This application claims the priority benefit of Taiwan application serial no. 104116032, filed on May 20, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
Field of the Invention
The invention relates to a signal processing apparatus, and more particularly, to a voice signal processing apparatus and a voice signal processing method.
Description of Related Art
In general, hearing-impaired people can clearly hear low frequency signals but have trouble receiving high frequency voice signals (e.g., a consonant signal). In the conventional technology, such issue is generally solved by lowering a frequency of the high frequency signal and overlapping signal frames. Since a time length is extended after lowering the frequency of the signal, it is required to use an interpolation method for calculating signal values between two consecutive sampling signals. Because a characteristic of a sound signal is relatively similar to a characteristic of a sinusoidal wave, a signal distortion often occurs on a frequency-lowered signal if interpolation signal values are calculated by a common method for calculating arithmetic mean. Furthermore, during the conventional operation for overlapping the signal frames, whether their phases match to each other is usually not taken into consideration. Therefore, a condition where a part of the signals are added while another part of the signals are subtracted may occur on an overlapping section to cause the signal distortion. Worth yet, the signal distortion becomes even more serious as a magnitude for lowering frequency gets larger.
The invention is directed to a voice signal processing apparatus and a voice signal processing method, capable of effectively solving an issue of a signal distortion caused by a phase mismatching condition occurred when signal frames are overlapped in a process of further lowering a frequency of a sampling signal.
The voice signal processing apparatus of the invention includes a processing unit, which is configured to lower a sampling voice signal to generate a frequency-lowered signal including a sequence of original frequency-lowered signal frames, and generate corresponding renovating frequency-lowered signal frames according to the original frequency-lowered signal frames. Herein, each of the original frequency-lowered signal frames includes p sampling points. The processing unit determines a first sampling point of an mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to a phase reference sampling point number according to the phase reference sampling point number of an (m−1)th original frequency-lowered signal frame corresponding to a middle sampling point of an (m−1)th renovating frequency-lowered signal frame, uses q consecutive sampling points starting from the first sampling point phase-matched to the sampling point corresponding to the phase reference sampling point number as the sampling points of an mth renovating frequency-lowered signal frame, overlaps adjacent two of the renovating frequency-lowered signal frames to generate an overlapped voice signal, wherein the phase reference sampling point number is a number of the sampling point of the (m−1)th original frequency-lowered signal frame corresponding to the middle sampling point of the (m−1)th renovating frequency-lowered signal frame, p and q are positive integers, and m is a positive integer greater than 1.
In an embodiment of the invention, a frequency of the frequency-lowered signal is one fourth the frequency of the sampling voice signal, and a length of each of the renovating frequency-lowered signal frames is equal to one half a length of each of the original frequency-lowered signal frames.
In an embodiment of the invention, each of the adjacent two of the renovating frequency-lowered signal frames includes a 50% overlapping section.
In an embodiment of the invention, the processing unit further counts a first count value and a second count value according to sampling values of the sampling points of the mth original frequency-lowered signal frame, wherein when the sampling point corresponding to the sampling value being 0 or a sampling point adjacent to the sampling point corresponding to the sampling value being 0 is counted, the processing unit returns the first count value or the second count value to zero, the processing unit uses the first count value or the second count value of the mth original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as a reference value, and determines the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number according to the reference value.
In an embodiment of the invention, the processing unit further determine whether the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number. If the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the processing unit uses the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as the reference value, and uses a very-first-sampled sampling point among the sampling points of the mth original frequency-lowered signal frame where the first count value is equal to the reference value as the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number; and if the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is not less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the processing unit uses the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as the reference value, and uses a very-first-sampled sampling point among the sampling points of the mth original frequency-lowered signal frame where the second count value is equal to the reference value as the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number.
In an embodiment of the invention, the processing unit further multiplies the frequency-lowered signal by a Hamming window.
