Audio bandwidth extension by insertion of temporal pre-shaped noise
n frequency domain
Description
The invention relates to speech and audio coding and particularly to audio
bandwidth extension (BWE).
Bandwidth extension techniques focus on enhancing the perceptible quality
of an audio codec by widening its effective output bandwidth. Instead of cod¬
ing the full bandwidth range with the underlying core coder, codecs using a
bandwidth extension technique allow for less bit consumption in the percep¬
tually less important higher frequency (HF) ranges. Thus, there are more bits
available to the core coder processing the more important lower frequency
(LF) range at a higher precision. For that reason, bandwidth extension tech¬
niques are commonly used in codecs, which need to realize proper percep¬
tual quality at low bit rates.
In general, there are two different basic bandwidth extension approaches that
need to be distinguished: Blind bandwidth extension and guided bandwidth
extension. In a blind bandwidth extension, no additional side information is
transmitted. Thus, the HF-content to be inserted on the decoder side is gen¬
erated using only information derived from the decoded LF-signal of the core
coder. Since a transmission of costly side information is not needed, Blind
bandwidth extension techniques are well suited for codecs operating at low¬
est bit rates or for backward-compatible post-processing procedures. On the
other hand, the lack of controllability oniy allows for a relatively small effective
extension of bandwidth using a Blind bandwidth extension (e.g. 6.4-7.0 kHz
in [1]). In contrast to the blind approach, in a guided bandwidth extension the
HF-content onstructed using parameters, which are extracted at the
encoder side and transmitted to the decoder as side information in the bitstream.
Hence, a guided bandwidth extension enables a better control of the
HF-reconstruction, rendering broader effective bandwidths possible. Due to
the additional bit consumption, guided bandwidth extension techniques are
commonly used for codecs operating at higher bit rates as systems incorpo¬
rating a blind bandwidth extension.
More specifically, there are different methodologies for realizing a bandwidth
extension:
In speech coding, usually source-filter model-based bandwidth extension
methods are used, which are closely related to their underlying core coders,
as e.g. in G.722.2 (AMR-WB) [1]. In AMR-WB, the output bandwidth of 6.4
kHz of the ACELP (algebraic code-excited linear prediction) core coder is
extended to 7.0 kHz by injecting white noise into the excitation domain. Sub¬
sequently, the extended excitation is shaped by a filter derived from the core
coder's linear prediction (LP) filter. Depending on the bit rate, the gain for
scaling of the inserted noise is either estimated using only core coder infor¬
mation or it is extracted in the encoder and transmitted. This bandwidth ex¬
tension method is heavily dependent to its underlying coding scheme, as it is
using its synthesis mechanisms and thus additionally has to be performed in
the same domain.
A well-known core coder independent bandwidth extension technique in au¬
dio coding is spectral band replication (SBR) [2]. In contrast to the previous
example, spectral band replication can be applied independently from its underlying
core coder. As a first step, the input signal is split into an LF- and an
HF-part on encoder side, for example by using a quadrature mirror filter anal¬
ysis filter bank (QMF). The LF-signal is fed to the core coder while the HFpart
is processed by spectral band replication. Therefore, parameters de¬
scribing the time-frequency-envelope of the HF-signal as well as the tonaiity/
noisiness of t .fc HF-signal relative to the LF-signal are extracted and
transmitted. After decoding, the signal is transformed using the same type of
analysis filter bank as used in the encoder. To reconstruct the HF-content,
the decoded signa! is copied, mirrored or transposed portion-wise to the HFrange,
post-processed to match the tonality/noisiness of the original and
shaped temporally as well as spectrally, considering the transmitted parame¬
ters. Subsequently, the time domain output signal is generated by a corresponding
synthesis filter bank.
In contrast to the previously noted (semi-)parametrical methods there are
also multiple layer approaches using multiple, bit rate selective layers for
bandwidth extension. This principle is also closely related to scalable coding
schemes. Those techniques are often used for extending existing coding sys¬
tems in an interoperable manner. In [3] a super wideband (SWB) bandwidth
extension for G.71 1.1 and G.722 is presented, which processes the addition¬
al bandwidth (8.0-14.4 kHz) with a modified discrete cosine transform
(MDCT) based coding scheme independent from the core coder. This approach
enables exact reconstruction of HF-parts, but at the expense of addi¬
tionally necessary, high bit consumption.
Although the above-mentioned bandwidth extension approaches are widely
spread in present speech and audio coding systems, all of them reveal specific
shortcomings or disadvantages, respectively.
It is an object of the present invention to provide an improved concept for
bandwidth extension.
This object is achieved by a decoder device for decoding a bitstream, where
in the audio decoder device comprises:
a bitstream receiver configured to receive the bitstream and to derive an e n
coded audio signal from the bitstream;
a core decoder module configured for deriving a decoded audio signal in a
time domain from the encoded audio signal;
a temporal envelope generator configured to determine a temporal envelope
of the decoded audio signal;
a bandwidth extension module configured to produce a frequency domain
bandwidth extension signal, wherein the bandwidth extension module com¬
prises a noise generator configured to produce a noise signal in time domain,
wherein the bandwidth extension module comprises a pre-shaping module
configured for temporal shaping of the noise signal depending on the tem¬
poral envelope of the decoded audio signal in order to produce a shaped
noise signal and wherein the bandwidth extension module comprises a timeto-
frequency converter configured to transform the shaped noise signal into a
frequency domain noise signal; wherein the frequency domain bandwidth
extension signal depends on the frequency domain noise signal;
a time-to-frequency converter configured to transform the decoded audio s ig
nal into a frequency domain decoded audio signal;
a combiner configured to combine the frequency domain decoded audio sig¬
nal and the frequency domain bandwidth extension signal in order to produce
a bandwidth extended frequency domain audio signal; and
a frequency-to-time converter configured to transform the bandwidth extend¬
ed frequency domain audio signal into a bandwidth-extended time domain
audio signal.
The invention provides a bandwidth extension concept, which can be basical
ly applied independent from the underlying core coding technique. Further¬
more, it offers a bandwidth extension up to super wideband frequency ranges
for low bit rate operating points, with high perceptual quality especially for
speech signals. This s achieved by generating temporally shaped noise signals
in time domain, which are transformed and inserted to the frequency
domain decoded audio signal.
The term frequency domain bandwidth extension signal refers to a signal
comprising frequencies, which are not contained in the decoded audio signal.
In flexible, signal-adaptive systems incorporating more than one single core
coder, e.g. as contained in the unified speech and audio coding (MPEG-D
USAC), switching artifacts that occur at the transition between different core
coders, might be emphasized as also the bandwidth extension has to be
switched at the same time. These problems can be overcome by applying a
core coder independent bandwidth extension technique according to the in
vention.
Spectral band replication introduces artifacts that might be annoying, espe¬
cially when speech is coded due to the patching of LF-components to the HFpart.
