Note: Descriptions are shown in the official language in which they were submitted.
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(replacement page)
Titel:Device for determining the quality of an output signal to be
generated by a signal processing circuit, and also method
A. Background of the invention
The invention relates to a device for determining the quality of
an output signal to be generated by a signal processing circuit with
respect to a reference signal, which device comprises a first series
circuit having a first input for receiving the output signal, a second
series circuit having a second.input for receiving the reference
signal, and a combining circuit, coupled to a first output of the
first series circuit and to a second output of the second series
circuit, for generating a quality signal at an output of the combining
circuit, which first series circuit is provided with
- a first signal processing arrangement, coupled to the first
input of the first series circuit, for generating a first signal
parameter as a function of time and frequency, and
- a first compressing arrangement, coupled to the first signal
processing arrangement, for compressing a first signal parameter and
for generating a first compressed signal parameter,
which second series circuit is provided with
- a second compressing arrangement, coupled to the second input,
for generating a second compressed signal parameter, and
which combining circuit is provided with
- a differential arrangement, coupled to the two compressing
arrangements, for determining a differential signal on the basis of
the compressed signal parameters,
- an integrating arrangement, coupled to the differential
arrangement, for integrating the differential signal with respect to
frequency, and
- a time-averaging arrangement, coupled to the integrating
arrangement, for integrating the integrated differential signal with
respect to time.
Such a device is disclosed in the first reference: J. Audio Eng.
Soc., Vol. 40, No. 12, December 1992, in particular "A Perceptual
Audio Quality Measure Based on a Psychoacoustic Sound Representation"
by John G. Beerends and Jan A. Stemerdink, pages 963 - 978, more
particularly Figure 7. The device described therein determines the
quality of an output signal to be generated by a signal processing
AMENDED SHEEN
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circuit, such <~s, :Eor example, a coder/decoder, or codec,
with respect to a reference signal. Said reference signal
is, for examplf=_, an inp7.zt:. signal to be ~>resented t:o the
signal processing circuit, although the possibilities also
include using <~s referea:zce signal a pre-calculated ideal
version of the output signal. The first signal parameter is
generated as a fun.~tion of time and frequency by means of
the first signal process_i.ng arrangement, associated with the
first series circuit, in response to the output signal,
after which th~= first signal parameter ~_s compressed by
means of the first compressing arrangement associated with
the first series c:~rcuir~. In this connectiora, intermediate
operational processing of said first signal parameter should
not be ruled out at all. The second signal parameter is
compressed by means of the second compressing arrangement
associated with the seco:nci series circuit in response to the
reference signal. In this connection, too, further
operational processing of said second signal parameter
should not be ruled out at a11. Of both compressed signal
parameters the differential signal is determined by means of
the differential arrangement associated with the combining
circuit, after which th.e quality signal is generated by
integrating t:he differential signal with respect to
frequency by means of the integrating arrangement associated
with the combining' circuit and b~~ then integrating the
integrated differential signal with respect to time by means
of the time-averaging arrangement: associated with the
combining circuit.
Such a device: has, intE~r aiia, the disadvantage
:s0 that the objective quality signa=i t.o be assessed by means of
said device ar~d a subj e::ctive quad it:y signal. to be assess.°_d
by human observers have a poor correlation.
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B Summery of the invention
In one aspect of the invention, therf=_ is provided
a device for d~=termining qwai.ity ~:of an output :signal to be
generated by a signal processing uircuit~ with -respect to a
reference signal, the d~ev:L~.:e comprising a firsi~ series
circuit having a f_Lrst iczpvrt for receiv~.ng the output
signal, a second series circuit having a second input for
receiving the reference signal, a.nd a combinin<~ circuit,
coupled to a first output of the first series wircuit and to
a second output of the second sex-ies circuit, for generating
an output quality signal at an output of the combining
circuit, wherein the .fi:rst: series; circuit comprises: a
first signal processing arrangemE~nt, coupled t:o the first:
input of the first series ci.rcuit., far generating a first.
signal parameter as a function of: tune and frequency; and a
first compre:>sing arrangement, coupled to the first signal
processing arrangement, for compz:essing the f:~rst: signal
parameter to generate a first compressed signal parameter;
wherein the :second series wircuit: comprises: a second
compressing arrangement., responsive to the second input, for
generating a second corrupressed s~_gnal parameter; and whe=rein
the combining circuit c°omprises: a differential
arrangement, coupled to the first. and second compressing
arrangements,. .for detex:~rr~ir.ing a c~.ifferential signal on the
basis of the first. and second compressed signal parameters;
an integrating arrangenuent, coup:led to the differential
arrangement, for i.ntegr-a.ting the differential signal with
respect to frequency sc> as to de:E ine an integrated
differential signal; arid a time-~~veraging arrangement,
coupled to thE: int:egrat:ing arrangement, for generating the
output quality signal );:oy in~.egratir~g the integrated
differential ~~ignal wit:~h respect to time; a comparing
arrangement for compar~~ng one of two signals with an other
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signal so as to yield a comparison result, said two signals
being an output. signal of= the integrating arrangement and an
output signal of the tune-averaging arrangement:.; and a
selecting arrangement, :,~.vesponsive tc_> the comparison result,
for making a selection w~.t.r, respe4~t to the output quality
signal to be generated i:~~~ the time-averaging arrangement.
In a second a:~pect of the invention, there is
provided a method for dc:,t:.ermining quality of aru output
signal to be generated f:~t° r~ signa~ ~~rocessing circuit with
respect to a reference :~igr:al, the method comprising the
steps of: gene rating a tir_st signal parameter as a function
of time and frequency irz response tc~ the output: signal;
compressing the first signal. parameter to genexvate a first
compressed signal parameter; generating a second compressed
signal parameter ir1 resi;~onse to the reference signal;
determining a differential. signal on the basis of the first
and second compressed s::i_c:~ria.l parameters; and generating a
quality signal by :i_ntega:~at=ing the d:ifferent:ial signal with
respect to frequency anc:~ time, wherein the quality signal
generating step comprises the steps of: comparing one of
two signals with am othc=_r signal so as to yield a comparison
result, said two signal: bes.ng a ~irst signal resulting from
integrating the di:~ferentwial signal with respect to
frequency and a second ~:i_gr~al resulting from integrating the
differential sa_gna:L with respect to frequency and time; and
making a selection with respect to the ciuality signal in
response to the comparison result.