In an embodiment of the invention, the processing unit further calculates a value of an interpolation parameter function corresponding to each of the original frequency-lowered signal frames according to three consecutive sampling values of each of the original frequency-lowered signal frames, and calculates an interpolation value between adjacent two of the sampling points of each of the original frequency-lowered signal frames according to the value of the interpolation parameter function corresponding to each of the original frequency-lowered signal frames.
In an embodiment of the invention, the processing unit further determines whether the value of the interpolation parameter function is less than an upper limit value and greater than or equal to a lower limit value, and if the value of the interpolation parameter function is not less than the upper limit value or not greater than or equal to the lower range value, the processing unit corrects the value of the interpolation parameter function, wherein if the value of the interpolation parameter function is greater than or equal to the upper limit value, the processing unit corrects the value of the interpolation parameter function to be the upper limit value, and if the value of the interpolation parameter function is less than the lower limit value, the processing unit corrects the value of the interpolation parameter function to be the lower value.
In an embodiment of the invention, the sampling voice signal is generated by sampling an original voice signal, and the upper limit value and the lower limit value are associated with a frequency of the original voice signal and a sampling frequency for sampling the original voice signal.
In an embodiment of the invention, the processing unit further calculates the interpolation parameter function corresponding to each of the original frequency-lowered signal frames according to a trigonometric function relationship of the three consecutive sampling values of each of the original frequency-lowered signal frames, wherein the interpolation parameter function is a trigonometric function.
The voice signal processing method of the invention includes the following steps. A frequency of a sampling voice signal is lowered to generate a frequency-lowered signal including a sequence of original frequency-lowered signal frames. Herein, each of the original frequency-lowered signal frames includes p sampling points, wherein p is a positive integer. A first sampling point of an mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to a phase reference sampling point number is determined according to the phase reference sampling point number of an (m−1)th original frequency-lowered signal frame corresponding to a middle sampling point of an (m−1)th renovating frequency-lowered signal frame. Herein, m is a positive integer greater than 1, and the phase reference sampling point number is a number of the sampling point of the (m−1)th original frequency-lowered signal frame corresponding to the middle sampling point of the (m−1)th renovating frequency-lowered signal frame. The q consecutive sampling points starting from the first sampling point phase-matched to the sampling point corresponding to the phase reference sampling point number are used as the sampling points of an mth renovating frequency-lowered signal frame. Herein, q is a positive integer. Adjacent two of the renovating frequency-lowered signal frames are overlapped to generate an overlapped voice signal.
In an embodiment of the invention, a frequency of the frequency-lowered signal is one fourth the frequency of the sampling voice signal, and a length of each of the renovating frequency-lowered signal frames is equal to one half a length of each of the original frequency-lowered signal frames.
In an embodiment of the invention, each of the adjacent two of the renovating frequency-lowered signal frames includes a 50% overlapping section.
In an embodiment of the invention, the step of determining the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number according to the phase reference sampling point number of the (m−1)th original frequency-lowered signal frame corresponding to the middle sampling point of the (m−1)th renovating frequency-lowered signal frame includes the following steps. A first count value and a second count value are counted according to sampling values of the sampling points of the mth original frequency-lowered signal frame. Herein when the sampling point corresponding to the sampling value being 0 or a sampling point adjacent to the sampling point corresponding to the sampling value being 0 is counted, the corresponding first count value or the corresponding second count value is returned to zero. The first count value or the second count value of the mth original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is used as a reference value. The first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number is determined according to the reference value.
In an embodiment of the invention, the step of using the first count value or the second count value of the mth original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as the reference value includes the following steps. Whether the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is determined. If the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is used as the reference value. If the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is not less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is used as the reference value.
In an embodiment of the invention, if the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the voice signal processing method further includes: using a very-first-sampled sampling point among the sampling points of the mth original frequency-lowered signal frame where the first count value is equal to the reference value as the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number.
In an embodiment of the invention, if the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the voice signal processing method further includes: using a very-first-sampled sampling point among the sampling points of the mth original frequency-lowered signal frame where the second count value is equal to the reference value as the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number.