Those artifacts arise due to the correlation of LF- and patched HFcontent,
on the one hand. On the other hand, the possible spectral mismatch
between LF- and HF-part leads to sharp sounding, inharmonic distortions. In
contrast to that, the decoder device according to the invention avoids produc¬
ing artifacts and sharp sounding.
Another shortcoming of spectral band replication is the restricted possibility to
manipulate the temporal structure of the patched HF-part. Due to the need of
a bit rate efficient parametric time-frequency-representation of the content,
the temporal resolution is limited. This might be disadvantageous for e.g.
processing female speech, where the pitch of the glottal pulses is high and
also exhibits a high temporal variability. The decoder device according to the
invention is, in contrast to spectral band replication, well suited for reproduc¬
ing female speech.
Lastly, a bandwidth extension based on multiple layers is ab e to reconstruct
HF-content in a both, spectrally and temporally exact manner, but on the oth¬
er hand its necessary bit consumption is significantly higher than for paramet¬
ric approaches. The decoder device according to the invention provides low¬
er bit consumption compelled to such approaches.
Thus, the present invention provides a new bandwidth extension concept,
which combines the benefits of the well-known, previously described band¬
width extension techniques, while omitting their drawbacks. More specifically
a concept is provided, that enables high quality, super wideband speech cod¬
ing at low bit rates, while being independent from the underlying core coder.
The invention provides at high perceptual quality especially for speech for
output bandwidths up to the super wideband range. The bandwidth extension
according to the invention is based on noise insertion. Additionally, the new
bandwidth extension is independent from its underlying core codec. There¬
fore, it is - in contrast to standard speech coding bandwidth extension - suit¬
able for being used on top of a switched system, incorporating fundamentally
different coding schemes.
As the mixing of the newly proposed bandwidth extension's and the core de¬
coder's signal is performed in a comparable time-frequency-representation to
spectral band replication, both techniques could be easily combined in a
combined system, where seamless switching on a frame-by-frame basis or
blending within a given frame would be possible. As the new bandwidth ex
tension focusses mainly on speech, this approach might be desirable for pro¬
cessing signals containing music or mixed content. Switching can be con¬
trolled either by transmitted side information or by parameters derived in the
decoder by analyzing the core signal.
According to the invention, generation and subsequent shaping of noise is
done in time domain, because time domain temporal resolution may be
higher than in solutions, n which noise is generated and shaped within a
time-frequency-representation, similar to the one applied in spectral band
replication processing, as the filter banks limit the time resolution, which is
essential for reproducing high pitched (e.g. female) speech.
To avoid above mentioned problems and yet fulfill the requirements, the new
bandwidth extension performs the following processing steps: First, a single
noise signal is generated in time domain, where the number of samples aris¬
es from the system's frame rate as well as the chosen sampling rate and the
noise signal's bandwidth. Subsequently, the noise signal is temporally pre¬
shaped, based on the temporal envelope of the decoded core coder's signal.
Furthermore, the combined time-frequency-represented signal is converted
to the bandwidth extended time domain audio signal by inverse transfor¬
mation.
Bandwidth extension techniques are commonly used in speech and audio
coding for enhancing the perceptual quality by widening the effective output
bandwidth. Thus the majority of available bits can be used within the core
coder, enabling a higher precision in the more important lower frequency
range. Although there are existing approaches, some of which gained wide
acceptance, they all lack of viability for speech processing by a system which
incorporates multiple, switchable core coders, based on different coding
schemes. As the bandwidth extension according to the invention is inde
pendent from the core decoder technology, the present invention proposes a
bandwidth extension technique, which is perfectly suited to the abovementioned
application and others.
Within the bandwidth extension according to the invention, fully synthetic ex
tension signals may be generated having a temporal envelope that can be
pre-shaped, and thereby adapted to the underlying core coder signal. Shap¬
ing of the temporal envelope of the extension signal can be done in a signifi¬
cantly higher time resolution than it is available within the genuine filter bank
or transform domain employed in the bandwidth extension post-shaping pro¬
cess.
According to a preferred embodiment of the invention is the frequency do¬
main bandwidth extension signal produced without spectral band replication.
By these features a computational effort necessary may be minimized.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module is configured in such way, that the temporal shaping of the noise
signal is done in an overemphasized manner. Instead of shaping the noise
signal based on the original temporal envelope of the decoded audio signal; it
is also possible to perform this shaping in an overemphasized manner. This
can be realized by spreading the temporal envelope in terms of amplitudes,
in other words by dynamic expansion, in particular by modifying the meas¬
ured envelope to represent pulses much sharper than have been measured,
before deriving pre-shaping gains on its basis. Although this overemphasis
does not represent the actual original envelope, the intelligibility of some sig¬
nal portions, like e.g. vowels, improves for very low bitrates.
According to preferred embodiment of the invention the bandwidth extension
module is configured in such way, that the temporal shaping of the noise s ig
nal is done subband-wise by splitting the noise signal into several subband
noise signals by a bank of band pass filters and performing a specific tem¬
poral shaping on each of the subband noise signals.
Instead of pre-shaping the noise signal uniformly, the shaping can be made
more precisely by splitting the noise signal into several subbands by a bank
of band pass filters and performing a specific shaping on every subband sig¬
nal.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a frequency range selector configured for setting a
frequency range of the frequency domain bandwidth extension signal. After
transforming the shaped noise signal into a time-frequency-representation,
the targeted bandwidth of the bandwidth extended frequency-domain audio
signal may be selected and, if necessary, shifted to its intended, spectral position.
By these features the frequency range of the bandwidth-extended time
domain audio signal may be chosen in an easy way.
According to a preferred embodiment of the invention comprises the band¬
width extension module a post-shaping module configured for temporal
and/or spectral shaping in frequency domain of the frequency domain band¬
width extension signal. By these features the frequency domain bandwidth
extension signal may be adapted with respect to an additional temporal trend
and/or a spectral envelope for refinement.
According to a preferred embodiment of the invention the bitstream receiver
is configured to derive a side information signal from the bitstream, wherein
the bandwidth extension module is configured to produce the frequency do
main bandwidth extension signal depending on the side information signal.
With other words, additional side information, which was extracted within the
encoder and transmitted via the bitstream, may be applied for further refine¬
ment of the frequency domain bandwidth extension signal. By these features
the perceived quality of the bandwidth-extended time domain audio signal
may be further increased.
According to a preferred embodiment of the invention the noise generator is
configured to produce the noise signal depending on the side information
signal. In this embodiment the noise generator can be controlled in a way to
obtain a noise signal with a spectral tilt, instead of spectrally fiat white noise,
in order to further improve the perceived quality of the bandwidth-extended
time domain audio signal.
According to a preferred embodiment of the invention the pre-shaping mod¬
ule is configured for temporal shaping of the noise signal depending on the
side information signal. Within the pre-shaping, side information can be used
to e.g. choose a certain target bandwidth of the core decoder signal, which is
used for pre-shaping.
