[0001] This invention relates to a noise suppressor for use in suppressing a noise signal
from a speech signal.
[0002] As a rule, a speech signal is subjected to pre-processing before the speech signal
is encoded into a sequence of encoded signals. For example, such pre-processing has
been made to judge either a speech duration or a non-speech duration, in an article
which is contributed by J.F. Lynch, Jr. et al to IEEE and which is entitled "SPEECH/SILENCE
SEGMENTATION FOR REAL-TIME CODING VIA RULE BASED ADAPTIVE ENDPOINT DETECTION" (Proceedings
ICASSP, pages 1348-1351, 1987). In the article, description is made only about detection
between the speech duration and the non-speech duration but is not made about suppressing
a noise signal from the speech signal during the pre-processing. In other words, Lynch
et al never consider about pre-processing which suppresses the noise signal from the
speech signal. Practically, even when the pre-processing described in the article
is used for suppressing the noise signal from the speech signal, it is difficult to
suppress the noise signal, namely, a non-speech signal within the speech duration.
[0003] On the other hand, spectrum subtraction has been proposed to remove a noise component
from the speech signal in JP-A-2-278298. Thereafter, the speech signal is encoded
into a sequence of encoded signals. With this method, only a noise spectrum which
results from the noise component is subtracted or removed from a spectrum including
the noise spectrum and produced as a noise-subtracted speech signal. Thus, the noise-subtracted
speech signal might be free from the noise component on the spectrum.
[0004] However, it is to be noted that speech encoding is usually carried out in connection
not only with the spectrum but also with a phase component of the speech signal. This
shows that a noise component can not be removed which is included in the phase component
in the above-mentioned method.
[0005] Therefore, the spectrum subtraction is disadvantageous in that the noise component
can not be completely suppressed from the speech signal.
[0006] Moreover, the spectrum subtraction can not be applied on post-processing which is
carried out after the encoded signal sequence is decoded into a sequence of decoded
signals.
[0007] At any rate, no consideration is made at all about suppressing a noise component
on post-processing, despite that noise suppression is necessary after decoding.
[0008] EP-A-459364 discloses a noise signal prediction system according to the preamble
of claim 1.
[0009] It is an object of this invention to provide a noise suppressor which is capable
of completely suppressing a noise component or signal from a speech signal.
[0010] It is another object of this invention to provide a noise suppressor of the type
described, which can be used either on pre-processing or on post-processing of the
speech signal.
[0011] It is still another object of this invention to provide a noise processor of the
type described, which can suppress the noise signal not only within a speech duration
but also within a non-speech duration.
[0012] These objects are attained with the features of the claims.
Fig. 1 is a block diagram of a noise suppressor according to a first embodiment of
this invention;
Fig. 2 is a block diagram for use in describing a part of the noise suppressor illustrated
in Fig. 1;
Fig. 3 is a block diagram of a noise suppressor according to a second embodiment of
this invention; and
Fig. 4 is a block diagram for use in describing a part of the noise suppressor illustrated
in Fig. 3.
[0013] Description will be at first made as regards a principle of this invention so as
to facilitate an understanding of this invention. Herein, it is assumed that a speech
signal is given in the form of a sequence of digital speech signals to be subjected
to pre-processing and post-processing to suppress a noise signal from the speech signal.
In addition, the pre-processing is carried out in response to an input signal specified
by the digital speech signal sequence which is not encoded yet while the post-processing
is carried out in response to an input signal specified by the digital speech signal
sequence which is already decoded. Therefore, it is noted that the terms "digital
speech signal sequence" and "input signal" may be used in two different meanings hereinunder
so as to include both the pre-processing and the post-processing.
[0014] At any rate, the input signal includes the speech signal (namely, the digital speech
signal sequence) and the noise signal and may be therefore considered as a combination
of the digital speech signal sequence and the noise signal.
[0015] According to this invention, feature parameters are extracted from the input signal
and may be, for example, selected one or ones of spectrum parameters representative
of features of a spectrum in the input signal, pitch prediction gains representative
of periodicity of the input signal, and the like. The feature parameters are used
to determine either a speech duration or a non-speech duration by comparing the feature
parameters with a threshold level.
[0016] Briefly, a preliminary sound source signal which specifies a sound source is obtained
by the use of the input signal and the feature parameters on the pre-processing and
the post-processing. Specifically, the preliminary sound source signal appears in
the form of an error signal which is produced on the pre-processing by allowing the
input signal to pass through an inverse filter controlled by the feature parameters.
[0017] On the other hand, the preliminary sound source signal appears in the form of a decoder
output signal or a sequence of decoded signals which is decoded by the use of the
feature parameters.
[0018] Since the speech signal has an amplitude greater than the noise signal in the preliminary
sound source signal, it is possible to suppress the noise signal alone by comparing
an amplitude of the preliminary sound source signal with a predetermined threshold
level and to therefore attain a noise-suppressed signal. The noise-suppressed signal
is reproduced by the use of the feature parameters into a noise-free output signal
on the pre-processing or is produced as a noise-free decoded signal on the post-processing.
