Apparatus and Method and Computer Program for Generating
a Stereo Output Signal for Providing Additional Output Channels
Specification
The present invention relates to audio processing and in particular to techniques for
generating a stereo output signal.
Audio processing has advanced in many ways. In particular, surround systems have
become more and more important. However, most music recordings are still encoded and
transmitted as a stereo signal and not as a multi-channel signal. As surround systems
comprise a plurality of loudspeakers, e.g. four or five, it has been subject of many studies
what signals to provide to which one of the loudspeakers, when there are only two input
signals available. Providing the first input signal unaltered to a first group of loudspeakers
and the second input signal unaltered to a second group would of course be a solution. But
the listener would not really get the impression of real-life surround sound, but instead
would hear the same sound from different speakers.
Moreover, consider a surround system comprising five loudspeakers including a center
speaker. To provide the user a real-life sound-experience, sounds that in reality originate
from a location in front of the listener should be reproduced by the front speakers and not
by the left and right surround loudspeakers behind the listener. Therefore, audio signals
should be available which do not comprise such sound portions.
Furthermore, listeners desiring to experience real-life surround sound, also expect highquality
audio sound from the left and right surround loudspeakers. Providing both surround
speakers with the same signal is not a desired solution. Sounds, that originate from the left
of the listener's location should not be reproduced by the right surround speaker and vice
versa.
However, as already mentioned, most music recordings are still encoded as stereo signals.
A lot of stereo music productions employ amplitude panning. Sound sources s are
recorded and are subsequently panned by applying weighting masks ak such that, in a
stereo system, they appear to originate from a particular position between a left
loudspeaker receiving a left stereo channel L of a stereo input signal and a right
loudspeaker receiving a right stereo channel of the stereo input signal. Moreover, such
recordings comprise ambient signal portions n1 n2, originating, e.g., from room
reverberation. Ambient signal portions appear in both channels, but do not relate to a
particular sound source. Therefore, the left XL and the right R channel of a stereo input
signal may comprise:
k
k
L : left stereo signal
X : right stereo signal
a : panning factor of sound source k
S : signal sound source k
nl n2, : ambient signal portions
In surround systems, commonly, only some of the loudspeakers are assumed to be located
in front of a listener's seat (for example, a center, a front left and a front right speaker),
while other speakers are assumed to be located to the left and to the right behind a
listener's seat (e.g., a left and a right surround speaker).
Signal components that are equally present in both channels of the stereo input signal
appear to originate from a sound source at a center position in front of the
listener. It may therefore be desirable, that these signals are not reproduced by the left and
the right surround speaker behind the listener.
It may moreover be desirable that signal components that are mainly present in the left
stereo channel (Sk -Sk) are reproduced by the left surround speaker; and that signal
components that are mainly present in the right stereo channel (Sk a -Sk) are reproduced
by the right surround speaker.
Moreover, it may furthermore be desirable, that ambient signal portion of the left stereo
channel shall be reproduced by the left surround speaker while the ambient the signal
portion n2 of the right stereo channel shall be reproduced by the right surround speaker.
To provide the left and the right surround speaker with suitable signals, it would therefore
be highly appreciated to provide at least two output channels from two channels of a stereo
input signal which are different from the two input channels and which possess the
described properties.
The desire for generating a stereo output signal from a stereo input signal is however not
limited to surround systems, but may also be applied in traditional stereo systems. A stereo
output signal might also be useful to provide a different sound experience, for example, a
wider sound field for traditional stereo systems having two loudspeakers, e.g., by providing
stereo-base widening. Regarding replay using stereo loudspeakers or earphones, a broader
and/or enveloping audio impression may be generated.
According to a first prior art method, a mono input source is processed to generate a stereo
signal for playback, thus creating two channels from the mono input source. By this, an
input signal is modified by complementary filters to generate a stereo output signal. When
being replayed by two loudspeakers, the generated stereo signal creates a wider sound than
the unfiltered replay of the same signal. However, the sound sources comprised in the
stereo signal are "smeared", as no directional information is generated. Details are
presented in:
Manfred Schroeder "An Artificial Stereophonic Effect Obtained From Using a Single
Signal", presented at the 9th annual AES meeting October 8-12 1957.
Another proposed approach is presented in WO 9215180 Al: "Sound reproduction systems
having a matrix converter". According to this prior art, a stereo output signal is generated
from a stereo input signal by applying a linear combination of the channels of the stereo
input signal. By applying this method, output signals may be generated which significantly
attenuate center-panned portions of the input signal. However, the method also results in a
lot of crosstalk (from the left channel to the right channel and vice versa). Crosstalk may
be reduced by limiting the influence of the right input signal to the left output signal and
vice versa, in that the corresponding weighting factor of the linear combination is adjusted.
This however, would also result in reduced attenuation of center-panned signal portions in
the surround speakers. Signals, originating from a front-center location would
unintentionally be reproduced by the rear surround speakers.
Another proposed concept of the prior art is to determine direction and ambience of a
stereo input signal in a frequency domain by applying complex signal analysis techniques.
This prior art concept is, e.g., presented in US7257231 Bl, US7412380 Bl and
US73 5624 B2. According to this approach, both input signals are examined with respect
to direction and ambience for each time-frequency bin and are repanned in a surround
system depending on the result of the direction and ambience analysis. According to this
approach, a correlation analysis is employed to determine ambient signal portions. Based
on the analysis, surround channels are generated which comprise predominantly ambient
signal portions and from which center-panned signal portions may be removed. However,
as both directional analysis as well as ambience extraction is based on estimations which
are not always free of errors, undesired artifacts may be generated. The problem of
generated undesired artifacts increases, if an input signal mix comprises several signals
(e.g., of different instruments) with superimposed spectra. An effective signal-dependent
filtering is required to remove center-panned portions from the stereo signal, which
however makes estimation errors caused by "musical noise" clearly visible. Moreover, the
combination of a direction analysis and ambience extraction furthermore results in an
addition of artifacts from both methods.
It is therefore an object of the present invention to provide improved concepts for
generating a stereo output signal. The object of the present invention is solved by an
apparatus for generating a stereo output signal according to claim 1, an upmixer according
to claim 14, an apparatus for stereo-base widening according to claim 15, a method for
generating a stereo output signal according to claim 16, an encoder according to claim 17,
and a computer program according to claim 18.
According to the present invention, an apparatus for generating a stereo output signal is
provided. The apparatus generates a stereo output signal having a first output channel and a
second output channel from a stereo input signal having a first input channel and a second
input channel.