According to a preferred embodiment of the invention the post shaping mod¬
ule is configured for temporal and/or the spectral shaping of the frequency
domain output noise signal depending on the side information signal. Using
side information in the post-shaping may ensure that the coarse timefrequency-
envelope of the frequency domain bandwidth extension signal fol¬
lows the original envelope.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a further noise generator configured to produce a
further noise signal in a time domain, a further pre-shaping module config¬
ured for temporal shaping of the further noise signal depending on the tem¬
poral envelope of the decoded audio signal in order to produce a further
shaped noise signal and a further time-to-frequency converter configured to
transform the further shaped noise signal into a further frequency domain
noise signal; wherein the frequency domain bandwidth extension signal de¬
pends on the further frequency domain noise signal. Producing the frequency
domain bandwidth extension signal using two or more frequency domain
noise signals may lead to an increase of the perceived quality of the band¬
width-extended time domain audio signal.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module is configured in such way, that the temporal shaping of the fur¬
ther noise signal is done in an overemphasized manner. Instead of shaping
the further noise signal based on the original temporal envelope of the de¬
coded audio signal; it is also possible to perform this shaping in an overem
phasized manner. This ca be realized by spreading the temporal envelope
in terms of amplitudes, before deriving pre-shaping gains on its basis. Alt¬
hough this overemphasis does not represent the actual original envelope, the
intelligibility of some signal portions, like e.g. vowels, improves for very low
bitrates.
According to preferred embodiment of the invention the bandwidth extension
module is configured in such way, that the temporal shaping of the further
noise signal is done subband-wise by splitting the further noise signal into
several further subband noise signals by a bank of band pass filters and per¬
forming a specific temporal shaping on each of the further subband noise
signals.
Instead of pre-shaping the further noise signal uniformly, the shaping can be
made more precisely by splitting the further noise signal into several subbands
by a bank of band pass filters and performing a specific shaping on
every subband signal.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a tone generator configured to produce a tone signal
in a time domain, a pre-shaping module configured for temporal shaping of
the tone signal depending on the temporal envelope of the decoded audio
signal in order to produce a shaped tone signal and a time-to-frequency con
verter configured to transform the shaped tone signal into a frequency do¬
main tone signal, wherein the frequency domain bandwidth extension signal
depends on the frequency domain tone signal.
Said tone generator may be functional to produce all kinds of tones, e.g. sine
tones, triangle and square wave tones, saw tooth tones, pulses that resemble
artificial voiced speech, etc. Additional to processing synthetic noise signals,
it is also possible to generate synthetic tonal components in time domain that
are temporal shaped and subsequently transformed into a frequency repre¬
sentation. I this case, shaping in time domain is beneficial : modeling
precisely the ADSR (attack, decay, sustain, release) phases of tones, which
is not possible in a common frequency domain representation. The addition¬
ally use of a frequency domain tone signal may further increase the quality of
the bandwidth extended time domain signal.
According to a preferred embodiment of the invention the core decoder mod¬
ule comprises a time domain core decoder and a frequency domain core de¬
coder, wherein either the time domain core decoder or the frequency domain
core decoder is used for deriving the decoded audio signal from the encoded
audio signal. These features allow using the invention in a unified speech
and audio coding (MPEG-D USAC) environment.
According to a preferred embodiment of the invention a control parameter
extractor is configured for extracting control parameters used by the core decoder
module from the decoded audio signal and wherein the bandwidth ex¬
tension module is configured to produce the frequency domain bandwidth
extension signal depending on the control parameters. Although the frequen¬
cy domain bandwidth extension signal may be produced blindly on the basis
of the core coder envelope or controlled by parameters derived from the core
coder signal, it can also be produced in a partly guided way, by means of
extracted and transmitted parameters from the encoder.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a shaping gains calculator configured for establishing
shaping gains for the pre-shaping module depending on the temporal enve¬
lope of the decoded audio signal and wherein the pre-shaping module is con
figured for temporal shaping of the noise signal depending on the shaping
gains for the pre-shaping module. These features allow implementing the
invention in an easy way.
According to a preferred embodiment of the invention the shaping gains cal¬
culator for establishing shaping gains for the pre-shapr r ' duie is configured
for establishing shaping gains for the pre-shaping module depending on
the control parameters. These features allow implementing the invention in
an easy way.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a shaping gains calculator configured for establishing
shaping gains for the further pre-shaping module depending on the temporal
envelope of the decoded audio signal and wherein the further pre-shaping
module is configured for temporal shaping of the further noise signal depend¬
ing on the shaping gains for the further pre-shaping module.
According to a preferred embodiment of the invention the shaping gains cal¬
culator for establishing shaping gains for the further pre-shaping module is
configured for establishing shaping gains for the further pre-shaping module
depending on the control parameters.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module comprises a shaping gains calculator configured for establishing
shaping gains for the tone pre-shaping module depending on the temporal
envelope of the decoded audio signal and wherein the tone pre-shaping
module is configured for temporal shaping of the tone signal depending on
the shaping gains for the tone pre-shaping module.
According to a preferred embodiment of the invention the shaping gains cal¬
culator for establishing shaping gains for the tone pre-shaping module is con¬
figured for establishing shaping gains for the further pre-shaping module de
pending on the control parameters.
In a further aspect the object is achieved by a method for decoding a bitstream,
wherein the method comprises the steps of:
receiving the bitstre ,d deriving an encoded audio signal from the bitstream
using a bitstream receiver;
deriving a decoded audio signal in a time domain from the encoded audio
signal using a core decoder module;
determining a temporal envelope of the decoded audio signal using a tem¬
poral envelope generator;
producing a frequency domain bandwidth extension signal using a bandwidth
extension module executing the steps of:
producing a noise signal in time domain using a noise generator of the
bandwidth extension module,
temporal shaping of the noise signal depending on the temporal
envelope of the decoded audio signal in order to produce a shaped
noise signal using a pre-shaping module of the bandwidth extension
module,
transforming the shaped noise signal into a frequency domain noise
signal; wherein the frequency domain bandwidth extension signal
depends on the frequency domain noise signal, using a
time-to-frequency converter of the bandwidth extension module;
transforming the decoded audio signal into a frequency domain decoded a u
dio signal using a further time-to-frequency converter;
combining the frequency domain decoded audio signal and the frequency
domain bandwidth extension signal in order to produce a bandwidth extend¬
ed frequency domain audio signal using a combiner; and
transforming the bandwi tended frequency domain audio signal into a
bandwidth-extended time domain audio signal using a frequency-to-time
converter.
In a further aspect the object is achieved by a computer program executing
the inventive method when running on a processor.
Preferred embodiments of the invention are subsequently discussed with re¬
spect to the accompanying drawings, in which:
Fig. 1 illustrates a first embodiment of an audio decoder device ac¬
cording to the invention in a schematic view;
Fig. 2 illustrates a second embodiment of an audio decoder device
according to the invention in a schematic view;
Fig. 3 illustrates a third embodiment of an audio decoder device ac¬
cording to the invention in a schematic view; and
Fig. 4 illustrates a forth embodiment of an audio decoder device according
to the invention in a schematic view.
