform 370 of the truncated and full-wave rectified sinusoidal input signal 102 where various discontinuity points 380 have occurred.

By applying clipping and / or rectification, or other methods of non-linear processing to generate discontinuous points 380, a broad spectrum with different frequencies is generated. Therefore, the patch generated by the patch algorithm as described above has a high spectral density.

FIG. 4 shows a block diagram of an apparatus 400 for generating a bandwidth extension signal 122 from an input signal 102 according to an embodiment of the present invention. This device 400 is similar to the device shown in FIG. 3 a, but additionally comprises a spectral line selector (line selector ) 410. Phase vocoder 310 and amplitude clipper 320 are connected to spectral line selector 410, which is connected to combiner 120. The spectral line selector 410 can select a plurality of frequency lines of the second patch 114 to obtain a single modified second patch 414 that supplements the first patch. The frequency line of the second patch 114 is selected when the corresponding frequency line of the first patch 112 disappears. In other words, the spectral line selector 410 may select the frequency line of the second patch 114 in order to fill the gap of the first patch 112 and ignore the frequency of the second patch already included by the first patch 112. In this way, the modified second patch 414 may have a gap in the frequency already included in the first patch 112.

In this embodiment, combiner 120 combines first patch 112, modified second patch 414, and the first band of input signal 102.

The spectral line selector 410 may be part of the patch generator 110, for example (as shown in FIG. 4), or may be a separate unit.

In the following, a possible configuration example of the phase vocoder 310 according to the present invention will be described with reference to FIGS. FIG. 5a shows the filter bank configuration of a phase vocoder, where the audio signal is input to input 500 and output 510. In particular, each channel of the filter bank schematically shown in FIG. 5 a has a bandpass filter 501 and a downstream oscillator 502. The output signals of all the oscillators coming from the respective channels are combined by a combiner 503 configured as an adder, for example, to obtain an output signal. Each filter 501 is configured to supply an amplitude signal on the one hand and a frequency signal on the other hand. These amplitude signal and frequency signal are time signals, one amplitude signal indicates a change in amplitude on the time axis in the filter 501, and the other frequency signal indicates a change in frequency of the signal filtered by the filter 501.

FIG. 5 b shows a schematic setup of the filter 501. Each filter 501 of FIG. 5a may be set up as shown in FIG. 5b. However, only the frequency fi input to the two input mixers 551 and the adder 552 is different for each channel. Both mixer output signals of the mixer 551 are low-pass filtered by the low-pass filter 553, and these low-pass signals are generated by the local oscillator frequency (LO frequency) and are therefore different from each other. Therefore, the phase is shifted by 90 degrees. The upper low-pass filter 553 outputs a quadrature signal 554, and the lower low-pass filter 553 outputs an in-phase signal 555. These two signals, Q and I, are input to a coordinate converter 556 that generates a magnitude phase representation from a rectangular representation. The absolute value signal or amplitude signal on each time axis of FIG. The phase signal is supplied to a phase unwrapper 558. At the output of element 558, there is no longer a phase value that is always between 0 and 360 degrees, and there is a linearly increasing phase value. This “unwrapped” phase value is supplied to a phase / frequency converter 559. The converter 559 may be configured as a simple phase difference calculator, for example, to obtain the current frequency value by subtracting the phase at a previous time from the current phase, or a phase derivative. May be configured as other means for obtaining an approximation of This frequency value is added to the constant frequency value fi of the filter channel i, resulting in a time-varying frequency value at the output 560. The frequency value at the output 560 has a direct component = fi and an alternating component = frequency deviation, which is the difference between the current frequency of the signal in the filter channel and the average frequency fi. Represents the frequency deviation between.

As described above with reference to FIGS. 5a and 5b, the phase vocoder divides spectrum information and time information. Spectral information is in a special channel or frequency fi that provides a direct component of the frequency to each channel, while time information is contained in frequency deviations or amplitude changes on the time axis.

FIG. 5c shows the processing performed to generate the first patch in accordance with the present invention, in particular the phase vocoder 310, and more particularly the processing performed in the circuit portion partitioned by broken lines in FIG. 5a. Indicates.