The noise-free output signal may be encoded by an encoder after the pre-processing
while the noise-free decoded signal may be converted into an audio signal after the
post-processing.
[0019] Noise suppression may be carried out only within a selected one of the speech duration
or the non-speech duration or within both the speech duration and the non-speech duration.
Thus, this invention enables to suppress the noise signal on a waveform by the use
of the feature parameters and is applicable to both the pre-processing and the post-processing.
[0020] Referring to Fig. 1, a noise suppressor according to a first embodiment of this invention
is applicable to the pre-processing and is therefore supplied through an input terminal
10 with an input signal IN which includes a speech signal and a noise signal superposed
on the speech signal. As mentioned before, the speech signal is given in the form
of a sequence of digital speech signals. The input signal IN is given to a frame division
circuit 11 and is divided by the frame division circuit 11 into a plurality of frames
each of which has a length of, for example, 40 milliseconds. Each frame is further
subdivided by a subframe division circuit 12 into a plurality of subframes each of
which has a length of, for example, eight milliseconds.
[0021] The input signal IN is divided into the subframes, as mentioned above, and is sent
in the form of a divided input signal sequence x(n) either at every frame or at every
subframe to a feature parameter calculator 15 on one hand and to a noise suppression
circuit 20 on the other hand. Herein, the divided input signal sequence x(n) may be
referred to as an internal input signal.
[0022] In the illustrated example, the feature parameter calculator 15 is supplied with
the internal input signal x(n) at every subframe. The feature parameter calculator
15 at first places a window to extract a piece of the internal input signal x(n) in
relation to each subframe. The window is longer than each subframe length and may
be, for example, 24 milliseconds.
[0023] Thereafter, the feature parameter calculator 15 calculates, as feature parameters,
spectrum parameters indicative of features of a spectrum in the input signal, pitch
prediction gains indicative of periodicity of the speech signal, and an average amplitude
in each subframe. In this event, average power may be calculated in the feature parameter
calculator 15. Such calculations of the feature parameters are known in the art and
will not be described any longer. In any event, the feature parameters are produced
as feature parameter signals from the feature parameter calculator 15.
[0024] Herein, it is to be noted that the feature parameter calculator 15 shown in Fig.
1 calculates the spectrum parameters of a predetermined order which may be, for example,
a tenth order. In addition, the following description will be made on the assumption
that linear prediction coefficients a
i are used as the spectrum parameters. Although such linear prediction coefficients
are calculated by using a well-known LPC analysis, Burg analysis, or the like, it
is assumed in connection with the illustrated example that the Burg analysis is used
to calculate the linear prediction coefficients. The Burg analysis is described in
detail in a book (pages 82 to 87) which is written by Nakamizo et al and which is
titled "Signal Analysis and System Identification" published by Corona Company Ltd,
Tokyo, in 1988. Accordingly, description will be omitted from the instant specification
as regards the Burg analysis.
[0025] Alternatively, the linear prediction coefficients may be also calculated by the use
of a covariance method or a correlation method.
[0026] As mentioned before, the pitch prediction gains are also calculated in the feature
parameter calculator 15. The pitch prediction gains are represented by P
g and are given by:
where T is a delay time representative of a pitch period; n, a sample number; and
N, a maximum sample number.
[0027] Instead of Equation (1), the pitch prediction gains P
g can be simply calculated by the use of the following equation:
[0028] The average amplitude is represented by R and is given by:
[0029] Herein, it is readily possible to implement circuits for calculating the above-mentioned
linear prediction coefficients, the pitch prediction gains P
g, and the average amplitude R by a combination of conventional circuit elements. Accordingly,
specific circuits for calculating the linear prediction coefficients, the pitch prediction
gains P
g, and the average amplitude will not be described later.
[0030] Thus, the feature parameter calculator 15 supplies a speech detection circuit 25
and the noise suppression circuit 20 with the feature parameter signals representative
of the feature parameters, as mentioned above. In the illustrated example, the speech
detection circuit 25 detects or determines either the speech duration or the non-speech
duration of the speech signal in response to at least one of the feature parameters.
To this end, a wide variety of methods can be applied to determine the speech duration
or the non-speech duration. For example, the illustrated speech detection circuit
25 at first smooths the pitch prediction gains P
g and the average amplitude R to obtain smoothed pitch prediction gains P
g' and a smoothed average amplitude R' and thereafter compares the smoothed pitch prediction
gains P
g' and the smoothed average amplitude R' with first and second threshold values TH1
and TH2, respectively.
[0031] The above-mentioned smoothing operation of the pitch prediction gains P
g and the average amplitude R is carried out in accordance with the following equation:
where P is representative of the pitch prediction gains or the average amplitude
to be smoothed; δ is representative of a time constant for smoothing and takes a value
between 0 and 1, both exclusive; and P'
j and P'
j-1 are representative of smoothed values at time instants j and j-1.