The apparatus may comprise a manipulation information generator which is adapted to
generate manipulation information depending on a first signal indication value of the first
input channel and on a second signal indication value of the second input channel.
Furthermore, the apparatus comprises a manipulator for manipulating a combination signal
based on the manipulation information to obtain a first manipulated signal as the first
output channel and a second manipulated signal as the second output channel.
The combination signal is a signal derived by combining the first input channel and the
second input channel. Moreover, the manipulator might be configured for manipulating the
combination signal in a first manner, when the first signal indication value is in a first
relation to the second signal indication value, or in a different second manner, when the
first signal indication value is in a different second relation to the second signal indication
value.
The stereo output signal is therefore generated by manipulating a combination signal. As
the combination signal is derived by combining the first and the second input channels and
thus contains information about both stereo input channels, the combination signal is a
suitable basis for generating a stereo output signal from two the input channels.
In an embodiment, the manipulation information generator is adapted to generate
manipulation information depending on a first energy value as the first signal indication
value of the first input channel and on a second energy value as the second signal
indication value of the second input channel. Furthermore, the manipulator is configured
for manipulating the combination signal in a first manner when the first energy value is in
a first relation to the second energy value, or in a different second manner, when the first
energy value is in a different second relation to the second energy value. In such an
embodiment, energy values of the first and the second input channel are used as
manipulation information. The energies of the two input channel provide a suitable
indication on how to manipulate a combination signal to obtain the first and the second
output channel, as they contain significant information about the first and the second input
channel.
In another embodiment the apparatus furthermore comprises a signal indication computing
unit to calculate the first and the second signal indication value.
In another embodiment, the manipulator is adapted to manipulate the combination signal,
wherein the combination signal represents a difference between the first and the second
input channel. This embodiment is based on the finding that employing a difference signal
provides significant advantages.
According to a further embodiment, the apparatus comprises a transformer unit for
transforming the first and second input channel from a time domain into a frequency
domain. This allows frequency dependent processing of signal sources.
Moreover, an apparatus according to an embodiment may be adapted to generate a first
weighting mask depending on the first signal indication value and a second weighting
mask depending on the second signal indication value. The apparatus may be adapted to
manipulate the combination signal by applying the first weighting mask to an amplitude
value of the combination signal to obtain a first modified amplitude value, and may be
adapted to manipulate the combination signal by applying the second weighting mask to an
amplitude value of the combination signal to obtain a second modified amplitude value.
The first and second weighting mask provide an effective way to modify the difference
signal based on the first and second input signal.
In a further embodiment, the apparatus comprises a combiner which is adapted to combine
the first amplitude value and a phase value of the combination signal to obtain the first
output channel, and to combine the second amplitude value and a phase value of the
combination signal to obtain the second output channel. In such an embodiment, the phase
value of the combination signal is left unchanged.
According to another embodiment, a first and/or a second weighting mask are generated by
determining a relation between a signal indication value of the first channel and a signal
indication value of the second channel. A tuning parameter may be employed.
According to a further embodiment, a transformer unit and a combination signal generator
are provided. In this embodiment, the input signals are transformed into a frequency
domain before a combination signal is generated. Transforming the combination signal into
a frequency domain is thus avoided which saves processing time.
Furthermore, an upmixer, an apparatus for stereo-base widening, a method for generating a
stereo output signal, an apparatus for encoding manipulation information and a computer
program for generating a stereo output signal are provided.
In the following, preferred embodiments will be explained referring to the accompanying
drawings in which:
Fig. 1 illustrates an apparatus for generating a stereo output signal according to an
embodiment;
Fig. 2 depicts an apparatus for generating a stereo output signal according to
another embodiment;
Fig. 3 shows an apparatus for generating a stereo output signal according to a
further embodiment;
Fig. 4 illustrates another embodiment of an apparatus for generating a stereo
output signal;
Fig. 5 illustrates a diagram displaying different weighting masks in relation to
energy values according to an embodiment of the present invention;
Fig. 6 depicts an apparatus for generating a stereo output signal according to a
further embodiment;
Fig. 7 illustrates an upmixer according to an embodiment;
Fig. 8 depicts an upmixer according to a further embodiment;
Fig. 9 shows an apparatus for stereo-base widening according to an embodiment;
Fig. 10 depicts an encoder according to an embodiment.
Fig. 1 illustrates an apparatus for generating a stereo output signal according to an
embodiment. The apparatus comprises a manipulation information generator 0 and a
manipulator 120. The manipulation information generator 110 is adapted to generate a first
manipulation information GL depending on a signal indication value VL of a first channel
of a stereo input signal. Furthermore, the manipulation information generator 110 is
adapted to generate a second manipulation information GR depending on a signal
indication value VR of a second channel of the stereo input signal.
In an embodiment, the signal indication value VL of the first channel is an energy value of
the first channel and the signal indication value VR of the second channel is an energy
value of the second channel. In another embodiment, the signal indication value VL of the
first channel is an amplitude value of the first channel and the signal indication value VR of
the second channel is an amplitude value of the second channel.
The generated manipulation information GL, GR is provided to a manipulator 120.
Furthermore, a combination signal d is fed into the manipulator 120. The combination
signal d is derived by the first and second input channel of the stereo input signal.
The manipulator 120 generates a first manipulated signal dL based on the first manipulation
information GL and on the combination signal d. Furthermore, the manipulator 120 also
generates a second manipulated signal d based on the second manipulation information
GR and on the combination signal d. The manipulator 120 is configured to manipulate the
combination signal d in a first manner, when the first signal indication value VL is in a first
relation to the second signal indication value VR, or in a different second manner, when the
first signal indication value V L is in a different second relation to the second signal
indication value VR.
In an embodiment, the combination signal d is a difference signal. For example, the second
channel of the stereo input signal may have been subtracted from the first channel of the
stereo input signal. Employing a difference signal as a combination signal is based on the
finding that a difference signal is particularly suitable for being modified to generate a
stereo output signal. This finding is based on the following:
A (mono) difference signal, also referred to as "S" (side) signal, is generated from a left
and a right channel of a stereo input signal, e.g., in a time domain, by applying the formula:
S = xL —xR ,
S: difference signal
L: left input signal
XR: right input signal
Employing the above definitions of L and x :
S = x L - xR = s + « , ) - fl j - s k + n )
k k
By generating a difference signal according to the above formula, sound sources S which
are equally present in both input channels (ak=l) are removed when generating the
difference signal. (Sound sources which are equally present in both stereo input channels
are assumed to originate from a location at a center position in front of the listener.)
