WO2007040883A2 - Detecteur d'activite vocale - Google Patents

Detecteur d'activite vocale Download PDF

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Publication number
WO2007040883A2
WO2007040883A2 PCT/US2006/034350 US2006034350W WO2007040883A2 WO 2007040883 A2 WO2007040883 A2 WO 2007040883A2 US 2006034350 W US2006034350 W US 2006034350W WO 2007040883 A2 WO2007040883 A2 WO 2007040883A2
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WO
WIPO (PCT)
Prior art keywords
signal
delay
value
delay period
speech
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Application number
PCT/US2006/034350
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English (en)
Other versions
WO2007040883A3 (fr
Inventor
Shani Stern
Itzhak Avayu
Lev Levshits
Original Assignee
Motorola, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola, Inc. filed Critical Motorola, Inc.
Publication of WO2007040883A2 publication Critical patent/WO2007040883A2/fr
Publication of WO2007040883A3 publication Critical patent/WO2007040883A3/fr

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
    • G10L25/78—Detection of presence or absence of voice signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/17—Time-division multiplex systems in which the transmission channel allotted to a first user may be taken away and re-allotted to a second user if the first user becomes inactive, e.g. TASI
    • H04J3/175—Speech activity or inactivity detectors

Definitions

  • the present invention relates to a voice activity detector.
  • a VAD voice activity detector
  • a VAD delivers an output signal that takes one of two possible values, respectively indicating that speech is detected to be present ('S') or speech is not detected to be present ('NS').
  • the value of the output signal will change with time according to whether or not speech is detected to be present in the analysed signal.
  • a VAD is often incorporated in a speech communication device such as a fixed or mobile telephone, a radio or a like device.
  • a VAD is an important enabling technology for a variety of speech based applications such as speech recognition, speech encoding and hands free telephony.
  • the primary function of a VAD is to provide an ongoing indication of speech presence as well to identify the beginning and end of a segment of speech.
  • Devices such as automatic gain controllers employ a VAD to detect when they should operate in a speech present mode.
  • VADs operate quite effectively in a relatively quiet environment, e.g. a conference room, they tend to be less accurate in noisy environments, such as in road vehicles, and in consequence they may generate detection errors. These detection errors include 'false alarms' which produce a signal indicating speech when none is present and 'mis-detects' which do not produce a signal to indicate speech when speech is present in noise.
  • detection errors include 'false alarms' which produce a signal indicating speech when none is present and 'mis-detects' which do not produce a signal to indicate speech when speech is present in noise.
  • There are many known types of algorithm employed in VADs to detect speech A review of some different known types of VAD algorithms is given for example in 'Efficient voice activity detection algorithms using long-term speech information' in Speech Communication 42, (2004) pages 217-287. Each of the known algorithms has advantages and disadvantages.
  • VADs may tend to produce false ala ⁇ ns and others may tend to produce mis-detects. Some VADs may tend to produce both false alarms and mis-detects in noisy environments.
  • a VAD it is known to employ an analyser, which analyses a signal to determine whether or not speech is present, and in some cases, a state change delay which delays a change in state detected by the analyser (i.e. a state of speech being present or not present) from becoming effective until a delay period has elapsed.
  • the delay period is known in the art as a 'hangover' and is typically one or more additional speech frames analysed.
  • This delay period is applied, for example, to reduce the clipping of speech at the end of a speech segment (where speech energy often falls to zero over several frames) and to avoid false alarms due to transient noise blips which might be wrongly detected as the beginning of speech following a period of no speech.
  • the delay period or hangover applied by the state change delay is a constant delay period for each given transition type (speech 'S' to no speech 'NS' or 'NS' to 'S').
  • the delay period is set at about 7 or 8 frames for an 'S' to 'NS' transition and about 1 to 3 frames for an 'NS' to 'S' transition.
  • the present inventors have found that, unfortunately, a constant delay period as typically selected and applied in the prior art is not ideal in all circumstances.
  • a voice activity detector as defined in claim 1 of the accompanying claims. Further features of the present invention are as defined in the accompanying dependent claims and are disclosed in the embodiments of the invention to be described.
  • the present invention provides a voice activity detector which includes an analyser for analysing an input signal representing an audio signal to determine if speech is present in the represented audio signal and for producing an output state signal indicating whether or not speech is detected by the analyser and at least one state change delay which applies a delay period ('hangover') which has a variable value and is set adaptively according to a value of current signal quality indicated by an output signal from a signal quality estimator.
  • the signal quality estimator enables a current measure of analysed signal quality to be obtained.
  • the signal quality estimator may estimate current signal to noise ratio or other known signal quality parameter.
  • the delay period applied by the state change delay may be adaptively set to a value which suits the current circumstances, i.e. whether or not the signal quality is good and on the type of transition (state change) detected, e.g. either from 'S' to 'NS' or from 'NS' to 'S'.
