Apparatus and method for generating a bandwidth extended signal

This application is a continuation of copending International Application No. PCT/EP2009/004603 filed Jun. 25, 2009, and also claims priority to U.S. Application No. 61/079,849, filed Jul. 11, 2008, which is incorporated herein by reference in its entirety.Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 8,880,410, the first being reissue application Ser. No. 18/518,193. Additionally, reissue applications Ser. Nos. 18/518,223, 18/518,246, 18/518,261, 18/518,288, 18/518,309, 18/518,326, 18/518,339, were filed, all of which are continuation reissues of U.S. Pat. No. 8,880,410.

This application, Ser. No. 18/518,261, filed Nov. 22, 2023, is a continuation reissue application of U.S. patent application Ser. No. 16/230,764 filed Dec. 21, 2018 and also a reissue of U.S. patent application Ser. No. 13/004,314, issued as U.S. Pat. No. 8,880,410 on Nov. 4, 2014 and U.S. patent application Ser. No. 16/230,764 is a continuation of reissue Ser. No. 15/341,763 filed Nov. 2, 2016, issued U.S. Pat. No. RE47,180 on Dec. 25, 2018, which is a reissue of U.S. patent application Ser. No. 13/004,314, issued as U.S. Pat. No. 8,880,410 which is a continuation of copending International Application No. PCT/EP2009/004603 filed Jun. 25, 2009, and also claims priority to U.S. application Ser. No. 61/079,849, filed Jul. 11, 2008, which is incorporated herein by reference in its entirety.

Embodiments according to the invention relate to audio signal processing and, in particular, to an apparatus and a method for generating a bandwidth extended signal from an input signal, an apparatus and a method for providing a bandwidth reduced signal based on an input signal and an audio signal.

Perceptually adapted coding of audio signals, providing a substantial data rate reduction for efficient storage and transmission of these signals, has gained wide acceptance in many fields. Many coding algorithms are known, e.g., MPEG 1/2 Layer 3 (“MP3”) or MPEG 4 AAC (Advanced Audio Coding). However, the coding used for this, in particular when operating at lowest bit rates, can lead to an reduction of subjective audio quality which is often mainly caused by an encoder side induced limitation of the audio signal bandwidth to be transmitted.

It is known from WO 98 57436 to subject the audio signal to a band limiting in such a situation on the encoder side and to encode only a lower band of the audio signal by means of a high quality audio encoder (“core coder”). The upper band, however, is only very coarsely characterized, i.e. by a set of parameters which reproduces the spectral envelope of the upper band. On the decoder side, the upper band is then synthesized. For this purpose, a harmonic transposition is proposed wherein the lower band of the decoded audio signal is supplied to a filterbank. Filterbank channels of the lower band are connected to filterbank channels of the upper band, or are “patched”, and each patched bandpass signal is subjected to an envelope adjustment. The synthesis filterbank belonging to a special analysis filterbank receives bandpass signals of the audio signal in the lower band and envelope-adjusted bandpass signals of the lower band which are harmonically patched into the upper band. The output signal of the synthesis filterbank is an audio signal extended with regard to its original bandwidth which is transmitted from the encoder side to the decoder side by the core coder operating a very low data rate. In particular, filterbank calculations and patching in the filterbank domain may become a high computational effort.

Complexity-reduced methods for a bandwidth extension of band-limited audio signals instead use a copying function of low-frequency signal portions (LF) into the high frequency range (HF) in order to approximate information missing due to the band limitation. Such methods are described in M. Dietz, L. Liljeryd, K. Kjörling and O. Kunz, “Spectral Band Replication, a novel approach in audio coding,” in 112th AES Convention, Munich, May 2002; S. Meltzer, R. Böhm and F. Henn, “SBR enhanced audio codecs for digital broadcasting such as “Digital Radio Mondiale” (DRM),” 112th AES Convention, Munich, May 2002; T. Ziegler, A. Ehret, P. Ekstrand and M. Lutzky, “Enhancing mp3 with SBR: Features and Capabilities of the new mp3PRO Algorithm,” in 112th AES Convention, Munich, May 2002; International Standard ISO/IEC 14496-3:2001/FPDAM 1, “Bandwidth Extension,” ISO/IEC, 2002, or “Speech bandwidth extension method and apparatus”, Vasu Iyengar et al. U.S. Pat. No. 5,455,888.