Furthermore, sound sources Sk which are panned such that the sound source is almost
equally present in both channels of the stereo input signal (ak~l) will be strongly
attenuated in the difference signal.
However, sound sources which are panned such that they are only present (or mainly
present) in the left channel of the stereo input signal (ak®0), will not be attenuated at all
(or will only be slightly attenuated). Moreover, sound sources which are panned such that
they are only present (or mainly present) in the right channel (ak»l), will also not be
attenuated at all (or will only slightly be attenuated).
In general, ambient signal portions and n2 of the left and right channel of a stereo input
signal are only slightly correlated. They are therefore only slightly attenuated when
forming the difference signal.
A difference signal may be employed in the process of generating a stereo output signal. If
the S-signal is generated in a time domain, no artifacts are generated.
Fig. 2 illustrates an apparatus for generating a stereo output system according to another
embodiment of the present invention. The apparatus comprises a manipulation information
generator 2 10, a manipulator 220 and, moreover, an signal indication computing unit 230.
A first channel L and a second channel of a stereo input signal are fed into a signal
indication computing unit 230. The signal indication computing unit 230 computes a first
signal indication value V L relating to the first input channel xL and a second signal
indication value VR relating to the second input channel L- For example, a first energy
value of the first input channel L is computed as the first signal indication value VL and a
second energy value of the second input channel x is computed as the second signal
indication value VR. Alternatively, a first amplitude value of the first input channel XL is
computed as the first signal indication value V L and a second amplitude value of the
second input channel X is computed as the second signal indication value VR.
In other embodiments, more than two channels are fed into the signal indication computing
unit 230 and more than two signal indication values are calculated, depending on the
number of input channels which are fed into the signal indication computing unit 230.
The computed signal indication values VL, VR are fed into the manipulation information
generator 2 0.
The manipulation information generator 210 is adapted to generate manipulation
information GL depending on the first signal indication value VL of the first channel XL of
the stereo input signal and to generate manipulation information GR depending on the
second signal indication value V of the second channel X of the stereo input signal.
Based on the manipulation information GL, GR generated by the manipulation information
generator 2 10, the manipulator 220 generates a first and a second manipulated signal dL, d
as a first and a second output channel of the stereo output signal, respectively.
Furthermore, the manipulator 220 is configured for manipulating the combination signal d
in a first manner when the first signal indication value VL is in a first relation to the second
signal indication value V , or in a different second manner, when the first signal indication
value VL is in a different second relation to the second signal indication value VR.
Fig. 3 illustrates an apparatus for generating a stereo output signal. A stereo input signal
having two input channels X ( XR( which are represented in a time domain are fed into a
transformer unit 320 and into a combination signal generator 310. The first X and the
second (t) input channel may be the left L(t) and the right xR(t) input channel of the
stereo input signal, respectively. The input signals XL( , xR(t) may be discrete-time signals.
The combination signal generator 310 generates a combination signal d(t) based on the
first x t) and the second x (t) input channel of a stereo input signal. The generated
combination signal d(t) may be a discrete-time signal d(t). In an embodiment, the
combination signal d(t) may be a difference signal and may, for example, be generated by
subtracting the second (e.g., right) input channel XR ) from the first (e.g., left) input
channel XL ) or vice versa, e.g., by applying the formula:
d(t) = xL(t) - x (t).
In another embodiment, other kinds of combination signals are employed. For example, the
combination signal generator 310 may generate a combination signal d(t) according to the
formula:
d(t) = a · xL(t) - b xR(t)
The parameters a and b are referred to as steering parameters. By selecting the steering
parameters a and b, such that a is different from b, even a signal sound source which is not
equally present in the channels X , (t) of the stereo input signal can be removed when
generating the combination signal d(t). Thus, by selecting a different from b, it is possible
to remove sound sources which have been arranged, e.g. by employing amplitude panning,
to a position left of the center or right of the center.
For example, consider the case where a sound source r(t) has been arranged such that it
appears to originate from a position left of the center, e.g., by setting:
xL(t) 2 r(t) + f(t);
xR(t) = 0.5 - r(t) + g(t).
Then, setting the steering parameters a and b to a = 0.5 and b = 2, removes the signal
source r(t) from the combination signal:
d(t) = a · xL(t) - b · x (t)
a · (2 · r(t) + f(t)) - b · (0.5 · r(t) + g(t))
= 0.5 · (2 · r(t) + f(t)) - 2 · (0.5 · r(t) + g(t))
= 0.5 · f(t) - 2 · g(t);
In embodiments, the combination signal d(t) = a · L(t) - b · XR( is employed to remove a
sound source originating from a certain position from the combination signal by setting the
steering parameters a and b to appropriate values. The dominant sound source may, for
example, be a dominant instrument in a music recording, e.g., an orchestra recording. The
steering parameters a, b may be set to a value such that sounds originating from the
position of the dominant sound source are removed when generating the combinantion
signal.
In an embodiment, the steering parameters a and b can be dynamically adjusted depending
on the input channels L(t), XR(Q of the stereo input signal. For example, the combination
signal generator 310 may be adjusted to dynamically adjust the steering parameters a and b
such that a dominant sound source is removed from the combination signal. The position
of the dominant sound source may vary. At one point in time, the dominant sound source is
located at a first position, and at another point in time, the dominant sound source is
located at a different second position, either, because the dominant sound source moves,
or, because another sound source has become the dominant sound source in the recording.
By dynamically adjusting the steering parameters a and b, the actual dominant sound
source can be removed from the combination signal.
In a further embodiment, an energy relationship of the first and second input signal may be
available in the combination signal generator 310. The energy relationship may, for
example, indicate the relationship of an energy value of the first input channel xL(t) to an
energy value of the second input channel XR(t). In such an embodiment, the values of the
steering parameters a and b may be dynamically determined based on that energy
relationship.
In an embodiment, the values of the steering parameters a and b may, for example, be
chosen such that a = 1; and b = E(xL(t)) / E(xR(t)); (E(y) = energy value of y;). In other
embodiments, other rules for determining the values of a and b may be employed.
Furthermore, in another embodiment, the combination signal generator may itself
determine an energy relationship of the the first and second input channel XL(t), , e.g.,
by analysing an energy relationship of the input channels in a time domain or a frequency
domain.
