Patent Application
20100131268
1. Field of the Invention
The present invention relates to communication equipment and, more specifically, to speech-recognition devices and communication systems employing the same.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Although the use of cell phones has been rapidly proliferating over the last decade, there are still circumstances in which the use of a conventional cell phone is not physically feasible and/or socially acceptable. For example, a relatively loud background noise in a nightclub, disco, or flying aircraft might cause the speech addressed to a remote party to become inaudible and/or unintelligible. Also, having a cell-phone conversation during a meeting, conference, movie, or performance is generally considered to be rude and, as such, is not normally tolerated. Today's response to most of these situations is to turn off the cell phone or, if physically possible, leave the noisy or sensitive area to find a better place for a phone call.
Problems in the prior art are addressed by a voice-estimation (VE) interface that probes the vocal tract of a user with sub-threshold acoustic waves to estimate the user's voice while the user speaks silently or audibly in a noisy or socially sensitive environment. In one embodiment, the VE interface is integrated into a cell phone that directs an estimated-voice signal over a network to a remote party. Advantageously, the VE interface enables the user to have a conversation with the remote party without disturbing other people, e.g., at a meeting, conference, movie, or performance, and enables the remote party to more-clearly hear the user whose voice would otherwise be overwhelmed by a relatively loud ambient noise due to the user being, e.g., in a nightclub, disco, or flying aircraft.
According to one embodiment, the present invention is an apparatus having: (i) a VE interface adapted to probe a vocal tract of a user; and (ii) a signal-converter (SC) module operatively coupled to the VE interface and adapted to process one or more signals produced by the VE interface to generate an estimated-voice signal corresponding to the user. The VE interface comprises a sub-threshold acoustic (STA) package adapted to direct STA bursts to the vocal tract and detect echo signals corresponding to the STA bursts. The estimated-voice signal is based on the echo signals.
According to another embodiment, the present invention is a method of estimating voice having the steps of: (A) probing a vocal tract of a user using a VE interface; and (B) processing one or more signals produced by the VE interface to generate an estimated-voice signal corresponding to the user. The VE interface comprises an STA package adapted to direct STA bursts to the vocal tract and detect echo signals corresponding to the STA bursts. The estimated-voice signal is based on the echo signals.
Other aspects, features, and benefits of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which:
VE interface 110 has one or more sensors (not explicitly shown) designed to collect one or more signals that characterize the vocal tract of person 102. In various embodiments, VE interface 110 might include (without limitation) one or more of the following sensors: a video camera, an infrared sensor or imager, a sub-threshold acoustic (STA) sensor, a millimeter-wave sensor, an electromyographic sensor, and an electromagnetic articulographic sensor. In a representative embodiment, VE interface 110 has at least an STA sensor.
Note that the shape and position of curve 101 are functions of background noise. More specifically, if the background noise is a “white” noise and its intensity increases, then curve 101 generally shifts up on the intensity scale. If the background noise is not “white,” i.e., has pronounced frequency bands, then the spectral shape of curve 101 might change accordingly. Furthermore, different people might have different physiological-perception thresholds.
With respect to VE interface 110, it is beneficial to have its STA functionality referenced to a physiological-perception threshold of a typical neighbor of person 102, and not to that of person 102. One reason for this type of referencing is that system 100 is designed with an understanding that, in certain modes of operation, VE interface 110 should not disturb other people around person 102. As a result, a physiological-perception threshold of a typical neighbor of person 102 ought to be factored in. In a representative embodiment, VE interface 110 operates so that, at a distance of about one meter, an average person does not perceive any bothersome effects of its operation. VE interface 110 might receive an input signal from a microphone configured to measure background acoustic noise and use that information to adjust its STA excitation pulses, e.g., so that their intensity is relatively high, but still remains imperceptible to a putative neighbor of person 102.