In these methods, no harmonic transposition is performed, but successive bandpass signals of the lower band are introduced into successive filterbank channels of the upper band. By this, a coarse approximation of the upper band of the audio signal is achieved. In a further step, this coarse approximation of the signal is then assimilated with respect to the original by a post processing using control information gained from the original signal. Here, e.g. scale factors serve for adapting the spectral envelope, an inverse filtering, and the addition of a noise floor for adapting tonality and a supplementation of sinusoidal signal portions for missing harmonics, as it is also described in the MPEG-4 High Efficiency Advanced Audio Coding (HE-AAC) standard.

Apart from this, further methods are using a phase vocoder for bandwidth extension. When applying the phase vocoder for spectral spreading, frequency lines move further apart from each other. If gaps exist in the spectrum, e.g. by quantization, the same are even increased by the spreading. In an energy adaption, remaining lines in the spectrum receive too much energy compared to the respective lines in the original signal.

shows a schematic illustration of a bandwidth extensionusing a phase vocoder. In this example, two patches,are added to a low frequency bandof a signal. The upper cut-off frequencyof the signal, also called Xover frequency (crossover frequency) is the low-end frequency of the neighboring patchand the double of the x-over frequency is the upper cut-off frequency of the neighboring patchand the lower cut-off frequency of the next patch. The phase vocoder doubles the frequency of the frequency lines of the low frequency bandof the signal to obtain the neighboring patchand triples the frequencies of the frequency lines of the low frequency bandof the signal to obtain the next patch. Therefore, a spectral density of the neighboring patchis only half of a spectral density of the low frequency bandof the signal and the spectral density of the next patchis only one third of the spectral density of the low frequency bandof the signal.

By the concentration of the energy in bands (patches) to only few frequency lines, a substantial change in timbre results which differs from the original. The energy of formerly more bands (frequency lines) is summed up to the fewer remaining ones.

Some examples for phase vocoders and their applications are presented in “Frederik Nagel and Sascha Disch, A Harmonic Bandwidth Extension Method for Audio Codecs,” ICASSP'09 and “M. Puckette. Phase-locked Vocoder. IEEE ASSP Conference on Applications of Signal Processing to Audio and Acoustics, Mohonk 1995.”, Röbel, 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″ and U.S. Pat. No. 6,549,884.

One approach for filling the gaps is shown in WO 00/45379. It contains a method and an apparatus for enhancement of source coding systems utilizing high frequency reconstruction. The application addresses the problem of insufficient noise contents in a reconstructed highband by adaptive noise-floor addition. Adding noise may fill the gaps, but the audio quality or subjective quality may not be increased sufficiently.

According to an embodiment, an apparatus for generating a bandwidth extended signal from an input signal, wherein the input signal is represented, for a first band by a first resolution data, and for a second band by a second resolution data, the second resolution being lower than the first resolution, may have: a patch generator configured to generate a first patch from the first band of the input signal according to a first patching algorithm and configured to generate a second patch from the first band of the input signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; and a combiner configured to combine the first patch, the second patch and the first band of the input signal to acquire the bandwidth extended signal, wherein the apparatus for generating a bandwidth extended signal is configured to scale the input signal according to the first patching algorithm and according to the second patching algorithm or to scale the first patch and the second patch, so that the bandwidth extended signal fulfills a spectral envelope criterion.

According to another embodiment, an apparatus for providing a bandwidth reduced signal based on an input signal may have: a spectral envelope data determiner configured to determine spectral envelope data based on a high-frequency band of the input signal; a patch scaling control data generator configured to generate patch scaling control data for scaling the bandwidth reduced signal at a decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion, wherein the spectral envelope criterion is based on the spectral envelope data wherein the first patch is generated from a first band of the bandwidth reduced signal according to a first patching algorithm and the second patch is generated from the first band of the bandwidth reduced signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; an output interface configured to combine a low frequency band of the input signal, the spectral envelope data and the patch scaling control data to acquire the bandwidth reduced signal and configured to provide the bandwidth reduced signal for transmission or storage.

According to another embodiment, an audio signal may have: a first band represented by a first resolution data; and a second band represented by a second resolution data, wherein the second resolution is lower than the first resolution, wherein the second resolution data is based on spectral envelope data of the second band and is based on patch scaling control data of the second band for scaling the audio signal at a decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion, wherein the spectral envelope criterion is based on the spectral envelope data, wherein the first patch is generated from the first band of the audio signal according to a first patching algorithm and the second patch is generated from the first band of the audio signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm.