Fig. 1 illustrates a first embodiment of an audio decoder device according to
the invention in a schematic view.
The audio decoder device 1 comprises:
a bitstream receiver 2 configured to receive the bitstream BS and to derive
an encoded audio signal EAS from the bitstream BS;
a core decoder module 3 configured for deriving a decoded audio signal DAS
in time domain from the encoded audio signal EAS;
a temporal envelope generator 4 configured to determine a temporal enve¬
lope TED of the decoded audio signal DAS;
a bandwidth extension module 5 configured to produce a frequency domain
bandwidth extension signal BEF, wherein the bandwidth extension module 5
comprises a noise generator 6 configured to produce a noise signal NOS in
time domain, wherein the bandwidth extension module 5 comprises a pre¬
shaping module 7 configured for temporal shaping of the noise signal NOS
depending on the temporal envelope TED of the decoded audio signal DAS
in order to produce a shaped noise signal SNS and wherein the bandwidth
extension module comprises 5 a time-to-frequency converter 8 configured to
transform the shaped noise signal SNS into a frequency domain noise signal
FNS, wherein the frequency domain bandwidth extension signal BEF de¬
pends on the frequency domain noise signal FNS;
a time-to-frequency converter 9 configured to transform the decoded audio
signal DAS into a frequency domain decoded audio signal FDS;
a combiner 10 configured to combine the frequency domain decoded audio
signal FDS and the frequency domain bandwidth extension signal BEF in
order to produce a bandwidth extended frequency domain audio signal BFS;
and
a frequency-to-time converter configured to transform the bandwidth ex
tended frequency domain audio signal BFS into a bandwidth-extended time
domain audio signal BAS.
The invention provides a bandwidth extension concept, which can be basical
ly applied independent from the underlying core coding technique. Further
more, it offers a bandwidth extension up to super wideband frequency ranges
for low bit rate operating points, with high perceptual quality especially for
speech signals. This is achieved by generating temporally shaped noise signa
s SNS in time domain, which are transformed and inserted to the f reque n
cy domain decoded audio signal FDS.
In flexible, signal-adaptive systems incorporating more than one single core
coder, e.g. as contained in the unified speech and audio coding (MPEG-D
USAC), switching artifacts that occur at the transition between different core
coders, might be emphasized as also the bandwidth extension has to be
switched at the same time. These problems can be overcome by applying a
core coder independent bandwidth extension technique according to the in
vention.
Spectral band replication introduces artifacts that might be annoying, espe¬
cially when speech is coded due to the patching of LF-components to the HFpart.
Those artifacts arise due to the correlation of LF- and patched HFcontent,
on the one hand. On the other hand, the possible spectral mismatch
between LF- and HF-part leads to sharp sounding, inharmonic distortions. In
contrast to that, the decoder device 1 according to the invention avoids pro¬
ducing artifacts and sharp sounding.
Another shortcoming of spectral band replication is the lack of possibility to
manipulate the temporal structure of the patched HF-part. Due to the need of
a bit rate efficient parametric time-frequency-representation of the content,
the temporal resolution is limited. This might be disadvantageous for e.g.
processing female speech, where the pitch of the glottal pulses is high and
also exhibits a high temporal variability. The decoder device 1 according to
the invention is, in contrast to spectral band replication, well suited for repro¬
ducing female speech.
Lastly, a bandwidth extension based on multiple layers is able to reconstruct
HF-content in a both, spectrally and temporally exact manner, but on the oth¬
er hand its necessary bit consumption is significantly higher than for parametric
approaches. The decoder device 1 according to the invention provides
lower bit consumption compelled to such approaches.
Thus, the present invention provides a new bandwidth extension concept,
which combines the benefits of the well-known, previously described band¬
width extension techniques, while omitting their drawbacks. More specifically
a concept is provided, that enables high quality, super wideband speech cod¬
ing at low bit rates, while being independent from the underlying core coder
3.
The invention provides at high perceptual quality especially for speech for
output bandwidths up to the super wideband range. The bandwidth extension
according to the invention is based on noise insertion. Additionally, the new
bandwidth extension is independent from its underlying core codec. Therefore,
it is - in contrast to standard speech coding bandwidth extension - suit¬
able for being used on top of a switched system, incorporating fundamentally
different coding schemes.
As the mixing of the newly proposed bandwidth extension's and the core decoder's
signal is performed in a comparable time-frequency-representation to
spectral band replication, both techniques could be easily combined in a
combined system, where seamless switching on a frame-by-frame basis or
blending within a given frame would be possible. As the new bandwidth ex¬
tension focusses mainly on speech, this approach might be desirable for processing
signals containing music or mixed content. Switching can be con¬
trolled either by transmitted side information or by parameters derived in the
decoder 3 by analyzing the core signal DAS.
According to the invention, generation and subsequent shaping of noise is
done time domain, because in time domain temporal resolution may be
higher than in solutions, in which noise is generated and shaped within a
time-frequency-representation, similar one applied in spectral band
replication processing, as the filter banks !imit the time resolution, which is
essential for reproducing high pitched (e.g. female) speech.
To avoid above mentioned problems and yet fulfill the requirements, the new
bandwidth extension performs the following processing steps: First, a single
noise signal NOS is generated in time domain, where the number of samples
arises from the system's frame rate as well as the chosen sampling rate and
the noise signal's bandwidth. Subsequently, the noise signal NOS is tempo¬
rally pre-shaped, based on the temporal envelope TED of the decoded core
coder's signal DAS. Furthermore, the combined time-frequency-represented
signal BFS is converted to the bandwidth extended time domain audio signal
BAS by inverse transformation.
Bandwidth extension techniques are commonly used in speech and audio
coding for enhancing the perceptual quality by widening the effective output
bandwidth. Thus the majority of available bits can be used within the core
coder 3, enabling a higher precision in the more important lower frequency
range. Although there are existing approaches, some of which gained wide
acceptance, they all lack of viability for speech processing by a system which
incorporates multiple, switchable core coders, based on different coding
schemes. As the bandwidth extension according to the invention is inde¬
pendent from the core decoder technology, the present invention proposes a
bandwidth extension technique, which is perfectly suited to the abovementioned
application and others.
Within the bandwidth extension according to the invention, fully synthetic ex¬
tension signals may be generated having a temporal envelope that can be
pre-shaped, and thereby adapted to the underlying core coder signal DAS.
Shaping of the temporal envelope of the extension signal SNS can be done
in a significantly higher time resolution than it is available within the genuine
filter bank or transform domain employed in the bandwidth extension postshaping
process.
According to preferred embodiment of the invention the frequency domain
bandwidth extension signal BEF is produced without spectral band replica¬
tion. By these features a computational effort necessary may be minimized.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 is configured in such way that the temporal shaping of the
noise signal NOS is done in an overemphasized manner. Instead of shaping
the noise signal NOS based on the original temporal envelope TED of the
decoded audio signal DAS; it is also possible to perform this shaping in an
overemphasized manner. This can be realized by spreading the temporal
envelope TED in terms of amplitudes, before deriving pre-shaping gains on
its basis. Although this overemphasis does not represent the actual original
envelope TED, the intelligibility of some signal portions, like e.g. vowels, improves
for very low bitrates.
