# Patent

## Title
Speech recognition apparatus and speech recognition method

## Abstract

A speech recognition apparatus and a speech recognition method are provided. In the invention, whether an original voice sampling signal corresponding to a target voice frame is a consonant signal is determined according to at least one of a ratio of an energy of a low-pass sampling signal to an energy of the original voice sampling signal and a ratio value of an energy of a second consonant frequency band signal.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 104102541, filed on Jan. 26, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a recognition apparatus, and more particularly, relates to a speech recognition apparatus and a speech recognition method.
Description of Related Art
In general, hearing-impaired people can clearly hear voice signals with low frequency but have trouble receiving voice signals with higher frequency (e.g., a consonant signal). In conventional determination method for the consonant signal, a signal processing is performed in a frequency domain by using the determination method mainly including a non real-time determination for the consonant signal and a real-time determination for the consonant signal. The non real-time determination for the consonant signal performs the determination mainly by using an energy and a zero-cross rate. The real-time determination for the consonant signal mainly determines whether the voice signal is the consonant signal according to whether a ratio of a high frequency signal to a total energy is greater than a fixed value and whether a ratio of a low frequency signal to the total energy is less than the fixed value. Although the conventional determination method for the consonant signal is capable of distinguishing the consonant signal and a noise signal, yet an accuracy of said method still fails to meet the actual demand.
SUMMARY OF THE INVENTION
The invention is directed to a speech recognition apparatus and a speech recognition method, which are capable of improving a recognition accuracy for the consonant signal.
A speech recognition apparatus of the invention includes a filter unit and a processing unit. The filter unit performs a low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band for a voice signal in order to generate a low-pass filter signal, a first band-pass filter signal and a second band-pass filter signal respectively. The processing unit is coupled to the filter unit, and divides the voice signal, the low-pass filter signal, the first band-pass filter signal and the second band-pass filter signal into a plurality of voice frames. Herein, each of the voice frames includes an N number of sampling signals, and N is a positive integer. The processing unit calculates energies of the sampling signals in a target voice frame in order to obtain an energy of an original voice sampling signal, an energy of the low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal, calculates a ratio value of the energy of the second consonant frequency band signal according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal, and determines whether the original voice sampling signal corresponding to the target voice frame is a consonant signal according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal.
In an embodiment of the invention, the processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is a noise signal according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal.
In an embodiment of the invention, the processing unit further determines whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively. If the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, the original voice sampling signal of the target voice frame is the noise signal.
In an embodiment of the invention, the processing unit further calculates an energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal, and calculates a ratio of the energy of the second consonant frequency band signal to the energy difference value in order to obtain the ratio value of the energy of the second consonant frequency band signal.
In an embodiment of the invention, the processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio, and according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio.
In an embodiment of the invention, if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within the preset energy ratio range and the ratio value of the energy of the second consonant frequency band signal is greater than the second preset ratio, the processing unit further calculates a weighted average of the energies of the voice frames having the original voice sampling signals previously determined as the noise signal in order to obtain a noise signal energy weighted average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average.
In an embodiment of the invention, a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame.
In an embodiment of the invention, the processing unit further calculates an average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame in order to obtain a low-pass sampling signal energy ratio average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the low-pass sampling signal energy ratio average is less than a preset average.
In an embodiment of the invention, the processing unit further calculates a weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal in order to obtain a consonant frequency band signal energy sum weighted average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average.
In an embodiment of the invention, a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame.
In an embodiment of the invention, the processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal is greater than or equal to a lower limit value.