According to another embodiment, a method for generating a bandwidth extended signal from an input signal, wherein the input signal is represented, for a first band by a first resolution data, and for a second band by a second resolution data, the second resolution being lower than the first resolution, may have the steps of: generating a first patch from the first band of the input signal according to a first patching algorithm; generating a second patch from the first band of the input signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; scaling the input signal according to the first patching algorithm and according to the second patching algorithm or scaling the first patch and the second patch, so that the bandwidth extended signal fulfills the spectral envelope criterion; and combining the first patch, the second patch and the first band of the input signal to acquire the bandwidth extended signal.

According to another embodiment, a method for providing a bandwidth reduced signal based on an input signal, may have the steps of: determining a spectral envelope data based on a high frequency band of the input signal; generating patch scaling control data for scaling the bandwidth reduced signal at a decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion, wherein the spectral envelope criterion is based on the spectral envelope data, wherein the first patch is generated from a first band of the bandwidth reduced signal according to a first patching algorithm and a second patch is generated from the first band of the bandwidth reduced signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; combining a low frequency band of the input signal, the spectral envelope data and the patch scaling control data to acquire the bandwidth reduced signal; providing the bandwidth reduced signal for a transmission or storage.

Another embodiment may have a computer program with a program code for performing the method for generating a bandwidth extended signal from an input signal, wherein the input signal is represented, for a first band by a first resolution data, and for a second band by a second resolution data, the second resolution being lower than the first resolution, which method may have the steps of: generating a first patch from the first band of the input signal according to a first patching algorithm; generating a second patch from the first band of the input signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; scaling the input signal according to the first patching algorithm and according to the second patching algorithm or scaling the first patch and the second patch, so that the bandwidth extended signal fulfills the spectral envelope criterion; and combining the first patch, the second patch and the first band of the input signal to acquire the bandwidth extended signal, when the computer program runs on a computer or a microcontroller.

Another embodiment may have a computer program with a program code for performing the method for providing a bandwidth reduced signal based on an input signal, which method may have the steps of: determining a spectral envelope data based on a high frequency band of the input signal; generating patch scaling control data for scaling the bandwidth reduced signal at a decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion, wherein the spectral envelope criterion is based on the spectral envelope data, wherein the first patch is generated from a first band of the bandwidth reduced signal according to a first patching algorithm and a second patch is generated from the first band of the bandwidth reduced signal according to a second patching algorithm, wherein a spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm; combining a low frequency band of the input signal, the spectral envelope data and the patch scaling control data to acquire the bandwidth reduced signal; providing the bandwidth reduced signal for a transmission or storage, when the computer program runs on a computer or a microcontroller.

An embodiment of the invention provides an apparatus for generating a bandwidth extended signal from an input signal. The input signal is represented, for a first band by a first resolution data and for a second band by a second resolution data, the second resolution being lower than the first resolution. The apparatus comprises a patch generator and a combiner. The patch generator is configured to generate a first patch from the first band of the input signal according to a first patching algorithm and configured to generate a second patch from the first band of the input signal according to a second patching algorithm. A spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm. The combiner is configured to combine the first patch, the second patch and the first band of the input signal to obtain the bandwidth extended signal. The apparatus for generating a bandwidth extended signal is configured to scale the input signal according to the first patching algorithm and according to the second patching algorithm or to scale the first patch and the second patch, so that the bandwidth extended signal fulfils a spectral envelope criterion.

Embodiments according to the present invention are based on the central idea that a patch with low spectral density (which means, for example, the patch comprises gaps in comparison to a low frequency band of the input signal) is combined with a patch with high spectral density (which means, for example, the patch comprises only few gaps or no gaps in comparison with the low frequency band of the input signal) for extending the bandwidth of an input signal. Since both patches are generated based on the input signal, the high frequency bandwidth extension of the low frequency band of the input signal may provide a good approximation of the original audio signal. Additionally, the first and the second patch may be scaled before (by scaling the input signal) or after generation to fulfill a spectral envelope criterion, since 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 the audio quality of the bandwidth extended signal may be significantly increased.