The object of tYh<~ invention is, inter alia, to
provide a device of the type mentioned in the preamble, the
objective quality signa:? to be assessed by means of said
device and a subjective quality signal_ to be assessed by
human observers having ;:x better correlation.
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For this purpose, the device according to the
invention has t:he charac~t~eristic that the combining circuit
is further provided with
- a compar_i.ng arrangement for comparing one of two
signals, said t:wo :_,igna_:is being ttie output signals of the
integrating arrangement
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and the time-averaging arrangement, with an other signal, and
- a selecting arrangement for, in dependence of the comparison
result, making a selection with respect to the quality signal to be
generated.
As a result of providing the device with the comparing
arrangement and the selecting arrangement, more relevant signals can
be distinguished from less relevant signals. Due to said comparing and
selecting, a good correlation is obtained between the objective
quality signal to be assessed by means of said device and a subjective
quality signal to be assessed by human observers.
The invention is based, inter alia, on the insight that the poor
_.
'- correlation between objective quality signals to be assessed by means
of known devices and subjective quality signals to be assessed by
human observers is the consequence, inter alia, of the fact that
certain distortions are found to be more objectionable by human
observers than other distortions, and is further based, inter alia, on
the insight that, inside the combining circuit, some (time-intervals
of) signals are more relevant than other (time-intervals of) signals.
The problem of the poor correlation is thus solved by
distinguishing more relevant signals from less relevant signals.
A first embodiment of the device according to the invention has
the characteristic that the comparing arrangement and the selecting
arrangement are situated between the integrating arrangement and the
time-averaging arrangement for comparing, per time-interval, the
output signal of the integrating arrangement with the other signal
having a predefined value and for in case the output signal of the
integrating arrangement being larger than the other signal supplying
the output signal of the integrating arrangement to the time-averaging
arrangement and for in case the output signal of the integrating
arrangement being smaller than the other signal not supplying the
output signal of the integrating arrangement to the time-averaging
arrangement.
As a result of placing the comparing arrangement and the
selecting arrangement between the integrating arrangement and the
time-averaging arrangement, per time-interval, the integrated
differential signal can be compared with the other signal having a
predefined value. By supplying the integrated differential signal to
the time-averaging arrangement in case the integrated differential
APJIENDi:D S~-lE'T
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signal is larger than the other signal and not supplying the
integrated differential signal to the time-averaging arrangement in
case the integrated differential signal is smaller than the other
signal, the greater relevance of integrated differential signals
having a relative high value is stressed.
Instead of supplying or not supplying, respectively, an
integrated differential signal to the time-averaging arrangement, it
would also be possible to, for example, multiply an integrated
differential signal with a large number or a small number,
respectively, etc., to stress the greater relevance of certain
signals.
t'
'-- A second embodiment of the device according to the invention has
the characteristic that the time-averaging arrangement is arranged for
producing at a first output a first quality signal associated with a
left channel of the signal processing circuit and at a second output a
second quality signal associated with a right channel of the signal
processing circuit, and in that the comparing arrangement and the
selecting arrangement are coupled to the first and second outputs of
the time-averaging arrangement for comparing the first quality signal
with the second quality signal, and for selecting the quality signal
having the largest value.
By placing the comparing arrangement and the selecting
arrangement in series with an output of the time-averaging
arrangement, a quality signal associated with a left channel of the
signal processing circuit can be compared with a quality signal
associated with a right channel of the signal processing circuit and
the quality signal having the largest value can be selected. Due to
the fact that according to this embodiment the signal processing
circuit has got a left and a right channel, two quality signals will
have to be determined: one for the left channel, and one for the right
channel. This can be done by either letting the device according to
the invention determine the quality of an entire left output signal
and then letting said device determine the quality of an entire right
output signal, or by, per time-interval, letting said device determine
the quality of the left and right output signals.
A third embodiment of the device according to the invention has
the characteristic that in case the second quality signal being larger
than a sum of the first quality signal and a signal having a further
~hrc:~.~;;~~ ~_~rcT
r,.... ,..
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predefined value, the second quality signal is selected and in case
the second quality signal being smaller than a sum of the first
quality signal and the signal having the further predefined value the
first quality signal is selected.
~ 5 ,( r.
- L.
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Due to the fact that in case the quality signal associated with
the right channel being larger than a sum of the quality signal
associated with the left channel and a signal having a further
predefined value the quality signal associated with the right channel
5 is selected and in case the quality signal associated with the right
channel being smaller than a sum of the quality signal associated with
the left channel and the signal having the further predefined value
the quality signal associated with the left channel is selected, the
greater relevance of the left output signal of the signal processing
circuit with respect to the right output signal is stressed.
A fourth embodiment of the device according to the invention has
the characteristic that the selecting arrangement is provided with a
multiplying arrangement for multiplying the selected quality signal
with a signal having a value which depends upon at least a correlation
between integrated differential signals associated with the left
channel and integrated differential signals associated with the right
channel.
By providing the selecting arrangement with a multiplying
arrangement for multiplying the selected quality signal with a signal
having a value which depends upon at least a correlation between
integrated differential signals associated with the left channel and
integrated differential signals associated with the right channel, a
very good correlation is obtained between the objective quality signal
to be assessed by means of said device and a subjective quality signal
to be assessed by human observers.
Although the first embodiment on the one hand and the second,
third and fourth embodiment on the other hand can be regarded to be
independent embodiments, the best correlation will be obtained in case
the first, second, third and fourth embodiments are used together.