According to a preferred embodiment of the invention the bandwidth exten
sion module 5 is configured in such way that the temporal shaping of the
noise signal NOS is done subband-wise by splitting the noise signal NOS into
several subband noise signals by a bank of band pass filters and performing
a specific temporal shaping on each of the subband noise signals.
Instead of pre-shaping the noise signal NOS uniformly, the shaping can be
made more precisely by splitting the noise signal NOS into several subbands
by a bank of band pass filters and performing a specific shaping on every
subband signal.
Furthermore, the invention relates to a method for decoding a bitstream BS,
wherein the method comprises he steps of:
receiving the bitstream BS and deriving an encoded audio signal EAS from
the bitstream BS using a bitstream receiver 2 ;
deriving a decoded audio signal DAS in a time domain from the encoded au¬
dio signal EAS using a core decoder module 3;
determining a temporal envelope TED of the decoded audio signal DAS us¬
ing a temporal envelope generator 4 ;
producing a frequency domain bandwidth extension signal BEF using a
bandwidth extension module 5 executing the steps of:
producing a noise signal NOS in time domain using a noise genera
tor 6 of the bandwidth extension module 5,
temporal shaping of the noise signal NOS depending on the temporal
envelope TED of the decoded audio signal DAS in order to produce
a shaped noise signal SNS using a pre-shaping module 7 of the
bandwidth extension module 5,
transforming the shaped noise signal SNS into a frequency domain
noise signal FNS; wherein the frequency domain bandwidth
extension signal BEF depends on the frequency domain noise
signal FNS, using a time-to-frequency converter 8 of the bandwidth
extension module 5;
transforming the decoded audio signal DAS into a frequency domain decod¬
ed audio signal FDS using a further time-to-frequency converter 9;
combining the frequency domain decoded audio signal FDS and the frequen¬
cy domain bandwidth extension signal BEF in order to produce a bandwidth
extended frequency domain audio signal BFS using a combiner 10; and
transforming the bandwidth extended frequency domain audio signal BFS
into a bandwidth-extended time domain audio signal BAS using a frequencyto-
time converter 11.
Moreover, the invention relates to the computer program, when running on a
processor, executing the method according to the invention.
Fig. 2 illustrates a second embodiment of an audio decoder device according
to the invention in a schematic view.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 comprises a frequency range selector 12 configured for setting
a frequency range of the frequency domain bandwidth extension signal BEF.
After transforming the shaped noise signal SNS into a time-frequencyrepresentation
FNS, the targeted bandwidth of the bandwidth extended fre¬
quency-domain audio signal BEF may be selected and, if necessary, shifted
to its intended, spectral position. By these features the frequency range of
the bandwidth-extended time domain audio signal BAS may be chosen in an
easy way.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 comprises a post-shaping module configured for temporal
and/or spectral shaping in frequency domain of the frequency domain band¬
width extension signal BEF. By these features the frequency domain bandwidth
extension signal BEF may be adapted with respect to an additional
temporal trend and/or a spectra! envelope for refinement.
According to a preferred embodiment of the invention the bitstream receiver
2 is configured to derive a side information signal SIS from the bitstream BS,
wherein the bandwidth extension module 5 is configured to produce th I."·
quency domain bandwidth extension signal BEF depending on the side in¬
formation signal SIS. With other words, additional side information, which
was extracted within the encoder and transmitted via the bitstream BS, may
be applied for further refinement of the frequency domain bandwidth exten¬
sion signal BEF. By these features the perceived quality of the bandwidthextended
time domain audio signal BAS may be further increased.
According to a preferred embodiment of the invention the noise generator 6
is configured to produce the noise signal NOS depending on the side infor¬
mation signal SIS. In this embodiment the noise generator 6 can be con¬
trolled in a way to obtain a noise signal with a spectral tilt, instead of spectrally
flat white noise, in order to further improve the perceived quality of the
bandwidth-extended time domain audio signal BAS.
According to a preferred embodiment of the invention the pre-shaping mod¬
ule 7 is configured for temporal shaping of the noise signal NOS depending
on the side information signal SIS. Within the pre-shaping, side information
can be used to e.g. choose a certain target bandwidth of the core decoder
signal DAS, which is used for pre-shaping.
According to a preferred embodiment of the invention the post-shaping module
13 is configured for temporal and/or the spectral shaping of the frequency
domain bandwidth extension signal BEF depending on the side information
signal SIS. Using side information in the post-shaping may ensure that the
coarse time-frequency-envelope of the frequency domain bandwidth exten¬
sion signal BEF follows the original envelope TED.
Fig. 3 illustrates a third embodiment of an audio decoder device according to
the invention in a schematic view.
According to a preferred embodiment of the invention the bandwidth extension
module 5 comprises a further noise generator 14 configured to produce
a further noise signal NOSF in time domain, a further pre-shaping module 15
configured for temporal shaping of the further noise signal NOSF depending
on the temporal envelope TED of the decoded audio signal DAS in order to
produce a further shaped noise signal SNSF and a further time-to-frequency
converter 6 configured to transform the further shaped noise signal SNSF
into a further frequency domain noise signal FNSF, wherein the frequency
domain bandwidth extension signal BEF depends on the further frequency
domain noise signal FNSF. Producing the frequency domain bandwidth ex¬
tension signal BEF using two frequency domain noise signals FNS, FNSF
may lead to an increase of the perceived quality of the bandwidth-extended
time domain audio signal BAS.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 is configured in such way that the temporal shaping of the fur¬
ther noise signal NOSF is done in an overemphasized manner. This can be
realized by spreading the temporal envelope in terms of amplitudes, before
deriving pre-shaping gains on its basis. Although this overemphasis does not
represent the actual original envelope, the intelligibility of some signal por¬
tions, like e.g. vowels, improves for very low bitrates.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 is configured in such way that the temporal shaping of the fur¬
ther noise signal NOSF is done subband-wise by splitting the further noise
signal NOSF into several further subband noise signals by a bank of band
pass filters and performing a specific temporal shaping on each of the further
subband noise signals.
Instead of pre-shaping the further noise signal uniformly, the shaping can be
made more precisely by splitting the further noise signal into several subbands
by a bank of band pass filters and performing a specific shaping on
every subband signal
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 comprises a tone generator 17 configured to produce a tone
signal TOS i a time domain, a tone pre-shaping module configured for
temporal shaping of the tone signal TOS depending on the temporal enve¬
lope TED of the decoded audio signal DAS in order to produce a shaped
tone signal STS and a time-to-frequency converter 19 configured to trans¬
form the shaped tone signal STS into a frequency domain tone signal FTS,
wherein the frequency domain bandwidth extension signal BEF depends on
the frequency domain tone signal FTS. Additional to processing synthetic
noise signals NOS, NOSF, it is also possible to generate synthetic tonal
components in time domain that are temporal shaped and subsequently
transformed into a frequency representation FTS. In this case, shaping in
time domain is beneficial e.g. for modeling precisely the ADSR (attack, de¬
cay, sustain, release) phases of tones, which is not possible in a common
frequency domain representation. The additionally use of a frequency domain
tone signal FTS may further increase the quantity of the bandwidth extended
time domain signal BAS.