Referring back to
In one embodiment, VE interface 110 and SC module 120 are parts of a transceiver (e.g., cell phone) 108 connected to a wireless, wireline, and/or optical transmission system, network, or medium 128. Cell phone 108 uses the unified estimated-voice signal generated by SC module 120 to generate a communication signal 124 that can be transmitted, in a conventional manner, over network 128 and be received as part of a communication signal 138 at a remote transceiver (e.g., cell phone) 140. Transceiver 140 processes communication signal 138 and converts it into a sound 142 that phonates the estimated-voice signal. Transceiver 108 might have an earpiece 122 that can similarly phonate the estimated-voice signal for person 102. Earpiece 122 plays a sound that is substantially similar to sound 142, which enables person 102 to make adjustments to her speech so that it becomes better perceptible at remote transceiver 140. Earpiece 122 can be particularly useful when the speech of person 102 is silent speech. In various embodiments, transceiver 108 can be a walkie-talkie, a head set, or a one-way radio. In one implementation, earpiece 122 can be a regular speaker of a cell phone. In another implementation, earpiece 122 can be a separate speaker dedicated to providing audio feedback to person 102 about her own speech.
If the processing power of SC module 120 is relatively low, then additional processing outside transceiver 108 might be necessary to generate a unified estimated-voice signal that appropriately represents the signals generated by the various sensors of VE interface 110. For such additional processing, system 100 might use a signal processor (e.g., a server) 130 connected to network 128. In one implementation, signal processor 130 can employ various speech-recognition and/or speech-synthesis techniques. Representative techniques that can be used in signal processor 130 are disclosed, e.g., in U.S. Pat. Nos. 7,251,601, 6,801,894, and RE 39,336, all of which are incorporated herein by reference in their entirety.
In an alternative embodiment, SC module 120 can be implemented as part of a server connected to network 128. Signal processor 130 can be implemented in transceiver 140. One skilled in the art will appreciate that other arrangements having SC module 120 and signal processor 130 at various physical locations within system 100 are also possible. In one embodiment, signal 124 and/or signal 138 can carry a sequence of phonemes and be substantially analogous to a text-message signal. In one embodiment, signal 138 can be converted into text, which is then displayed on a display screen of transceiver 140 in addition to or instead of being played as sound 142. Alternatively, signal 138 can be a regular cell-phone signal similar to those conventionally received by cell phones. Similarly, signal 124 can be converted into text, which is then displayed on a display screen of transceiver 108 in addition to or instead of being played as sound on earpiece 122.
Cartilage structures of the larynx can rotate and tilt variously to change the configuration of the vocal folds. When the vocal folds are open, breathing is permitted. The opening between the vocal folds is known as the glottis. When the vocal folds are closed, they form a barrier between the laryngopharynx and the trachea. When the air pressure below the closed vocal folds (i.e., sub-glottal pressure) is sufficiently high, the vocal folds are forced open. As the air begins to flow through the glottis, the sub-glottal pressure drops and both elastic and aerodynamic forces return the vocal folds into the closed state. After the vocal folds close, the sub-glottal pressure builds up again, thereby forcing the vocal folds to reopen and pass air through the glottis. Consequently, the sub-glottal pressure drops, thereby causing the vocal folds to close again. This periodic process (known as phonation) produces a sound corresponding to the configuration of the vocal folds and can continue for as along as the lungs can build up sufficient sub-glottal pressure.
The sound produced by the vocal folds is modified as it passes through the upper portion of the vocal tract. More specifically, various chambers of the vocal tract act as acoustic filters and/or resonators that modify the sound produced by the vocal folds. The following principal chambers of the vocal tract are usually recognized: (i) the pharyngeal cavity located between the esophagus and the epiglottis; (ii) the oral cavity defined by the tongue, teeth, palate, velum, and uvula; (iii) the labial cavity located between the teeth and lips; and (iv) the nasal cavity. The shapes of these cavities and, therefore, their acoustic properties can be changed by moving the various articulators of the vocal tract, such as the velum, tongue, lips, jaws, etc.
