Patent Application
20130325455
This invention relates generally to voice signal processing, and specifically to extracting a maximum phase component of a voice signal.
Discrete Fourier transforms and Z-transforms are commonly used to analyze time domain signals and functions. A discrete Fourier transform transforms a function into a frequency domain representation of the original function, which is often a function in the time domain. Typically, a discrete Fourier transform requires an input function that is discrete and whose non-zero values have a limited (i.e., finite) duration. Inputs for discrete Fourier transforms are often created by sampling a continuous function (e.g., a person's voice). A Z-transform converts a discrete time-domain signal, which is a sequence of real or complex numbers, into a complex frequency-domain representation.
Time domain functions, discrete Fourier transforms and Z-transforms are related in the sense that one can be derived from any of the other. In other words, a discrete Fourier transform or a Z-transform can be derived from a time signal, a discrete Fourier transform or a time signal can be derived from a Z-transform, and a Z-transform or a time signal can be derived from a discrete Fourier transform.
There is provided, in accordance with an embodiment of the present invention a method, including receiving a time domain voice signal, extracting a single pitch cycle from the received signal, transforming the extracted single pitch cycle to a frequency domain, identifying and correcting misclassified roots of the frequency domain, and generating, using the corrected roots, an indication of a maximum phase of the frequency domain.
There is also provided, in accordance with an embodiment of the present invention an apparatus, including a memory, and a processor coupled to the memory and configured to receive a time domain voice signal, to extract a single pitch cycle from the received signal, to transform the extracted single pitch cycle to a frequency domain, to identify and correct misclassified roots of the frequency domain, and to generate, using the corrected roots, an indication of a maximum phase of the frequency domain.
There is further provided, in accordance with an embodiment of the present invention a computer program product, the computer program product including a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code including computer readable program code configured to receive a time domain voice signal, computer readable program code configured to extract a single pitch cycle from the received signal, computer readable program code configured to transform the extracted single pitch cycle to a frequency domain, computer readable program code configured to identify and correcting misclassified roots of the frequency domain, and computer readable program code configured to generate, using the corrected roots, an indication of a maximum phase of the frequency domain.
The disclosure is herein described, by way of example only, with reference to the accompanying drawings, wherein:
In human speech, pronunciation of vowels typically comprises two steps. Initially, air flows through vocal chords causing the vocal chords to vibrate, and then the vibration is modulated in spaces such as the mouth, nasal cavity etc. Air flowing through the glottis (i.e., the vocal chords and the space between the folds) is called a “glottal flow”, and comprises a “maximum phase” (also referred to herein as a “vocal source”) where the glottis opens, and a “minimum phase” where the glottis closes. A single cycle, comprising an opening-phase and a closing-phase of the glottis is called a “pitch cycle” or a “glottal pulse”, and the point in time where the glottis closes is called a glottal closure instant (GCI).
Embodiments of the present invention provide methods and systems for extracting a maximum-phase component of a voice signal, as a representation of the opening-phase part of the vocal source. In some embodiments a single pitch cycle is first extracted from a time domain voice signal, and the extracted pitch cycle is then transformed to a frequency domain function. Misclassified roots (i.e., roots that are associated with a minimum phase of the extracted pitch cycle, but should be associated with the maximum phase of the pitch cycle, and vice versa) of the frequency domain function are identified, and a root scaling function is used to correct (i.e., reclassify) the misclassified roots. In some embodiments, an indication of the maximum phase (e.g., a time domain signal) can be derived from reclassified roots.
By accurately extracting the maximum phase of a voice signal, embodiments of the present invention can be used to develop automatic diagnosis-assistive solutions that can aid in detection and screening of early-stage voice pathology for a general population or for populations at risk. For example, early stage laryngeal diseases can be detected by analyzing the maximum phase of sustained vowel phonations.
Processor 24 typically comprises a general-purpose computer configured to carry out the functions described herein. Software operated by the processor may be downloaded to the memories in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of the processor may be carried out by dedicated or programmable digital hardware components, or by using a combination of hardware and software elements.
As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system”. Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.
Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).
Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.
