Microphone initialization enhancement for speech recognition

A method and arrangement for improved speech recognition in a telephonically challenging speakerphone in-car environment. The method includes receiving a signal from a microphone representative of speech to be recognized, performing detection of a transition in the signal indicative of switch on of the microphone, and, in response to the detection, performing speech recognition on the signal with reduced contribution from an initial portion thereof. The initial portion may be treated as optional speech, the speech recognition may be performed with a predetermined redundant sound, and a user may be requested to speak the predetermined redundant sound when speech recognition has fallen below a predetermined threshold. Thus, recognition may be made possible when otherwise it would not be possible, recognition match scoring will be increased as the low weighting given by deleted initial sounds will be eliminated and therefore confusion of the recognized phrase will be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of United Kingdom Patent Application No. 0414711.2 filed Jul. 1, 2004.

FIELD OF THE INVENTION

This invention relates to speech recognition, and more particularly to a microphone initialization enhancement for automated speech recognition systems.

BACKGROUND OF THE INVENTION

In the field of this invention it is known that many speaker phones and mobile phone car installations suppress the microphone while sound is being played out in order to eliminate echo and feedback. According to conventional teachings, the microphone remains in an off state until a relatively high volume audio signal is received. This microphone enablement technique causes the microphone to remain in an off state when a user speaks in a low to medium volume. Because the speaker phone or mobile kit does not react until after a high energy audio signal is received, any low level sounds at the start of the utterance can be lost. Accordingly, the system only receives a truncated part of the utterance resulting in a speech recognition of the utterance being unsuccessful.

This approach has the disadvantage that the spoken phrase is highly likely to be rejected outright or possibly confused with other candidate phrases. A need therefore exists for method of increasing speech recognition performance in such systems wherein the abovementioned disadvantage(s) may be alleviated.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there is provided a method of speech recognition for use with a system having a microphone. The method includes receiving a signal from the microphone representative of speech to be recognized, performing detection of a transition in the signal indicative of switch on of the microphone, and, in response to the detection, performing speech recognition on the signal with reduced contribution from an initial portion thereof.

In accordance with a second aspect of the present invention there is provided a speech recognition system for use with a system having a microphone. The system includes means for receiving a signal from the microphone representative of speech to be recognized, means for performing detection of a transition in the signal indicative of switch on of the microphone, and means for performing, in response to the detection, speech recognition on the signal with reduced contribution from an initial portion thereof.

It should be noted that various aspects of the invention can be implemented as a program for controlling computing equipment to implement the functions described herein, or a program for enabling computing equipment to perform processes corresponding to the steps disclosed herein. This program may be provided by storing the program in a magnetic disk, an optical disk, a semiconductor memory, any other recording medium, or can also be provided as a digitally encoded signal conveyed via a carrier wave. The described program can be a single program or can be implemented as multiple subprograms, each of which interact within a single computing device or interact in a distributed fashion across a network space.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly toFIG. 1, in a known speech recognition system (not shown), the system receives a waveform10resulting from speaking of the words “Balance of account”20. Because, as discussed above, the system microphone (not shown) is typically suppressed while sound is being played out in order to eliminate echo and feedback, the system does not react until after a high energy audio signal is received; therefore, sounds at the beginning of the utterance are lost. Thus, the recognition system hears “lance of account” which does not contain all of the sounds expected to be heard in “Balance of account”. Typically, such a speech recognition system is looking for a specific sequence of sounds and will either not match the expected phrase or will score the match with a low probability.

Referring now toFIG. 2, a telephone based automated speech recognition system for use by a user100in challenging telephony environments (such as in-car) includes a speakerphone arrangement200having a controller201which controls operation of a speaker202and microphone203. A speech recognition arrangement300is coupled to the speakerphone arrangement200and has a speech detector301, a speech recognition controller302and a speech recognition engine303.

The speech detector301serves to automatically detect and enable the following mode of operation: the speech detector301identifies if the profile of the audio energy received from the speakerphone arrangement200is silence or close to silence followed by a high energy edge (rapid transition caused by the microphone203switching on); then, this situation will be notified by the speech recognition controller302to the speech recognition engine303.

The speech recognition engine303will process the utterance but will, in light of the signal from the speech detector301, automatically modify its behavior to not expect to match the initial sounds of the utterance. In effect, the initial sounds will become an optional part of the utterance.

Another example is to say that the recognition engine will accept deletions of sounds at the start of the utterance. Exactly how much (time) of the utterance might be allowed to be missing may be established by tuning the system for optimum recognition.

Alternatively, the grammars and call flows of the speech recognition engine may be constructed to optionally accept a redundant word (such as “please”) at the start of every utterance. This word is defined with special purpose “sound sequences” for this method which allow all possible tail ends of the utterance to match.

When the system detects repeated failures, it suggests to the user that they use the “microphone enabling” word which has the effect that the first thing the user says to interrupt the system is not required to match.

Good recognition can proceed with the significant portion of the grammar after this redundant word.

The core of this alternative mode of operation is illustrated with reference toFIG. 3. As shown inFIG. 3, the speech recognition arrangement300receives a waveform410resulting from speaking of the words “Please balance of account”. Because, as discussed above, the microphone203is typically suppressed while sound is being played out in order to eliminate echo and feedback, the system does not react until a high energy audio signal is received. Thus, the recognition system receives “ease balance of account”, but it is expecting phrases such as:“Please balance of account” or“lease balance of account” or“ease balance of account”—(Match) or“se balance of account” or“balance of account”
Therefore the desired phrase is successfully recognised.

FIG. 4shows the steps of a method of speech recognition for use with a system having a microphone according to the present invention. At step401, a signal representative of a speech to be recognized is received from the microphone which was turned off before receiving the signal. At step402, an initial portion of the speech is identified. The initial portion contains omitted sounds. At step403, speech recognition is performed on the signal with reduced contribution from the initial portion of the speech. A quantity by which the contribution of the initial portion is reduced is a configurable parameter. When speech recognition has fallen below a predetermined threshold, at step404, a user is requested to speak a predetermined redundant word before an intended speech. The predetermined redundant word turns on the microphone and is user configurable. At step405, the intended speech after the predetermined redundant word is speech recognized.

It will be understood that this method can be implemented without modification to speech recognition system software, only the speech recognition controller being new in this alternative.

It will be understood that in this alternative, the special word (“please” in the above example) can be redefined to match alternate “baseform” sequences (as known in WVS—WebSphere™ Voice Server—terminology) which, in this case, are the various truncated endings of the sound. The special word will not be usable in other grammars where it is not permissible to accept truncated utterances.

It will be understood that the above-described preferred embodiment's method of increasing speech recognition performance with speaker phones and car kits provides the following advantages.

While the reliability of recognition may be reduced when compared with a good (microphone unsuppressed or full duplex) telephony situation, especially with short utterances, recognition will be made possible when it is often impossible without this method.

Recognition match scoring will be increased as the low weighting given by deleted initial sounds will be eliminated and therefore confusion of the recognized phrase will be reduced.

The method described with reference toFIG. 3has the advantage that no modifications are required to the system software but requires the cooperation of the user and may be most appropriate to expert and high value systems where the user has a lot to gain by making the system work for themselves.