For time scaling, for example, the amplitude signal A (t) in each channel or the frequency signal f (t) in each channel is decimated or interpolated. For the purpose of transposition, which is useful for the present invention, interpolation of the signal A (t) and the signal f (t), i.e., time expansion or expansion, is performed, and the expanded signal A ′ (t) and the signal f '(t) is obtained. At this time, the interpolation is controlled by the expansion coefficient 598. This stretch factor may be selected, for example, so that the phase vocoder generates a harmonic frequency. By interpolating the phase change, i.e., interpolating the value before adding the constant frequency by the adder 552, the frequency of each individual oscillator 502 in FIG. 5a does not change. However, the temporal change in the overall audio signal is delayed by a factor of 2. The result is an original fundamental with an original pitch and a time-extended tone, or harmonics.

By performing the signal processing shown in FIG. 5c, the audio signal is reduced to its original duration, for example by a decimation factor of 2, while all frequencies are doubled simultaneously. As a result, a pitch shift by a factor of 2 is provided, resulting in an audio signal having the same length as the original audio signal, ie, the same number of samples.

Instead of the filter band embodiment described with reference to FIG. 5a, a transformation operation configuration in a phase vocoder as shown in FIG. 6 may be used. Here, the audio signal 698 is supplied as a sequence of time samples to an FFT (Fast Fourier Transform) processor, or more generally a Short Time Fourier Transform (STFT) processor 600. The FFT processor 600 performs time windowing of the audio signal and then calculates both the amplitude spectrum and the phase spectrum by the subsequent FFT. This calculation is performed for a continuous spectrum related to strongly overlapping blocks of the audio signal.

In extreme cases, one new spectrum may be calculated for all new audio signal samples, for example, a new spectrum may be calculated for every 20th new sample. The distance “a” of the sample between the two spectra is preferably given by the controller 602. The controller 602 is also configured to output to an IFFT (Inverse Fast Fourier Transform) processor 604, which performs an overlap addition operation. In particular, IFFT processor 604 performs an inverse short-time Fourier transform by performing one IFFT per spectrum based on a certain amplitude spectrum and phase spectrum, and then performs an overlap addition operation. As a result, a time signal is obtained. This overlap addition operation removes the blocking effect introduced by the analysis window.

When the two spectra are processed by the IFFT processor 604, a time signal stretch is performed by the distance b between the two spectra, which is longer than the distance a between the spectra in the generation of the FFT spectrum. The basic idea is to simply decompress the audio signal by inverse FFT so that it has a larger interval than the analysis FFT. As a result, the spectrum in the synthesized audio signal changes at a slower rate than in the original audio signal.

If it was assumed that there was no phase rescaling in block 606, the configuration would result in frequency artifacts. For example, a single frequency bin is considered, and the phase value is continuously changed by 45 degrees with respect to this frequency. In other words, the signal in this filter band means that the phase increases at a rate of 1/8 of one period for each time interval, that is, 45 degrees, and the time interval here is a continuous FFT. Is the time interval between. If the inverse FFTs are farther apart, a 45 degree phase increase will occur over a longer time interval. That is, the frequency of this signal part is changed unintentionally. In order to eliminate such artifacts, the phase is rescaled by a factor that is exactly the same as the factor when the audio signal is stretched in time. The phase of each FFT spectrum value is thus increased by the coefficient b / a, and as a result, the unintended frequency change described above can be eliminated.

In the embodiment shown in FIG. 5c, the amplitude / frequency control signal interpolation was performed for one signal oscillator in the filter bank configuration of FIG. 5a, but the expansion in FIG. 6 is between two FFT spectra. This is achieved by a distance between two IFFT spectra longer than the distance, i.e. "b" longer than "a". However, phase rescaling is performed with the ratio “b / a” to prevent artifacts. The distance “b” can be selected, for example, such that the phase vocoder produces a harmonic frequency.