In an embodiment of the invention, the processing unit further calculates a first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal and calculates an average zero-cross rate of the original voice sampling signals in the target voice frame and a plurality of the voice frames in front of the target voice frame in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively. The first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value.
In an embodiment of the invention, the processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the second zero-cross rate is greater than or equal to a preset zero-cross rate.
A speech recognition method of the invention includes the following steps. A low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band are performed for a voice signal in order to generate a low-pass filter signal, a first band-pass filter signal and a second band-pass filter signal respectively. The voice signal, the low-pass filter signal, the first band-pass filter signal and the second band-pass filter signal are divided into a plurality of voice frames. Herein, each of the voice frames includes an N number of sampling signals, and N is a positive integer. Energies of the sampling signals in a target voice frame are calculated in order to obtain an energy of an original voice sampling signal, an energy of the low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal. A ratio value of the energy of the second consonant frequency band signal is calculated according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal. Whether the original voice sampling signal corresponding to the target voice frame is a consonant signal is determined according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal.
In an embodiment of the invention, said speech recognition method further includes: determining whether the original voice sampling signal corresponding to the target voice frame is a noise signal according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal.
In an embodiment of the invention, said speech recognition method further includes the following steps. Whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively is determined. If the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, the original voice sampling signal of the target voice frame is the noise signal.
In an embodiment of the invention, said speech recognition method further includes the following steps. An energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal is calculated. A ratio of the energy of the second consonant frequency band signal to the energy difference value is calculated in order to obtain the ratio value of the energy of the second consonant frequency band signal.
In an embodiment of the invention, said speech recognition method further includes: determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio, and according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio.
In an embodiment of the invention, if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within the preset energy ratio range and the ratio value of the energy of the second consonant frequency band signal is greater than the second preset ratio, the speech recognition method further includes the following steps. A weighted average of the energies of the original voice sampling signals previously determined as the noise signal is calculated in order to obtain a noise signal energy weighted average. Whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average.
In an embodiment of the invention, a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame.
In an embodiment of the invention, said speech recognition method further includes the following steps. An average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame is calculated in order to obtain a low-pass sampling signal energy ratio average. Whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to whether the low-pass sampling signal energy ratio average is less than a preset average.
In an embodiment of the invention, said speech recognition method further includes the following steps. A weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal is calculated in order to obtain a consonant frequency band signal energy sum weighted average. Whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average.
In an embodiment of the invention, a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame.
In an embodiment of the invention, said speech recognition method further includes: determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal is greater than or equal to a lower limit value.
In an embodiment of the invention, said speech recognition method further includes the following steps. A first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal are calculated and an average zero-cross rate of the original voice sampling signals in the target voice frame and a plurality of the voice frames in front of the target voice frame is calculated in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate. The first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value. Whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively.
In an embodiment of the invention, said speech recognition method further includes: determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the second zero-cross rate is greater than or equal to a preset zero-cross rate.
Based on the above, in the embodiments of the invention, whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to at least one of the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal. As a result, occurrences of the situation where the original voice sampling signal is mistakenly determined as the consonant signal may be reduced to improve the recognition accuracy for the consonant signal.
To make the above features and advantages of the invention more comprehensible, several embodiments accompanied with drawings are described in detail as follows.