A fifth embodiment of the device according to the invention has
the characteristic that the second series circuit is furthermore
provided with
- a second signal processing arrangement, coupled to the second
input, for generating a second signal parameter as a function of both
time and frequency, the second compressing arrangement being coupled
to the second signal processing arrangement in order to compress the
second signal parameter.
If the second series circuit is furthermore provided with the
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second signal processing arrangement, the second signal parameter is
generated as a function of both time and frequency. In this case, the
input signal to be presented to the signal processing circuit, such
as, for example, a coder/decoder, or codec, whose quality is to be
determined, is used as reference signal, in contrast to when a second
signal processing arrangement is not used, in which case a pre-
calculated ideal version of the output signal should be used as
reference signal.
A sixth embodiment of the device according to the invention has
the characteristic that a signal processing arrangement is provided
with
- a multiplying arrangement for multiplying in the time domain a
signal to be fed to an input of the signal processing arrangement by a
window function, and
- a transforming arrangement, coupled to the multiplying
arrangement, for transforming a signal originating from the
multiplying arrangement to the frequency domain,
which transforming arrangement generates, after determining an
absolute value, a signal parameter as a function of time and
frequency.
In this connection, the signal parameter is generated as a
function of time and frequency by the first and/or second signal
processing arrangement as a result of using the multiplying
arrangement and the transforming arrangement, which transforming
arrangement also performs, for example, the absolute-value
determination.
A seventh embodiment of the device according to the invention
has the characteristic that a signal processing arrangement is
provided with
- a subband filtering arrangement for filtering a signal to be fed
to an input of the signal processing arrangement,
which subband filtering arrangement generates, after determining an
absolute value, a signal parameter as a function of time and
frequency.
In this connection, the signal parameter is generated as a
function of time and frequency by the first and/or second signal
processing arrangement as a result of using the subband filtering
arrangement which also performs, for example, the absolute-value
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determination.
An eighth embodiment of the device according to the invention
has the characteristic that the signal processing arrangement is
furthermore provided with
S - a converting arrangement for converting a signal parameter
represented by means of a time spectrum and a frequency spectrum into
a signal parameter represented by means of a time spectrum and a Bark
spectrum.
In this connection, the signal parameter generated by the first
and/or second signal processing arrangement and represented by means
of a time spectrum and a frequency spectrum is converted into a signal
parameter represented by means of a time spectrum and a Bark spectrum
by using the converting arrangement.
The invention furthermore relates to a method for determining
the quality of an output signal to be generated by a signal processing
circuit with respect to a reference signal, which method comprises the
following steps of
- generating a first signal parameter as a function of time and
frequency in response to the output signal,
- compressing a first signal parameter and generating a first
compressed signal parameter,
- generating a second compressed signal parameter in response to
the reference signal,
- determining a differential signal on the basis of the compressed
f-
signal parameters, and
- generating a quality signal by integrating the differential
signal with respect to frequency and time.
The method according to the invention has the characteristic
that the step of generating the quality signal comprises the following
substeps of
- comparing one of two signals, said two signals being the
integrated differential signal respectively integrated with respect
to frequency and time with an other signal, with an other signal, and
- making a selection with respect to the quality signal to be
generated, in dependence of the comparison result.
A first embodiment of the method according to the invention has
the characteristic that the substep of comparing includes comparing,
per time-interval, the differential signal which has been integrated
p,nrGt~IDED S'~EcT
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with respect to frequency with the other signal having a predefined
value and in case the integrated differential signal being larger than
the other signal integrating said integrated differential signal with
respect to time and in case the differential signal which has been
integrated with respect to frequency being smaller than the other
signal not integrating said integrated differential signal with
respect to time.
A second embodiment of the method according to the invention has
the characteristic that the step of of generating the quality signal
comprises the further substep of producing a first quality signal
associated with a left channel of the signal processing circuit and a
second quality signal associated with a right channel of the signal
processing circuit, and that the substep of comparing includes
comparing the first quality signal with the second quality signal, and
the substep of making a selection includes selecting the quality
signal having the largest value.
A third embodiment of the method according to the invention has
the characteristic that in case the second quality signal being larger
than a sum of the first quality signal and a signal having a further
predefined value the second quality signal is selected and in case the
second quality signal being smaller than a sum of the first quality
signal and the signal having the further predefined value the first
quality signal is selected.
A fourth embodiment of the method according to the invention has
y 25 the characteristic that the selected quality signal is multiplied with
a signal having a value which depends upon at least a correlation
between differential signals which have been integrated with respect
to frequency and associated with the left channel and differential
signals which have been integrated with respect to frequency and
associated with the right channel.
A fifth embodiment of the method according to the invention has
the characteristic that the step of generating a second compressed
signal parameter in response to the reference signal comprises the
following substeps of
- generating a second signal parameter in response to the
reference signal as a function of both time and frequency, and
- compressing a second signal parameter.
Aiu~~~~l~tii ~:-~r~~.
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(replacement page)
C References
J. Audio Eng. Soc., Vol. 40, No. 12, December 1992, in
particular, "A Perceptual Audio Quality Measure Based on a
Psychoacoustic Sound Representation" by John G. Beerends and Jan
S A. Stemerdink, pages 963 - 978
..0 S~~C~C'~
,.
pcS~~N~
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9
. "Modelling a Cognitive Aspect in tkze Measurement of the Quality
of Music Godecs", by John G. Beerends arid Jan A. Stemerdink,
presented at the 96th (:onvention 26 February - 1 March 1994,
Amsterdam
r US 4,860,360
EP 0 627 727
. EP 0 417 739
DE 37 08 002
WO EP96 / 01102
WO EP96 / 01143
. WO EP96 / 00849
D Exemplary embodiment
The invention will be explained in greater detail by reference
to an exemplary embodiment shown in the figures. In the figures:
Figure 1 shows a device according to the invention, comprising
known signal processing arrangements, known compressing arrangements,
a scaling circuit, and a combining circuit according to the invention,
Figure 2 shows a known signal processing arrangement for use in
the device according to the invention,
Figure 3 shows a known compressing arrangement for use in the
device according to the invention,
Figure 4 shows a scaling circuit for use in the device according
to the invention,
Figure 5 shows a first embodiment of a combining circuit
according to the invention for use in the device according to the
invention, and
Figure 6 shows a second embodiment of a combining circuit
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according to the invention for use in the device according to the
invention.