In some embodiments according to the invention, the first patching algorithm is a harmonic patching algorithm. In other words, the first patch is generated so that only frequencies that are integer multiples of frequencies of the first band of the input signal are contained by the first patch. In addition, the second patching algorithm may be a mixing patching algorithm. This means, for example, that the second patch may be generated, so that the second patch contains frequencies that are integer multiples of frequencies of the first band of the input signal and frequencies that are not integer multiples of frequencies of the first band of the input signal. 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, missing frequency lines of the first patch may be filled by frequency lines of the second patch. In this way, the gaps of the harmonic bandwidth extension according to the first patching algorithm may be filled by the second patch and the audio quality of the bandwidth extended signal may be significantly improved.

Some embodiments according to the invention relate to an apparatus for providing a bandwidth reduced 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 spectral envelope data determiner is configured to determine spectral envelope data based on the high frequency band of the input signal. The patch scaling control data generator is configured to generate patch scaling control data for scaling the bandwidth reduced signal at the decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion. The spectral envelope criterion is based on the spectral envelope data. The first patch is generated from a low frequency band of the bandwidth reduced signal according to a first patch algorithm and the second patch is generated from the low frequency band of the bandwidth reduced signal according to a second patching algorithm. A spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generated according to the first patching algorithm. The output interface is configured to combine a low frequency band of the input signal, the spectral envelope data, and the power scaling control data to obtain the bandwidth reduced signal. Further, the output interface is configured to provide the bandwidth reduced 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 a first resolution data and the second band is represented by a second resolution data. The second resolution is lower than the first resolution. The second resolution data is based on spectral envelope data of the second band and patch-scaling control data of the second band for scaling the audio signal at a decoder or for scaling a first patch and a second patch by the decoder, so that a bandwidth extended signal generated by the decoder fulfills a spectral envelope criterion. 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 a first patching algorithm and the second patch is generated from the first band of the audio signal according to a second patching algorithm. A spectral density of the second patch generated according to the second patching algorithm is higher than a spectral density of the first patch generator according to the first patching algorithm.

In the following, the same reference numerals are partly used for objects and functional units having the same or similar functional properties and the description thereof with regard to a figure shall apply also to other figures in order to reduce redundancy in the description of the embodiments.

shows a block diagram of an apparatusfor generating a bandwidth extended signalfor an input signalaccording to an embodiment of the invention. The input signalis represented, for a first band by a first resolution data, and for a second band by a second resolution data, the second resolution being lower than the first resolution. The apparatuscomprises a patch generatorconnected to a combiner. The patch generatorgenerates a first patchfrom the first band of the input signalaccording to a first patching algorithm and generates a second patchfrom the first band of the input signalaccording to a second patching algorithm. A spectral density of the second patchgenerated according to the second patching algorithm is higher than a spectral density of the first patchgenerated according to the first patching algorithm. The combinercombines the first patch, the second patchand the first band of the input signalto obtain the bandwidth extended signal. Further, the apparatusfor generating a bandwidth extended signalscales the input signalaccording to the first patching algorithm and according to the second patching algorithm or scales the first patchand the second patchso that the bandwidth extended signalfulfills a spectral envelope criterion.

Spectral density means, for example, the density of different frequencies or frequency lines within a frequency band. For example, a frequency band reaching from 0 Hz to 10 kHz comprising frequency portions with frequencies of 4 kHz and 8 kHz has a lower spectral density than the same frequency band comprising frequency portions with frequencies of 2 kHz, 4 kHz, 6 kHz, 8 kHz and 10 kHz. Since the spectral density of the first patchis lower than the spectral density of the second patch, the first patchcomprises gaps in comparison with the second patch. Therefore, the second patchmay be used to fill these gaps. Since both patches are based on the first band of the input signal, both patches are related to the characteristic of the original signal corresponding to the input signal. Therefore, the bandwidth extended signalmay be a good approximation of the original signal and the subjective quality or the audio quality of the bandwidth extension signalmay be significantly improved by using the described concept. In this way, more energy may be distributed between the remaining lines and, for example, a unnatural sound may be avoided.

For example, the first patching algorithm may be a harmonic patching algorithm. Therefore, the patch generatormay generate the first patchcomprising only frequencies that are integer multiples of frequencies of the first band of the input signal. A harmonic bandwidth extension may provide a good approximation of the tonal structure of the original signal, but this patching algorithm will leave gaps between the harmonic frequencies. These gaps may be filled by the second patch. For example, the second patching algorithm may be a mixing patching algorithm, which means that the patch generatormay generate the second patchcomprising integer multiples of frequencies of the first band of the input signal(harmonic frequencies) and frequencies that are not integer multiples of the frequencies of the first band of the input signal(non-harmonic frequencies). The non-harmonic frequencies may be used for filling the gaps of the first patch. It may also be possible to combine the whole second patch(including the harmonic frequencies) with the first patch. In this example, an amplification of the harmonic frequencies due to the combination of the harmonic frequency portions of the first patchand the second patchmay be taken into account by appropriately scaling the first patchand/or the second patch.