The frequency domain noise signal FNS, the further frequency domain signal
FNSF and/or the frequency domain tone signal may be combined by a com
biner 20.
Fig. 4 illustrates a forth embodiment of an audio decoder device ac-cording to
the invention in a schematic view.
According to a preferred embodiment of the invention the core decoder mod¬
ule 5 comprises a time domain core decoder 2 1 and a frequency domain
core decoder 22, wherein either the time domain core decoder 2 1 or the fre¬
quency domain core decoder 22 is selectable for deriving the decoded audio
signal DAS from the encoded audio signal AS. These features allow using
the invention t in a unified speech and audio coding (MPEG-D USAC) envi¬
ronment.
According to a preferred embodiment of the invention a control parameter
extractor 23 is configured for extracting control parameters CP used by the
core decoder module 3 from the decoded audio signal DAS and wherein the
bandwidth extension module 5 is configured to produce the frequency domain
bandwidth extension signal BEF depending on the control parameters
CP. Although the frequency domain bandwidth extension signal BEF may be
produced blindly on the basis of the core coder envelope or controlled by pa¬
rameters derived from the core coder signal, it can also be produced in a
partly guided way, by means of extracted and transmitted parameters from
the encoder.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 comprises a shaping gains calculator 24 configured for estab¬
lishing shaping gains SG for the pre-shaping module 7 depending on the
temporal envelope TED of the decoded audio signal DAS and wherein the
pre-shaping module 7 is configured for temporal shaping of the noise signal
NOS depending on the shaping gains SG for the pre-shaping module 7 .
These features allow implementing the invention in an easy way.
According to a preferred embodiment of the invention the shaping gains cal¬
culator 24 for establishing shaping gains SG for the pre-shaping module 7 is
configured for establishing shaping gains SG for the pre-shaping module 7
depending on the control parameters CP.
According to preferred embodiment of the invention the bandwidth extension
module 5 comprises a shaping gains calculator configured for establishing
shaping gains for the further pre-shaping module 15 depending on the tem¬
poral envelope TED of the decoded audio signal DAS and wherein the further
pre-shaping module 14 is configured for temporal shaping of the further noise
signal NOSF depending on the shaping gains for the further pre-shaping
module 14.
According to a preferred embodiment of the invention the shaping gains cal¬
culator for establishing shaping gains for the further pre-shaping module 15 is
configured for establishing shaping ga i s for the further pre-shaping module
15 depending on the control parameters CP.
According to a preferred embodiment of the invention the bandwidth exten¬
sion module 5 comprises a shaping gains calculator configured for establish¬
ing shaping gains for the tone pre-shaping module 18 depending on the tem¬
poral envelope TED of the decoded audio signal DAS and wherein the tone
pre-shaping module 18 is configured for temporal shaping of the tone signal
TOS depending on the shaping gains for the tone pre-shaping module 18.
According to a preferred embodiment of the invention the shaping gains cal¬
culator for establishing shaping gains for the tone pre-shaping module 18 is
configured for establishing shaping gains for the further pre-shaping module
18 depending on the control parameters CP.
Figure 4 illustrates a preferred embodiment of the new bandwidth extension
step-by-step as an enhancement of a switched coding system. The exempla¬
ry system comprises a time domain core decoder 2 1 and a frequency domain
core coder 22, running at an internal sampling rate of 12.8 kHz and 20ms
framing, each. This given setting results in 256 decoder output samples per
frame and an output bandwidth of 6.4 kHz. By the application of the band¬
width extension, the system's effective output bandwidth is supposed to be
extended up to 14.4 kHz with one noise signal, at a sampling rate of 32.0
kHz. Hence, following steps may be performed for each frame.
At the step of noise generation a noise frame of 8.0 kHz effective bandwidth
(14.4 kHz - 6.4 kHz) may be obtained by generating 20ms of white noise at a
sampling o kHz, resulting in 320 noise samples.
At the step of control parameter extraction parameters from the core decod¬
er, e.g. fundamental frequency and speech coder's ong term predictor (LTP)
gain may be re-used. Furthermore, parameters from core decoder output
signal, e.g. spectral centroid and zero-crossing rate ma be extracted. Moreover,
a decision on strength of pre-shaping may be based on control parame¬
ters, e.g.: strong shaping for high fundamental frequency and high long time
predictor gain (high pitched vowel) and weak or no shaping for high spectral
centroid and zero-crossing rate (sibilant).
At the step of temporal envelope generation a high-pass filter may be used to
remove DC part and very low frequencies from the core decoder output sig¬
nal DAS, time samples may be converted to energies and linear prediction
coding (LPC) coefficients may be calculated from the energies.
At the step of calculation of shaping gains linear prediction coding coeffi¬
cients may be converted to frequency response of 320 samples length, which
represents the smoothed temporal envelope and smooth temporal envelope
samples may be converted to gain values considering targeted shaping
strength.
At the step of temporal pre-shaping pre-shaping gain values may be applied
to noise samples.
At the step of time-to-frequency conversion the core decoder output signal
DAS may be processed by an analysis quadrature mirror filter-bank incorpo
rating filters of 400 Hz bandwidth and 1.25ms hop size, which results in a
time-to-frequency-matrix of 20 quadrature mirror filter-subbands and 16 time
slots. Furthermore, the noise frame may be processed by a further quadra¬
ture mirror filter-bank incorporating the same settings as for the decoder output
signal, which results i a time-to-frequency-matrix of 16 quadrature mirror
filter-subbands and i e slots.
At the step transposition (bandwidth selection) the noise frame may be shift¬
ed to a targeted frequency range and stack up on top of decoder signal ma¬
trix to an output T/F-matrix of 36 quadrature mirror filter-subbands and
time slots.
At the step of temporal and spectral post-shaping correct temporal trend for
critical signal portions (e.g. transients) may be ensured by temporal postshaping
of transposed quadrature mirror filter-envelope by means of trans¬
mitted side-information. Moreover, original spectral tilt and over-all energy
may be approximated by spectral post-shaping of transposed quadrature mir¬
ror filter-envelope by means of transmitted side-information.
At the step of synthesizing an output time-to frequency-matrix of 36 subbands
may be processed by a 40 subband synthesis quadrature mirror filterbank,
which results in a super wideband time domain output signal BAS of
32.0 kHz sampling rate and an effective bandwidth of 14.4 kHz
With respect to the decoder and the methods of the described embodiments
the following shall be mentioned:
Although some aspects have been described in the context of an apparatus,
it is clear that these aspects also represent a description of the correspond¬
ing method, where a block or device corresponds to a method step or a fea¬
ture of a method step. Analogously, aspects described in the context of a
method step also represent a description of a corresponding block or item or
feature of a corresponding apparatus.
