Voice signal processing device

Abstract: Cepstrum calculating means (5) obtains a cepstrum of a voice signal and mean-value calculation means (7) makes equal the cepstrum output. Threshold setting means (10) sets a voice detection threshold level on the basis of the cepstrum mean-value output. A cepstrum addition section (8) adds cepstrum value exceeding the cepstrum mean-value. A comparator (9) compares the cepstru output from the cepstrum addition section (8) with the threshold output signal from the threshold setting means (10), thereby to output voice-detected signal.

Description: The present invention relates to a speech signal detection device and a speech signal detection method, in particular in connection with voice recognition techniques. Recently, speech (or voice) detection devices for detecting the presence/absence of a speech have been widely used for applications such as speech recognition, speaker recognition, equipment operation by speech, and input to computer by speech. Fig. 1 is a block diagram showing a prior art voice detection device, whose configuration and operation will be explained hereinafter. A power detection section 19 detects a power value in an input signal to render the value to be compared by a comparator 21, and then the comparator 21 compares the value with a predetermined set value of a threshold setting section 20 to output a voice-detected signal when the value is larger than the predetermined set value. According to the prior art voice detection device as described above, however, even if a voice input is small , when the input signal contains a noise other than the voice, a power detected by the power detection section 19 larger than the set value of the threshold setting section 20, causes the voice-detected signal to be outputted, thereby developing an inconvience of frequent erroneous detections. Using cepstral techniques is known in connection with voiced/unvoiced decision in speech signals. The article "Cepstrum pitch determination", A. Michael Noll, The Journal of the Acoustical Society of America, Vol.41, No.2, 1967, p293-309, for instance, teaches to ascertain the cepstrum of an input speech signal and to find out where this cepstrum has a peak. The article "Auswertung von Echtzeit-Ceptra zur schnellen Detektion von stimmhafter Laute" of M. Timme, H. Idler und T. Lay, Nachrichtentechnische Zeitschrift, 1973, Vol. 7, pp. 112 and following teaches to use a cepstrum of a speech signal for voiced/unvoiced decision in connection with speech recognition. It is the object of the present invention to provide an improved method of recognizing speech signals. This object is solved in accordance with the features of the independent claims, dependent claims are directed on preferred embodiments of the invention. With a configuration according to the present invention, cepstrum calculation means calculates a cepstrum value of an input signal to obtain the calculated signal and a cepstrum mean-value signal by the calculated signal. Then a voice detection is performed on the basis of a signal exceeding the cepstrum mean-value signal, and controlled by a threshold signal calculated and set by the cepstrum mean-value signal. Fig. 1 is a block diagram of a voice detection device of a prior art ; Fig. 2 is a block diagram of a voice detection device in an embodiment of the present invention; Fig. 3 is a block diagram of a voice detection device in an embodiment of another present invention; Fig. 4 is a cepstrum characteristic graph; Fig. 5 is a block diagram of a voice detection device in an embodiment of another present invention; Fig. 6 is a time-dependent cepstrum characteristic graph; Referring to drawings, an embodiment of the present invention will be explained hereinafter. Fig. 2 shows a block diagram of a voice detection device in an embodiment of the present invention. With reference to Fig. 2, the configuration and operation of the device will be explained. A voice signal is inputted into a cepstrum calculation section 1 as cepstrum calculation means which in turn obtains a cepstrum of the signal. The term "cepstrum" which is derived from the term "spectrum" is in this application symbolized by c(τ) and obtained by inverse-Fourier-transforming the logarithm of a short-time spectrum S(ω). The dimension of τ is time and τ(time) is named "quefrency" which is derived from the word "frequency". Then part of the cepstrum is supplied to a mean-value calculation section 2 as mean-value calculation means which in turn obtains a cepstrum mean-value. A voice detection section 3 as voice detection means is supplied with the cepstrum from the cepstrum calculation section 1 and the cepstrum mean-value from the mean-value calculation section 2. Then, the voice detection section 3 detects a peak of a cepstrum being equal to or more than the cepstrum mean-value, detects the presence/absence of a voice by the peak value, and when a cepstrum exceeding the cepstrum mean-value is larger than a threshold set value, generates a voice-detected signal. At that time, a threshold setting section 4 as threshold setting means generates a peak-value control signal having a value calculated according to a specified equation on the basis of the cepstrum mean-value from the mean-value calculation section 2, and specifies the minimum level of the voice detection in the voice detection section 3 according to