The first patchand the second patchcomprise at least partly the same frequency range. For example, the first patchcomprises a frequency band reaching from 4 kHz to 8 kHz and the second patchcomprises a frequency band from 6 kHz to 10 kHz. In some embodiments according to the invention, a lower cut of frequency of the first patch is equal to a lower cut of frequency of the second patch and an upper cut of frequency of the first patchis equal to an upper cut of frequency of the second patch. For example, both patches comprise a frequency band reaching from 4 kHz to 8 kHz.

show an example for a first patchaccording to a first patching algorithmand a second patchaccording to a second patching algorithm. For better illustration,shows only the first patchesandshows the first patchesand the corresponding second patches.illustrates an examplefor the first bandof the input signaland two first patchesgenerated according to the first patching algorithm. In this example, a patch comprises the same bandwidth as the first bandof the input signal. The bandwidth may also be different. The upper cut-off frequencyof the first bandof the input signalis denoted ‘Xover’ frequency (crossover frequency). In the example shown in, patches start at a frequency equal to a multiple of the crossover frequency Xover. The frequency lines within the first patchesare integer multiples of the frequency lines of the first bandof the input signaland may, for example, be generated by a phase vocoder. These first patchescomprise gaps in terms of missing frequency lines in comparison to the first bandof the input signal.

additionally shows an examplefor the two corresponding second patches. These patches are generated according to the second patching algorithmand comprise harmonic and non-harmonic frequencies. The non-harmonic frequency lines may be used to fill the gaps of the first patches. The frequency lines of the second patchesmay be generated, for example, by a non-linear distortion.

In this way, the gaps may not be filled arbitrarily as, for example, by filling the gaps with noise. The gaps are filled based on the first resolution data of the first band of the input signal and, therefore, based on the original signal.

The first band of the input signalmay represent, for example, the low frequency band of an original audio signal encoded with high resolution. The second band of the input signalmay represent, for example, a high frequency band of the original audio signal and may be quantized by one or more parameters as, for example, spectral envelope data, noise data and/or missing harmonic data with low resolution. An original audio signal may be, for example, an audio signal recorded by a microphone before processing or encoding.

Scaling the input signal according to the first patching algorithm and according to the second patching algorithm means, for example, that the input signal is scaled once according to the first patching algorithm before the first patch is generated and then the first patch is generated based on the scaled input signal, and that the input signal is scaled once according to the second patching algorithm before the second patch is generated and then the second patch is generated based on the scaled input signal, so that after the combination of the first patch, the second patch and the first band of the input signal, the bandwidth extended signal fulfills a spectral envelope criterion. Alternatively, the first patch and the second patch are scaled after their generation, so that the bandwidth extended signal also fulfills a spectral envelope criterion. Also a scaling of the input signal according to the first patching algorithm and according to the second patching algorithm in combination with a scaling of the first patch and the second patch may be possible.

The combinermay be, for example, an adder and the bandwidth extended signalmay be a weighted sum of the first patch, the second patchand the first band of the input signal.

Fulfilling a spectral envelope criterion means, for example, that a spectral envelope of the bandwidth extended signal is based on a spectral envelope data contained by the input signal. The spectral envelope data may be generated by an encoder and may represent the second band of an original signal. In this way, the spectral envelope of the bandwidth extended signal may be a good approximation of the spectral envelope of the original signal.

The apparatusmay also comprise a core decoder for decoding the first band of the input signal.

The patch generatorand the combinermay be, or example, specially designed hardware or part of a processor or micro controller or may be a computer program configured to run on a computer or a micro controller. The apparatusmay be part of a decoder or an audio decoder.

shows a block diagram of an apparatusfor generating a bandwidth extended signalfrom an input signalaccording to an embodiment of the invention. In this example, the patch generatorcomprises a phase vocoderfor generating the first patch and an amplitude clipperfor generating the second patch. The phase vocoderand the amplitude clipperare connected to the combiner. The phase vocodermay spread the first band of the input audio signalto generate the first patchcomprising harmonic frequencies. In a non-linear processing step, the amplitude clippermay clip the input signalto generate the second patchcomprising harmonic and non-harmonic frequencies. Alternatively to the amplitude clipper, also a half-wave rectifier, a full-wave rectifier, a mixer or a diode used in the quadratic region of the characteristic curve may be used to generate non-harmonic frequencies based on the input signalby a non-linear processing step.

show examples for clipped and/or rectified input signalsto generate non-harmonic frequencies.shows a schematic illustrationof a clipped sinusoidal input signal. By clipping the signal, points of discontinuity in the form of abrupt changes of the signal slopeare caused and harmonic and non-harmonic portions with higher frequencies are generated.