The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
In an initial step 40 in the flow diagram, processor 24 receives voice signal 30. In the configuration shown in
In an extraction step 42, processor 24 applies a window function (also commonly referred to as an apodization function or a tapering function) that is configured to extract single pitch cycle 72 centered on a GCI 74 in voice signal 30. Graph 70 in
Using techniques known in the art, in an extraction step 44, processor 24 derives a Z-transform from extracted pitch cycle 72. Graph 80 in
In a second derivation step 48, processor 24 calculates a maximum-phase spectrum, which comprises a discrete Fourier transform derived from the maximum phase roots of the Z-transform. In a comparison step 50, the processor checks if any frequencies in the maximum phase spectrum have amplitudes greater than a reference signal such as maximum spectral envelope 102. As shown in
Graph 100 in
Amplitudes of the maximum-phase spectrum typically have values below the maximal phase spectrum. In other words, any amplitudes in the maximum-phase spectrum that is greater than a corresponding change in amplitude in the maximum-phase spectral envelope likely due to a given root 82 (i.e., associated with the amplitude greater than the maximal phase spectrum) that was incorrectly classified as being associated with the maximum phase.
Returning to comparison step 50, processor 24 checks if there are any angular frequencies in the maximum-phase spectrum whose amplitude is greater than a amplitude of a corresponding angular frequency in maximum spectral envelope 102. Graph 110 in
If, as shown in graph 112 (i.e., near angular frequency n/2), there are any differences greater than zero, then processor 24 calculates a root scaling function in a calculation step 52 to correct the roots 82, as explained in detail hereinbelow. The processor then applies the root scaling function to roots 82 (i.e., the roots of both the minimum and the maximum phases) in an application step 54, and the method continues with step 48.
In some embodiments, the root scaling function can be derived for example from difference 112 shown in
In some embodiments, processor 24 can iteratively search for the scalar function until a “correct” function is found (in other words, when the maximum phase roots of the spectrum are below zero). Assuming that E comprises a small value that processor 24 uses to changes the amplitude of the root scaling function, then processor 24 can iteratively search for the scaling function using the following sequence:
1−E, 1+E, 1−2*E, 1+2*E, 1−3*E, 1+3E . . .
For example, if E=0.01, then the iteration comprises:
0.99, 1.01, 0.98, 1.02, 0.97, 1.03 . . . 0.90, 1.10
The iteration stops upon first “correct” result, or when a limit for E is reached (0.1 in the example shown hereinabove). The inventors have found that a typical value for E is approximately 0.001*M, where M comprises a maximum value of the positive function before applying the scaling function.
Graph 110 shows a specific case where a single pair of conjugate roots drifted slightly, possibly due to numerical errors in calculating the roots of the Z-transform, just enough to falsely cross the unit circle. A simple “fix” (i.e., via the root scaling function) restores the correct maximum-phase component. In general, multiple pairs of roots may need to be manipulated.
In operation, upon applying the proper root scaling function with the proper scalar factor (i.e., following the iterative search described supra), the scaling function shifts relevant roots across the Z-plane, so that the spectrum of the maximum phase signal is corrected. This correction (i.e., via the root scaling function described hereinabove) is due to the spectrum comprising a function of the location of the roots of the Z-transform.
Returning to step 50, the method ends when there are any no angular frequencies in the maximum-phase spectrum (i.e., the initial maximum phase spectrum, or the maximum phase spectrum after applying the root scaling function) whose amplitude is greater than an amplitude of a corresponding angular frequency in maximum spectral envelope 102. In other words, all frequencies have been shifted to the genuine signal zone.
Graph 130 in
As described supra, an indication of the maximum phase (e.g., a time domain signal) can be derived using the reclassified roots (i.e., the roots for the corrected maximum-phase spectrum that is referenced in graph 130 (i.e.,
In the graphs shown in
As shown in signals 172, 182, 192 and 202, the typical signals tend to be asymmetric with an abrupt descent, whereas the pathological signals tend to be more symmetric with a gradual descent. Therefore, as discussed supra, embodiments of the present invention can be used to develop automatic diagnosis-assistive solutions that can aid in detection and screening of early-stage voice pathology.
The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.