The device according to the invention shown in Figure 1
comprises a first signal processing arrangement 1 having a first input
5 7 for receiving an output signal originating from a signal processing
circuit such as, for example, a coder/decoder, or codec. A first
output of first signal processing arrangement 1 is connected via a
coupling 9 to a first input of a scaling circuit 3. The device
according to the invention furthermore comprises a second signal
10 processing arrangement 2 having a second input 8 for receiving an
input signal to be fed to the signal processing circuit such as, for
example, the coder/decoder, or codec. A second output of second signal
processing arrangement 2 is connected via a coupling 10 to a second
input of scaling circuit 3. A first output of scaling circuit 3 is
connected via a coupling 11 to a first input of a first compressing
arrangement 4, and a second output of scaling circuit 3 is connected
via a coupling 12 to a second input of a second compressing
arrangement 5. A first output of first compressing arrangement 4 is
connected via a coupling 13 to a first input of a combining circuit 6,
and a second output of second compressing arrangement 5 is connected
via a coupling 16 to a second input of combining circuit 6. A third
output of scaling circuit 3 is connected via a coupling 14 to a third
input of combining circuit 6, and the second output of second
compressing arrangement 5, or coupling 16, is connected via a coupling
15 to a fourth input of combining circuit 6 which has an output 17 for
generating a quality signal. First signal processing arrangement 1 and
first compressing arrangement 4 jointly correspond to a first series
circuit, and second signal processing arrangement 2 and second
compressing arrangement 5 jointly correspond to a second series
circuit.
The known first (or second) signal processing arrangement 1 (or
2) shown in Figure 2 comprises a first (or second) multiplying
arrangement 20 for multiplying in the time domain the output signal
(or input signal) to be fed to the first input 7 (or second input 8)
of the first (or second) signal processing arrangement 1 (or 2) and
originating from the signal processing circuit such as, for example,
the coder/decoder, or codec, by a window function, a first (or second)
transforming arrangement 21, coupled to the first (or second)
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multiplying arrangement 20, for transforming the signal originating
from the first (or second) multiplying arrangement 20 to the frequency
domain, a first (or second) absolute-value arrangement 22 for
determining the absolute value of the signal originating from the
first (or second) transforming arrangement 21 for generating a first
(or second) positive signal parameter as a function of time and
frequency, a first (or second) converting arrangement 23 for
converting the first (or second) positive signal parameter originating
from the first (or second) absolute-value arrangement 22 and
represented by means of a time spectrum and a frequency spectrum into
a first (or second) signal parameter represented by means of a time
spectrum and a Bark spectrum, and a first (or second) discounting
arrangement 24 for discounting a hearing function in the case of the
first (or second) signal parameter originating from the first (or
second) converting arrangement and represented by means of a time
spectrum and a Bark spectrum, which signal parameter is then
transmitted via the coupling 9 (or 10).
The known first (or second) compressing arrangement 4 (or 5)
shown in Figure 3 receives via coupling 11 (or 12) a signal parameter
which is fed to a first (or second) input of a first (or second) adder
30, a first (or second) output of which is connected via a coupling
31, on the one hand, to a first (or second) input of a first (or
second) multiplier 32 and, on the other hand, to a first (or second)
nonlinear convoluting arrangement 36 which is furthermore connected to
a first (or second) compressing unit 37 for generating via coupling 13
(or 16) a first (or second) compressed signal parameter. First (or
second) multiplier 32 has a further first (or second) input for
receiving a feed signal and has a first (or second) output which is
connected to a first (or second) input of a first (or second) delay
arrangement 34, a first (or second) output of which is coupled to a
further first (or second) input of the first (or second) adder 30.
The scaling circuit 3 shown in Figure 4 comprises a further
integrating arrangement 40, a first input of which is connected to the
first input of scaling circuit 3 and consequently to coupling 9 for
receiving a first series circuit signal (the first signal parameter
represented by means of a time spectrum and a Bark spectrum) and a
second input of which is connected to the second input of scaling
circuit 3 and consequently to coupling 10 for receiving a second
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12
series circuit signal (the second signal parameter represented by
means of a time spectrum and a Bark spectrum). A first output of
further integrating arrangement 40 for generating the integrated first
series circuit signal is connected to a first input of a further
comparing arrangement 41 and a second output of further integrating
arrangement 40 for generating the integrated second series circuit
signal is connected to a second input of further comparing arrangement
41. The first input of scaling circuit 3 is connected to the first
output and, via scaling circuit 3, coupling 9 is consequently
connected through to coupling 11. The second input of scaling circuit
3 is connected to a first input of a further scaling unit 42 and a
second output is connected to an output of further scaling unit 42
and, via scaling circuit 3, coupling 10 is consequently connected
through to coupling 12 via further scaling unit 42. An output of
further comparing arrangement 41 for generating a control signal is
connected to a control input of further scaling unit 42. The first
input of scaling circuit 3, or coupling 9 or coupling 11, is connected
to a first input of a ratio-determining arrangement 43 and the output
of further scaling unit 42, or coupling 12, is connected to a second
input of ratio-determining arrangement 43, an output of which is
connected to the third output of scaling circuit 3 and consequently to
coupling 14 for generating a further scaling signal.