In an embodiment of the invention, the voice signal processing method includes multiplying the frequency-lowered signal by a Hamming window.
In an embodiment of the invention, the voice signal processing method includes the following steps. A value of an interpolation parameter function corresponding to each of the original frequency-lowered signal frames is calculated according to three consecutive sampling values of each of the original frequency-lowered signal frames. Whether the value of the interpolation parameter function is less than an upper limit value and greater than or equal to a lower limit value is determined, and if the value of the interpolation parameter function is not less than the upper limit value or not greater than or equal to the lower range value, the value of the interpolation parameter function is corrected. An interpolation value between adjacent two of the sampling points of each of the frequency-lowered signal frames is calculated according to the value of the interpolation parameter function corresponding to each of the frequency-lowered signal frames.
In an embodiment of the invention, if the value of the interpolation parameter function is greater than or equal to the upper limit value, the value of the interpolation parameter function is corrected to be the upper limit value, and if the value of the interpolation parameter function is less than the lower limit value, the value of the interpolation parameter function is calculated to be the lower value. Herein, the sampling voice signal is generated by sampling an original voice signal, and the upper limit value and the lower limit value are associated with a frequency of the original voice signal and a sampling frequency for sampling the original voice signal.
In an embodiment of the invention, the voice signal processing method includes: calculating the interpolation parameter function corresponding to each of the original frequency-lowered signal frames according to a trigonometric function relationship of the three consecutive sampling values of each of the original frequency-lowered signal frames, wherein the interpolation parameter function is a trigonometric function.
Based on the above, according to the embodiments of the invention, a first sampling point of an mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to a phase reference sampling point number is determined according to the phase reference sampling point number of an (m−1)th original frequency-lowered signal frame corresponding to a middle sampling point of an (m−1)th renovating frequency-lowered signal frame, and the q consecutive sampling points starting from the first sampling point phase-matched to the sampling point corresponding to the phase reference sampling point number are used as the sampling points of an mth renovating frequency-lowered signal frame. As a result, when the frequency of the sampling voice signal is further lowered (e.g., when the frequency is to be lowered to be one fourth), the issue of the signal distortion caused by the phase mismatching condition occurred when the signal frames are overlapped may still be effectively solved.
To make the above features and advantages of the present disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
Referring to
The processing unit 102 may select a part of sampling points from among the original frequency-lowered signal frames to obtain renovating frequency-lowered signal frames (e.g., renovating frequency-lowered signal frames WL1′ to WL4′ in
Specifically, a part of the sampling points of the original frequency-lowered signal frames may be obtained by executing an interpolation operation. The processing unit 102 may first calculate a value of an interpolation parameter function corresponding to each of the original frequency-lowered signal frames according to three consecutive known sampling values of each of the original frequency-lowered signal frames, and then calculate an interpolation value between adjacent two of known sampling points of each of the original frequency-lowered signal frames according to the value of the interpolation parameter function corresponding to each of the original frequency-lowered signal frames. Herein, the interpolation parameter function is a trigonometric function such as a sine function or a cosine function, but the invention is not limited thereto.
For instance, referring to
Herein, g is 0 or a positive integer, Cm(g) is a function value of the interpolation parameter function at a time-point g, and the interpolation parameter function Cm(g) is a trigonometric function.
