EP0335521A1
Expired / Lapsed
EP
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Voice activity detection
Assignee: LG Electronics Inc
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Filing: 1989-03-10
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Granted: —
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Expires: 2009-03-10
Abstract
Abstract Voice activity detector (VAD) for use in an LPC coder in a mobile radio system, uses autocorrelation coefficients R₀, R₁..... of the input signal, weighted and combined, to provide a measure M which depends on the power within that part of the spectrum containing no noise, which is thresholded against a variable threshold to provide a speech/no speech logic output. The measure is where H i are the autocorrelation coefficients of the impulse response of an Nth order FIR inverse noise filter derived from LPC analysis of previous non-speech signal frames. Threshold adaption and coefficient update are controlled by a second VAD responsive to rate of spectral change between frames.
Inventors
- 👤 Daniel Kenneth Freeman
- 👤 Ivan Boyd
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-25 03:49
CPC Classifications
G; G10; G10L; G10L25/00; G10L25/78; G10L25/84
Claims Analysis
Total Claims: 30
Claim 1
Independent Claim
83 words
Voice activity detection apparatus comprising means for receiving an input signal, means for estimating the noise signal component of the input signal, means for continually forming a measure M of the spectral similarity between a portion of the input signal and the noise signal component, and means for comparing a parameter derived from the measure M with a threshold value T to produce an output to indicate the presence or absence of speech in dependence upon whether or not that value is exceeded.
Claim 2
Dependent Claim
83 words
Voice activity detection apparatus comprising means for receiving an input signal, means for estimating the noise signal component of the input signal, means for continually forming a measure M of the spectral similarity between a portion of the input signal and the noise signal component, and means for comparing a parameter derived from the measure M with a threshold value T to produce an output to indicate the presence or absence of speech in dependence upon whether or not that value is exceeded.
Claim 3
Dependent Claim
83 words
Apparatus according to claim 1, in which the noise estimating means comprises means for computing the autocorrelation coefficients A i of the impulse response of an FIR filter having a response approximating the inverse of the short term spectrum of the noise signal component, and the measure forming means comprises means for computing the autocorrelation coefficients R i of the signal, means connected to receive R i and A i , and to calculate M therefrom, the parameter being the value of M.
Claim 4
Dependent Claim
7 words
Apparatus according to claim 2, in which
Claim 5
Dependent Claim
7 words
Apparatus according to claim 2, in which
Claim 6
Dependent Claim
50 words
Apparatus according to any one of claims 2 to 4, further comprising an input arranged to receive a second signal, similarly subject to noise, from which speech is absent, in which the A i computing means comprises LPC analysis means for deriving values of A i from the second signal.
Claim 7
Dependent Claim
85 words
Apparatus according to any one of claims 2 to 4, further comprising a buffer connected to store data from which the autocorrelation coefficients A i of the said filter response may be derived, in which the said filter response is periodically calculated from the signal by LPC analysis means, the apparatus being so connected and controlled that the measure M is calculated using the said stored data, and the said stored data is updated only from periods in which speech is indicated to be absent.
Claim 8
Dependent Claim
20 words
Apparatus according to any one of claims 1 to 4 in which the noise estimating means includes an adaptive filter.
Claim 9
Dependent Claim
41 words
Apparatus according to any one of claims 2 to 6 characterised in that the means for computing the autocorrelation coefficients of the signal are arranged to do so in dependence upon the autocorrelation coefficients of several successive portions of the signal.
Claim 10
Dependent Claim
15 words
Apparatus according to claim 1 in which the measure M is a spectral distortion measure.
Claim 11
Dependent Claim
15 words
Apparatus according to claim 9 in which the measure M is the Itakura-Saito Distortion measure.
Claim 12
Dependent Claim
28 words
Apparatus according to any one of the preceding claims, further comprising means for adjusting the said predetermined threshold T during periods when speech is indicated to be absent.
Claim 13
Dependent Claim
25 words
Apparatus detector according to claim 11, further comprising second voice activity detection means arranged to prevent adjustment of the threshold value when speech is present.
Claim 14
Dependent Claim
43 words
Apparatus detector as claimed in claim 11 or claim 12, in which the threshold value T is, when adjusted, adjusted to be equal to the mean of the measure plus a term which is a function of the standard deviation of the measure.
Claim 15
Dependent Claim
69 words
Voice activity detection apparatus comprising: means for continually forming a spectral distortion measure of the similarity between a portion of the input signal and earlier portions of the input signal and means for comparing the degree of variation between successive values of the measure with a threshold value to produce an output indicating the presence or absence of speech in dependence upon whether or not that value is exceeded.
Claim 16
Dependent Claim
69 words
Voice activity detection apparatus comprising: means for continually forming a spectral distortion measure of the similarity between a portion of the input signal and earlier portions of the input signal and means for comparing the degree of variation between successive values of the measure with a threshold value to produce an output indicating the presence or absence of speech in dependence upon whether or not that value is exceeded.
Claim 17
Dependent Claim
26 words
Apparatus as claimed in claim 14, wherein the degree of variation is measured as the standard deviation of a block of successive values of the measure.
Claim 18
Dependent Claim
38 words
Apparatus according to Claim 6 further comprising means for indicating the absence of speech to control the updating of the said stored data, the means for indicating the absence of speech being a second voice activity detection means.
Claim 19
Dependent Claim
24 words
Apparatus according to Claim 16 and Claim 13 in which the said second voice activity detection means controls both threshold adaption and data updating.
Claim 20
Dependent Claim
28 words
Apparatus according to Claim 13 or Claim 16 or Claim 17 in which said second voice activity detection means is apparatus according to Claim 14 or Claim 15.
Claim 21
Independent Claim
38 words
A method of detecting speech activity in a signal, comprising the steps of comparing the signal spectrum with an estimated noise spectrum, forming a variable measure of the spectral similarity therebetween, and comparing that measure with a threshold.
Claim 22
Independent Claim
38 words
A method of detecting speech activity in a signal, comprising the steps of comparing the signal spectrum with an estimated noise spectrum, forming a variable measure of the spectral similarity therebetween, and comparing that measure with a threshold.
Claim 23
Independent Claim
48 words
A method of detecting speech activity in a signal, comprising the steps of comparing the signal spectrum with a preceding portion of the signal, forming a variable measure of the spectral similarity therebetween, and comparing the degree of variation between successive values of the measure with a threshold.
Claim 24
Independent Claim
48 words
A method of detecting speech activity in a signal, comprising the steps of comparing the signal spectrum with a preceding portion of the signal, forming a variable measure of the spectral similarity therebetween, and comparing the degree of variation between successive values of the measure with a threshold.
Claim 25
Dependent Claim
19 words
Voice activity detection apparatus substantially as herein described, with reference to Figure 1 or Figure 2 or Figure 3.
Claim 26
Dependent Claim
19 words
Voice activity detection apparatus substantially as herein described, with reference to Figure 1 or Figure 2 or Figure 3.
Claim 27
Dependent Claim
12 words
Apparatus for encoding speech signals including apparatus according to any preceding claim.
Claim 28
Dependent Claim
10 words
Mobile telephone apparatus including apparatus according to any preceding claim.
Claim 29
Independent Claim
9 words
A method of detecting speech substantially as herein described.
Claim 30
Independent Claim
9 words
A method of detecting speech substantially as herein described.
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