In a further embodiment, an amplitude relationship of the first and second input channel
), XR( is available in the combination signal generator 3 10. The amplitude relationship
may, for example, indicate the relationship of an amplitude value of the first input channel
X t ) to an amplitude value of the second input channel XR.(t). In such an embodiment, the
values of the steering parameters a, b may be dynamically determined based on the
amplitude relationship. The determination of the steering parameters a and b may be
conducted similar as in the embodiments, wherein a and b are determined based on an
energy relationship. In a further embodiment, the combination signal generator may itself
determine an amplitude relationship of the first and second input channel X t) , XR( , for
example, by transforming the input channels X ( , XR(I) from a time domain into a
frequency domain, e.g., by applying Short-Time Fourier Transformation, by determining
the amplitude values of the frequency domain representations of both channels XL( ), XR( )
and by setting one or a plurality of amplitude values of the first input channel XL into a
relationship to one or a plurality of amplitude values of the second input channel X (t).
When a plurality of amplitude values of the first input channel is set into a
relationship to a plurality of amplitude values of the second input channel XR(t), a mean
value for the first and a mean value for the second plurality of amplitude values may be
calculated.
The apparatus in the embodiment of Fig. 3 furthermore comprises a first transformer unit
320. The combination signal generator 310 feeds the combination signal d(t) into the first
transformer unit 320. Moreover, the first xL(t) and second input channel of the stereo
input signal are also fed into the first transformer unit 320. The first transformer unit 320
transforms the first input channel xi,(t), the second input channel X (t) and the difference
signal d(t) into a frequency domain by employing a suitable transformation method.
In the embodiment of Fig. 3, the first transformer unit 320 employs a filter bank to
transform the discrete-time input channels XL , XR(t) and the discrete-time difference
signal d(t) into a frequency domain, e.g., by employing Short-Time Fourier Transform
(STFT). In other embodiments, the first transformer unit 320 may be adapted to employ
other kinds of transformation methods, e.g., a QMF (Quadrature Mirror Filter) filter bank,
to transform the signals from a time domain into a frequency domain.
After transforming the input channels L( , XR(X) and the difference signal d(t) by
employing Short-Time Fourier Transform, the frequency domain difference signal D(m,k)
and the frequency domain first XL(m,k) and second X (m,k) input channel represent
complex spectra, m is the STFT time index, k is the frequency index.
The first transformer unit 320 feeds the complex frequency domain signal D(m,k) of the
difference signal into an amplitude-phase computing unit 350. The amplitude-phase
computing unit computes the amplitude spectra | D(m,k) | and the phase spectra (m,k)
from the complex spectra of the frequency domain difference signal D(m,k).
Furthermore, the first transformer unit 320 feeds the complex frequency domain first
X L(m,k) and second X R(m,k) input channel into an signal indication computing unit 330.
The signal indication computing unit 330 computes first signal indication values from the
first frequency domain input channel XL(m,k) and second signal indication values from the
second frequency domain input channel XR(m,k). More specifically, in the embodiment of
Fig. 3, the signal indication computing unit 330 computes first energy values EL(m,k) as
first signal indication values from the first frequency domain input channel X m,k) and
second energy values ER(m,k) as second signal indication values from the second
frequency domain input channel X (m,k) .
The signal indication computing unit 330 considers each signal portion, e.g., each timefrequency
bin (m,k), of the first X (m,k) and second XR(m,k) frequency domain input
channel. With respect to each time-frequency bin, the signal indication computing unit 330
in the embodiment of Fig. 3 computes a first energy EL(m,k) relating to the first frequency
domain input channel XL(m,k) and a second energy ER(m,k) relating to the second
frequency domain input channel X (m,k). For example, the first and second energies
EL(m,k) and E (m,k) may be computed according to the following formulae:
E (m, k =(Re{X m, k)})2+( n{X (m, k)})2
ER{m,k) =( {XR(m,k)}) +( {X R(m, k)}) .
In another embodiment, the signal indication computing unit 330 computes amplitude
values of the first X m,k) frequency domain input channel as first signal indication values
and amplitude values of the second X m,k) frequency domain input channel as second
signal indication values. In such an embodiment, the signal indication computing unit 330
may determine an amplitude value for each time-frequency bin of the first frequency
domain input signal X L(m,k) to derive the first signal indication values. Futhermore, the
signal value computing unit 330 may determine an amplitude value for each timefrequency
bin of the second frequency domain input signal (m,k) to derive the second
signal indication values.
The signal indication computing unit 330 of Fig. 3 passes the signal indication values, e.g.,
the energy values EL(m,k), E (m,k), of the first and second input channel L(m,k),
X (m,k) to a manipulation information generator 340.
In the embodiment of Fig. 3, the manipulation information generator 340 generates a
weighting mask, e.g., a weighting factor, for each time-frequency bin of each input signal
X (m,k), XR(m,k). Depending on the relationship of the first and second signal indication
values, e.g., depending on the energy relations of the left and the right frequency-domain
signal, the weighting mask GL(m,k) relating to the first input signal XL(m,k), and the
weighting mask G (m,k) relating to the second input signal XR(m,k) are generated.
Regarding a particular time-frequency bin, GL( I, k) has a value close to 1, if E m, k) »
E ( , k). On the other hand, G , k) has a value close to 0, if E (m, k) » E m, k). For
the right weighting mask the opposite applies. In embodiments where the manipulation
information generator receives amplitude values as first and second signal indication
values, the same applies likewise.
The weighting masks may, for example, be calculated according to the formulae:
E L ( , k )
GL (m,k) ; and
E (m,k) + E R (m,k)
E R (m,k)
E (m,k) + E R (m,k)
An adjustable parameter may be employed to calculate the weighting masks, which
becomes relevant, if a sound source is not located at the far left or at the far right, but in
between these values. Other examples on how to compute the weighting masks GL(m,k),
G (m,k) will be described later on with reference to Fig. 5.
The signal value computing unit 330 feeds the generated first weighting mask GL(m,k) into
a first manipulator 360. Moreover, the amplitude-phase computing unit 350 feeds the
amplitude values | D(m,k) | of the difference signal D(m,k) into the first manipulator 360.
The first weighting mask G (m,k) is then applied to an amplitude value of the difference
signal to obtain a first modified amplitude value j DL(m,k) | of the difference signal
D(m,k). The first weighting mask GL(m,k) may be applied to the amplitude value
D(m,k) of the difference signal D(m,k), e.g., by multiplying the amplitude value
D(m,k) Iby GL(m,k), wherein | D(m,k) | and GiXm,k) relate to the same time-frequency
bin (m, k). The first manipulator 360 generates modified amplitude values [D L(m,k) | for
all time-frequency bins for which it receives a weighting mask value GL(m,k) and a
difference signal amplitude value | D(m,k) | .