Because noises may occur during the signal process of the voice signal processing apparatus, the calculated value of the interpolation parameter function may include noise components which influence an accuracy of the processing unit 102 for obtaining the interpolation value. The processing unit 102 may check whether the value of the interpolation parameter function suffers a noise interference by determining whether the value of the interpolation parameter function falls within a preset range. For example, whether the value of the interpolation parameter function is less than an upper limit value and greater than or equal to a lower limit value may be determined. If the value of the interpolation parameter function is not less than the upper limit value or is not greater than or equal to the lower limit value, it indicates that the value of the interpolation parameter function suffers the noise interference. As such, the processing unit 102 may correct the value of the interpolation parameter function, so as to remove the noise components included in the value of the interpolation parameter function. For example, if the value of the interpolation parameter function is greater than or equal to the upper limit value, the processing unit 102 may correct the value of the interpolation parameter function to be the upper limit value; if the value of the interpolation parameter function is less than the lower limit value, the processing unit 102 may correct the value of the interpolation parameter function to be the lower limit value; and if the value of the interpolation parameter function is less than the upper limit value and greater than or equal to the lower limit value, there is no need to correct the value of the interpolation parameter function. For instance, in the embodiment of
Namely, the upper limit value and the lower limit value in the embodiment of
After obtaining the value of the interpolation parameter function, the processing unit 102 may calculate the interpolation value between adjacent two of the sampling points of the original frequency-lowered signal frame according to the interpolation parameter function. Taking the embodiment of
In formula (3) and formula (4), n is 0 or a positive even number.
Similarly, the square points in
Herein, n is 0 or a positive even number, and correction of the value of the interpolation parameter function Cm′(n) may be represented by the following formula:
An interpolation point sm(4n+1) between the sampling point sm(4n) and the interpolation point sm(4n+2) and an interpolation point sm(4n+3) between the interpolation point sm(4n+2) and the sampling point sm(4n+4) in the original frequency-lowered signal frame Wm may respectively be represented by the following formulas:
In addition, the processing unit 102 may obtain the interpolation parameter function Cm″(n) according to the trigonometric function relationship of the sampling point sm(4n+4), the interpolation point sm(4n+6) and the sampling point sm(4n+8), and the corresponding interpolation parameter function Cm″(n) within the time range of the original frequency-lowered signal frame Wm may be represented by the following formula:
Herein, n is 0 or a positive even number, and correction of the value of the interpolation parameter function Cm″(n) may be represented by the following formula:
An interpolation point sm(4n+5) between the sampling point sm(4n+4) and the interpolation point sm(4n+6) and an interpolation point sm(4n+7) between the interpolation point sm(4n+6) and the sampling point sm(4n+8) in the original frequency-lowered signal frame Wm may respectively be represented by the following formulas:
By analogy, the interpolation value between the sampling points or the interpolation value between the sampling point and the interpolation point in each other original frequency-lowered signal frames may also be obtained by the same method, and persons skilled in the art should be able to infer their implementations based on teachings in the foregoing embodiment, which are not repeated hereinafter.
As described above, in the present embodiment, the interpolation value between the sampling points (or the interpolation value between the sampling point and the interpolation value) is estimated by using the trigonometric function, and the interpolation value between the adjacent two of the sampling points of the original frequency-lowered signal frame (or the interpolation value between the sampling point and the interpolation value which are adjacent to each other) is calculated according to the interpolation parameter function, the interpolation values are used to serve as sampling values of new sampling points between the known sampling points of the frequency-lowered signal. Because a characteristic of the trigonometric function is relatively similar to a characteristic of a sound signal, as compared to the conventional technology which simply obtains the interpolation value by using the arithmetic mean, a more accurate interpolation value may be obtained by the calculation used in the present embodiment to effectively avoid occurrences of the signal distortion on the frequency-lowered signal after the frequency is lowered.
In addition, each of said original frequency-lowered signal frames may include p sampling points (wherein p is a positive integer, and P may be equal to 4N−3 where N is a positive integer greater than 1 in the present embodiment), the processing unit 102 may use a number of a sampling point of an (m−1)th original frequency-lowered signal frame corresponding to a middle sampling point of an (m−1)th renovating frequency-lowered signal frame as a phase reference sampling point number, determine a first sampling point of the mth original frequency-lowered signal frame phase-matched to a sampling point corresponding to the phase reference sampling point number according to the phase reference sampling point number, and use q consecutive sampling points starting from the first sampling point as sampling points of an mth renovating frequency-lowered signal frame (wherein q is a positive integer, and q may be 2N−1 where N is a positive integer greater than 1 in the present embodiment), so that the middle sampling point of the (m−1)th renovating frequency-lowered signal frame is phase-matched to the initial sampling point of the mth renovating frequency-lowered signal frame, wherein m is a positive integer larger than 1. Accordingly, when a 50% signal frame overlapping operation is performed on the (m−1)th renovating frequency-lowered signal frame and the mth renovating frequency-lowered signal frame (i.e., for making each of the (m−1)th renovating frequency-lowered signal frame and the renovating frequency-lowered signal frame to include a 50% overlapping section), occurrences of the phase mismatching may be substantially reduced to solve the issue of the signal distortion.