FIG. 7 shows a block diagram of an apparatus 700 for generating a bandwidth extension signal 122 from an input signal 102 according to one embodiment of the present invention. This apparatus 700 is similar to the apparatus shown in FIG. 1 except that it includes a power controller 710, first power adjustment means 720, and second power adjustment means 730. The power controller 710 is connected to the first power adjustment unit 720 and the second power adjustment unit 730. The first power adjustment unit 720 and the second power adjustment unit 730 are connected to the patch generator 110. The power controller 710 controls the scaling of the input signal based on the spectral envelope data included in the input signal and the patch scaling control data included in the input signal according to the first and second patch algorithms. Good. Instead of the patch scaling control data included in the input signal, at least one stored patch scaling control parameter may be used. The patch scaling control parameter may be stored by a patch scaling control parameter memory, which may be part of the power controller 710 or another unit. The first power adjustment means 720 may scale the input signal 102 according to the first patch algorithm, and the second power adjustment means 730 may scale the input signal 102 according to the second patch algorithm. In other words, the input signal 102 may be scaled before generating the first and second patches so that the bandwidth extension signal meets the spectral envelope criteria. To that end, the spectral envelope data determines the spectral envelope of the bandwidth extension signal 122 and the patch scaling control data or patch scaling control parameter sets the ratio between the first patch 112 and the second patch 114 or the first patch. The absolute value of 112 and / or the second patch 114 may be set. The first power adjustment means 720 and the second power adjustment means 730 may be part of the power controller 710 shown in FIG. 7 or another unit. The power controller 710 may also be part of the patch generator 110 or another unit shown in FIG. The power adjustment units 720 and 730 may be amplifiers or filters controlled by the power controller 710, for example.

Alternatively, scaling may be performed after the patch is generated. As a preferred example, FIG. 8 shows a block diagram of an apparatus 800 according to one embodiment of the present invention for generating a bandwidth extension signal 122 from an input signal 102. This apparatus 800 is similar to the apparatus shown in FIG. 7 except that power adjustment means 720, 730 are disposed between the patch generator 110 and the coupler 120. In this embodiment, the patch generator 110 is connected to the first power adjustment means 720 and the second power adjustment means 730. The first power adjustment unit 720 and the second power adjustment unit 730 are connected to the coupler 120. In this way, the first patch 112 can be scaled by the first power adjustment means 720 according to the first patch algorithm, and the second patch 114 can be scaled by the second power adjustment means 730 according to the second patch algorithm. As described above, these power adjustment units are controlled by the power controller 710 based on the spectrum envelope data and the patch scaling control data or the patch scaling control parameter.

Alternatively, after scaling or power adjusting only one of the two patches, combining the patches by the combiner 120 and before combining the combined patch with the first band of the input signal 102, Scaling is also possible. In other words, one patch is scaled (e.g., based on patch scaling control data) to achieve a predetermined ratio between the two patches, and then the combined patch is met (e.g., the spectral envelope criteria). It may be scaled (based on the envelope data).

The patch scaling control data may include, for example, a simple coefficient for power distribution scaling and a plurality of parameters. The patch scaling control data may indicate, for example, the power ratio of the first patch to the second patch over the entire second band or the entire high frequency, and the first patch and / or the second patch over the entire second band or the entire high frequency. The absolute value of the power of two patches may be indicated, or may be expressed by at least one parameter. Alternatively, the patch scaling data may include one coefficient for each of a plurality of subbands that together comprise a second band or a high frequency band, similar to the spectral envelope data for each subband in a spectral band replication application. . Further, the patch scaling data may indicate a conversion function of the filter. For example, the parameters of the conversion function of the filter for scaling the first patch and / or the parameters of the conversion function of the filter for scaling the second patch may be included in the input signal. Thus, the parameter may represent a function of frequency. In another variation, the patch scaling control data may represent a difference function between the first patch and the second patch. According to this example, the scaling of the input signal or the scaling of the first patch and the second patch may be based on patch scaling control data including at least one parameter.