Furthermore, the signal value computing unit 330 feeds the generated second weighting
mask G (m,k) into a second manipulator 370. Moreover, the amplitude-phase computing
unit 350 feeds the amplitude spectra j D(m,k) | of the difference signal D(m,k) into the
second manipulator 370. The second weighting mask G (m,k) is then applied to an
amplitude value of the difference signal to obtain a second modified amplitude value
DL(m,k) of the difference signal D(m,k). Again, the second weighting mask G (m,k)
may be applied to the amplitude value | D(m,k) | of the difference signal D(m,k), e.g., by
multiplying the amplitude value | D(m,k) | by G (m,k), wherein | D(m,k) | and GR(m,k)
relate to the same time-frequency bin (m,k). The second manipulator 370 generates
modified amplitude values jD R(m,k) | for all time-frequency bins for which it receives a
weighting mask value G (m,k) and a difference signal amplitude value | D(m,k) | .
The first modified amplitude values | D L(m,k) [ as well as the second modified amplitude
values | D (m,k) | are fed into a combiner 380. The combiner 380 combines each one of
the first modified amplitude values | D (m,k) | with the corresponding phase value (the
phase value which relates to the same time-frequency bin) of the difference signal pD(m,k)
to obtain a complex first frequency domain output channel DL(m,k). Moreover, the
combiner 380 combines each one of the second modified amplitude values | D (m,k) |
with the corresponding phase value (which relates to the same time-frequency bin) of the
difference signal ( , to obtain a complex second frequency domain output channel
DR(m,k).
According to another embodiment, the combiner 380 combines each one of the first
amplitude values | D L(m,k) | with the corresponding phase value (the phase value which
relates to the same time-frequency bin) of the first, e.g., left, input channel L(m,k), and
furthermore combines each one of the second amplitude values jDR(m,k) | with the
corresponding phase value (the phase value which relates to the same time-frequency bin)
of the second, e.g., right, input channel X (m,k).
In other embodiments, the first | DL(m,k) | and the second | DR(m,k) | amplitude values
may be combined with a combined phase value. Such a combined phase value p mb(m,k)
may, for example, be obtained, by combining a phase value of the first input signal
p l(m,k) and a phase value of the second input signal f, , , e.g., by applying the
formula:
pcomb (m,k) = ( (m,k) + 2(m,k)) /2.
In other embodiments a first combination of the first and second amplitude values is
applied to the phase values of the first input signal and a second combination of the first
and second amplitude values is applied to the phase values of the second input signal.
The combiner 380 of Fig. 3 feeds the generated first and second complex frequency
domain output signals DL(m,k), D (m,k) into a second transformer unit 390. The second
transformer unit 390 transforms the first and second complex frequency domain output
signals DL(m,k), D (m,k) into a time domain, e.g,. by conducting Inverse Short-Time
Fourier Transform (ISTFT), to obtain a first time domain output signal d t) from the first
frequency domain output signal DL(m,k) and to obtain a second time domain output signal
d (t) from the second frequency domain output signal D R(m,k), respectively.
Fig. 4 illustrates a further embodiment. The embodiment of Fig. 4 differs from the
embodiment depicted in Fig. 3 insofar, as transformer unit 420 is only transforming a first
and second input channel x t), XR(t) from a time domain into a spectral domain. However,
transformer unit does not transform a combination signal. Instead, a combination signal
generator 410 is provided which generates a frequency domain combination signal from
the first and second frequency domain input channel XL(m,k) and XR(m,k). As the
combination signal is generated in a frequency domain, a transformation step has been
saved, as transforming the combination signal into a frequency domain is avoided. The
combination signal generator 4 0 may, for example, generate a frequency domain
difference signal, e.g., by applying the following formula for each time-frequency bin:
D(m,k) = XL(m, k) - X (m, k).
In another embodiment, the combination signal generator may employ any other kind of
combination signal, for example:
D(m,k) = a · XL(m, k) - b · XR(m, k).
Fig. 5 illustrates the relationship between weighting masks GL, GR and energy values EL,
E , taking a tuning parameter a into account. While the following explanations primarily
relate to the relationship of weighting masks and energy values, they are equally applicable
to the relationship of weighting masks and amplitude values, for example, in the case when
a manipulation information generator generates weighting masks based on amplitude
values of the first and second input channel. Therefore, the explanations and formulae are
equally applicable for amplitude values.
Conceptually, weighting masks are generated based on the rules for calculating the center
of gravity between two points:
X -
m, x, +m-, x
i -
c : center of gravity
x : point 1
x2: point 2
: mass at point 1
m2: mass at point 2
If this formula is used for calculating the "center of gravity" of the energy values EiXm,k)
and E R(m, k), this results in:
EL{m,k)-x +ER( ,k)-x C(m,k) = 2
EL(m,k) +ER( ,k)
C(m,k) : center of gravities of the energy values E L( I, k) and E R(m, k).
To obtain a weighting mask for the left channel, is set to =ϊ and x2 is set to x2=0:
EL{m,k)
GL(m,k) =
E (m, k) +ER(m, k)
Such a weighting mask G L(m,k) has the desired result that G L(m,k) ® 1 in case of leftpanned
signals (E m, k) » E (m, k)) and the desired result that G (m,k) ® 0 in case of
right-panned signals (ER(m, k) » EL(m, k)).
Similarly, a weighting mask for the right channel is obtained by setting =0 and x =l:
ER ,k )
E (m,k) + ER (m,k)
This weighting mask GR(m,k) has the desired result that GR(m,k) ® 1 in case of rightpanned
signals (ER(m, k) » EL(m, k)) and the desired result that G (m,k) ® 0 in case of
left-panned signals (E m, k) » E (m, k)).
Regarding center-panned input signals (EL(m,k) = ER(m,k)), the weighting masks GL(m,k)
and GR(m,k) are equal to 0.5. A parameter a is used to steer the behavior of the weighting
masks regarding center-panned signals and signals which are panned close to center,
wherein a is an exponent applied on the weighting masks according to:
R {m,k)
GR (m,k) =
EL (m, k ) + ER (m, k )
The weighting masks GL(m, k) and GR(m, k) are calculated based on the energies by means
of these formulas.
As stated above, these formulas are equally applicable for amplitude values |XL(m,k)|,
|XR(m,k)| of a first and a second input channel. In that case, EL(m,k) has the value of
|XL(m,k)| and E (m,k) has the value of (XR(m,k)|, e.g., in embodiments, where a
manipulation information generator generates weighting masks based on amplitude values
instead of energy values.