the cepstrum mean-value. According to the present embodiment as described above, the device can detect accurately the peak of a cepstrum even when subjected to a noise, thereby allowing a voice detection to be performed with a high accuracy. That is, the present invention has a configuration comprising a cepstrum calculation section for calculating a cepstrum value from a voice signal, a mean-value calculation section for calculating a mean-value of the cepstrum at a set-quefrency interval, a voice detection section for determining the peak of the cepstrum and comparing the determined value with a reference value to discriminate the presence/absence of a voice, and a threshold setting section for setting the reference value of the voice detection section utilizing the mean-value of the cepstrum, with an effect that the cepstrum peak can be accurately detected even under an environment having noise, thereby allowing a voice detection to be performed with a high accuracy. Referring to drawings, an embodiment of another present invention will be explained hereinafter. Fig. 3 shows a block diagram of a voice detection device in the embodiment of the present invention. Fig. 4 shows a cepstrum of the cepstrum calculation section 1 in Fig. 3, which is expressed with an envelope, though actually a discrete value. The configuration and operation of the voice detection device of the present embodiment shown in Fig. 3 together with Fig. 4 will be explained. First, a voice signal is inputted into a cepstrum calculation section 5 which in turn obtains a cepstrum. Then, part of the cepstrum is supplied to a mean-value calculation section 7 which in turn obtains a cepstrum mean-value level m at the quefrency interval a-b shown in Fig. 3. A cepstrum addition section 8 is supplied with the cepstrum from the cepstrum calculation section 5 and the cepstrum mean-value from the mean-value calculation section 7. Then, the cepstrum addition section 8 adds a cepstrum value being equal to or more than the cepstrum mean-value level m at a quefrency width w within the scope of the quefrency interval a-b, and supplies the cepstrum-added result to a comparator 9. The comparator 9 is supplied with the cepstrum-added result from the cepstrum addition section 8 and a set output from a threshold setting section 10, and when the cepstrum-added result is larger than the threshold set value, outputs a voice-detected signal. At that time, the threshold setting section 10 calculates a threshold according to a specified equation on the basis of the cepstrum mean-value level m shown in Fig. 4, and supplies the threshold set value to be compared with the cepstrum-added result to the comparator 9. According to the present invention as described above, the cepstrum peak can be accurately detected and the dependence on the cepstrum shape near the cepstrum peak becomes less, so that the ability of the cepstrum peak detection becomes large, thereby allowing a voice detection to be performed with a high accuracy. Also, setting a threshold according to the cepstrum mean-value allows a voice detection to be performed without depending to the magnitude of an input signal. That is, the voice detection section is allowed to have a configuration comprising a cepstrum addition section for adding cepstrum when larger than the cepstrum mean-value, and a comparator for comparing the set value from the threshold setting section with the added result from the cepstrum addition section to perform a voice detection, with an effect that the dependence of the peak detection on the shape of the cepstrum peak becomes less, thereby allowing a voice detection to be performed with a high accuracy. An effect is further obtained that the determining of a threshold set value according to the cepstrum mean-value allows a voice detection to be performed without depending on the magnitude of an input signal. Referring to drawings, an embodiment of another present invention will be explained hereinafter. Fig. 5 shows a block diagram of a voice detection device in an embodiment of the present invention, and Fig. 6 shows a cepstrum output of a cepstrum calculation section 11. In Fig. 6, the a-b indicates a quefrency interval, the m₁ and m n are cepstrum mean-values at the interval a-b at the time of t₁ and t n , and the w is a peak detection width. Using Fig. 6, the configuration and operation of the embodiment shown in Fig. 5 will be explained. First, a voice signal is inputted into the cepstrum calculation section 11 which in turn obtains a cepstrum output. The, part of the cepstrum output is supplied to a mean-value calculations section 13 which in turn obtains a cepstrum mean-value at the quefrency interval a-b shown in Fig. 6. A memory group 17 having a plurality of n storage places is supplied with the cepstrum mean-value from the mean-value calculation section 13, stores the values from the cepstrum mean-value m₁ at the time t₁ to the cepstrum mean-value m n at the time t n shown in Fig. 6, and supplies the stored values to a cepstrum addition section 14. A memory group 16 having n-set storage places is supplied with the cepstrum output from the cepstrum calculation section 11, stores the cepstrum from the value at the time t₁ to the value at the time t n , and supplies the stored values to the cepstrum addition section 14. The cepstrum addition section 14 is supplied with the cepstrum