FIG. 9 shows a block diagram of an apparatus 900 for generating a bandwidth extension signal 122 from an input signal 102 in accordance with one embodiment of the present invention. This device 900 is similar to the device shown in FIG. 8, except that it further includes a noise adder 910, an erasure harmonic adder 920, a noise power adjustment means 940, and an erasure harmonic power adjustment means 950. The noise adder 910 is connected to the noise power adjustment unit 940, and the noise power adjustment unit 940 is connected to the coupler 120. Vanishing harmonic adder 920 is connected to vanishing harmonic power adjustment means 950, and vanishing harmonic power adjustment means 950 is connected to coupler 120. Further, the power controller 710 is connected to the noise power adjustment means 940 and the disappearance harmonic power adjustment means 950. The noise adder 910 generates a noise patch 912 based on the noise data included in the input signal 102.

The noise patch 912 is scaled by the noise power adjusting means 940. The power controller 710 controls the noise power adjustment unit 940 based on the spectral envelope data and / or noise scaling data included in the input signal 102. In this way, the noise of the original signal is approximated and the audio quality of the bandwidth extension signal can be improved.

The lost harmonic adder 920 generates a lost harmonic patch 922 based on the lost harmonic data included in the input signal. The missing harmonic patch 922 may include a harmonic frequency that occurs only in the high frequency band of the original signal, and if only the low frequency band information of the original signal is available for the first band of the input signal 102, this Harmonic frequencies may not be reproducible. Missing harmonic data may provide information about these missing harmonics. The vanishing harmonic patch 922 is scaled by the vanishing harmonic power adjustment means 950. The power controller 710 controls the erasure harmonic power adjustment unit 950 based on the spectral envelope data or the erasure harmonic scaling data included in the input signal 102.

The combiner 120 combines the first patch 112, the second patch 114, the first band of the input signal 102, the noise patch 912, and the erasure harmonic patch 922 to obtain the bandwidth extension signal 122. The power controller 710 scales the first patch 112, the second patch 114, the noise patch 912, and the lost harmonic patch 922 based on the spectral envelope data so as to satisfy the spectral envelope criterion together with the power adjustment unit.

FIG. 10 shows a block diagram of an apparatus 1000 for providing a bandwidth reduction signal 1032 based on an input signal 1002, in accordance with one embodiment of the present invention. The apparatus 1000 includes a spectrum envelope data determiner 1010, a patch scaling control data generator 1020, and an output interface 1030. The spectrum envelope data determiner 1010 and the patch scaling control data generator 1020 are connected to the output interface 1030. The spectrum envelope data determiner 1010 can determine the spectrum envelope data 1012 based on the high frequency band of the input signal 1002. The patch scaling control data generator 1020 scales the bandwidth reduction signal 1032 at the decoder or the first patch at the decoder so that the bandwidth extension signal generated at the decoder satisfies the spectral envelope criterion. Patch scaling control data 1022 for scaling the second patch is generated. This spectral envelope criterion is based on spectral envelope data. The first patch is generated from the first band of the bandwidth reduction signal 1032 according to the first patch algorithm, and the second patch is generated from the first band of the bandwidth reduction signal 1032 according to the second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm. The output interface 1030 combines the low frequency band of the input signal 1002, the spectral envelope data 1012, and the patch scaling control data 1022 to obtain a bandwidth reduction signal 1032. In addition, the output interface 1030 provides this bandwidth reduction signal 1032 for transmission or storage.

Apparatus 1000 may comprise a core encoder for encoding the low frequency band of the input signal. The core encoder may be, for example, a differential encoder, an entropy encoder or a perceptual audio encoder.

The apparatus 1000 may be configured as part of an encoder that provides signals for the decoder described above. The patch scaling control data 1022 may include, for example, a simple coefficient for power distribution scaling and a plurality of parameters. The patch scaling control data may indicate, for example, a power ratio between the first patch and the second patch over the entire high frequency band, or indicate an absolute value of the power of the first patch and / or the second patch over the entire high frequency region. Alternatively, it may be expressed by at least one parameter. Alternatively, the patch scaling data may include one coefficient determined for each of a plurality of subbands that together make up the high frequency band, as well as the spectral envelope data for each subband in a spectral band replication application. Further, the patch scaling data may indicate a conversion function of the filter. For example, a parameter of a filter conversion function for scaling the first patch and / or a parameter of a filter conversion function for scaling the second patch may be determined to generate the patch scaling control data. Good. Thus, the parameter is generated based on a function of frequency. In another variation, patch scaling control data representing a difference function between the first patch and the second patch may be generated.