The combining circuit 6 shown in Figures 5 and 6 comprises a
still further comparing arrangement 50, a first input of which is
connected to the first input of combining circuit 6 for receiving the
first compressed signal parameter via coupling 13 and a second input
of which is connected to the second input of combining circuit 6 for
receiving the second compressed signal parameter via coupling 16. The
first input of combining circuit 6 is furthermore connected to a first
input of a differential arrangement 54,56. An output of still further
comparing arrangement 50 for generating a scaling signal is connected
via a coupling 51 to a control input of scaling arrangement 52, an
input of which is connected to the second input of combining circuit 6
for receiving the second compressed signal parameter via coupling 16
and an output of which is connected via a coupling 53 to a second
input of differential arrangement 54,56 for determining a differential
signal on the basis of the mutually scaled compressed signal
parameters. A third input of the differential arrangement 54,56 is
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13
connected to the fourth input of the combining circuit 6 for
receiving, via coupling 15, the second compressed signal parameter to
be received via coupling 16. Differential arrangement 54,56 comprises
a differentiator 54 for generating a differential signal and a further
absolute-value arrangement 56 for determining the absolute value of
the differential signal, an output of which is connected to an input
of scaling unit 57, a control input of which is connected to the third
input of combining circuit 6 for receiving the further scaling signal
via coupling 14. An output of scaling unit 57 is connected to an input
of an integrating arrangement 58 for integrating the scaled absolute
value of the differential signal with respect to frequency.
According to a first embodiment of combining circuit 6 (Figure
5), an output of integrating arrangement 58 is coupled .to an input of
selecting arrangement 61 and to a first input of comparing arrangement
60. A second input of comparing arrangement 60 is coupled to a
connection 62 for receiving an other signal having a predefined value.
An output of comparing arrangement 60 is coupled, via a connection 63,
to a control input of selecting arrangement 61. An output of selecting
arrangement 61 is coupled to an input of a time-averaging arrangement
59, an output of which is connected to the output 17 of combining
circuit 6 for generating the quality signal.
According to a second embodiment of combining circuit 6 (Figure
6), an output of integrating arrangement 58 is coupled to an input of
a time-averaging arrangement 59, of which a first output is connected
via a connection 72 to a first input of selecting arrangement 71 and a
second output is connected via a connection 73 to a second input of
selecting arrangement 71. The output of integrating arrangement 58 is
also coupled to a third input of selecting arrangement 71 via a
connection 75. The respective first and second outputs of time-
averaging arrangement 59 are further coupled via the respective
connections 72 and 73 to respective first and second inputs of
comparing arrangement 70, of which an output is coupled via a
connection 74 to a control input of selecting arrangement 71, of which
an output is connected to the output 17 of combining circuit 6 for
generating the quality signal.
ThE operation of a standard device for determining the quality
of the output signal to be generated by the signal processing circuit
such as, for example, the coder/decoder, or codec, which standard
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14
device is formed without the scaling circuit 3 shown in greater detail
in Figure 4, the couplings 10 and 12 consequently being mutually
connected through, and which known device is formed using a standard
combining circuit 6, the third input of differential arrangement 54,56
and scaling unit 57 and the comparing arrangement 60 and/or 70 and
selecting arrangement 61 and/or 71, shown in greater detail in Figures
5 and 6, consequently being missing, is as follows and, indeed, as
also described in the first reference.
The output signal of the signal processing circuit such as, for
example, the coder/decoder, or codec, is fed to input 7, after which
the first signal processing circuit 1 converts said output signal into
a first signal parameter represented by means of a time spectrum and a
Bark spectrum. This takes place by means of the first multiplying
arrangement 20 which multiplies the output signal represented by means
of a time spectrum by a window function represented by means of a time
spectrum, after which the signal thus obtained and represented by
means of a time spectrum is transformed by means of first transforming
arrangement 21 to the frequency domain, for example by means of an
FFT, or fast Fourier transform, after which the absolute value of the
signal thus obtained and represented by means of a time spectrum and a
frequency spectrum is determined by means of the first absolute-value
arrangement 22, for example by squaring, after which the signal
parameter thus obtained and represented by means of a time spectrum
and a frequency spectrum is converted by means of first converting
arrangement 23 into a signal parameter represented by means of a time
spectrum and a Bark spectrum, for example by resampling on the basis
of a nonlinear frequency scale, also referred to as Bark scale, which
signal parameter is then adjusted by means of first discounting
arrangement 24 to a hearing function, or is filtered, for example by
multiplying by a characteristic represented by means of a Bark
spectrum.
The first signal parameter thus obtained and represented by
means of a time spectrum and a Bark spectrum is then converted by
means of the first compressing arrangement 4 into a first compressed
signal parameter represented by means of a time spectrum and a Bark
spectrum. This takes place by means of first adder 30, first
multiplier 32 and first delay arrangement 34, the signal parameter
represented by means of a time spectrum and a Bark spectrum being
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multiplied by a feed signal represented by means of a Bark spectrum
such as, for example, an exponentially decreasing signal, after which
the signal parameter thus obtained and represented by means of a time
spectrum and a Bark spectrum is added, with a delay in time, to the
5 signal parameter represented by means of a time spectrum and a Bark
spectrum, after which the signal parameter thus obtained and
represented by means of a time spectrum and a Bark spectrum is
convoluted by means of first nonlinear convoluting arrangement 36 with
a spreading function represented by means of a Bark spectrum, after
10 which the signal parameter thus obtained and represented by means of a
time spectrum and a Bark spectrum is compressed by means of first
compressing unit 37.
In a corresponding manner, the input signal of the signal
processing circuit such as, for example, the coder/decoder, or codec,
15 is fed to input 8, after which the second signal processing circuit 2
converts said input signal into a second signal parameter represented
by means of a time spectrum and a Bark spectrum, and the latter is
converted by means of the second compressing arrangement 5 into a
second compressed signal parameter represented by means of a time
spectrum and a Bark spectrum.