Specifically, the processing unit 102 may count a first count value and a second count value according to the sampling values of the sampling points of the mth original frequency-lowered signal frame. Herein, when the sampling point corresponding to the sampling value being 0 or a sampling point adjacent to the sampling point corresponding to the sampling value being 0 (e.g., a previous one or a next one of the adjacent sampling points, but the invention is not limited thereto) is counted by the processing unit 102, the first count value or the second count value is returned to zero. Specifically, a method for counting aforesaid count values may be represented by the following formulas (13) to (16):
Among them, m is a positive integer greater than 1, n=0, 1, 2, . . . , 4N−4, N is a positive integer greater than 1, sm(n) is the sampling value of the sampling point of a number n of the mth original frequency-lowered signal frame, and PNm(n) is used to convert the sampling value sm(n) into values represented by “10”, “3” or “0”, wherein PNm(−1)=PNm(0). Cotm+(n) is the first count value corresponding to the sampling point of the number n of the mth original frequency-lowered signal frame, and Cotm−(n) is the second count value corresponding to the sampling point of the number n of the mth original frequency-lowered signal frame, wherein Cotm+(−1)=2N−2 and Cotm−(−1)=2N−2. In view of formulas (15) and (16), it can be known that, Cotm+(n) is an accumulated count value corresponding to the frequency-lowered signal in a positive half cycle, whereas Cotn−(n) is an accumulated count value corresponding to the frequency-lowered signal in a negative half cycle. As shown in formulas (13) to (16), in the present embodiment, the sampling value sm(n) being greater than 0, the sampling value sm(n) being equal to 0 and the sampling value sm(n) being less than 0 are set to 10, 3 and 0 respectively, the first count values corresponding to PNmD(n) being equal to 10 or 7 are returned to zero when the first count value Cotm+(n) is counted, and the second count values corresponding to PNmD(n) being equal to −10 or −3 are also returned to zero when the second count value Cotm−(n) is counted. Because the sampling value is set to be 3 when the sampling value sm(n) is equal to 0, positions of the values of PNmD(n) being equal to 10, 7, −10 or −3 will appear at positions of the sampling points adjacent to the sampling point where the sampling value sm(n) is equal to 0.
The processing unit 102 may use the first count value or the second value of the mth original frequency-lowered signal frame corresponding to the sampling point of the phase reference sampling point number obtained from the (m−1)th original frequency-lowered signal frame (which is obtained by the processing unit 102 which counts in the (m−1)th original frequency-lowered signal frame, and a counting method thereof is identical to the counting method used by the processing unit 102 in the mth original frequency-lowered signal frame) as a reference value, and determine the first sampling point of the mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to the phase reference sampling point number according to the reference value. For example, the processing unit 102 may determine whether the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, and such determination may be represented by the following formula (17):
Cotm-1+S≧Cotm-1−S (17)
Herein, Cotm-1+S is the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, and Cotm-1−S is the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number.