[0032] As a result of comparison, when the smoothed pitch prediction gains P
g' and the smoothed average amplitude R' are lower than the first and the second threshold
values TH1 and TH2, respectively, the speech detection circuit 25 judges that the
non-speech duration lasts in the internal input signal x(n). Otherwise, the speech
detection circuit 25 judges that the speech duration lasts in the internal input signal
x(n). Thus, the non-speech and the speech durations are detected by the speech detection
circuit 25. In the example, the first and the second threshold values TH1 and TH2
may be invariable or variable with time.
[0033] As mentioned before, the speech detection circuit 25 comprises a calculation circuit
for calculating the smoothed values (namely, the smoothed pitch prediction gains P
g' and the smoothed average amplitude R') in accordance with Equation 4 and a comparator
unit for comparing the smoothed values with the first and the second threshold values
TH1 and TH2. As a result, the illustrated speech detection circuit 25 can produce
the smoothed average amplitude R' at every frame or at every subframe and a detection
signal DT representative of either the speech or the non-speech duration at every
frame or at every subframe.
[0034] The smoothed average amplitude R' is delivered to a memory circuit 30 while the detection
signal DT is sent to the noise suppression circuit 20.
[0035] Referring to Fig. 2 in addition to Fig. 1, the noise suppression circuit 20 is operable
to suppress the noise signal within at least one of the speech and the non-speech
durations. In Fig. 2, the noise suppression circuit 20 comprises an inverse filter
201 supplied with the internal input signal x(n) from the input terminal 10 through
the frame and the subframe division circuits 11 and 12. The feature parameters a
i are also supplied from the feature parameter calculator 15 to the inverse filter
201. The inverse filter 201 carries out an inverse filtering operation to produce
an inverse-filtered signal e(n) which may be called a preliminary sound source signal
because the inverse-filtered signal e(n) specifies a sound source. Herein, the inverse-filtered
signal e(n) is given by:
where P represents an order of the inverse filter 201. Thus, the inverse-filtered
signal e(n) is dependent on the feature parameters and specifies the sound source.
[0036] The inverse-filtered signal e(n) includes a speech signal component and a noise signal
component superposed on the speech signal component and appears in the form of a continuous
signal. The inverse filter 201 may be simply called a filter circuit.
[0037] Now, it is to be noted that the inverse-filtered signal e(n) is specified by a comparatively
large amplitude pulse within a portion of the speech signal component appearing in
the speech duration because the speech signal has a pitch. On the other hand, the
inverse-filtered signal e(n) exhibits a comparatively small amplitude within a portion
of the noise signal.
[0038] Accordingly, it is possible to suppress the noise signal by comparing the inverse-filtered
signal e(n) with a threshold level TH1.
[0039] More specifically, the noise suppression circuit 20 illustrated in Fig. 2 comprises
a threshold value calculation circuit 202 supplied with the smoothed average amplitude
R' which is calculated by the feature parameter calculator 15 in accordance with Equation
4 and which is memorized into the memory circuit 30. The threshold value calculation
circuit 202 calculates the threshold value TH1 given by:
to produce a threshold value signal representative of the threshold value TH1, where
K2 is greater than zero. Thus, the threhold value TH1 is determined by the average
amplitude R memorized in the memory circuit 30.
[0040] The inverse-filtered signal e(n) and the threshold value signal are sent to a suppressor
unit 203 which is also given the detection signal DT from the speech detection circuit
25. The suppressor unit 203 is put into an active state or into an inactive state
in response to the detection signal DT. In this event, the suppressor unit 203 may
suppress the noise signal within at least one of the speech duration and the non-speech
duration. In the illustrated example, it is assumed that the suppressor unit 203 is
put into the active state within the non-speech duration in response to the detection
signal DT, although the suppressor unit 203 may be put into the active state within
the speech duration.
[0041] In addition, the suppressor unit 203 compares the inverse-filtered signal e(n) with
the threshold value signal. The suppressor unit 203 attenuates the inverse-filtered
signal e(n) by a predetermined amount or renders the inverse-filtered signal e(n)
into zero when the inverse-filtered signal e(n) is smaller than the threshold value
TH1. As a result, the suppressor unit 203 produces a noise-suppressed signal e' specified
by:
where K is greater than zero and smaller than unity.
[0042] At any rate, a combination of the threshold value calculation circuit 202 and the
suppressor unit 203 serves to suppress the noise signal included in the inverse-filtered
signal e(n) and to produce the noise-suppressed signal e'(n) and may be collectively
called a noise suppression portion.
[0043] The noise-suppressed signal e'(n) is sent to a reproduction circuit 204 together
with the feature parameters a
i. The reproduction circuit 204 reproduces the noise-suppressed signal e'(n) into a
noise-suppressed speech signal x'(n) with reference to the feature parameters ai.