Fig. 5 illustrates the effects of applying tuning parameter a by illustrating curves relating to
different values of the tuning parameter. If a is set to a=0.4, bins, which comprise equal or
similar energies in the left and right input channel are slightly attenuated. Only bins, which
have a significantly higher energy in the right channel are strongly attenuated by the left
weighting mask G , k). Analogously, bins, which have a significantly higher energy in
the left channel are strongly attenuated by the right weighting mask GR(m, k). As only few
signal portions are strongly attenuated by such a filter, such a setting of the tuning
parameter may be referred to as "low selectivity".
A higher parameter value, for example, a=2 results in considerably "higher selectivity". As
can be seen in Fig. 5, bins having equal or similar energy in the left and the right channel
are heavily attenuated. Depending on the application, the desired selectivity may be steered
by the tuning parameter a .
Fig. 6 illustrates an apparatus for generating a stereo output signal according to a further
embodiment. The apparatus of Fig. 6 differs from the embodiment of Fig. 3 inter alia, as it
further comprises a signal delay unit 605. A first LA and a second XRA(X) input channel
of a stereo input signal are fed into the signal delay unit 605. The first and the second input
channel LA ), XRA are also fed into a first transformer unit 620.
The signal delay unit 605 is adapted to delay the first input channel LA© and/or the
second input channel A . In an embodiment, the signal delay unit determines a delay
time, by employing a correlation analysis of the first and second input channel XLA ,
XRA (t) . For example, XLA and RA(t) are time-shifted on a step-by-step basis. For each
step, a correlation analysis is conducted. Then, the time-shift with the maximum
correlation is determined. Assuming that delay panning has been employed to arrange a
signal source in the stereo input signal, such that it appears to originate from a particular
position, the time-shift with the maximum correlation is assumed to correspond to the
delay originating from the delay panning. In an embodiment, the signal delay unit may
rearrange the delay-panned signal source such that it is rearranged to a center position. For
example, if the correlation analysis indicates that input channel LA( has been delayed by
At, then signal delay unit 605 delays input channel RA by At.
The eventually modified first XLB and second X B( ) channel are subsequently fed into
the combination signal generator 620 which generates a combination signal. In an
embodiment, the combination signal generator generates a difference signal as a
combination signal by applying the formula:
d(t) = xLB(t)-XRB (t).
As the delay-panned signal source has been rearranged to a center position, the signal
source is then equally present in the eventually modified first and second channels LB© ,
RB(t), and will therefore be removed from the difference signal d(t). By employing an
apparatus according to the embodiment of Fig. 6, it is therefore possible to generate a
combination signal without corresponding delay-panned signal sources.
Fig. 7 illustrates an upmixer 700 for upmixing a stereo input signal to five output channels,
e.g. five channels of a surround system. The stereo input signal has a first input channel L
and a second input channel R which are fed into the upmixer 700. The five output channels
may be a center channel, a left front channel, a right front channel, a left surround channel
5 and a right surround channel. The center channel, the left front channel, the right front
channel, the left surround channel and the right surround channel are provided to a center
loudspeaker 720, a left front loudspeaker 730, a right front loudspeaker 740, a left surround
loudspeaker 750 and a right surround loudspeaker 760, respectively. The loudspeakers may
be positioned around a listener's seat 710.
10
The upmixer 700 generates the center channel for the center loudspeaker 720 by adding the
left input channel L and the right input channel R of the stereo input signal. The upmixer
700 may provide the left input channel L unmodified to the left front loudspeaker 730 and
may further provide the right input channel R unmodified to the right front loudspeaker
15 740. Furthermore, the upmixer comprises an apparatus 770 for generating a stereo output
signal according to one of the above-described embodiments. The left input channel L and
the right input channel R are fed into the apparatus 770, as a first and second input channel
of the apparatus for generating a stereo output signal 770, respectively. The first output
channel of the apparatus 770 is provided to the left surround speaker 750 as the left
0 surround channel, while the second output channel of the apparatus 770 is provided to the
right surround speaker 760 as the right surround channel.
Fig. 8 illustrates a further embodiment of an upmixer 800 having five output channels, e.g.
five channels of a surround system. The stereo input signal has a first input channel L and a
5 second input channel R which are fed into the upmixer 800. As in the embodiment
illustrated in Fig. 7, the five output channels may be a center channel, a left front channel,
a right front channel, a left surround channel and a right surround channel. The center
channel, the left front channel, the right front channel, the left surround channel and the
right surround channel are provided to a center loudspeaker 820, a left front speaker 830, a
0 right front speaker 840, a left surround speaker 850 and a right surround speaker 860,
respectively. Again, the loudspeakers may be positioned around a listener's seat 810.
The center channel provided to the center loudspeaker 820 is generated by adding the left
L and the right R input channel Furthermore, the upmixer comprises an apparatus 870 for
5 generating a stereo output signal according to one of the above-described embodiments.
The left input channel L and the right input channel R are fed into the apparatus 870. The
apparatus 870 generates a first and second output channel of a stereo output signal. The
first output channel is provided to the left front loudspeaker 830; the second output channel
is provided to the right front loudspeaker 840. Furthermore, the first and the second output
channel generated by the apparatus 870 are provided to an ambience extractor 880. The
ambience extractor 880 extracts a first ambience signal component from the first output
channel generated by the apparatus 870 and provides the first ambience signal component
to the left surround loudspeaker 850 as the left surround channel. Furthermore, the
ambience extractor 880 extracts a second ambience signal component from the second
output channel generated by the apparatus 870 and provides the second ambience signal
component to right surround loudspeaker 860 as the right surround channel.
Fig. 9 illustrates an apparatus for stereo-base widening 900 according to an embodiment.
In Fig. 9, a first input channel L and a second input channel R of a stereo input signal are
fed into the apparatus 900. The apparatus for stereo-base widening 900 comprises an
apparatus 910 for generating a stereo output signal according to one of the above-described
embodiments. The first and the second input channel L, R of the apparatus for stereo-base
widening 900 are fed into the apparatus 910 for generating a stereo output signal.
The first output channel of the apparatus for generating a stereo output signal 910 is fed
into a first combiner 920 which combines the first input channel L and the first output
channel of the apparatus for generating a stereo output signal 910 to generate a first output
channel of the apparatus for stereo-base widening 900.