from the memory 16 and the cepstrum mean-value from the memory 17, adds cepstrum values larger than the cepstrum mean-value at each time during from the time t₁ to the time t n and at the width w of the quefrency interval a-b shown in Fig. 6, and supplies the cepstrum-added result to a comparator 15. The comparator 15 is supplied with the cepstrum-added result from the cepstrum addition section 14 and a threshold-set value calculated by a threshold setting section 18, and when the cepstrum-added result is larger than the threshold-set value, outputs a voice-detected signal. At that time, according to the cepstrum mean-value at the time from t₁ to t n shown if Fig. 6, the threshold setting section 18 supplies the threshold-set value to be compared with the cepstrum-added result to the comparator 15. The memory groups 16 and 17 are in a condition that, when a new input is inputted into the memory groups, old data is shifted to the next storage place so that a plurality of data can always be referred in parallel. According to the present embodiment as described above, the referring of the time-dependent changes of the cepstrum peak allows a more accurate voice detection to be performed. As apparent by the above explanation, the present invention has a configuration comprising a cepstrum calculation section for calculating a cepstrum value from a voice signal, a mean-value calculation section for calculating a mean-value of the cepstrum at a set-quefrency interval, a voice detection section for determining the peak of the cepstrum and comparing the determined value with a reference value to discriminate the presence/absence of a voice, and a threshold setting section for setting the reference value of the voice detection section utilizing the mean-value of the cepstrum, with an effect that the cepstrum peak can be accurately detected even under an environment having noise, thereby allowing a voice detection to be performed with a high accuracy. That is , the voice detection section is allowed to have a configuration comprising a first memory group consisting of n sets for storing cepstrum, a second memory group consisting of n sets for storing the cepstrum mean-value, a cepstrum addition section for adding cepstrums when larger than the cepstrum mean-value, and a comparator for comparing the set value from the threshold setting section with the added result from the cepstrum addition section to perform a voice detection, with an effect that the accumulating of data in time series on the memory groups allows the time-dependent changes of cepstrum to be detected and a more accurate voice detection to be performed.

Claims: A speech signal detection device characterized in comprising: cepstrum calculating means (1, 5, 11) for obtaining a cepstrum of an input signal, mean-value calculation means (2, 7, 13) for obtaining from the cepstrum output from said cepstrum calculating means (1, 5, 11) a cepstrum mean value on a given quefrency interval; threshold setting means (4, 10, 18) for setting a voice detection threshold level on the basis of the cepstrum mean-value output from said mean-value calculation means (2, 7, 13), and voice detection means (3, 8, 9, 14-17) to which the cepstrum mean-value output from said mean-value calculation means (2, 7, 13), the cepstrum output from said cepstrum calculating means (1, 5, 11) and the threshold output signal from said threshold setting means (4, 10, 18) are supplied and which compares a cepstrum output exceeding said cepstrum mean-value output with said threshold output signal to detect the presence/absence of a speech signal in the input signal. 2. A signal detection device in accordance with claim 1, characterized in that said voice detection means (3, 8, 9, 14-17) has a cepstrum addition section (8, 14) for adding cepstrum value exceeding said cepstrum mean-value and a comparator (9, 15) for comparing the cepstrum-added output from said cepstrum addition section (8, 14) with said threshold output signal. A signal detection device in accordance with claim 1, characterized in that said voice detection means (3, 8, 9, 14-17) has: an n-set first memory group (16) for storing said cepstrum, a plurality of n second memory group (17) for storing said cepstrum mean-value, a cepstrum addition section (14) for adding the first memory output exceeding the output from the second memory (17) set corresponding to said first memory (16), and a comparator (15) for comparing the cepstrum-added output from said cepstrum addition section (14) with the threshold output signal from said threshold setting means (18). A speech signal detection method characterized in comprising the steps of: calculating a cepstrum for obtaining a cepstrum of an input signal, calculating a mean-value on a given quefrency interval of the cepstrum output from said cepstrum calculating step, setting a threshold for setting a voice detection threshold level on the basis of the cepstrum mean-value output from said mean-value calculation step, and detecting the presence/absence of speech signal in the input signal by comparing a cepstrum output exceeding said cepstrum mean-value output from said mean-value calculating step with said threshold output signal from said threshold setting step.

Inventors: KANE JOJI, NOHARA AKIRA, KANE, JOJI, NOHARA, AKIRA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: G10L3
IPC codes: G10L11