Alternatively,shows a schematic illustrationof a half-wave rectified sinusoidal input signal, also causing points of discontinuity.

Further, a combination of clipping and rectifying may be possible.shows a schematic illustrationof a clipped and full-wave rectified sinusoidal input signalcausing different points of discontinuity.

By clipping and/or rectifying or applying other methods of nonlinear processing generating points of discontinuity, a wide spectrum of different frequencies may be generated. Therefore, a patch generated according to such a patching algorithm may comprise a high spectral density.

shows a block diagram of an apparatusfor generating a bandwidth extended signalfrom an input signalaccording to an embodiment of the invention. The apparatusis similar to the apparatus shown in, but additionally comprises a spectral line selector. The phase vocoderand the amplitude clipperare connected to the spectral line selectorand the spectral line selectoris connected to the combiner. The spectral line selectormay select a plurality of frequency lines of the second patchto obtain a modified second patchthat may be complementary to the first patch. A frequency line of the second patchmay be selected if a corresponding frequency line of the first patchis missing. In other words, the spectral line selectorselects frequency lines of the second patchfor filling gaps of the first patchand may disregard frequencies of the second patchalready contained by the first patch. In this way, the modified second patchmay comprise gaps at frequencies already contained by the first patch.

In this example, the combinercombines the first patch, the modified second patchand the first band of the input signal.

The spectral line selectormay be, for example, part of the patch generator(as shown in) or a separate unit.

In the following, with reference to, possible implementations for a phase vocoderare illustrated according to the present invention.shows a filterbank implementation of a phase vocoder, wherein an audio signal is fed to an inputand obtained at an output. In particular, each channel of the schematic filterbank illustrated inincludes a bandpass filterand a downstream oscillator. Output signals of all oscillators from every channel are combined by a combiner, which is, for example, implemented as an adder and indicated atin order to obtain the output signal. Each filteris implemented such that it provides an amplitude signal on the one hand and a frequency signal on the other hand. The amplitude signal and the frequency signal are time signals illustrating a development of the amplitude in a filterover time, while the frequency signal represents a development of the frequency of the signal filtered by a filter.

A schematical setup of filteris illustrated in. Each filterofmay be set up as in, wherein, however, only the frequencies f, supplied to the two input mixersand the adderare different from channel to channel. The mixer output signals of the mixersare both lowpass filtered by lowpasses, wherein the lowpass signals are different insofar as they were generated by local oscillator frequencies (LO frequencies), which are out of phase by 90°. The upper lowpass filterprovides a quadrature signal, while the lower filterprovides an in-phase signal. These two signals, i.e. Q, and I are supplied to a coordinate transformerwhich generates a magnitude phase representation from the rectangular representation. The magnitude signal or amplitude signal, respectively, ofover time is output at an output. The phase signal is supplied to a phase unwrapper. At the output of the element, there is no phase value present any more, which is between 0 and 360°, but a phase value, which increases linearly. This “unwrapped” phase value is supplied to a phase/frequency converterwhich may, for example, be implemented as a simple phase difference calculator, which subtracts a phase of a previous point in time from a phase at a current point in time to obtain a frequency value for the current point in time or any other means for obtaining an approximation of a phase derivative. This frequency value is added to the constant frequency value fof the filter channel i to obtain a temporarily varying frequency value at the output. The frequency value at the outputhas a direct component=fand an alternating component=the frequency deviation by which a current frequency of the signal in the filter channel deviates from the average frequency f.

Thus, as illustrated in, the phase vocoder achieves a separation of the spectral information and the temporal information. The spectral information is contained in the special channel or in the frequency f, which provides the direct portion of the frequency for each channel, while the temporal information is contained in the frequency deviation or the magnitude evolution over time, respectively.

shows a manipulation as it is executed for the generation of the first patch according to the invention, in particular, using the phase vocoderand, in more detail, inserted at the location of the dashed line of the illustrated circuit in.