If the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, the processing unit 102 uses the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as the reference value, and uses a very-first-sampled sampling point among the sampling points whose first count values are equal to the reference value of the mth original frequency-lowered signal frame as the first sampling point. Aforesaid operations may be represented by the following formulas (18) and (19):
In view of formulas (18) and (19), it can be known that, when the first count value of the mth original frequency-lowered signal frame corresponding to the sampling point of the number n is equal to the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, nCot
Conversely, if the first count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number is not less than or equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number (i.e., formula (17) is not satisfied), the processing unit 102 uses the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number as the reference value, and uses a very-first-sampled sampling point among the sampling points of the mth original frequency-lowered signal frame corresponding to the second count value being equal to the reference value as the first sampling point. Aforesaid operations may be represented by the following formulas (20) and (21):
In view of formulas (20) and (21), it can be known that, when the second count value of the mth original frequency-lowered signal frame corresponding to the sampling point of the number n is equal to the second count value of the (m−1)th original frequency-lowered signal frame corresponding to the sampling point corresponding to the phase reference sampling point number, nCot
For instance, it is assumed that each of the original frequency-lowered signal frames WL1 to WL4 in
In order to locate an initial sampling point of the renovating frequency-lowered signal frame WL3′, the processing unit 102 may count the first count value Cot3+(n) of the original frequency-lowered signal frame WL3, so as to obtain the numbers of the sampling points whose first count values Cot3+(n) are equal to 18 (because the first count value Cot2+(188) of the original frequency-lowered signal frame WL2 corresponding to the sampling point of the number being 188 is less than the corresponding second count value Cot2−(188), the first count value Cot2+(188) is used as the reference value). As shown by the schematic diagram illustrating the frequency-lowered signal frame WL3 in
It should be noted that, because the original frequency-lowered signal frame WL1 is the first original frequency-lowered signal frame, the sampling points of the renovating frequency-lowered signal frame WL1′ may be any 201 consecutive sampling points selected from the original frequency-lowered signal frame WL1 (e.g., the sampling points starting from the number 100 to the number 300 in the present embodiment), and the number of the sampling point of the original frequency-lowered signal frame WL1 corresponding to the middle sampling point of the renovating frequency-lowered signal frame WL1′ may be used as the phase reference sampling point number (e.g., the sampling point of the number 200 in the present embodiment). In the present embodiment, the number of the first sampling point of the original frequency-lowered signal frame WL2 phase-matched to the middle sampling point of the original frequency-lowered signal frame WL1 is 188. Herein, a method for obtaining the first sampling point (the sampling point of the number 188) is similar to that used in foregoing embodiment, and person skilled in the art should be able to infer its implementation based on teachings in the foregoing embodiment, which are not repeated hereinafter.
After obtaining the renovating frequency-lowered signal frames, the processing unit 102 may then perform the 50% overlapping operation on the adjacent renovating frequency-lowered signal frames to generate an overlapped voice signal. Because the middle sampling point of each of the renovating frequency-lowered signal frames is phase-matched to the initial sampling point of the next renovating frequency-lowered signal frame, the issue of the signal distortion caused by the phase mismatching condition occurred when the signal frames are overlapped may be substantially solved. Furthermore, in some embodiments, after the renovating frequency-lowered signal frames corresponding to the original frequency-lowered signal frames are obtained, the frequency-lowered signal may be multiplied by a Hamming window to improve a continuity between the right-end and the left-end of the frequency-lowered signal. As shown by
Referring to
Referring back to
Referring to
In summary, according to the embodiments of the invention, a first sampling point of an mth original frequency-lowered signal frame phase-matched to the sampling point corresponding to a phase reference sampling point number is determined according to the phase reference sampling point number of an (m−1)th original frequency-lowered signal frame corresponding to a middle sampling point of an (m−1)th renovating frequency-lowered signal frame, and q consecutive sampling points starting from the first sampling point phase-matched to the sampling point corresponding to the phase reference sampling point number are used as the sampling points of an mth renovating frequency-lowered signal frame. As a result, when the frequency of the sampling voice signal is further lowered (e.g., when the frequency is to be lowered to be one fourth), the issue of the signal distortion caused by the phase mismatching condition occurred when the signal frames are overlapped may still be effectively solved.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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104116032 A | May 2015 | TW | national |
Number | Name | Date | Kind |
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20150049879 | Young | Feb 2015 | A1 |
20160210987 | Sugiyama | Jul 2016 | A1 |
Number | Date | Country | |
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20160343388 A1 | Nov 2016 | US |