The patch scaling control data 1022 can be generated by analyzing the input signal 1002 and selecting a patch scaling control parameter stored in the patch scaling control parameter memory based on the analysis of the input signal 1002. 1022 is acquired.

Alternatively, the generation of the patch scaling control data 1022 can be realized by analysis means by synthesis. For this purpose, the patch scaling control data generator 1020 additionally comprises a patch generator (as drawn for the decoder) and a comparator. The patch generator generates a first patch from the low frequency band of the input signal 1002 according to the first patch algorithm, and generates a second patch from the low frequency band of the input signal 1002 according to the second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm. The comparator compares the first patch, the second patch, and the high frequency band of the input signal, and obtains patch scaling control data 1022. In other words, the concept described above also applies to the device 1000. In this way, the device 1000 can derive patch scaling control data 1022 by comparing patches or combined patches with an input signal, eg, an original audio signal. Furthermore, the device 1000 may include a spectral line selector, a power controller, a noise adder and / or an erasure harmonic adder as described above. In this manner, noise data, noise patch scaling control data, lost harmonic data, and / or lost harmonic patch scaling control data can be extracted by an analysis technique using synthesis.

Some embodiments according to the invention relate to an audio signal comprising a first band and a second band. The first band is represented by first resolution data, the second band is represented by second resolution data, and the second resolution is lower than the first resolution. The second resolution data may be used to scale the audio signal at the decoder or at the decoder so that the spectral envelope data of the second band and the bandwidth extension signal generated by the decoder meet the spectral envelope criteria. Based on the second band patch scaling control data for scaling the first patch and the second patch. The spectral envelope criterion is based on spectral envelope data. The first patch is generated from the first band of the audio signal according to the first patch algorithm, and the second patch is generated from the first band of the audio signal according to the second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm.

The audio signal may be a bandwidth reduction signal based on an original signal, for example. The first band of the audio signal may represent a low frequency band of the original audio signal encoded with high resolution. The second band of the audio signal may represent a high frequency band of the original audio signal, and includes at least two parameters: a spectral envelope parameter expressed by the spectral envelope data and a patch scaling control parameter expressed by the patch scaling control data. And may be quantized. Based on such an audio signal, a decoder according to the above concept can generate a bandwidth extension signal that has an improved audio quality compared to the known concept and provides a good approximation of the original audio signal. .

FIG. 11 shows a flowchart of a method 1100 for generating a bandwidth extension signal from an input signal in an embodiment of the present invention. The first band of the input signal is represented by first resolution data, the second band is represented by second resolution data, and the second resolution is lower than the first resolution. The method 1100 includes a step 1110 for generating a first patch, a step 1120 for generating a second patch, a step 1130 for scaling an input signal, a step 1130 for scaling a first patch and a second patch, and a first patch. And a step 1140 for combining the second patch and the first band of the input signal to obtain a bandwidth extension signal. The first patch is generated 1110 from the first band of the input signal according to the first patch algorithm, and the second patch is generated 1120 from the first band of the input signal according to the second patch algorithm. The spectral density of the second patch generated 1120 according to the second patch algorithm is higher than the spectral density of the first patch generated 1110 according to the first patch algorithm. The input signal is scaled 1130 according to the first and second patch algorithms, or the first and second patches are scaled 1130 such that the bandwidth extension signal meets the spectral envelope criterion.

Further, the method 1100 may be extended by steps in accordance with the concepts described above. The method 1100 may be implemented, for example, as a computer program that runs on a computer or microcontroller.