  • a relatively long period may be used.
  • the delay period applied for such a transition in the prior art with poor signal quality may be too short to avoid speech clipping.
  • a relatively short period may beneficially be used.
  • the delay period applied for such a transition in the prior art may unnecessarily be too long and this can lead to a waste of valuable energy.
  • the VAD is used in a wireless communications device in conjunction with a transmitter or receiver which is switched on only when speech is detected, valuable battery energy is wasted if the transmitter or receiver is switched on for longer than necessary.
  • energy may be saved and interference may be minimised by use of a shortened delay period where the signal quality is detected to be relatively good.
  • a relatively short delay period may be used in the VAD of the invention. This beneficially allows the start of speech to be detected quickly in such conditions.
  • the fixed delay period applied in the prior art may unnecessarily be too long causing clipping at the start of a speech segment.
  • the delay period may be increased with reduced risk of not detecting the start of speech.
  • the delay period adaptively selected respectively for each of an 'S' to 'NS' transition and for a 'NS' to 'S' transition is integral to a number of speech frames analysed.
  • FIG. 1 is a block schematic diagram showing a voice activity detector embodying the present invention.
  • FIG. 2 is a block schematic diagram of a modified voice activity detector embodying the present invention.
  • Speech segments are the parts of a signal where speech is present. In the parts where no speech is present, the signal may be considered to consist of noise segments. Typically, a speech segment lasts for one to two seconds.
  • Frames are the consecutive units into which a signal is divided in order to be analysed to determine whether speech is present in the unit of the signal being analysed. Typically, the length of a frame is from 20 msec to 30 msec depending on the particular analysis procedure to be used.
  • FIG. 1 is a block schematic diagram showing a VAD (voice activity detector)
  • An input electrical signal Il to be analysed representing an audio signal
  • an analyser 101 which operates a voice activity sensing algorithm to analyse frames of the input signal to determine if speech is present or not in each frame.
  • the algorithm operated by the analyser 101 may be known per se.
  • the algorithm may be one of: (i) a pitch detection algorithm; (ii) an LPC (linear prediction coding coefficients) distance algorithm; and (iii) a cepstral distance algorithm.
  • the analyser 101 may be one of: (i) a pitch detection algorithm; (ii) an LPC (linear prediction coding coefficients) distance algorithm; and (iii) a cepstral distance algorithm.
  • the analyser 101 may be one of: (i) a pitch detection algorithm; (ii) an LPC (linear prediction coding coefficients) distance algorithm; and (iii) a cepstral distance algorithm.
  • the analyser 101 may be one of: (i) a pitch detection algorithm; (ii) an LPC (linear
  • the cepstral distance algorithm uses 'cepstral analysis' which is a well known non-linear technique to detect perceptual harmonic
  • the analyzer 101 computes a parameter
  • cep(i) is the i-th cepstral coefficient of the current
  • cep_noise(i) is the i-th cepstral coefficient of the noise.
  • N is the order of associated linear prediction coefficients.
  • the analyzer 101 calculates cep_noise(i) according to an internal decision from the VAD that no speech is present, and updates the calculation with a factor obtained from a first order IER (infinite impulse response filter). If the result is below a set threshold then the algorithm in the analyzer 101 gives a 'no speech' indication; otherwise 'speech' is determined to be present.
  • IER infinite impulse response filter
  • the analyser 101 produces an output state signal Ol having one of two possible values, namely a value 'S' (speech detected) or 'NS' (speech not detected).
  • the value of the output signal Ol can change with time between frames if a transition between speech and no speech segments is detected.
  • the output state signal Ol is applied to a state change delay 103.
  • the state change delay 103 detects whether there is a change of value, i.e. indicating an 'S' to 'NS' transition or an 'NS' to 'S' transition as appropriate. Where such a change is detected, the state change delay 103 maintains the present value of the output state signal 02 for a delay period ( 'hangover') consisting of one or more additional frames calculated in a manner to be described later.
  • An output state signal 02 is produced by the state change delay 103. If the change of value of the state signal Ol is still indicated to be correct after the applied delay period, the value of the state signal 02 is changed to match the changed value of the state signal 01. Thus, the state change delay 103 produces an output state signal O2 which has the same value as the output state signal Ol from the analyser 101 except that a change in the value of the state signal Ol is allowed in the state of the output state signal O2 only if the change is determined to be correct after the given delay period.
  • a value of the state signal Ol which has changed to a new value must be constant and equal to the new value for all frames of the delay period, otherwise the value of the output state signal O2 is unchanged (from the value immediately prior to the applied delay period).
  • the VAD 100 includes a signal quality estimator 105 and a delay calculator 113.
  • the signal quality estimator 105 includes a signal power estimator 109 and a noise power estimator 111.
  • the signal power estimator 109 and the noise power estimator 111 receive the input signal II.
  • the signal power estimator 109 estimates in a known manner a power value for a current frame of the received signal Il .