BRIEF DESCRIPTION OF THE DRAWINGS
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.
FIG. 1 is a schematic view illustrating a speech recognition apparatus according to an embodiment of the invention.
FIGS. 2A and 2C are schematic flowcharts illustrating a speech recognition method according to an embodiment of the invention.



DESCRIPTION OF THE EMBODIMENTS
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 FIG. 1, FIG. 1 is a schematic view illustrating a speech recognition apparatus according to an embodiment of the invention. The speech recognition apparatus includes a filter unit 102 and a processing unit 104, and the filter unit 102 is coupled to the processing unit 104. The filter unit 102 may perform a low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band for a voice signal S1 in order to generate a low-pass filter signal S4, a first band-pass filter signal S2 and a second band-pass filter signal S3 respectively. The filter unit 102 may be implemented by a low-pass filter and a band-pass filter, for example; and the processing unit 104 may be implemented by a central processing unit, for example. In the present embodiment, a cutting-off frequency of the low-pass filtering is 0 to 2 kHz, and the first consonant frequency band and the second consonant frequency band are 2 kHz to 4 kHz and 4 kHz to 10 kHz respectively, but the invention is not limited thereto.
The processing unit 104 may sample the voice signal S1, the low-pass filter signal S4, the first band-pass filter signal S2 and the second band-pass filter signal S3, and divide the voice signal S1, the low-pass filter signal S4, the first band-pass filter signal S2 and the second band-pass filter signal S3 into a plurality of voice frames. Herein, each of the voice frames may include an N number of sampling signals of the voice signal S1, an N number of sampling signals of the low-pass filter signal S4, an N number of sampling signals of the first band-pass filter signal S2 and an N number of sampling signals of the second band-pass filter signal S3. The processing unit 104 may further calculate energies of the sampling signals in each of the voice frames in order to obtain an energy of an original voice sampling signal, an energy of a low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal. Herein, the energy of the original voice sampling signal, the energy of the low-pass sampling signal, the energy of the first consonant frequency band signal and the energy of the second consonant frequency band signal are corresponding to the energies of the sampling signals of the voice signal S1, the sampling signals of the low-pass filter signal S4, the sampling signals of the first band-pass filter signal S2 and the sampling signals of the second band-pass filter signal S3 in the voice frames respectively. After obtaining the energy of the original voice sampling signal, the energy of the low-pass sampling signal, the energy of the first consonant frequency band signal and the energy of the second consonant frequency band signal, the processing unit 104 may determine whether the original voice sampling signal corresponding to each of the voice frames is a noise signal according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal.
Specifically, the processing unit 104 may determine whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively. If the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, the original voice sampling signal of a target voice frame is the noise signal.
For instance, a method for the processing unit 104 to determine whether the original voice sampling signal corresponding to the target voice frame (e.g., a mth voice frame, where m is a positive integer) is the noise signal may include use of the following formulas:




  
    
      
        0.7
        <
        
          
            EB
            ⁢
            
              
            
            ⁢
            
              1
              m
            
          
          
            EB
            ⁢
            
              
            
            ⁢
            
              2
              m
            
          
        
        <
        1.3
      
    
    
      
        (
        1
        )
      
    
  
  
    
      
        0.25
        <
        
          
            EB
            ⁢
            
              
            
            ⁢
            
              2
              m
            
          
          
            E
            m
          
        
        <
        0.5
      
    
    
      
        (
        2
        )
      
    
  
  
    
      
        0.25
        <
        
          
            EB
            ⁢
            
              
            
            ⁢
            
              1
              m
            
          
          
            E
            m
          
        
        <
        0.5
      
    
    
      
        (
        3
        )
      
    
  




Herein, EB1m is the energy of the first consonant frequency band signal, EB2m is the energy of the second consonant frequency band signal and Em is the energy of the original voice sampling signal. When formulas (1), (2) and (3) are all satisfied, the processing unit 104 may determine that the original voice sampling signal of the mth voice frame is the noise signal.
After determining the original voice sampling signal of the target voice frame as the noise signal, the processing unit 104 further calculates a weighted average of the energies of the voice frames having the original voice sampling signals previously determined as the noise signal in front of the target voice frame in order to obtain a noise signal energy weighted average, and determines whether the original voice sampling signal corresponding to the target voice frame is a consonant signal according to whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average.
For instance, the noise signal energy weighted average may be obtained by calculating the weighted average of the energies of three voice frames having the original voice sampling signals previously determined as the noise signal in front of the target voice frame. Assuming that the three voice frames recently determined as the noise signal in front of the mth voice frame are a (m−10)th voice frame, a (m−12)th voice frame and a (m−20)th voice frame, respectively, the noise signal energy weighted average AKm corresponding to the mth voice frame may be represented by the following formula:




  
    
      
        
          AK
          m
        
        =
        
          
            
              a
              ⁢
              
                
              
              ⁢
              0
              ×
              
                E
                
                  m
                  -
                  10
                
              
            
            +
            
              a
              ⁢
              
                
              
              ⁢
              1
              ×
              
                E
                
                  m
                  -
                  12
                
              
            
            +
            
              a
              ⁢
              
                
              
              ⁢
              2
              ×
              
                E
                
                  m
                  -
                  20
                
              
            
          
          
            
              a
              ⁢
              
                
              
              ⁢
              0
            
            +
            
              a
              ⁢
              
                
              
              ⁢
              1
            
            +
            
              a
              ⁢
              
                
              
