Audio encoder and bandwidth extension decoder
An audio encoder for providing an output signal using an input audio signal includes a patch generator, a comparator and an output interface. The patch generator generates at least one bandwidth extension high-frequency signal, wherein a bandwidth extension high-frequency signal includes a high-frequency band. The high-frequency band of the bandwidth extension high-frequency signal is based on a low frequency band of the input audio signal. A comparator calculates a plurality of comparison parameters. A comparison parameter is calculated based on a comparison of the input audio signal and a generated bandwidth extension high-frequency signal. Each comparison parameter of the plurality of comparison parameters is calculated based on a different offset frequency between the input audio signal and a generated bandwidth extension high-frequency signal. Further, the comparator determines a comparison parameter from the plurality of comparison parameters, wherein the determined comparison parameter fulfills a predefined criterion.
1. Audio encoder for providing an output signal using an input audio signal, comprising:
a patch generator configured to generate a bandwidth extension high-frequency signal, wherein the bandwidth extension high-frequency signal comprises a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is derived from a low frequency band of the input audio signal by shifting the low-frequency part by a fixed value using a side band modulation;
a comparator configured to perform a comparison of the input audio signal filtered by a bandpass filter and the bandwidth extension high-frequency signal using a cross correlation calculation in regular time intervals between amplitude spectra of windowed signal sections of the input audio signal filtered by the bandpass filter and the bandwidth extension high-frequency signal to determine a lag for a maximum correlation for a signal section; and
an output interface configured to provide the output signal for transmission or storage, wherein the output signal comprises a parameter indication based on the lag for the maximum correlation; wherein
at least one of the patch generator, the comparator, and the output interface comprises a hardware implementation.
2. Audio encoder according to claim 1 , comprising a power density comparator configured to compare a parameter based on a power density of the high-frequency band of a generated bandwidth extension high-frequency signal and a corresponding frequency band of the input audio signal to obtain a power density parameter, wherein the power density parameter indicates a ratio based on the power density of the high-frequency band of the generated bandwidth extension high-frequency signal and the corresponding frequency band of the input audio signal, and wherein the output interface is configured to provide the output signal so that the parameter indication of the output signal is based on the power density parameter.
3. Audio encoder according to claim 1 , wherein the side band modulation is a single sideband modulation.
4. Audio encoder according to claim 1 , being configured to interpolate wherein the lag for the maximum correlation determined for a windowed signal section is interpolated for each time step of the windowed signal section.
5. Audio encoder according to claim 1 , wherein the patch generator is configured to apply a Hilbert transform to the audio input signal, the input audio signal being a real valued signal, so that an analytical signal is obtained and to low pass filter the analytical signal.
6. Audio encoder of claim 5 , wherein the patch generator is configured to generate an analytical modulator function and to modulate a low pass filtered analytical signal to obtain a modulated signal.
7. Audio encoder of claim 6 , wherein the comparator is configure to perform a windowing with or without overlap of the analytical signal and of the modulated signal to obtain the windowed signal sections and a subsequent Fourier transform of the windowed signal sections to obtain the amplitude spectra of windowed signal sections of the input audio signal filtered by the bandpass filter and the bandwidth extension high-frequency signal.
8. Bandwidth extension decoder for providing a bandwidth extended audio signal based on an input audio signal and a parameter signal, wherein the parameter signal comprises an indication of an offset frequency and an indication of a power density parameter, the bandwidth extension decoder comprising:
a patch generator configured to generate a bandwidth extension high-frequency signal comprising a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is generated by a modulation of the input audio signal based on the offset frequency and the power density parameter to obtain the bandwidth extension high-frequency signal, wherein the patch generator is configured to perform the modulation in a time domain;
a combiner configured to combine the bandwidth extension high-frequency signal and the input audio signal to obtain the bandwidth extended audio signal; and
an output interface configured to provide the bandwidth extended audio signal; wherein
at least one of the patch generator, the combiner, and the output interface comprises a hardware implementation.
9. Bandwidth extension decoder according to claim 8 , wherein the patch generator is configured to generate the bandwidth extension high-frequency signal based on a single side band modulation.
10. Bandwidth extension decoder according to claim 8 , comprising an interpolation means, wherein a time frame comprises a plurality of time steps, wherein each time frame comprises a corresponding offset frequency, wherein the interpolation means is configured to interpolate an offset frequency of a time frame or a plurality of offset frequencies of different time frames for each time step of a time frame to obtain an interpolated offset frequency for each time step.
11. Bandwidth extension decoder according to claim 8 , wherein the patch generator is configured to calculate the bandwidth extension high-frequency signal based on the following equations:
ψ
(
n
)
=
∑
k
=
1
k
m
a
x
φ
LF
k
(
n
)
·
μ
k
(
n
)
+
noise
(
n
)
or
ψ( n )=φ LF ( n )·μ( n )+noise( n ),
and
o ( n )=Re(ψ( n ))
wherein n is a time index, k is a patch index, ψ is a time domain complex signal, is the input audio signal, μ is a modulation function, noise is a noise signal, o is the bandwidth extension high-frequency signal, and Re is a function for taking the real part.