  • the current frame is the same as that analysed by the analyser 101.
  • the noise power estimator 111 estimates a noise value in a known manner.
  • the noise power estimator 111 may for example use a first order IIR filter as referred to earlier to carry out an estimation of the detected received power for the current frame in a known manner.
  • the noise power estimation is not carried out in every frame, but only in frames that are determined by the analyser 101 not to contain speech.
  • Signals representing the values estimated by the signal power estimator 109 and the noise power estimator 111 are delivered to a divider 112 which determines a value of the signal power value divided by the noise power value.
  • the divider 112 thereby produces an output signal 03 representing a signal to noise ratio as a signal quality value for the current frame.
  • the signal O3 is delivered to and stored by the delay calculator 113 and used by the delay calculator 113 in one of the ways described later.
  • An output signal 04 is produced by the delay calculator 113 and is delivered to the state change delay 103.
  • the delay period applied by the state change delay 103 is the latest value of delay value which the state change delay 103 has received from the delay calculator 113 as indicated by the signal 04.
  • the VAD 100 includes a current state detector 107 which receives either the output state signal Ol produced by the analyser 101 or the output state signal 02 produced by the state change delay 103.
  • the current state detector 107 thereby determines for the frame immediately before that currently being analysed by the analyser 101 whether a segment of speech or a segment of noise is present.
  • the type of segment detected indicates the current state of the VAD 100.
  • the current state detector 107 applies a current state signal indicating the detected current state to the delay calculator 113 accordingly.
  • the value of the current state signal applied by the current state detector 107 to the delay calculator 113 indicates speech present ('S'), i.e.
  • the delay calculator 113 is activated to calculate a first delay period by a first procedure using the signal 03 provided by the divider 112, e.g. in a manner to be described later.
  • the delay calculator 113 is activated to calculate a second delay period by a second procedure using the signal 03 provided by the divider 112, e.g. in a manner to be described later.
  • the first and second delay periods calculated by the delay calculator 113 can vary as the value of the signal 03 from the divider 112 changes.
  • each of the first and second delay periods are set adaptively, according to the measured signal quality as indicated by the signal 03, e.g. in a manner to be described later.
  • the first delay period may for example be in the range of from 2 frames to 30 frames, more particularly from 5 frames to 15 frames, and the second delay period may for example be in the range of from 1 frame to 5 frames.
  • the delay calculator 113, the state change delay 103 and the current state detector 107 may be incorporated within a common delay unit 117.
  • the common delay unit 117 and all other components of the VAD 100 may be fabricated in the form of an integrated circuit such as a semiconductor microprocessor programmed to carry out the functions of the VAD 100.
  • the delay calculator 113 operates an algorithm to calculate a delay period or 'hangover' to be applied currently by the state change delay 103 by employing a current value of the signal 03 which it receives from the signal quality estimator 105. Examples of how the delay period may be calculated by the delay calculator 113 are described as follows.
  • the delay calculator 113 may use the current signal quality value indicated by the signal 03 as follows.
  • the delay calculator 113 may calculate a first delay period which is an inverse function of the signal quality. In other words, when the signal 03 indicates a poor (low) signal quality, the first delay period is relatively high, and when the signal 03 indicates a relatively good (high) signal quality, the delay period is relatively low.
  • the first delay period applied may for example be in a range between a minimum delay period of 2 frames and a maximum delay period of 30 frames, more particularly between 5 and 15 frames. Each value of the first delay period is conveniently selected to be an integral number of frames.
  • the delay calculator 113 may use the received values of the signal 03 for consecutive frames to calculate a signal quality value averaged over a number of frames.
  • the delay calculator 113 may use the received signal 03 to calculate a first average signal quality value averaged over all frames for the current detected speech segment up to the frame immediately preceding that currently being analysed by the analyser 101 .
  • the delay calculator 113 may calculate a second average signal quality value averaged over a finite (fixed) number of frames, e.g. ten frames, up to the frame immediately preceding that currently being analysed by the analyser 101.
  • the delay calculator 113 may calculate for the current detected speech segment, for frames up to the frame immediately preceding that currently being analysed by the analyser 101, a maximum value of the first average signal quality value and/or a maximum value of the second average signal quality value.
  • One particular way in which the delay calculator 113 may suitably employ the first average signal quality value and the second average signal quality value is for example to calculate a first delay period Dl according to a relationship:
  • Dl a +(b/Qs)- cQm Equation 1
  • a, b and c are predetermined constants
  • Q s is an average value of the first signal quality value
  • Q m is a maximum value for the current detected speech segment of the second signal quality value.
  • the first delay period Dl is then conveniently chosen as an integral number of frames by rounding the result of Dl from Equation 1 to the next highest integer.