The first and second compressed signal parameters, respectively,
are then fed via the respective couplings 13 and 16 to combining
circuit 6, it being assumed for the time being that this is a standard
combining circuit which lacks the third input of differential
arrangement 54,56 and scaling unit 57 shown in greater detail in
Figure 5. The two compressed signal parameters are integrated by still
further comparing arrangement 50 and mutually compared, after which
still further comparing arrangement 50 generates the scaling signal
which represents, for example, the average ratio between the two
compressed signal parameters. Said scaling signal is fed to scaling
arrangement 52 which, in response thereto, scales the second
compressed signal parameter (that is to say, increases or reduces it
as a function of the scaling signal). Obviously, scaling arrangement
52 could also be used, in a manner known to the person skilled in the
art, for scaling the first compressed signal parameter instead of for
scaling the second compressed signal parameter and use could
furthermore be made, in a manner known to the person skilled in the
art, of two scaling arrangements for mutually scaling the two
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compressed signal parameters at the same time. The differential signal
is derived by means of differentiator 54 from the mutually scaled
compressed signal parameters, the absolute value of which differential
signal is then determined by means of further absolute-value
arrangement 56. The signal thus obtained is integrated by means of
integrator 58 with respect to a Bark spectrum and is integrated by
means of time-averaging arrangement 59 with respect to a time spectrum
and generated by means of output 17 as quality signal which indicates
in an objective manner the quality of the signal processing circuit
such as, for example, the coder/decoder or codec.
The operation of an improved device for determining the quality
of the output signal to be generated by the signal processing circuit
such as, for example, the coder/decoder, or codec, which device
according to the invention is consequently formed with the scaling
circuit 3 shown in greater detail in Figure 4, the couplings 10 and 12
consequently being coupled through mutually via further scaling unit,
and which improved device is formed with an expanded combining circuit
6 according to the invention to which the third input of differential
arrangement 54,56 shown in greater detail in Figures 5,6 and scaling
unit 57 have consequently been added is as described above,
supplemented by what follows.
The first series circuit signal (the first signal parameter
represented by means of a time spectrum and a Bark spectrum) to be
received via coupling 9 and the first input of scaling circuit 3 is
fed to the first input of further integrating arrangement 40 and the
second series circuit signal (the second signal parameter represented
by means of a time spectrum and a Bark spectrum) to be received via
the coupling 10 and the second input of scaling circuit 3 is fed to
the second input of further integrating arrangement 40, which
integrates the two series circuit signals with respect to frequency,
after which the integrated first series circuit signal is fed via the
first output of further integrating arrangement 40 to the first input
of further comparing arrangement 41 and the integrated second series
circuit signal is fed via the second output of further integrating
arrangement 40 to the second input of further comparing arrangement
41. The latter compares the two integrated series circuit signals and
generates, in response thereto, the control signal which is fed to the
control input of further scaling unit 42. The latter scales the second
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series circuit signal (the second signal parameter represented by
means of a time spectrum and a Bark spectrum) to be received via
coupling 10 and the second input of scaling circuit 3 as a function of
said control signal (that is to say increases or reduces the amplitude
of said second series circuit signal) and generates [sic] the thus
scaled second series circuit signal via the output of further scaling
unit 42 to the second output of scaling circuit 3, while the first
input of scaling arrangement 3 is connected through in this example in
a direct manner to the first output of scaling circuit 3. In this
IO example, the first series circuit signal and the scaled second series
circuit signal, respectively are passed via scaling circuit 3 to first
compressing arrangement 4 and second compressing arrangement 5,
respectively.
As a result of this further scaling, a good correlation is
obtained between the objective quality signal to be assessed by means
of the device according to the invention and a subjective quality
signal to be assessed by human observers. This invention is based,
inter alia, on the insight that the poor correlation between objective
quality signals to be assesssed by means of known devices and
subjective quality signals to be assessed by human observers is the
consequence, inter alia, of the fact that certain distortions are
found to be more objectionable by human observers than other
distortions, which poor correlation is improved by using the two
compressing arrangements, and is furthermore based, inter alia, on the
insight that, as a result of using scaling circuit 3, the two
compressing arrangements 4 and 5 function better with respect to one
another, which improves the correlation further. The problem of the
poor correlation is consequently solved by an improved functioning of
the two compressing arrangements 4 and 5 with respect to one another
as a result of using scaling circuit 3.
As a result of the fact that the first input of scaling circuit
3, or coupling 9 or coupling 11, is connected to the first input of
ratio-determining arrangement 43 and the output of further scaling
unit 42, or coupling 12, is connected to the second input of ratio-
determining arrangement 43, ratio-determining arrangement 43 is
capable of assessing the mutual ratio of the first series circuit
signal and the scaled second series circuit signal and of generating a
further scaling signal as a function thereof by means of the output of
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ratio-determining arrangement 43, which further scaling signal is fed
via the third output of scaling circuit 3 and consequently via
coupling 14 to the third input of combining circuit 6. Said further
scaling signal is fed in combining circuit 6 to scaling unit 57 which
scales, as a function of said further scaling signal, the absolute
value of the differential signal originating from the differential
arrangement 54,56 (that is to say increases or reduces the amplitude
of said absolute value). As a consequence thereof, the already
improved correlation is improved further as a result of the fact an
(amplitude) difference still present between the first series circuit
signal and the scaled second series circuit signal in the combining
circuit is discounted and integrating arrangement 58 and time-
averaging arrangement 59 function better as a result.
A further improvement of the correlation is obtained if
differentiator 54 (or further absolute-value arrangement 56) is
provided with a further adjusting arrangement, not shown in the
figures, for example in the form of a subtracting circuit which
somewhat reduces the amplitude of the differential signal. Preferably,
the amplitude of the differential signal is reduced as a function of a
series circuit signal, just as in this example it is reduced as a
function of the scaled and compressed second signal parameter
originating from second compressing arrangement 5, as a result of
which integrating arrangement 58 and time-averaging arrangement 59
function still better. As a result, the already very good correlation
is improved still further.
It is observed that ratio-determining arrangement 43 could also
be placed between couplings 13 and 16 (in other words between
compressing arrangements 4 and 5, on the one hand, and combining
circuit 6 on the other hand). In this case, the correlation is
improved by using the results of both compressing arrangements 4 and 5
in a better way.