Correspondingly, the second output channel of the apparatus for generating a stereo output
signal 910 is fed into a second combiner 930 which combines the second input channel R
and the second output channel of the apparatus for generating a stereo output signal 910 to
generate a second output channel of the apparatus for stereo-base widening 900.
By this, a widened stereo output signal is generated. The combiners may combine both
received channels, e.g., by adding both channels, by employing a linear combination of
both channel, or by another method of combining two channels.
Fig. 10 illustrates an encoder according to an embodiment. A first L(m,k) and second
X .(m,k) channel of a stereo signal are fed into the encoder. The stereo signal may be
represented in a frequency domain.
The encoder comprises an signal indication computing unit 1010 for determining a first
signal indication value and a second signal indication value V of the first and second
channel X L(m,k), X R(m,k) of a stereo signal, e.g., a first and second energy value EL(m,k),
ER(m,k) of the first and second channel XiXm,k), XR(m,k). The encoder may be adapted to
determine the energy values EL(m,k), E (m,k) in a similar way as the apparatus for
generating a stereo output signal in the above-described embodiments. For example, the
encoder may determine the energy values by employing the formulae:
EL(m, k) =( {X (m, k)}f + l {X (m, k)})
ER(m,k) =(Re{XR(m,k)})2+ l {XR(m, k)})2 .
In another embodiment, the signal indication computing unit 1010 may determine
amplitude values of the first and second channel X L(m,k), X R(m,k). In such an
embodiment, the signal indication computing unit 1010 may determine the amplitude
values of the first and second channel XiXm,k), X (m,k) in a similar way as the apparatus
for generating a stereo output signal in the above-described embodiments.
The signal value computing unit 1010 feeds the determined energy values EL(m,k),
ER(m,k) and/or the determined amplitude values into a manipulation information generator
1020. The manipulation information generator 1020 then generates manipulation
information, e.g., a first GL(m,k) and a second GR(m,k) weighting mask based on the
received energy values E (m,k), E (m,k) and/or amplitude values, by applying similar
concepts as the apparatus for generating a stereo output signal in the above-described
embodiments, particularly as explained with respect to Fig. 5.
In an embodiment, the manipulation information generator 1020 may determine the
manipulation information based on the amplitude values of the first and second channel
X L(m,k), X R(m,k). In such an embodiment, the manipulation information generator 1020
may apply similar concepts as the apparatus for generating a stereo output signal in the
above-described embodiments.
The manipulation information generator 1020 then passes the weighting masks GL(m,k)
and G (m,k), to an output module 1030.
The output module 1030 outputs the manipulation information, e.g., the weighting masks
GL( , ) and G (m,k), in a suitable data format, e.g., in a bit stream or as values of a signal.
The outputted manipulation information may be transmitted to a decoder which generates a
stereo output signal by applying the transmitted manipulation information, e.g., by
combining the transmitted weighting masks with a difference signal or with a stereo input
signal as described with respect to the above-described embodiments of the apparatus for
generating a stereo output signal.
Although some aspects have been described in the context of an apparatus, it is clear that
these aspects also represent a description of the corresponding method, where a block or
device corresponds to a method step or a feature 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 invention 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, a 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 having
electronically readable control signals, which are capable of cooperating with a
programmable computer system, such that one of the methods described 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, stored on a machine readable carrier or a non-transitory storage medium.
In other words, an embodiment of the inventive method is, therefore, a computer program
having a program code for performing one of the methods described 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, recorded thereon, the
computer program for performing one of the methods described 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 for example be configured to be
transferred via a data communication connection, for example via the Internet.
A further embodiment comprises a processing means, for example a computer, or a
programmable logic device, configured to 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 programmable
gate array) may be used to perform some or all of the functionalities of the methods
described herein. In some embodiments, a field programmable gate array may cooperate
with a microprocessor in order to perform one of the methods described herein. Generally,
the methods are preferably performed by any hardware apparatus.
The above described embodiments are merely illustrative for the principles of the present
invention. It is understood that modifications and variations of the arrangements and the
details described herein will be apparent to others skilled in the art. It is the intent,
therefore, to be limited only by the scope of the impending patent claims and not by the
specific details presented by way of description and explanation of the embodiments
herein.
Claims
An apparatus for generating a stereo output signal having a first output channel and
a second output channel from a stereo input signal having a first input channel and
a second input channel comprising:
a manipulation information generator ( 110; 210; 340; 440; 640) being adapted to
generate manipulation information depending on a first signal indication value of
the first input channel and on a second signal indication value of the second input
channel; and
a manipulator (120; 220; 360, 370; 460, 470; 660, 670) for manipulating a
combination signal based on the manipulation information to obtain a first
manipulated signal as the first output channel and a second manipulated signal as
the second output channel;
wherein the combination signal is a signal derived by combining the first input
channel and the second input channel; and
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is configured for
manipulating the combination signal in a first manner, when the first signal
indication value is in a first relation to the second signal indication value, or in a
different second manner, when the first signal indication value is in a different
second relation to the second signal indication value.
An apparatus according to claim 1,
wherein the manipulation information generator ( 110; 210; 340; 440; 640) is
adapted to generate the manipulation information depending on a first energy value
as the first signal indication value of the first input channel and on a second energy
value as the second signal indication value of the second input channel; and
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is configured for
manipulating the combination signal in a first manner when the first energy value is
in a first relation to the second energy value, or in a different second manner, when
the first energy value is in a different second relation to the second energy value.
An apparatus according to claim 1,
wherein the manipulation information generator ( 110; 210; 340; 440; 640) is
adapted to generate the manipulation information depending on the first signal
indication value of the first input channel and on the second signal indication value
of the second input channel,
wherein the first signal indication value of the first input channel depends on an
amplitude value of the first input channel;
wherein the second signal indication value of the second input channel depends on
an amplitude value of the second input channel; and
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is configured for
manipulating the combination signal in a first manner when the first signal
indication value is in a first relation to the second signal indication value, or in a
different second manner, when the first signal indication value is in a different
second relation to the second signal indication value.
4. An apparatus according to one of the preceding claims,
wherein the apparatus furthermore comprises a signal indication computing unit
(230; 330; 430; 630) being adapted to calculate the first signal indication value
based on the first input channel, and being furthermore adapted to calculate the
second signal indication value based on the second input channel.
5. An apparatus according to one of the preceding claims,
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is adapted to
manipulate the combination signal, wherein the combination signal is generated
according to the formula
d(t) = a -x (t) - b - x (t),
wherein d(t) represents the combination signal, wherein xL(t) represents the first
input channel, wherein X (Q represents the second input channel and wherein a and
b are steering parameters.