Depending on certain implementation requirements, embodiments of the in¬
vention can be implemented in hardware or in software. The implementation
can be performed using a digital storage medium, for example a floppy disk,
a DVD, a CD, a ROM, PROM, an EPROM, an EEPROM or a FLASH
memory, having electronically readable control signals stored thereon, which
cooperate (or are capable of cooperating) with a programmable computer
system such that the respective method is performed.
Some embodiments according to the invention comprise a data carrier hav¬
ing electronically readable control signals, which are capable of cooperating
with a programmable computer system such that one of the methods de¬
scribed herein is performed.
Generally, embodiments of the present invention can be implemented as a
computer program product with a program code, the program code being
operative for performing one of the methods when the computer program
product runs on a computer. The program code may for example be stored
on a machine readable carrier.
Other embodiments comprise the computer program for performing one of
the methods described herein, which is stored on a machine readable carrier
or a non-transitory storage medium.
In other words, an embodiment of the inventive method is, therefore, a com¬
puter program having a program code for performing one of the methods de¬
scribed herein, when the computer program runs on a computer.
A further embodiment of the inventive methods is, therefore, a data carrier (or
a digital storage medium, or a computer-readable medium) comprising, rec¬
orded thereon, the computer program for performing one of the methods de
scribed herein.
A further embodiment of the inventive method is, therefore, a data stream or
a sequence of signals representing the computer program for performing one
of the methods described herein. The data stream or the sequence of signals
may be configured, for example, to be transferred via a data communication
connection, for example via the Internet.
A further embodiment comprises a processing means, for example a com¬
puter, or a programmable logic device, configured or adapted to perform one
of the methods described herein.
A further embodiment comprises a computer having installed thereon the
computer program for performing one of the methods described herein.
In some embodiments, a programmable logic device (for example a field pro¬
grammable gate array) may be used to perform some or all of the functionali¬
ties of the methods described herein. In some embodiments, a field pro¬
grammable gate array may cooperate with a microprocessor in order to per¬
form one of the methods described herein. Generally, the methods are ad¬
vantageously performed by any hardware apparatus.
While this invention has been described in terms of several embodiments,
there are alterations, permutations, and equivalents which fall within the
scope of this invention. It should also be noted that there are many alterna¬
tive ways of implementing the methods and compositions of the present in¬
vention. It is therefore intended that the following appended claims be inter¬
preted as including all such alterations, permutations and equivalents as fall
within the true spirit and scope of the present invention.
Reference signs:
1 audio decoder device
2 bitstream receiver
3 core decoder module
4 temporal envelope generator
5 bandwidth extension module
6 noise generator
7 pre-shaping module
8 time-to-frequency converter
9 time-to-frequency converter
10 combiner
1 frequency-to-time converter
12 frequency range selector
13 post-shaping module
14 further noise generator
15 further pre-shaping module
16 further time-to-frequency converter
17 tone generator
18 tone pre-shaping module
19 time-to-frequency converter
20 combiner
2 1 time domain core decoder
22 frequency domain core decoder
23 control parameter extractor
24 is shaping gains calculator
BS bitstream
EAS encoded audio signal
DAS decoded audio signal
TED temporal envelope
BEF frequency domain bandwidth extension signal
NOS noise signal
SNS shaped noise signal
FNS frequency domain noise signal
FDS frequency domain decoded audio signal
BFS bandwidth-extended frequency domain audio signal
BAS bandwidth-extended time domain audio signal
FSR frequency range selected frequency domain noise signai
SIS side information signal
NOSF further noise signal
SNSF further shaped noise signal
FNSF further frequency-domain noise signal
TOS tone signal
STS shaped tone signal
FTS frequency domain tone signal
SG shaping gains
CP control parameters
References:
[1] Bessette, B.; et al.: "The Adaptive Multirate Wideband Speech Codec
(AMR-WB)", IEEE Transactions on Speech and Audio Processing,
Vol. 10, No. 8, November 2002
[2] Dietz, M.; et al.: "Spectral Band Replication, a novel approach in audio
coding", Proceedings of the 12th AES Convention, May 2002
[3] Miao, L ; et al.: "G.71 . Annex D and G.722 Annex B - New ITU-T
Super Wideband Codecs", IEEE ICASSP 201 1, pp. 5232-5235

Claims
Audio decoder device for decoding a bitstream (BS), the audio decoder
device (1) comprising:
a bitstream receiver (2) configured to receive the bitstream (BS) and to
derive an encoded audio signal (EAS) from the bitstream (BS);
a core decoder module (3) configured for deriving a decoded audio signal
(DAS) in time domain from the encoded audio signal (EAS);
a temporal envelope generator (4) configured to determine a temporal
envelope (TED) of the decoded audio signal (DAS);
a bandwidth extension module (5) configured to produce a frequency do¬
main bandwidth extension signal (BEF), wherein the bandwidth extension
module (5) comprises a noise generator (6) configured to produce a noise
signal (NOS) in time domain, wherein the bandwidth extension module (5)
comprises a pre-shaping module (7) configured for temporal shaping of
the noise signal (NOS) depending on the temporal envelope (TED) of the
decoded audio signal (DAS) in order to produce a shaped noise signal
(SNS) and wherein the bandwidth extension module comprises (5) a timeto-
frequency converter (8) configured to transform the shaped noise sig¬
nal (SNS) into a frequency domain noise signal (FNS), wherein the fre¬
quency domain bandwidth extension signal (BEF) depends on the fre¬
quency domain noise signal (FNS);
a time-to-frequency converter (9) configured to transform the decoded
audio signal (DAS) into a frequency domain decoded audio signal (FDS);
a combiner ' ,. configured to combine the frequency domain decoded
audio signal (FDS) and the frequency domain bandwidth extension signal
(BEF) in order to produce a bandwidth extended frequency domain audio
signal (BFS); and
a frequency-to-time converter ( 1 1 configured to transform the bandwidth
extended frequency domain audio signal (BFS) into a bandwidthextended
time domain audio signal (BAS).
2 . Audio decoder device according to the preceding claim, wherein the fre¬
quency domain bandwidth extension signal (BEF) is produced without
spectral band replication.
3 . Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) is configured in such way that the
temporal shaping of the noise signal (NOS) is done in an overemphasized
manner.
4 . Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) is configured in such way that the
temporal shaping of the noise signal (NOS) is done subband-wise by
splitting the noise signal (NOS) into several subband noise signals by a
bank of band pass filters and performing a specific temporal shaping on
each of the subband noise signals.
5. Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) comprises a frequency range selec¬
tor (12) configured for setting a frequency range of the frequency domain
bandwidth extension signal (BEF).
6 . Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) comprises a post-shaping module
configured for temporal and/or spectral shaping in frequency domain of
the frequency domain bandwidth extension signal (BEF).