FIG. 12 shows a flowchart of a method 1200 for providing a bandwidth reduction signal based on an input signal according to an embodiment of the present invention. The method 1200 includes a step 1210 of determining spectral envelope data based on a high frequency band of the input signal, a step 1220 of generating patch scaling control data, and a low frequency band and spectrum of the input signal to obtain a bandwidth reduction signal. Combining envelope data and patch scaling control data 1230 and providing a bandwidth reduction signal 1240 for transmission or storage. The patch scaling control data is used to scale the bandwidth reduction signal at the decoder or by the decoder to scale the bandwidth reduction signal so that the bandwidth extension signal generated by the decoder meets the spectral envelope criterion. Generated 1220 to scale. The spectral envelope criterion is based on spectral envelope data. The first patch is generated from the low frequency band of the bandwidth reduction signal according to the first patch algorithm, and the second patch is generated from the low frequency band of the bandwidth reduction signal according to the second patch algorithm. The spectral density of the second patch generated according to the second patch algorithm is higher than the spectral density of the first patch generated according to the first patch algorithm.

Further, the method 1200 may be extended by steps in accordance with the concepts described above. The method 1200 may be implemented as a computer program that runs on, for example, a computer or microcontroller.

Some embodiments according to the invention relate to an apparatus for generating a bandwidth extension signal using a phase vocoder for bandwidth extension combined with non-linear distortion and noise filling for denser spectra. . When a phase vocoder is applied for spectral expansion, the frequency lines are further separated. If there are gaps in the spectrum, for example by quantization, the expansion further increases the gaps. In energy adaptation, the lines remaining in the spectrum receive too much energy. This can be prevented by filling the gap with further harmonics obtained by noise or non-linear distortion of the signal. In this way, more energy is distributed among the remaining lines. Energy concentration on just a few frequency lines in the band results in an unnatural or metallic sound. The energy of the band that previously existed is summed into the remaining band.

There are no gaps in the spectrum, but at least if there is noise, some of the energy remains in the noise floor. With the application of non-linear distortion, on the one hand the spectrum is again densified by noise generated by the distortion and on the other hand by further harmonic parts guided by the appropriate selection of signal parts to be distorted.

The bandwidth extension signal may then be a weighted sum of, for example, a filtered and distorted signal and a signal generated with the help of a phase vocoder. In other words, the bandwidth extension signal may be a weighted sum of the first patch, the second patch, and the first band of the input signal.

Some embodiments according to the invention relate to a concept suitable for all audio applications where not all the bandwidth is available. For example, the concepts described above can be applied for broadcasting audio content using digital radio services, Internet streaming, or other audio communication applications.

Although the present invention has been described with reference to several embodiments, modifications, substitutions, and equivalents may be made without departing from the spirit of the present invention. It should also be noted that there are many alternatives to the method and configuration of the present invention. Therefore, the appended claims should be construed to include all these modifications, substitutions, and equivalents included within the spirit of the invention.

In particular, it should be noted that the configuration of the present invention may be configured as software depending on the situation. The invention may be a flexible disk or CD containing control signals that can be read electronically in cooperation with a digital storage medium, in particular a programmable computer system, so that the corresponding method is carried out. In general, the present invention is included in a computer program product stored on a machine readable carrier for performing the method of the present invention when the computer program product is run on a computer. In other words, the present invention is realized as a computer program having a program code for executing the method of the present invention when the computer program product is operated on a computer.

Claims (17)