In this event, the noise-suppressed speech signal x' is given by:
[0044] The noise-supressed speech signal x'(n) is delivered through an output terminal 35
of the noise suppression circuit 20 to an encoder (not shown) to be encoded. Thus,
the noise-suppressed speech signal x'(n) is produced during the pre-processing prior
to the encoding. Since the noise-suppression is carried out with reference to the
feature parameters of the input signal IN, a phase component of the noise signal can
also be suppressed in the above-mentioned example.
[0045] Referring to Fig. 3, a noise suppressor (depicted at 40) according to a second embodiment
of this invention is operable to carry out post-processing after decoding. To this
end, the illustrated noise processor 40 is connected to a decoder 45 which is supplied
as a decoder input signal or an input signal DIN with feature parameters of a speech
signal and an index signal related to a sound source. The decoder 45 itself may be
similar to that known in the art and produces a sequence of decoded sound source signals
v(n) representative of a sound source together with the feature parameters and the
index signal, in a known manner. The decoded sound source signal sequence v(n) and
the feature parameters and the index signal are sent to the noise suppressor 40.
[0046] In the noise suppressor 40, the decoded sound source signal sequence v(n) is given
to a noise suppression circuit which is depicted at 50 and which is operable in a
manner to be described later in detail. Furthermore, the illustrated noise suppressor
40 comprises a speech detection circuit 25' and a memory circuit 30' which may be
similar to those illustrated in Fig. 1, respectively. From this fact, it is readily
understood that the speech detection circuit 25' is operated in response to the feature
parameters, such as the spectrum parameters, the pitch prediction gains P
g, and the average amplitude R, to detect either the speech duration or the non-speech
duration. Thus, the speech detection circuit 25' supplies the noise suppression circuit
50 with a detection signal DT' indicative of either the speech duration or the non-speech
duration. Like in Fig. 1, the speech detection circuit 25' calculates the smoothed
average amplitude R' which is stored in the memory circuit 30'.
[0047] Referring to Fig. 4 together with Fig. 3, the noise suppression circuit 50 comprises
a threshold calculator 501 supplied with the smoothed average amplitude R' to calculate
a threshold value signal representative of a threshold value TH2, like in the threshold
value calculation circuit 202. The threshold value signal is given to the suppressor
unit 502 together with the detection signal DT'.
[0048] The suppressor unit 502 is put into an active state within at least one of the speech
and the non-speech durations. Herein, it is assumed that the illustrated suppressor
unit 502 becomes active only within the non-speech duration, like in the suppressor
unit 203. In any event, the suppressor unit 502 produces a sequence of noise-suppressed
sound source signals v'(n) given by:
where K is identical with K shown in Equation 7. The threshold value TH2 may be equal
to that of Equation 7.
[0049] Turning back to Fig. 3, the noise-suppressed sound source signals v'(n) are sent
to a speech reproducing circuit 52 which is supplied with the feature parameters from
the decoder 45. The speech reproducing circuit 52 reproduces the noise-suppressed
sound signals into a reproduced speech signal with reference to the feature parameters
in a known manner. The reproduced speech signal is delivered to a loudspeaker or the
like.
[0050] Thus, the noise suppressor according to this invention can be used in post-processing
the decoded sound source signals DIN in the above-mentioned manner.
[0051] While this invention has thus far been described in conjunction with a few embodiments
thereof, it will readily be possible for those skilled in the art to put this invention
into practice in various other manners. For example, the feature parameters need not
be always restricted to the linear prediction coefficients but may be any other parameters
known in the art. In addition, it is possible to use any other parameters than the
average amplitude, and the pitch prediction gains. The speech detection circuit 25
or 25' may be operated in a manner different from that illustrated in Figs. 1 and
3.
[0052] Moreover, the post-processing can be carried out to suppress the noise signal even
when the feature parameters are not transmitted from a transmitter and are not received
by the decoder 45 (Fig. 3). In this case, the speech signal is once reproduced by
a receiver to form a reproduced speech waveform and to thereafter calculate feature
parameters from the reproduced speech waveform in the manner mentioned in conjunction
with Fig. 1. Thus, the calculated feature parameters can be used to suppress the noise
signal in the above-mentioned manner.
[0053] With this structure, the noise suppression is possible during both the pre-processing
and the post-processing of the speech signal. Moreover, it is also possible to suppress
not only the noise signal appearing within the non-speech duration but also a non-speech
signal superposed on the speech signal appearing within the speech duration. Such
suppression can be accomplished on the waveform.
1. A noise suppressor supplied with an internal input signal (IN) which includes both
a speech signal and a noise signal to produce an output signal substantially free
from said noise signal, said speech signal being specified by a sound source, said
noise suppressor comprising feature parameter calculating means (15) supplied with
said internal input signal for calculating a feature parameter specifying a feature
of said speech signal to produce a feature parameter signal representative of said
feature parameter, and noise suppressing means (20) coupled to said feature parameter
calculating means (15) for suppressing said noise signal from said internal input
signal to produce said output signal, wherein said noise suppressing means comprises:
a suppression unit (203) for suppressing the noise signal from a residual signal (e(n))
by estimating said noise signal to produce a nose-suppressed signal (e'(n)); and
output means (204) for producing said noise-suppressed signal as said output signal;
and is characterized by
filter means (201) supplied with said feature parameter signal (ai) and said internal input signal for filtering said internal input signal (x(n)) to
produce a filtered signal which is dependent on said feature parameter (ai) and which specifies said sound source in that said residual signal (e(n)) is calculated
which represents the difference between said feature parameter signal representation
and said internal input signal; wherein the suppression unit is coupled to said filter
means (201).