12. Bandwidth extension decoder according to claim 8 , wherein the patch generator is configured to use a modulation function to be multiplied by the input audio signal, wherein the modulation function is based on the following equation:
μ
~
k
(
n
)
=
ς
k
(
n
)
e
2
π
j
∑
m
=
1
n
(
γ
k
(
m
)
+
λ
k
(
m
)
)
,
wherein k is a patch index, n is a time index, {tilde over (μ)}(n) is a value of a modulation function for a time index n, ζ k (n) is an interpolated power density parameter for a time index n and a patch index k, m is an integer index, j is the complex number, γ k (m) is a phase increment for the patch index k and the integer index m, and λ k (m) is an interpolated lag value for the patch index k and the integer index m, the interpolated lag value being derived from the parameter signal comprising an indication of an offset frequency.
13. Bandwidth extension decoder according to claim 8 , wherein the patch generator is configured to use a modulation function to be multiplied by the input audio signal, wherein the modulation function is based on the following equation:
μ
~
(
n
)
=
∑
k
=
1
k
max
ς
k
(
n
)
e
2
π
j
∑
m
=
1
n
(
γ
k
(
m
)
+
λ
k
(
m
)
)
,
wherein k is a patch index, k max is a maximum number of patches, n is a time index, {tilde over (μ)}(n) is a value of a modulation function for a time index n, ζ k (n) is an interpolated power density parameter for a time index n and a patch index k, m is an integer index, j is the complex number, γ k (m) is a phase increment for the patch index k and the integer index m, and λ k (m) is an interpolated lag value for the patch index k and the integer index m, the interpolated lag value being derived from the parameter signal comprising an indication of an offset frequency.
14. Method for providing an output signal using an input audio signal, the method comprising:
generating, by a patch generator, a bandwidth extension high-frequency signal, wherein the bandwidth extension high-frequency signal comprises a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is derived from a low frequency band of the input audio signal by shifting the low-frequency part by a fixed value using a side band modulation;
performing, by a comparator, a comparison of the input audio signal filtered by a bandpass filter and the bandwidth extension high-frequency signal using a cross correlation calculation in regular time intervals between amplitude spectra of windowed signal sections of the input audio signal filtered by the bandpass filter and the bandwidth extension high-frequency signal to determine a lag for a maximum correlation for a signal section; and
providing, by an output interface, the output signal for transmission or storage; wherein
the output signal comprises a parameter indication based on the lag for the maximum correlation; and
at least one of the patch generator, the comparator, and the output interface comprises a hardware implementation.
15. Method for providing a bandwidth extended audio signal based on an input audio signal and a parameter signal, wherein the parameter signal comprises an indication of an offset frequency and an indication of a power density parameter, the method comprising:
generating, by a patch generator, a bandwidth extension high-frequency signal comprising a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is generated by a modulation of the input audio signal based on the offset frequency and the power density parameter to obtain the bandwidth extension high-frequency signal, wherein the patch generator is configured to perform the modulation in a time domain;
combining, by a combiner, the bandwidth extension high-frequency signal and the input audio signal to obtain a bandwidth extended audio signal; and
providing, by an output interface, the bandwidth extended audio signal; herein
at least one of the patch generator, the combiner, and the output interface comprises a hardware implementation.
16. Non-transitory storage medium having stored thereon a computer program with a program code for performing, when the computer program runs on a computer or a microcontroller, a method for providing an output signal using an input audio signal, the method comprising:
generating a bandwidth extension high-frequency signal, wherein the bandwidth extension high-frequency signal comprises a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is derived from a low frequency band of the input audio signal by shifting the low-frequency part by a fixed value using a side band modulation; and
performing a comparison of the input audio signal filtered by a bandpass filter and the bandwidth extension high-frequency signal using a cross correlation calculation in regular time intervals between amplitude spectra of windowed signal sections of the input audio signal filtered by the bandpass filter and the bandwidth extension high-frequency signal to determine a lag for a maximum correlation for a signal section, wherein the output signal comprises a parameter indication based on the lag for the maximum correlation.
17. Non-transitory storage medium having stored thereon a computer program with a program code for performing, when the computer program runs on a computer or a microcontroller, a method for providing a bandwidth extended audio signal based on an input audio signal and a parameter signal, wherein the parameter signal comprises an indication of an offset frequency and an indication of a power density parameter, the method comprising:
generating a bandwidth extension high-frequency signal comprising a high-frequency band, wherein the high-frequency band of the bandwidth extension high-frequency signal is generated by a modulation of the input audio signal based on the offset frequency and the power density parameter to obtain the bandwidth extension high-frequency signal, wherein the patch generator is configured to perform the modulation in a time domain; and
combining the bandwidth extension high-frequency signal and the input audio signal to obtain a bandwidth extended audio signal.