An apparatus (100; 300; 400; 700; 800; 900) for generating a bandwidth extension signal (122) from an input signal (102), wherein the first band of the input signal is represented by first resolution data. The second band is represented by the second resolution data, the second resolution being lower than the first resolution,
A first patch (112) is generated from a first band of the input signal (102) according to a first patch algorithm and a second patch (114) according to a second patch algorithm from the first band of the input signal (102) A patch generator (110) for generating a spectral density of the second patch (114) generated according to the second patch algorithm, wherein the first patch (112) generated according to the first patch algorithm ) With a patch generator that is higher than the spectral density of
A combiner (120) for combining the first patch (112), the second patch (114), and the first band of the input signal (102) to obtain the bandwidth extension signal (122); ,
The apparatus for generating a bandwidth extension signal scales the input signal (102) according to the first patch algorithm and the second patch algorithm such that the bandwidth extension signal satisfies a spectral envelope criterion; Alternatively, the apparatus scales the first patch (112) and the second patch (114). The apparatus of claim 1, wherein the first patch algorithm is a harmonic patch algorithm, and the patch generator (110) is configured such that the first patch (112) is a frequency of the first band of the input signal (102). The first patch (112) is generated so as to include only an integral multiple of a frequency. The apparatus according to claim 1 or 2, wherein the second patch algorithm is a mixed patch algorithm of a harmonic patching algorithm and a non-harmonic patching algorithm, and the patch generator (110) includes a second patch (114). ) Include a frequency that is an integer multiple of the frequency of the first band of the input signal (102) and a frequency that is not an integer multiple of the frequency of the first band of the input signal (102). A device characterized by generating. 4. The apparatus according to claim 1, wherein the lower cutoff frequency of the first patch (112) is equal to the lower cutoff frequency of the second patch (114). The upper cut-off frequency of (112) is equal to the upper cut-off frequency of the second patch (114). Apparatus according to any of the preceding claims, characterized in that it comprises a phase vocoder (310) for generating the first patch (112) according to the first patch algorithm. 6. An apparatus as claimed in claim 1, wherein the second patch (114) is generated by cutting a first band of the input signal (102) according to the second patch algorithm. 320). 7. The apparatus according to claim 1, further comprising a spectral line selector (410) for selecting a plurality of frequency lines of the second patch (114) to obtain a modified second patch (414). When the corresponding frequency line of the first patch (112) disappears, the frequency line is selected, and the combiner (120) selects the first patch (112) and the modified second patch (414). And a first band of the input signal (102). 8. Apparatus according to any of claims 1 to 7, wherein the scaling of the input signal (102) is controlled according to the first and second patch algorithms, or the first patch (112) and the second patch (114). A power controller (710) for controlling the scaling of the input signal (102) based on spectral envelope data contained in the input signal (102) and at least one stored patch scaling control An apparatus for controlling the scaling based on a parameter or patch scaling control data included in the input signal (102). 9. The apparatus according to claim 8, wherein first power adjusting means (720) for scaling the input signal (102) or scaling the first patch (112) according to a first patch algorithm, and a second patch. Second power adjustment means (730) for scaling the input signal (102) or scaling the second patch (114) according to an algorithm, wherein the power controller (710) is the first power adjustment means. (720) and 2nd power adjustment means (730), The apparatus characterized by the above-mentioned. 10. The apparatus according to claim 8 or 9, comprising a noise adder (910) and an erasure harmonic adder (920), wherein the noise adder (910) is a noise based on noise data contained in the input signal. Generating a patch (912), and the erasure harmonic adder (920) generates an erasure harmonic patch (922) based on the erasure harmonic data included in the input signal (102), and the power controller (710) Controls the scaling of the noise patch (912) and the erasure harmonic patch (922) based on the spectral envelope data, and the combiner (120) includes a first patch (112), a second patch (114) and an input signal. Bandwidth combining the first band of (102), the noise patch (912) and the erasure harmonic patch (922) A tension signal (122) is obtained, and the power controller (710) determines the first patch (112) and the second patch (114) based on the spectral envelope data so that the spectral envelope criterion is satisfied. , Controlling the scaling of the noise patch (912) and the disappearing harmonic patch (922). An apparatus (1000) for providing a bandwidth reduction signal (1032) based on an input signal (1002), comprising:
A spectral envelope data determiner (1010) for determining spectral envelope data (1012) based on a high frequency band of the input signal (1002);