2. A noise suppressor as claimed in Claim 1, said speech signal being divisible into
a speech duration and a non-speech duration, wherein said noise suppressor (20) further
comprises:
speech detection means (25) coupled to said feature parameter calculating means (15)
for detecting said speech and said non-speech durations in response to the feature
parameter signal to produce a detection signal representative of either one of said
speech and said non-speech durations;
average calculation means (30) coupled to said speech detection means for calculating
an average value of either power or an amplitude within said non-speech duration to
produce an average signal representative of said average value;
said noise suppressing means (20) further comprising:
threshold level calculating means (202) for calculating a threshold level from said
average signal to supply said suppression unit (203) with a threshold level signals
(TH1) representative of said threshold level, to make said suppression unit 203 compare
said filtered signal with said threshold level signal, and to make said suppression
unit suppress said noise signal.
3. A noise suppressor as claimed in Claim 2,
wherein said suppression unit 203 is further supplied with said detection signal (DT)
to be put into an active state within at least one of said speech and said non-speech
durations.
4. A noise suppressor as claimed in Claim 1, 2 or 3,
wherein said feature parameter calculating means (15) calculates, as said feature
parameter (ai), spectrum parameters representative of a spectrum of said internal input signal,
a pitch period of said internal input signal, and an average amplitude of said internal
input signal.
5. A noise suppressor according to claims 1, 2, 3, or 4, wherein said internal input
signal is divided into a sequence of frames each of which lasts for a predetermined
interval of time, said speech signal is generated by a sound source and has a spectrum
specified by at least one feature parameter and is divisible into a speech duration
and a non-speech duration, said noise suppressor comprises feature parameter calculating
means for calculating said at least one feature parameter to produce a feature parameter
signal representative of said at least one feature parameter and speech detection
means coupled to said feature parameter calculating means (15) for detecting said
speech and said non-speech durations in response to the feature parameter signal to
produce a detection signal representative of either one of said speech and said non-speech
durations,
average memory means is coupled to said speech detection means for memorizing an average
value of either one of power and an amplitude of said internal input signal within
said non-speech duration to produce an average signal representative of said average
value; and
said noise suppressing means (20) is coupled to said feature parameter calculating
means (15) said speech detection means, and said average calculating means for suppressing
said noise signal with reference to said feature parameter signal, said detection
signal, said average signal, and said internal input signal to produce said output
signal.
6. A noise suppressor operable in response to a feature parameter signal specifying a
speech signal and to a sound source signal (v(n)) representative of a sound source
of said speech signal to suppress a noise signal from the sound source signal and
to produce an output signal (v'(n)) substantially free from said noise signal, said
speech signal being divisible into a speech duration and a non-speech duration, said
sound source signal appearing in the form of an error signal which is produced on
the preprocessing by allowing an input signal to pass through an inverse filter controlled
by said feature parameter signal,
said noise suppressor being characterized by:
a noise suppressing circuit (50) for suppressing said noise signal from said sound
source signal with reference to said feature parameter signal to produce a noise-suppressed
signal (v'(n));
means (52) for producing said noise-suppressed signal as said output signal.
7. A noise suppressor as claimed in Claim 6, characterized by:
speech detection means (25') supplied with said feature parameter signals for detecting
said speech and said non-speech durations to produce a detection signal representative
of either one of said speech and said non-speech durations; and
average memory means (30') coupled to said speech detection means for memorizing an
average value of either one of power and an amplitude of said speech signal within
said non-speech duration to produce an average signal representative of said average
value;
said noise suppressing circuit (50) suppressing said noise signal with reference to
said average signal also.