The operation of a device according to the invention for
determining the quality of the output signal to be generated by the
signal processing circuit such as, for example, the coder/decoder, or
codec, which device according to the invention is consequently formed
with either at least the first embodiment of the combining circuit 6
shown in greater detail in Figure 5 and comprising comparing
arrangement 60 and selecting arrangement 70, or at least the second
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embodiment of the combining circuit 6 shown in greater detail in
Figure 6 and comprising comparing arrangement 61 and selecting
arrangement 71, is as described above, supplemented by what follows.
In case of the first embodiment (Figure 5), the differential
signal which has been integrated with respect to frequency by
integrating arrangement 58, is supplied to comparing arrangement 60
and selecting arrangement 61. Comparing arrangement 60 compares, for
each time-interval of for example 40 msec., a value of said signal
with an other signal having a predefined value. In case the integrated
differential signal is larger (much distortion) than the other signal,
comparing arrangement 60 controls selecting arrangement 61 such that
the integrated differential signal is supplied (or multiplied by a
large number) to time-averaging arrangement 59. In case. the integrated
differential signal is smaller (little distortion) than the other
signal, comparing arrangement 60 controls selecting arrangement 61
such that the integrated differential signal is not supplied (or
multiplied by a small number) to time-averaging arrangement 59. Due to
this, the greater relevance of (time-intervals of) signals indicating
much distortion is stressed with respect to (time-intervals of)
signals indicating little distortion, which results in better
correlation.
In case of the second embodiment (Figure 6), the differential
signal which has been integrated with respect to frequency by
integrating arrangement 58, is supplied to time-averaging arrangement
59 and to the third input of selecting arrangement 71. Time-averaging
arrangement generates two quality signals, a first quality signal
associated with a left channel of the signal processing circuit, and a
second quality signal associated with a right channel of the signal
processing circuit. This can be done by either letting the device
according to the invention determine the quality of an entire left
output signal and then letting said device determine the quality of an
entire right output signal, or by, per time-interval (of for example
10 sec.), letting said device determine the quality of firstly the
left and secondly the right output signals. To a person skilled in the
art it will be obvious that in at least one of both cases at least
some of the circuits and/or arrangements will have to be provided with
memories.
Comparing arrangement 70 compares these two quality signals. In
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case the second quality signal associated with the right channel being
larger than a sum of the first quality signal associated with the left
channel and a signal having a further predefined value the selecting
arrangement 71 is controlled such that the second quality signal
5 associated with the right channel is selected. In case the second
quality signal associated with the right channel being smaller than a
sum of the first quality signal associated with the left channel and
the signal having the further predefined value the selecting
arrangement 71 is controlled such that the first quality signal
10 associated with the left channel is selected. Then, inside selecting
arrangement 71, the selected quality signal is multiplied with a
signal for example having a value (1.2-c)4 which depends upon at least
a correlation (c) between integrated differential signals associated
with the left channel and integrated differential signals associated
15 with the right channel. Thereto, selecting arrangement 70 comprises
for example a multiplying arrangement for multiplying the selected
quality signal with said value, and a correlating arrangement for
correlating both integrated differential signals, and a memory for
storing integrated differential signals. Due to this, the disturbance
20 of distortions causing binaural image shift is stressed.
The components shown in Figure 2 of first signal processing
arrangement 1 are described, as stated earlier, adequately and in a
manner known to the person skilled in the art in the first reference.
A digital output signal which originates from the signal processing
circuit such as, for example, the coder/decoder, or codec, and which
is, for example, discrete both in time and in amplitude is multiplied
by means of first multiplying arrangement 20 by a window function such
as, for example, a so-called cosine square function represented by
means of a time spectrum, after which the signal thus obtained and
represented by means of a time spectrum is transformed by means of
first transforming arrangement 21 to the frequency domain, for example
by an FFT, or fast Fourier transform, after which the absolute value
of the signal thus obtained and represented by means of a time
spectrum and a frequency spectrum is determined by means of the first
absolute-value arrangement 22, for example by squaring. Finally, a
power density function per time/frequency unit is thus obtained. An
alternative way of obtaining said signal is to use a subband filtering
arrangement for filtering the digital output signal, which subband
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filtering arrangement generates, after determining an absolute value,
a signal parameter as a function of time and frequency in the form of
the power density function per time/frequency unit. First converting
arrangement 23 converts said power density function per time/frequency
unit, for example by resampling on the basis of a nonlinear frequency
scale, also referred to as Bark scale, into a power density function
per time/Bark unit, which conversion is described comprehensively in
Appendix A of the first reference, and first discounting arrangement
24 multiplies said power density function per time/Bark unit, for
example by a characteristic, represented by means of a Bark spectrum,
for performing an adjustment on a hearing function.
The components, shown in Figure 3, of first compressing
arrangement 4 are, as stated earlier, described adequately and in a
manner known to the person skilled in the art in the first reference.
The power density function per time/Bark unit adjusted to a hearing
function is multiplied by means of multiplier 32 by an exponentially
decreasing signal such as, for example, exp(-T/z(z)). Here T is equal
to S0~ of the length of the window function and consequently
represents half of a certain time interval, after which certain time
interval first multiplying arrangement 20 always multiplies the output
signal by a window function represented by means of a time spectrum
(for example, 50~ of 40 cosec is 20 cosec). In this expression, z(z) is
a characteristic which is represented by means of the Bark spectrum
and is shown in detail in Figure 6 of the first reference. First delay
arrangement 34 delays the product of this multiplication by a delay
time of length T, or half of the certain time interval. First
nonlinear convolution arrangement 36 convolutes the signal supplied by
a spreading function represented by means of a Bark spectrum, or
spreads a power density function represented per time/Bark unit along
a Bark scale, which is described comprehensively in Appendix B of the
first reference. First compressing unit 37 compresses the signal
supplied in the form of a power density function represented per
time/Bark unit with a function which, for example, raises the power
' density function represented per time/Bark unit to the power a, where
0 < a < 1.