  • the delay calculator 113 may for example use the current value of the signal O3 in a particular form of the second procedure as follows.
  • the delay calculator 113 may calculate a second delay period D2 which is an increasing function of the signal quality value indicated by the signal 03. In other words, when the value of the signal O3 is relatively low, the second delay period D2 is set to be low, and when the value of the signal O3 is higher, the second delay period D2 is set to be higher.
  • the second delay period which is selected by the delay calculator 113 may, as noted earlier, be in a range between a minimum delay period of one frame and a maximum of five frames. The second delay period is conveniently selected to be an integral number of frames.
  • the delay period ('hangover') calculated for each frame by the delay calculator 113 is provided to the state change delay 103 by the signal O4 and is employed by the state change delay 103 on a frame by frame basis to update the delay period to be applied to delay any detected change in the current value of the signal Ol to be allowed in the output signal 02 until the applied delay period has elapsed.
  • VAD 100 embodying the invention We have compared the VAD 100 embodying the invention with a prior art voice activity detector using the same VAD analyser (analysis 101 in the VAD 100) and a known signal as the analysed input signal representing an audio signal.
  • the prior art detector used a fixed delay period of seven frames for an 'S' to 'NS' transition and two frames for a 'NS' to 'S' transition.
  • the results obtained showed better performance by the VAD 100 embodying the invention.
  • the results showed that there is much less clipping of speech segments where the signal quality is low, and, where the signal quality is suitably high, the delay periods may be shortened without affecting performance.
  • using such shortened delay periods when the measured signal quality is suitably high beneficially allows less processing power to be used (e.g. by reducing a period for which an associated transmitter or receiver is switched on) and this leads to a saving in battery life.
  • FIG. 2 is a block schematic diagram of a modified VAD 200 embodying the present invention.
  • the modification of this embodiment is an example of the use of multiple VADs to produce a single decision as to whether or not speech is present.
  • Such an arrangement and a procedure using it is the subject of a copending UK patent application No. GB0518213.4 by the present Applicant.
  • an input signal is applied in parallel to a first analyser 201, a second analyser 205 and a third analyser 209.
  • Each of the first analyser 201, the second analyser 205 and the third analyser 209 operates a voice activity sensing algorithm to analyse frames of the input signal to determine if speech is present or not.
  • the algorithms operated are different in each case although each of the algorithms may be known per se.
  • Output state signals are produced by each of the analysers 201, 205 and 209.
  • An output state signal 05 is produced by the analyser 201 and is applied to a state change delay 203.
  • An output state signal 06 is produced by the analyser 205 and is applied to a state change delay 207.
  • An output state signal 07 is produced by the analyser 209 and is applied to a state change delay 211.
  • the state change delay 203 produces an output state signal 08.
  • the state change delay 203 detects whether there is a change of value, i.e. indicating an 'S' to 'NS' transition or an 'NS' to 'S' transition as appropriate in the state signal 05 which it receives from the analyser 201. Where such a change is detected, the state change delay 203 maintains the present value of the output state signal 08 for a delay period ('hangover') consisting of one or more additional frames. If the change of value of the state signal 05 is still indicated to be correct after the applied delay period, the value of the state signal 08 is changed to match the changed value of the state signal O5.
  • the state change delays 207 and 211 operate in a manner similar to the state change delay 203 producing output state signals 09 and OIO respectively.
  • the VAD 200 includes a combiner 213 which receives as input signals the output state signals 08, 09 and OIO from the state change delays 203, 207 and 211 respectively.
  • the combiner 213 applies a combining algorithm to the signals 08 to OIO to produce a single output state signal Oil.
  • the combiner 213 may operate in one of the ways described by the Applicant in the copending UK patent application referred to earlier.
  • the output state signal Oil is applied to a further state change delay 215 which operates in a manner similar to the state change delay 203 producing an overall output state signal 012.
  • one or more, preferably all, of the state change delays 203, 207, 211 and 215 operate to apply a delay which is adaptively set in the manner described earlier with reference to FIG. 1 each using its own delay calculator (operating in a manner similar to the delay calculator 113 described earlier with reference to FIG. 1) based on an output signal from a signal quality estimator (operating in a manner similar to the signal quality estimator 105 described earlier with reference to FIG. 1).
  • the VADs 100 and 200 embodying the invention which have been described with reference to HGS. 1 and 2 may be used in any of the known applications in which voice activity detectors are used.
  • the VADs 100 and 200 may for example be used in landline telephony applications and in mobile communications, particularly in transmitters or receivers of portable and/or mobile communications terminals.
  • the VAD 100 or 200 may for example be used in conjunction with a transmitter or a receiver to determine when to switch the transmitter or receiver or a component thereof, e.g. an automatic gain control (AGC) circuit of a receiver, on and off.
  • AGC automatic gain control