1. Rauschunterdrückungseinrichtung, die mit einem internen Eingangssignal IN, das sowohl
ein Sprachsignal als auch ein Rauschsignal aufweist, versorgt wird, um ein Ausgangssignal
zu erzeugen, das im wesentlichen frei von dem Rauschsignal ist, wobei das Sprachsignal
von einer Schallquelle bestimmt wird, wobei die Rauschunterdrückungseinrichtung aufweist:
eine Merkmalparameterberechnungseinrichtung (15), die mit dem internen Eingangssignal
versorgt wird, zur Berechnung eines Merkmalparameters, der ein Merkmal des Sprachsignals
bestimmt, um ein Merkmalparametersignal zu erzeugen, das den Merkmalparameter darstellt,
und eine Rauschunterdrückungseinrichtung (20), die mit der Merkmalparameterberechnungseinrichtung
(15) verbunden ist, zur Entfernung des Rauschsignals aus dem internen Eingangssignal,
um das Ausgangssignal zu erzeugen,
wobei die Rauschunterdrückungseinrichtung aufweist:
eine Unterdrückungseinheit (203) zum Entfernen des Rauschsignals aus einem Restsignal
(e(n)) durch Schätzen des Rauschsignals, um ein rauschunterdrücktes Signal (e'(n))
zu erzeugen; und
eine Ausgangseinrichtung (204) zum Erzeugen des rauschunterdrückten Signals als das
Ausgangssignal; und gekennzeichnet ist durch
eine Filtereinrichtung (201), die mit dem Merkmalparametersignal (ai) und dem internen Eingangssignal versorgt wird, zum Filtern des internen Eingangssignals
(x(n)), um ein gefiltertes Signal zu erzeugen, das von dem Merkmalparameter (ai) abhängig ist und das die Schallquelle in dem Restsignal (e(n)) berechnet, das die
Differenz zwischen der Merkmalparametersignaldarstellung und dem internen Eingangssignal
darstellt; wobei die Unterdrückungseinheit mit der Filtereinrichtung (201) gekoppelt
ist.
2. Rauschunterdrückungseinrichtung nach Anspruch 1, wobei das Sprachsignal in eine Sprechdauer
und eine Nichtsprechdauer teilbar ist, wobei die Rauschunterdrückungseinrichtung (20)
ferner aufweist:
eine Sprachdetektionseinrichtung (25), die mit der Merkmalparameterberechnungseinrichtung
(15) gekoppelt ist, zur Berechnung der Sprech- und der Nichtsprechdauer als Antwort
auf das Merkmalparametersignal, um ein Detektionssignal zu erzeugen, das entweder
die Sprech- oder die Nichtsprechdauer darstellt;
eine Mittelwertberechnungseinrichtung (30), die mit der Sprachdetektionseinrichtung
gekoppelt ist, zum Berechnen eines Mittelwerts entweder der Leistung oder einer Amplitude
in der Nichtsprechdauer, um ein Mittelwertsignal zu erzeugen, das den Mittelwert darstellt;
wobei die Rauschunterdrückungseinrichtung (20) ferner aufweist:
eine Schwellwertberechnungseinrichtung (202) zum Berechnen des Schwellwerts aus dem
Mittelwertsignal, um die Unterdrückungseinheit (203) mit einem Schwellwertsignal (TH1)
zu versorgen, das den Schwellwert darstellt, um zu bewirken, daß die Unterdrückungseinheit
(203) das gefilterte Signal mit dem Schwellwertsignal vergleicht und daß die Unterdrückungseinheit
das Rauschsignal unterdrückt.
3. Rauschunterdrückungseinrichtung nach Anspruch 2, wobei die Unterdrückungseinheit (203)
ferner mit dem Detektionssignal (DT) versorgt wird, um in mindestens einer, nämlich
der Sprech- und/oder der Nichtsprechdauer in einen aktiven Zustand versetzt zu werden.
4. Rauschunterdrückungseinrichtung nach Anspruch 1, 2 oder 3, wobei die Merkmalparameterberechnungseinrichtung
(15) als den Merkmalparameter (ai) Spektralparameter, die ein Spektrum des internen Eingangssignals darstellen, eine
Grundfrequenzperiode des internen Eingangssignals und eine mittlere Amplitude des
internen Eingangssignals berechnet.
5. Rauschunterdrückungseinrichtung nach Anspruch 1, 2, 3 oder 4, wobei das interne Eingangssignal
in eine Sequenz von Rahmen geteilt wird, von denen jeder für ein vorbestimmtes Zeitintervall
andauert, das Sprachsignal von einer Schallquelle erzeugt wird und ein Spektrum aufweist,
das mindestens von einem Merkmalparameter bestimmt wird, und in eine Sprechdauer und
eine Nichtsprechdauer teilbar ist, die Unterdrückungseinrichtung aufweist: eine Merkmalparameterberechnungseinrichtung
zum Berechnen des mindestens einen Merkmalsparameters, um ein Merkmalparametersignal
zu erzeugen, das den mindestens einen Merkmalparameter darstellt, und eine Sprachdetektionseinrichtung,
die mit der Merkmalparameterberechnungseinrichtung (15) gekoppelt ist, zum Ermitteln
der Sprech- und der Nichtsprechdauer als Antwort auf das Merkmalparametersignal, um
ein Detektionssignal zu erzeugen, das entweder die Sprech- oder die Nichtsprechdauer
darstellt,
eine Mittelwertspeichereinrichtung mit der Sprachdetektionseinrichtung gekoppelt ist,
zum Speichern eines Mittelwerts entweder der Leistung oder einer Amplitude des internen
Eingangssignals in der Nichtsprechdauer, um ein Mittelwertsignal zu erzeugen, das
dem Mittelwert entspricht; und
die Rauschunterdrückungseinrichtung (20) mit der Merkmalparameterberechnungseinrichtung
(15), der Sprachdetektionseinrichtung und der Mittelwertberechnungseinrichtung gekoppelt
ist, zum Unterdrücken des Rauschsignals unter Berücksichtigung des Merkmalparametersignals,
des Detektionssignals, des Mittelwertsignals und des internen Eingangssignals, um
das Ausgangssignal zu erzeugen.