The components, shown in Figure 4, of scaling circuit 3 can be
formed in a manner known to the person skilled in the art. Further
integrating arrangement 40 comprises, for example, two separate
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integrators which separately integrate the two series circuit signals
supplied by means of a Bark spectrum, after which further comparing
arrangement 41 in the form of, for example, a divider, divides the two
integrated signals by one another and feeds the division result or the
inverse division result as control signal to further scaling unit 42
which, in the form of, for example, a multiplier or a divider,
multiplies or divides the second series circuit signal by the division
result or the inverse division result in order to make the two series
circuit signals, viewed on average, of equal size. Ratio-determining
arrangement 43 receives the first and the scaled second series circuit
signal in the form of compressed, spread power density functions
represented per time/Bark unit and divides them by one another to
generate the further scaling signal in the form of the division result
represented per time/Bark unit or the inverse thereof, depending on
whether scaling unit 57 is constructed as multiplier or as divider.
The components, shown in Figures 5 and 6, of combining circuit 6
are, as stated earlier, described adequately and in a manner known to
the person skilled in the art in the first reference, with the
exception of the component 57 and a portion of component 54 and
comparing arrangement 60,61 and selecting arrangement 70,71. Still
further comparing arrangement 50 comprises, for example, two separate
. integrators which separately integrate the two series circuit signals
supplied over, for example, three separate portions of a Bark spectrum
and comprises, for example, a divider which divides the two integrated
signals by one another per portion of the Bark spectrum and feeds the
division result or the inverse division result as scaling signal to
scaling arrangement 52 which, in the form of, for example, a
multiplier or a divider, multiplies or divides the respective series
circuit signal by the division result or the inverse division result
in order to make the two series circuit signals, viewed on average, of
equal size per portion of the Bark spectrum. All this is described
comprehensively in Appendix F of the first reference. Differentiator
54 determines the difference between the two mutually scaled series
circuit signals. According to the improved device, if the difference
is negative, said difference can then be augmented by a constant value
and, if the difference is positive, said difference can be reduced by
a constant value, for example by detecting whether it is less or
greater than the value zero and then adding or subtracting the
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constant value. It is, however, also possible first to determine the
absolute value of the difference by means of further absolute-value
arrangement 56 and then to deduct the constant value from said
absolute value, in which connection a negative final result must
obviously not be permitted to be obtained. In this last case,
absolute-value arrangement 56 should be provided with a subtracting
circuit. Furthermore, it is possible, according to the improved
device, to discount from the difference a (portion of a) series
circuit signal in a similar manner instead of the constant value or
together with the constant value.
According to the invention (Figure 5) integrating arrangement 58
integrates the signal originating from scaling unit 57 with respect to
a Bark spectrum and comparing arrangement 60 compares the value of the
integrated differential signal (comprising for example one value per
time-interval of 40 cosec.) with the predefined value of the other
signal arriving via connection 62. In response to the comparison
result, selecting arrangement 61 blocks said integrated differential
signal or supplies said integrated differential signal to time-
averaging arrangement 59 which integrates the signal thus obtained
with respect to a time spectrum, as a result of which the quality
signal is obtained which has a value which is the smaller, the higher
the quality of the signal processing circuit is. So, selecting
arrangement 61 could be in the form of a switch, or for example in the
form of a multiplier for multiplying said integrated differential
signal with a small or a large number.
According to the invention (Figure 6) integrating arrangement 58
integrates the signal originating from scaling unit 57 with respect to
a Bark spectrum and time-averaging arrangement 59 integrates the
signal thus obtained with respect to a time spectrum, as a result of
which the first and second quality signals are obtained which have a
value which is the smaller, the higher the quality of the left and
right channel of the signal processing circuit is. Comparing
arrangement 70 compares both quality signals, and in response to the
comparison result selecting means 71 select one of both quality
signals. Selecting means 71 comprise a memory for storing integrated
differential signals, a correlating arrangement for correlating
integrated differential signals associated with the left channel and
integrated differential signals associated with the right channel,
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resulting in a value c, a calculating arrangement for calculating the
value (1.2-c)4, and a multiplying arrangement for multiplying the
selected quality signal with said value (1.2-c)4.
As already described earlier, the correlation between the
objective quality signal to be assessed by means of the device
according to the invention and a subjective quality signal to be
assessed by human observers is improved by expanding the combining
circuit 6 of the device with comparing arrangement 60 and/or 70 and
selecting arrangement 61 and/or 71. Two factors can be viewed
separately from one another:
- the use of comparing arrangement 60 and selecting arrangement
61, and
- the use of comparing arrangement 70 and selecting. arrangement
71.
The best correlation is obtained by simultaneous use of all the
possibilities.
The widest meaning should be reserved for the term signal
processing circuit, in which connection, for example, all kinds of
audio and/or video equipment can be considered. Thus, the signal
processing circuit could be a codec, in which case the input signal is
the reference signal with respect to which the quality of the output
signal should be determined. The signal processing circuit could also
be an equalizer, in which connection the quality of the output signal
should be determined with respect to a reference signal which is
calculated on the basis of an already existing virtually ideal
equalizer or is simply calculated. The signal processing circuit could
even be a loudspeaker, in which case a smooth output signal could be
used as reference signal, with respect to which the quality of a sound
output signal is then determined (scaling already takes place
automatically in the device according to the invention). The signal
processing circuit could furthermore be a loudspeaker computer model
which is used to design loudspeakers on the basis of values to be set
in the loudspeaker computer model, in which connection a low-volume
output signal of said loudspeaker computer model serves as the
reference signal and in which connection a high-volume output signal
of said loudspeaker computer model then serves as the output signal of
the signal processing circuit.
In the case of a calculated reference signal, the second signal
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processing arrangement of the second series circuit could be omitted
as a result of the fact that the operations to be performed by the
second signal processing arrangement can be discounted in calculating
the reference signal.