7 . Audio decoder device according to one of the preceding claims, wherein
the bitstream receiver (2) is configured to derive a side information signal
(SIS) from the bitstream (BS), wherein the bandwidth extension module
(5) is configured to produce the frequency domain bandwidth extension
signal (BEF) depending on the side information signal (SIS).
8. Audio decoder device according to the preceding claim, wherein the noise
generator (6) is configured to produce the noise signal (NOS) depending
on the side information signal (SIS).
9. Audio decoder device according to one of the claims 7 or 8, wherein the
pre-shaping module (7) is configured for temporal shaping of the noise
signal (NOS) depending on the side information signal (SIS).
10. Audio decoder device according to one of the claims 7 to 9 , wherein the
post-shaping module (13) is configured for temporal and/or the spectral
shaping of the frequency domain bandwidth extension signal (BEF) de
pending on the side information signal (SIS).
1 .Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) comprises a further noise generator
(14) configured to produce a further noise signal (NOSF) in time domain,
a further pre-shaping module (15) configured for temporal shaping of the
further noise signal (NOSF) depending on the temporal envelope (TED) of
the decoded audio signal (DAS) in order to produce a further shaped
noise signal (SNSF) and a further time-to-frequency converter (16) con¬
figured to transform the further shaped noise signal (SNSF) into a further
frequency domain noise signal (FNSF), wherein the frequency domain
bandwidth extension signal (BEF) depends on the further frequency do¬
main noise signal (FNSF).
12. Audio decoder device according to the preceding claim, wherein the
bandwidth extension module (5) is configured in such way that the tem¬
poral shaping of the further noise signal (NOSF) is done in an overem¬
phasized manner.
13. Audio decoder device according to claim or 12, wherein the bandwidth
extension module (5) is configured in such way that the temporal shaping
of the further noise signal (NOSF) is done subband-wise by splitting the
further noise signal (NOSF) into several further subband noise signals by
a bank of band pass filters and performing a specific temporal shaping on
each of the further subband noise signals.
14. Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) comprises a tone generator (17) con¬
figured to produce a tone signal (TOS) in a time domain, a tone preshaping
module (18) configured for temporal shaping of the tone signal
(TOS) depending on the temporal envelope (TED) of the decoded audio
signal (DAS) in order to produce a shaped tone signal (STS) and a timeto-
frequency converter (19) configured to transform the shaped tone sig¬
nal (STS) into a frequency domain tone signal (FTS), wherein the fre¬
quency domain bandwidth extension signal (BEF) depends on the fre¬
quency domain tone signal (FTS).
15. Audio decoder device according to one of the preceding claims, wherein
the core decoder module (5) comprises a time domain core decoder (21)
and a frequency domain core decoder (22), wherein either the time do¬
main core decoder (21) or the frequency domain core decoder (22) is
used for deriving the decoded audio signal (DAS) fr the encoded audio
signal (EAS).
16. Audio decoder device according to the preceding claim, wherein a control
parameter extractor (23) is configured for extracting control parameters
(CP) used by the core decoder module (3) from the decoded audio signal
(DAS) and wherein the bandwidth extension module (5) is configured to
produce the frequency domain bandwidth extension signal (BEF) depend¬
ing on the control parameters (CP).
17. Audio decoder device according to one of the preceding claims, wherein
the bandwidth extension module (5) comprises a shaping gains calculator
(24) configured for establishing shaping gains (SG) for the pre-shaping
module (7) depending on the temporal envelope (TED) of the decoded
audio signal (DAS) and wherein the pre-shaping module (7) is configured
for temporal shaping of the noise signal (NOS) depending on the shaping
gains (SG) for the pre-shaping module (7).
18. Audio decoder device according to claim 16 and 17, wherein the shaping
gains calculator (24) for establishing shaping gains (SG) for the preshaping
module (7) is configured for establishing shaping gains (SG) for
the pre-shaping module (7) depending on the control parameters (CP).
19. Audio decoder device according to one of the 1 to 18, wherein the
bandwidth extension module (5) comprises a shaping gains calculator
configured for establishing shaping gains for the further pre-shaping mod¬
ule (15) depending on the temporal envelope (TED) of the decoded audio
signal (DAS) and wherein the further pre-shaping module (14) is config¬
ured for temporal shaping of the further noise signal (NOSF) depending
on the shaping gains for the further pre-shaping module (14).
20. Audio decoder device according to claims 16 and 19, wherein the shaping
gains calculator for establishing shaping gains for the further pre-shaping
module ( ) is configured for establishing shaping gains for the further
pre-shaping module (15) depending on the control paramet< ) .
2 1.Audio decoder device according to one of the claims 14 to 20, wherein
the bandwidth extension module (5) comprises a shaping gains calculator
configured for establishing shaping gains for the tone pre-shaping module
(18) depending on the temporal envelope (TED) of the decoded audio
signal (DAS) and wherein the tone pre-shaping module (18) is configured
for temporal shaping of the tone signal (TOS) depending on the shaping
gains for the tone pre-shaping module (18).
22. Audio decoder device according to claims 16 and 2 1, wherein the shaping
gains calculator for establishing shaping gains for the tone pre-shaping
module ( 8) is configured for establishing shaping gains for the further
pre-shaping module (18) depending on the control parameters (CP).
23. Method for decoding a bitstream (BS), the method comprising the steps
of:
receiving the bitstream (BS) and deriving an encoded audio signal (EAS)
from the bitstream (BS) using a bitstream receiver (2);
deriving a decoded audio signal (DAS) in a time domain from the encoded
audio signal (EAS) using a core decoder module (3);
determining a temporal envelope (TED) of the decoded audio signal
(DAS) using a temporal envelope generator (4);
producing a frequency domain bandwidth extension signal (BEF) using a
bandwidth extension module (5) executing the steps of:
producing a noise signal (NOS) in time domain using a noise genera
tor (6) of the bandwidth extension module (5),
temporal shaping of the noise signal (NOS) depending on the temporal
envelope (TED) of the decoded audio signal (DAS) in order to produce
a shaped noise signal (SNS) using a pre-shaping module (7) of the
bandwidth extension module (5),
transforming the shaped noise signal (SNS) into a frequency domain
noise signal (FNS); wherein the frequency domain bandwidth
extension signal (BEF) depends on the frequency domain noise
signal (FNS), using a time-to-frequency converter (8) of the bandwidth
extension module (5);
transforming the decoded audio signal (DAS) into a frequency domain
decoded audio signal (FDS) using a further time-to-frequency converter
(9);
combining the frequency domain decoded audio signal (FDS) and the fre¬
quency domain bandwidth extension signal (BEF) in order to produce a
bandwidth extended frequency domain audio signal (BFS) using a com¬
biner (10); and
transforming the bandwidth extended frequency domain audio signal
(BFS) into a bandwidth-extended time domain audio signal (BAS) using a
frequency-to-time converter ( 1 1).
24. Computer program, when running on a processor, executing the method
according to the preceding claim.