6. Rauschunterdrückungseinrichtung, die als Antwort auf ein Merkmalparametersignal, das
ein Sprachsignal bestimmt, und auf ein Schallquellensignal (v(n)), das eine Schallquelle
des Sprachsignals darstellt, betriebsfähig ist, um ein Rauschsignal aus dem Schallquellensignal
zu entfernen und ein Ausgangssignal (v'(n)) zu erzeugen, das im wesentlichen frei
von dem Rauschsignal ist, wobei das Sprachsignal in eine Sprechdauer und eine Nichtsprechdauer
teilbar ist, wobei das Schallquellensignal in Form eines Fehlersignals auftritt, das
bei der Vorverarbeitung dadurch erzeugt wird, daß ein Eingangssignal durch ein Umkehrfilter
laufen gelassen wird, das von dem Merkmalparametersignal gesteuert wird, wobei die
Rauschunterdrückungseinrichtung gekennzeichnet ist durch:
eine Rauschunterdrückungsschaltung (50) zum Entfernen des Rauschsignals aus dem Schallquellensignal
unter Berücksichtigung des Merkmalparametersignals, um ein rauschunterdrücktes Signal
(v'(n)) zu erzeugen;
eine Einrichtung (52) zum Erzeugen des rauschunterdrückten Signals als das Ausgangssignal.
7. Rauschunterdrückungseinrichtung nach Anspruch 6, gekennzeichnet durch:
eine Sprachdetektionseinrichtung (25'), die mit den Merkmalparametersignalen versorgt
wird, zum Ermitteln der Sprech- und der Nichtsprechdauer, um ein Detektionssignal
zu erzeugen, das entweder die Sprech- oder die Nichtsprechdauer darstellt; und
eine Mittelwertspeichereinrichtung (30'), die mit der Sprachdetektionseinrichtung
gekoppelt ist, zum Speichern eines Mittelwerts entweder der Leistung oder einer Amplitude
des Sprachsignals in der Nichtsprechdauer, um ein Mittelwertsignal zu erzeugen, das
den Mittelwert darstellt;
wobei die Rauschunterdrückungsschaltung (50) das Rauschsignal auch unter Berücksichtigung
des Mittelwertsignals unterdrückt.
1. Dispositif de suppression de bruit auquel est fourni un signal d'entrée interne (IN)
qui comprend à la fois un signal de parole et un signal de bruit pour produire un
signal de sortie sensiblement exempt dudit signal de bruit, ledit signal de parole
étant spécifié par une source sonore, ledit dispositif de suppression de bruit comprenant
des moyens de calcul de paramètre de caractéristique (15) auxquels est fourni ledit
signal d'entrée interne pour calculer un paramètre de caractéristique spécifiant une
caractéristique dudit signal de parole afin de produire un signal de paramètre de
caractéristique représentatif dudit paramètre de caractéristique, et des moyens de
suppression de bruit (20) couplés auxdits moyens de calcul de paramètre de caractéristique
(15) pour supprimer ledit signal de bruit dans ledit signal d'entrée interne afin
de produire ledit signal de sortie,
dans lequel lesdits moyens de suppression de bruit comprennent :
une unité de suppression (203) pour supprimer le signal de bruit dans un signal résiduel
(e(n)) en évaluant ledit signal de bruit afin de produire un signal à bruit supprimé
(e'(n)) ; et,
des moyens de sortie (204) pour produire ledit signal à bruit supprimé comme dit signal
de sortie ;
et qui est caractérisé par :
des moyens de filtrage (201) auxquels sont fournis ledit signal de paramètre de caractéristique
(ai) et ledit signal d'entrée interne pour filtrer ledit signal d'entrée interne (X(n))
afin de produire un signal filtré qui est dépendant dudit paramètre de caractéristique
(ai) et qui spécifie ladite source sonore en ce que ledit signal résiduel (e(n)) est
calculé, celui-ci représentant la différence entre ladite représentation de signal
de paramètre de caractéristique et ledit signal d'entrée interne ;
dans lequel l'unité de suppression est couplée auxdits moyens de filtrage (201).