Silent speech is a phenomenon in which the above-described machinery of the vocal tract is activated in a normal manner, except that the vocal folds are not being forced to oscillate. The vocal folds will not oscillate if they are (i) not sufficiently close to one another, (ii) not under sufficient tension, or (iii) under too much tension, or if the pressure differential across the larynx is not sufficiently large. A person can activate the machinery of the vocal tract when she speaks to herself, i.e., “speaks” without producing a sound or by producing a sound that is below the physiological-perception threshold. By going through a mental act of “speaking to oneself,” a person subconsciously causes the brain to send appropriate signals to the muscles that control the various articulators in the vocal tract while preventing the vocal folds from oscillating. It is well known that an average person is capable of silent speech with very little training or no training at all. One skilled in the art will also appreciate that silent speech is different from whisper.
Referring to
STA speaker 316 is designed to periodically (e.g., with a repetition rate of about 50 Hz or higher) or non-periodically emit short (e.g., shorter than about 1 ms) bursts of STA waves for probing the configuration of the user's vocal tract. In a representative configuration, a burst of STA waves enters the vocal tract through the slightly open mouth of the user and undergoes multiple reflections within the various cavities of the vocal tract. The reflected STA waves interfere with each other to form a decaying echo signal, which is picked up by STA microphone 318. In one embodiment, STA speaker 316 is a Model GC0101 speaker commercially available from Shogyo International Corporation of Syosset, N.Y., and STA microphone 318 is a Model SPM0204 microphone commercially available from Knowles Acoustics of Burgess Hill, United Kingdom. In various embodiments, various types of cell phones (e.g., non-foldable cell phones) can similarly be used to implement transceiver 108.
Referring to
In one embodiment, cell phone 300 might be configured to use conventional microphone 312 or a separate dedicated microphone (not explicitly shown) to determine the level of ambient acoustic noise and use that information to configure pulse generator 352 to set the intensity and/or frequency of the excitation pulses emitted by STA speaker 316. Since it is desirable not to disturb other people around the user of cell phone 300, the physiological-perception threshold of those people, rather than that of the user, ought to be considered for setting the parameters of the STA emission. Since the spectral shape and location of a physiological-perception threshold curve generally depends on the characteristics of ambient acoustic noise (see the description
Referring to
One skilled in the art will appreciate that drive circuit 350 and detect circuit 370 are merely exemplary circuits. In various embodiments, other suitable drive and detect circuits can similarly be used in cell phone 300 without departing from the scope and principles of the invention.
One skilled in the art will appreciate that echo signals analogous to echo signals 402 are produced when the user speaks audibly, rather than silently. As already indicated above, the vocal-tract configuration corresponding to a speech phone spoken silently is substantially the same as the vocal-tract configuration corresponding to the same speech phone spoken audibly, except that, during the silent speech, the vocal folds are not vibrating. As used herein, the term “speech phone” refers to a basic unit of speech revealed via phonetic speech analysis and possessing distinct physical and/or perceptual characteristics. For example, each of the different vowels and consonants used to convey human speech is a speech phone. Since an echo signal is a function of the geometry of the various cavities in the vocal tract and depends very little on whether the vocal folds are vibrating or not vibrating, an echo signal that is substantially similar to echo signal 402a is produced when the user speaks the vowel “ah” audibly, rather than silently. Similarly, an echo signal substantially similar to echo signal 402u is produced when the user speaks the vowel “yu” audibly, rather than silently. In general, a substantial similarity between the echo signals corresponding to silent and normal speech exists for other speech phones as well.
Method 500 has branches 510 and 520 corresponding to two different operating modes of SC module 120. If SC module 120 is in a “training” mode, then the processing of method 500 is directed by a mode-switch 502 to training branch 510 having steps 512-518. If SC module 120 is in a “work” mode, then the processing of method 500 is directed by mode-switch 502 to work branch 520 having steps 522-526. In one implementation, a user of cell phone 300 can generally manually reconfigure mode switch 502 from one mode to the other.
In the training mode, SC module 120 is configured to collect user-specific reference data that can then be used to process echo signals originating from that particular user during a subsequent occurrence of the work mode. If two or more different users intend to use the VE interface functionality of cell phone 300 at different times, then separate training sessions might be conducted for each individual user to collect the corresponding user-specific reference data. Cell phone 300 having multiple users might be configured to use an appropriate user-login procedure to be able to identify the current user and relay that identification to SC module 120.