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Computational Linguistics (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Human Computer Interaction (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Abstract

La présente invention concerne un détecteur d'activité vocale (100) comprenant un analyseur (101) qui analyse un signal d'entrée représentant un signal audio pour savoir si de la parole est présente dans le signal audio et pour produire un signal d'état de sortie (O1) correspondant, un temporisateur de changement d'état (103) pour recevoir un signal d'état de sortie (O1) de l'analyseur, pour détecter un changement de valeur du signal d'état de sortie reçu, et pour entretenir un état courant du signal d'état de sortie reçu jusqu'à échéance d'une période de temporisation définie de façon à produire un signal d'état de sortie (O2), et un évaluateur (105) pour évaluer une valeur de qualité courante du signal d'entrée analysé et pour produire un signal de sortie (O3) indiquant la valeur évaluée. En outre, le temporisateur de changement d'état (103) sert à appliquer une temporisation de valeur variable calculée au coup par coup en fonction d'une valeur de courant du signal de sortie (O3) de l'évaluateur de qualité du signal.
PCT/US2006/034350 2005-09-30 2006-09-02 Detecteur d'activite vocale WO2007040883A2 (fr)

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GB0519880.9 2005-09-30
GB0519880A GB2430853B (en) 2005-09-30 2005-09-30 Voice activity detector

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WO2007040883A2 true WO2007040883A2 (fr) 2007-04-12
WO2007040883A3 WO2007040883A3 (fr) 2007-06-21

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6522746B1 (en) * 1999-11-03 2003-02-18 Tellabs Operations, Inc. Synchronization of voice boundaries and their use by echo cancellers in a voice processing system

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Publication number Priority date Publication date Assignee Title
GB9912577D0 (en) * 1999-05-28 1999-07-28 Mitel Corp Method of detecting silence in a packetized voice stream
US7020257B2 (en) * 2002-04-17 2006-03-28 Texas Instruments Incorporated Voice activity identiftication for speaker tracking in a packet based conferencing system with distributed processing
US7412376B2 (en) * 2003-09-10 2008-08-12 Microsoft Corporation System and method for real-time detection and preservation of speech onset in a signal

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US6522746B1 (en) * 1999-11-03 2003-02-18 Tellabs Operations, Inc. Synchronization of voice boundaries and their use by echo cancellers in a voice processing system
US6526140B1 (en) * 1999-11-03 2003-02-25 Tellabs Operations, Inc. Consolidated voice activity detection and noise estimation
US6526139B1 (en) * 1999-11-03 2003-02-25 Tellabs Operations, Inc. Consolidated noise injection in a voice processing system
US7003097B2 (en) * 1999-11-03 2006-02-21 Tellabs Operations, Inc. Synchronization of echo cancellers in a voice processing system

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GB2430853A (en) 2007-04-04
GB0519880D0 (en) 2005-11-09
WO2007040883A3 (fr) 2007-06-21

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