2. Dispositif de suppression de bruit selon la revendication 1, ledit signal de parole
étant divisible en une durée de parole et une durée de non-parole, dans lequel ledit
dispositif de suppression de bruit (20) comprend en outre :
des moyens de détection de parole (25) couplés auxdits moyens de calcul de paramètre
de caractéristique (15) pour détecter lesdites durées de parole et de non-parole en
réponse au signal de paramètre de caractéristique afin de produire un signal de détection
représentatif de l'une desdites durées de parole et de non-parole ;
des moyens de calcul de moyenne (30) couplés auxdits moyens de détection de parole
pour calculer une valeur moyenne soit de puissance, soit d'amplitude, dans ladite
durée de non-parole afin de produire un signal de moyenne représentatif de ladite
valeur moyenne ;
lesdits moyens de suppression de bruit (20) comprenant en outre :
des moyens de calcul de niveau de seuil (202) pour calculer un niveau de seuil à partir
dudit signal de moyenne afin de fournir à ladite unité de suppression (203) un signal
de niveau de seuil (TH1) représentatif dudit niveau de seuil, afin de faire en sorte
que ladite unité de suppression (203) compare ledit signal filtré audit signal de
niveau de seuil, et afin de faire en sorte que ladite unité de suppression supprime
ledit signal de bruit.
3. Dispositif de suppression de bruit selon la revendication 2, dans lequel ladite unité
de suppression (203) reçoit en outre ledit signal de détection (DT) pour la mettre
à un état actif dans au moins l'une desdites durées de parole et de non-parole.
4. Dispositif de suppression de bruit selon la revendication 1, 2 ou 3, dans lequel lesdits
moyens de calcul de paramètre de caractéristique (15) calculent, comme dit paramètre
de caractéristique (ai), des paramètres de spectre représentatifs d'un spectre dudit signal d'entrée interne,
une période de hauteur de son dudit signal d'entrée interne, et une amplitude moyenne
dudit signal d'entrée interne.
5. Dispositif de suppression de bruit selon la revendication 1, 2, 3 ou 4, dans lequel
ledit signal d'entrée interne est divisé en une séquence de trames dont chacune dure
un intervalle de temps prédéterminé, ledit signal de parole est engendré par une source
sonore et a un spectre spécifié par au moins un paramètre de caractéristique et est
divisible en une durée de parole et une durée de non-parole, ledit dispositif de suppression
de bruit comprend des moyens de calcul de paramètre de caractéristique pour calculer
ledit au moins un paramètre de caractéristique afin de produire un signal de paramètre
de caractéristique représentatif dudit au moins un paramètre de caractéristique et
des moyens de détection de parole couplés auxdits moyens de calcul de paramètre de
caractéristique (15) pour détecter lesdites durées de parole et de non-parole en réponse
au signal de paramètre de caractéristique afin de produire un signal de détection
représentatif de l'une desdites durées de parole et de non-parole,
des moyens à mémoire de moyenne sont couplés auxdits moyens de détection de parole
pour mémoriser une valeur moyenne soit d'une puissance, soit d'une amplitude, dudit
signal d'entrée interne dans ladite durée de non-parole afin de produire un signal
de moyenne représentatif de ladite valeur moyenne ; et,
lesdits moyens de suppression de bruit (20) sont couplés auxdits moyens de calcul
de paramètre de caractéristique (15), auxdits moyens de détection de parole et auxdits
moyens de calcul de moyenne pour supprimer ledit signal de bruit en référence audit
signal de paramètre de caractéristique, audit signal de détection, audit signal de
moyenne, et audit signal d'entrée interne afin de produire ledit signal de sortie.
6. Dispositif de suppression de bruit pouvant être mis en fonctionnement en réponse à
un signal de paramètre de caractéristique spécifiant un signal de parole et à un signal
de source sonore (v(n)) représentatif d'une source sonore dudit signal de parole afin
de supprimer un signal de bruit dans le signal de source sonore et de produire un
signal de sortie (v'(n)) sensiblement exempt dudit signal de bruit, ledit signal de
parole étant divisible en une durée de parole et une durée de non-parole, ledit signal
de source sonore apparaissant sous la forme d'un signal d'erreur qui est produit dans
le prétraitement en permettant à un signal d'entrée de traverser un filtre inverse
commandé par ledit signal de paramètre de caractéristique, ledit dispositif de suppression
de bruit étant caractérisé par :
un circuit de suppression de bruit (50) pour supprimer ledit signal de bruit dans
ledit signal de source sonore en référence audit signal de paramètre de caractéristique
afin de produire un signal à bruit supprimé (V'(n)) ;
des moyens (52) pour produire ledit signal à bruit supprimé comme dit signal de sortie.
7. Dispositif de suppression de bruit selon la revendication 6, caractérisé par :
des moyens de détection de parole (25') auxquels sont fournis lesdits signaux de paramètre
de caractéristique pour détecter lesdites durées de parole et de non-parole afin de
produire un signal de détection représentatif de l'une desdites durées de parole et
de non-parole ; et,
des moyens à mémoire de moyenne (30') couplés auxdits moyens de détection de parole
pour mémoriser une valeur moyenne soit d'une puissance, soit d'une amplitude, dudit
signal de parole dans ladite durée de non-parole afin de produire un signal de moyenne
représentatif de ladite valeur moyenne ;
ledit circuit de suppression de bruit (50) supprimant ledit signal de bruit en référence
audit signal de moyenne également.