6. An apparatus according to one of claims 1 to 4,
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is adapted to
manipulate the combination signal, wherein the combination signal represents a
difference between the first and the second input channel.
An apparatus according to one of the preceding claims,
wherein the apparatus furthermore comprises a transformer unit (320; 420; 620) for
transforming the first and the second input channel of the stereo input signal from a
time domain into a frequency domain.
An apparatus according to one of the preceding claims,
wherein the manipulation information generator ( 10; 210; 340; 440; 640) is
adapted to generate a first weighting mask depending on the first signal indication
value, and to generate a second weighting mask depending on the second signal
indication value; and
wherein the manipulator (120; 220; 360, 370; 460, 470; 660, 670) is adapted to
manipulate the combination signal by applying the first weighting mask to an
amplitude value of the combination signal to obtain a first modified amplitude
value, and to manipulate the combination signal by applying the second weighting
mask to an amplitude value of the combination signal to obtain a second modified
amplitude value.
An apparatus according to claim 8,
wherein the apparatus furthermore comprises a combiner (380; 480; 680) being
adapted to combine the first modified amplitude value and a phase value of the
combination signal to obtain the first manipulated signal as the first output channel;
and
wherein the combiner (380; 480; 680) is adapted to combine the second modified
amplitude value and a phase value of the combination signal to obtain the second
manipulated signal as the second output channel.
An apparatus according to claim 8 or 9,
wherein the manipulation information generator (110; 210; 340; 440; 640) is
adapted to generate the first weighting mask G m, k) according to the formula
EL , k )
GL (m,k) =
EL (m,k) + ER (m,k)
or wherein the manipulation information generator ( 10; 210; 340; 440; 640) is
adapted to generate the second weighting mask G ( I, k) according to the formula
E R (m,k)
GR (m,k) =
E (m, k + E R , k
wherein G m, k) denotes the first weighting mask for a time-frequency bin (m, k),
wherein Ga(m,k) denotes the second weighting mask for a time-frequency bin
(m,k), wherein EL(m,k) is an signal indication value of the first input channel for
the time-frequency bin (m,k), wherein E ( , ) is an signal indication value of the
second input channel for the time-frequency bin (m,k) and wherein a is a tuning
parameter.
An apparatus according to claim 10,
wherein the manipulation information generator ( 110; 210; 340; 440; 640) is
adapted to generate the first or the second weighting mask, wherein the tuning
parameter a is a=l.
An apparatus according to one of the preceding claims,
wherein the apparatus comprises a transformer unit (320; 420; 620) and a
combination signal generator (310; 410; 610);
wherein the transformer unit (320; 420; 620) is adapted to receive the first and the
second input channel and to transform the first and second input channel from a
time domain into a frequency domain to obtain a first and a second frequency
domain input channel;
and wherein the combination signal generator (310; 410; 610) is adapted to generate
a combination signal based on the first and the second frequency domain input
channel.
An apparatus according to one of the preceding claims,
wherein the apparatus further comprises a signal delay unit (605) being adapted to
delay the first input channel and/or the second input channel.
An upmixer (700; 800) for generating at least three output channels from at least
two input channels comprising:
an apparatus for generating a stereo output signal (710; 810) according to one of
claims 1 to 13 being arranged to receive two of the input channels of the upmixer
(700; 800) as input channels; and
a combining unit (770; 870) for combining at least two of the input signals of the
upmixer (700; 800) to provide a combination channel;
wherein the upmixer (700; 800) is adapted to output the first output channel of the
apparatus for generating a stereo output signal (710; 810) or a signal derived from
the first output channel of the apparatus for generating a stereo output signal (710;
810) as a first output channel of the upmixer (700; 800);
wherein the upmixer (700; 800) is adapted to output the second output channel of
the apparatus for generating a stereo output signal (710; 810) or a signal derived
from the second output channel of the apparatus for generating a stereo output
signal (710; 810) as a second output channel of the upmixer (700; 800); and
wherein the upmixer (700; 800) is adapted to output the combination channel as a
third output channel of the upmixer (700; 800).
15. An apparatus for stereo-base widening (900) for generating two output channels
from two input channels, comprising:
an apparatus for generating a stereo output signal (910) according to one of claims
1 to 13, being arranged to receive the two input channels of the apparatus for
stereo-base widening (900) as input channels; and
a combining unit (920, 930) for combining at least one of the output channels of the
apparatus for generating a stereo output signal (910) with at least one of the input
channels of the apparatus for stereo-base widening (900) to provide a combination
channel;
wherein the apparatus for stereo-base widening (900) is adapted to output the
combination channel or a signal derived from the combination channel.
A method for generating a stereo output signal having a first output channel and a
second output channel from a stereo input signal having a first input channel and a
second input channel comprising:
generating manipulation information depending on a first signal indication value of
the first input channel and on a second signal indication value of the second input
channel; and
manipulating a combination signal based on the manipulation information to obtain
a first manipulated signal as the first output channel and a second manipulated
signal as the second output channel;
wherein the combination signal is derived by combining the first input channel and
the second input channel; and
wherein the manipulation of the combination signal is conducted by manipulating
the combination signal in a first manner when the first signal indication value is in a
first relation to the second signal indication value, or in a different second manner,
when the first signal indication value is in a different second relation to the second
signal indication value.
An apparatus for encoding manipulation information, comprising:
a signal indication computing unit (1010) for determining a first signal indication
value of a first channel of a stereo input signal and for determining a second signal
indication value of a second channel of the stereo input signal;
a manipulation information generator (1020) being adapted to generate
manipulation information depending on a first signal indication value of the first
input channel and on a second signal indication value of the second input channel;
and
an output module (1030) for outputting the manipulation information;
wherein the manipulation information is suitable for manipulating a combination
signal based on the manipulation information to generate a first channel and a
second channel of a stereo output signal;
wherein the combination signal is a signal derived by combining the first input
channel and the second input channel; and
wherein the manipulation information indicates a relation of the first signal
indication value to the second signal indication value;
and wherein the relation of the first signal indication value to the second signal
indication value indicates that the combination signal should be manipulated in a
first manner to generate the stereo output signal, when the first signal indication
value is in a first relation to the second signal indication value, or that the
combination signal should be manipulated in a second different manner to generate
the stereo output signal, when the first signal indication value is in a second
different relation to the second signal indication value.
A computer program for generating a stereo output signal having a first and a
second output channel from a stereo input signal having a first input channel and a
second input channel, implementing a method according to claim 16.