In order to scale the bandwidth reduction signal (1032) in the decoder so that the bandwidth extension signal generated by the decoder meets the spectral envelope criterion, or by the decoder, the first patch and the second patch A patch scaling control data generator (1020) for generating patch scaling control data (1022) for scaling, wherein the spectral envelope criterion is based on the spectral envelope data (1012), and the first patch is A second patch is generated from a first band of the bandwidth reduction signal (1032) according to a first patch algorithm, and the second patch is generated from a first band of the bandwidth reduction signal (1032) according to a second patch algorithm, Spectrum of the second patch generated according to the patch algorithm of 2 Once again higher than the spectral density of the first patch generated according to the first patch algorithm and the patch scaling control data generator,
The low frequency band of the input signal (1002), the spectral envelope data (1012), and the patch scaling control data (1022) are combined to obtain the bandwidth reduction signal (1032), and the bandwidth reduction An output interface (1030) for providing a signal (1032) for transmission or storage. 12. The apparatus of claim 11, wherein the patch scaling control data generator is
Patch generation for generating a first patch from a low frequency band of the input signal (1002) according to a first patch algorithm and generating a second patch from a low frequency band of the input signal (1002) according to a second patch algorithm A patch generator, wherein a spectral density of the second patch generated according to the second patch algorithm is higher than a spectral density of the first patch generated according to the first patch algorithm;
A comparator that compares the first patch, the second patch, and a high frequency band of the input signal (1002) to obtain the patch scaling control data (1022); 12. The apparatus of claim 11, comprising a patch scaling control parameter memory for storing and providing a plurality of patch scaling control parameters, wherein the patch scaling control data generator (1020) is the input signal (1002). And generating the patch scaling control data (1022) according to stored patch scaling control parameters selected based on an analysis of the input signal (1002). A computer-readable storage medium storing an audio signal having a first band expressed by first resolution data and a second band expressed by second resolution data, wherein the second resolution Is lower than the first resolution, the second resolution data is based on the spectral envelope data of the second band, and the bandwidth extension signal generated by the decoder satisfies the spectral envelope criterion. Based on second-band patch scaling control data for scaling the audio signal or scaling the first patch and the second patch by the decoder, wherein the spectral envelope reference is based on the spectral envelope data. And the first patch is a first patch algorithm from a first band of the audio signal. And the second patch is generated from a first band of the audio signal according to a second patch algorithm, and the spectral density of the second patch generated according to the second patch algorithm is the first patch. A storage medium characterized by being higher than the spectral density of the first patch generated according to an algorithm. A method (1100) for generating a bandwidth extension signal from an input signal, wherein the first band of the input signal is represented by first resolution data, the second band is represented by second resolution data, and The resolution of 2 is lower than the first resolution,
Generating (1110) a first patch from a first band of the input signal according to a first patch algorithm;
Generating a first patch from a first band of the input signal according to a second patch algorithm (1120), wherein a spectral density of the second patch generated according to the second patch algorithm is the first patch A step that is higher than the spectral density of the first patch generated according to a patch algorithm;
Scaling the input signal according to the first patch algorithm and the second patch algorithm, or scaling the first patch and the second patch such that the bandwidth extension signal satisfies a spectral envelope criterion. (1130)
Combining the first patch, the second patch, and the first band of the input signal to obtain the bandwidth extension signal (1140). A method (1200) of providing a bandwidth reduction signal based on an input signal comprising:
Determining spectral envelope data based on a high frequency band of the input signal (1210);
To scale the bandwidth reduction signal at the decoder or to scale the first and second patches by the decoder so that the bandwidth extension signal generated by the decoder meets the spectral envelope criterion Generating (1220) patch scaling control data for the spectrum envelope criteria based on the spectrum envelope data, wherein the first patch is a first patch algorithm from a first band of the bandwidth reduction signal. And the second patch is generated from the first band of the bandwidth reduction signal according to a second patch algorithm, and the spectral density of the second patch generated according to the second patch algorithm is the first patch Compared to the spectral density of the first patch generated according to the patch algorithm High Te, and the step,
Combining the low frequency band of the input signal, the spectral envelope data, and the patch scaling control data to obtain the bandwidth reduction signal (1230);
Providing (1240) the bandwidth reduction signal for transmission or storage. A computer program comprising program code for executing the method of claim 15 or 16 when run on a computer or microcontroller.

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