At step 512 of training branch 510, SC module 120 sends a request to the user to silently speak one or more training phrases. A training phrase can be a sentence, a word, a syllable, or an individual speech sound. Each training phrase might have to be repeated several times to sample the natural speech variance inherent to that particular user. SC module 120 might use display screen 306 of cell phone 300 to convey to the user the contents of the training phrases and the appropriate speaking instructions.
At step 514, SC module 120 records a series of echo signals detected by cell phone 300 while the user silently speaks the various training phrases specified at step 512. Each of the recorded echo signals is generally analogous to echo signal 402 shown in
At step 516, SC module 120 processes the recorded echo signals to derive a plurality of reference echo responses (RERs). In one embodiment, each RER represents a different respective speech phone. SC module 120 might generate each RER by temporally aligning and then intensity averaging a plurality of echo signals corresponding to different occurrences of the same speech phone in the training phrase(s). In other embodiments of step 516, SC module 120 processes the recorded echo signals to more generally define a mapping procedure for mapping a signal space corresponding to echo signals onto a signal space corresponding to audio signals of the user's speech.
Note that each RER normally corresponds to a phoneme. As used herein, the term “phoneme” refers to a smallest unit of potentially meaningful sound within a given language's system of recognized sound distinctions. Each phoneme in a language acquires its identity by contrast with other phonemes for which it cannot be substituted without potentially altering the meaning of a word. For example, recognition of a difference between the words “level” and “revel” indicates a phonemic distinction in the English language between /l/ and /r/ (in transcription, phonemes are indicated by two slashes). Unlike a speech phone, a phoneme is not an actual sound, but rather, is an abstraction representing that sound.
Two or more different RERs can correspond to the same phoneme. For example, the “t” sounds in the words “tip,” “stand,” “water,” and “cat” are pronounced somewhat differently and therefore represent different speech phones. Yet, each of them corresponds to the same /t/. Furthermore, substantially the same perceptible audio sound (which corresponds to a plurality of audio sounds that are within the error bar of sound perception by the human ear) can be represented by several noticeably different RERs because that perceptible audio sound can generally be produced by several different configurations of the voice tract. The training phrases used at step 514 are preferably designed so that the phoneme corresponding to each particular RER is relatively straightforward to determine.
At step 518, SC module 120 stores the RERs generated at step 516 in a reference database corresponding to the user. As further explained below, the RERs and their corresponding phonemes are invoked during the signal processing implemented in work branch 520.
At step 522 of work branch 520, SC module 120 receives a stream of echo signals detected by cell phone 300 during an actual (i.e., non-training) silent-speech session. Each of the received echo signals is generally analogous to echo signal 402 shown in
At step 524, SC module 120 compares each of the received echo signals with the RERs stored at step 518 in a reference database to determine a closest match. In one embodiment, the closest match is determined by calculating a plurality of cross-correlation values, each based on a cross-correlation function between the echo signal and an RER. A cross-correlation value can be calculated, e.g., by (i) temporally aligning the echo signal and the RER; (ii) sampling each of them at a specified sampling rate, e.g., about 500 samples per millisecond; (iii) multiplying each sample of the echo signal by the corresponding sample of the RER; and (iv) summing up the products. Generally, the RER corresponding to a highest correlation value is deemed to be the closest match, provided that said correlation value is higher than a specified threshold value. If all calculated cross-correlation values fall below the threshold value, then the corresponding echo signal is deemed to be non-interpretable and is discarded.
In alternative embodiments of step 524, other suitable signal-processing techniques can be used to determine a closest match for each received echo signal. For example, spectral-component analyses, artificial neural-network processing, and/or various signal cross-correlation techniques can be utilized without departing from the scope and principles of the invention.
At step 526, based on the sequence of closest matches determined at step 524, SC module 120 generates an estimated-voice signal corresponding to the silent-speech session. In one embodiment, the estimated-voice signal is a sequence of time-stamped phonemes corresponding to the closest RER matches determined at step 524. Note that each phoneme is time-stamped with the time at which the corresponding echo signal was detected by cell phone 300.
Referring to
At step 612 of training branch 610, SC module 120 sends a request to the user to audibly (e.g., in a normal manner) say one or more training phrases. Each training phrase might have to be repeated several times to sample the natural speech variance inherent to that particular user. SC module 120 might use display screen 306 of cell phone 300 to convey to the user the contents of the training phrases and the appropriate speaking instructions.
At step 614, SC module 120 records a series of audio waveforms and a corresponding series of echo signals corresponding to the various training phrases specified at step 612. The audio waveforms are generated by conventional acoustic microphone 312 as it picks up the sound of the user's voice. At the same time, STA package 314 picks up the STA echo signals from the user's voice tract. BP filter 372 (see
At step 616, an artificial neural network of SC module 120 is trained using the audio waveforms and echo signals recorded at step 614 to implement a voice-estimation algorithm. In one embodiment, an echo signal is Fourier-transformed to generate a corresponding spectrum. As an example,
As further explained below, the trained artificial neural network of SC module 120 produced at step 616 is used during the signal processing implemented in work branch 620. In a representative embodiment, the artificial neural network might have about 500 artificial neurons organized in one or more neuron layers. A suitable processor that can be used to implement an artificial neural network in SC module 120 is disclosed, e.g., in U.S. Patent Application Publication No. 2008/0154815, which is incorporated herein by reference in its entirety.
At step 622 of work branch 620, SC module 120 receives a stream of echo signals detected by cell phone 300 during a silent-speech session. Each of the received echo signals is generally analogous to echo signal 402 shown in
At step 624, each of the received echo signals is applied to the trained artificial neural network to generate a corresponding audio waveform.
At step 626, SC module 120 uses the audio waveforms generated at step 624 are used to generate an estimated-voice signal corresponding to the silent-speech session. Additional speech-synthesis techniques might be employed in SC module 120 and/or signal processor 130 to further manipulate (e.g., merge, filter, discard, etc.) the audio waveforms to ensure that synthesized sound 142 has a relatively high quality.
In various embodiments, various features of methods 500 and 600 can be utilized to create an alternative signal-processing method that can be employed in SC module 120 and/or signal processor 130. For example, a signal processing method that does not have a training branch is contemplated. More specifically, earpiece 122 (see
Referring back to
In one embodiment, an STA package (such as STA package 314,
Various embodiments of system 100 can advantageously be used to phonate silent speech produced (i) in a noisy or socially sensitive environment; (ii) by a disabled person whose vocal tract has a pathology due to a disease, birth defect, or surgery; and/or (iii) during a military operation, e.g., behind enemy lines. Alternatively or in addition, various embodiments of system 100 can advantageously be used to improve the perception quality of normal speech when it is burdened by ambient acoustic noise. For example, if the noise level is relatively tolerable, then STA package 314 can be used as a secondary sensor to enhance the voice signal produced by conventional acoustic microphone 312. If the noise level is intermediate between relatively tolerable and intolerable, then acoustic microphone 312 can be used as a secondary sensor to enhance the quality of the estimated-voice signal generated based on the echo signals picked up by STA package 314. If the noise level is intolerable, then acoustic microphone 312 can be turned off, and the estimated-voice signal can be generated solely based on the echo signals picked up by STA package 314. In one embodiment, STA package 314 can be installed in a mouthpiece of scuba-diving gear, e.g., to enable a scuba diver to talk to other scuba divers and/or to the people that monitor the dive from a boat. The scuba diver can use a speaking technique that is similar to silent speech to produce audible speech at the intended receiver.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the described embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the principle and scope of the invention as expressed in the following claims.
Certain embodiments of the present invention may be implemented as circuit-based processes, including possible implementation on a single integrated circuit. As would be apparent to one skilled in the art, various functions of circuit elements may also be implemented as processing steps in a software program. Such software may be employed in, for example, a digital signal processor, micro-controller, or general-purpose computer.
Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value or range.
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.
It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present invention.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
Also, for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements.