              ⁢
              2
            
          
        
      
    
    
      
        (
        4
        )
      
    
  




Herein, Em-10, Em-12 and Em-20 are the energies of the original voice sampling signals of the (m−10)th voice frame, the (m−12)th voice frame and the (m−20)th voice frame respectively; and a0, a1 and a2 are weight values corresponding to the (m−10)th voice frame, the (m−12)th voice frame and the (m−20)th voice frame respectively. The weight values a0, a1 and a2 may be fixed values or variable values. For instance, a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal may change with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame. For example, in the present embodiment, the weighted values a0, a1 and a2 may change with the different lengths of the interval from each of the voice frames to the mth voice frame. The original voice sampling signal corresponding to the mth voice frame may be determined as the consonant signal when the noise signal energy weighted average AKm satisfies the following formula:

Em>AKm  (5)

In addition, the processing unit may calculate a weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal in order to obtain a consonant frequency band signal energy sum weighted average, and determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average. For instance, the consonant frequency band signal energy sum weighted average may be obtained by calculating the weighted average of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals in three voice frames having the original voice sampling signals previously determined as the noise signal in front of the target voice frame. Assuming that the three voice frames recently determined as the noise signal in front of the mth voice frame are a (m−10)th voice frame, a (m−12)th voice frame and a (m−20)th voice frame, respectively, the consonant frequency band signal energy sum weighted average ASm corresponding to the mth voice frame may be represented by the following formula:




  
    
      
        
          AS
          m
        
        =
        
          
            
              
                
                  
                    c
                    ⁢
                    
                      
                    
                    ⁢
                    0
                    ×
                    
                      (
                      
                        
                          EB
                          ⁢
                          
                            
                          
                          ⁢
                          
                            1
                            
                              m
                              -
                              10
                            
                          
                        
                        +
                        
                          EB
                          ⁢
                          
                            
                          
                          ⁢
                          
                            2
                            
                              m
                              -
                              10
                            
                          
                        
                      
                      )
                    
                  
                  +
                  
                    c
                    ⁢
                    
                      
                    
                    ⁢
                    1
                    ×
                  
                
              
            
            
              
                
                  
                    (
                    
                      
                        EB
                        ⁢
                        
                          
                        
                        ⁢
                        
                          1
                          
                            m
                            -
                            12
                          
                        
                      
                      +
                      
                        EB
                        ⁢
                        
                          
                        
                        ⁢
                        
                          2
                          
                            m
                            -
                            12
                          
                        
                      
                    
                    )
                  
                  +
                  
                    c
                    ⁢
                    
                      
                    
                    ⁢
                    2
                    ×
                    
                      (
                      
                        
                          EB
                          ⁢
                          
                            
                          
                          ⁢
                          
                            1
                            
                              m
                              -
                              20
                            
                          
                        
                        +
                        
                          EB
                          ⁢
                          
                            
                          
                          ⁢
                          
                            2
                            
                              m
                              -
                              20
                            
                          
                        
                      
                      )
                    
                  
                
              
            
          
          
            
              c
              ⁢
              
                
              
              ⁢
              0
            
            +
            
              c
              ⁢
              
                
              
              ⁢
              1
            
            +
            
              c
              ⁢
              
                
              
              ⁢
              2
            
          
        
      
    
    
      
        (
        6
        )
      
    
  




Herein, EB1m-10, EB1m-12 and EB1m-20 are the energies of the first consonant frequency band signals of the (m−10)th voice frame, the (m−12)th voice frame and the (m−20)th voice frame respectively; EB2m-10, EB2m-12 and EB2m-20 are the energies of the second consonant frequency band signals of the (m−10)th voice frame, the (m−12)th voice frame and the (m−20)th voice frame respectively; and c0, c1 and c2 are weight values corresponding to the (m−10)th voice frame, the (m−12)th voice frame and the (m−20)th voice frame respectively. The weight values c0, c1 and c2 may be fixed values or variable values. For instance, a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame. For example, in the present embodiment, the weighted values c0, c1 and c2 may change with the different lengths of the interval from each of the voice frames to the mth voice frame. The original voice sampling signal corresponding to the mth voice frame may be determined as the consonant signal when the first consonant energy ratio weighted average ASm satisfies the following formula:

Em−ELm>ASm  (7)

Herein, ELm is the energy of the low-pass sampling signal corresponding to the mth voice frame.
In addition, the processing unit 104 may also calculate an average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame in order to obtain a low-pass sampling signal energy ratio average. For example, in regard to the mth voice frame, the low-pass sampling signal energy ratio average AUm may be represented by the following formula:




  
    
      
        
          AU
          m
        
        =
        
          
            
              
                EL
                m
              
              
                E
                m
              
            
            +
            
              
                EL
                
                  m
                  -
                  1
                
              
              
                E
                
                  m
                  -
                  1
                
              
            
          
          2
        
      
    
    
      
        (
        8
        )
      
    
  




Herein, ELm and ELm-1 are the energies of the low-pass sampling signals corresponding to the mth voice frame and a (m−1)th voice frame respectively; and Em and Em-1 are the energies of the original voice sampling signals of the mth voice frame and the (m−1)th voice frame respectively. The processing unit 104 may determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the low-pass sampling signal energy ratio average is less than a preset average. For example, in regard to the mth voice frame, aforesaid determination method may be represented by the following formula:

AUm<0.6  (9)

In the present embodiment, the preset average is 0.6, but the invention is not limited thereto. The preset average may also be adjusted to be other values based on actual situations. In addition, a number of the voice frames used for calculating the low-pass sampling signal energy ratio average AUm is not limited by the present embodiment.
Further, the processing unit 104 may also calculate a ratio value of the energy of the second consonant frequency band signal according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal, and determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal. For example, the processing unit 104 may calculate an energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal, and calculate a ratio of the energy of the second consonant frequency band signal to the energy difference value in order to obtain the ratio value of the energy of the second consonant frequency band signal. After the ratio value of the energy of the second consonant frequency band signal is calculated, the processing unit 104 may determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio, and according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio.
For instance, in regard to the mth voice frame, aforesaid determination method may be represented by the following formula:




  
    
      
        
          
            EL
            m
          
          
            E
            m
          
        
        <
        0.5
      
    
    
      
        (
        10
        )
      
    
  
  
    
      
        0.5
        ≤
        
          
            EL
            m
          
          
            E
            m
          
        
        <
        0.6
      
    
    
      
        (
        11
        )
      
    
  
  
    
      
        
          
            EB
            ⁢
            
              
            
            ⁢
            
              2
              m
            
          
          
            
              E
              m
            
            -
            
              EL
              m
            
          
        
        >
        1.3
      
    
    
      
        (
        12
        )
      
    
  




In the present embodiment, the first preset ratio is 0.5, the second preset ratio is 1.3, the preset energy ratio range is 0.5 to 0.6, but the invention is not limited thereto. In the present embodiment, the first preset ratio, the second preset ratio and the preset energy ratio range may also be adjusted to be other values based on actual situation.
In addition, the processing unit 104 may also determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal is greater than or equal to a lower limit value. For example, in regard to the mth voice frame, aforesaid determination method may be represented by the following formula:

Em≧50  (13)

In the present embodiment, the lower limit value is 50, but the invention is not limited thereto. In some other embodiments, the lower limit value may also be adjusted based on actual situations.
Because a situation may arise where the consonant signal may have different sizes of energy, the portion of the signal with less energy may be deemed as the noise signal. To avoid such situation, other than determining whether the original voice sampling signal is the consonant signal according to the energies, the processing unit 104 may also determine whether the original voice sampling signal is the consonant signal according to zero-cross rates. The processing unit 104 may calculate a first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal and calculate an average zero-cross rate of the original voice sampling signals in the target voice frame and a plurality of the voice frames in front of the target voice frame in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate, and determine whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively. Herein, the first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value.
In regard to the mth voice frame, an original zero-cross rate Zm0 may be represented by the following formula:




  
    
      
        
          Z
          m
          0
        
        =
        
          
            ∑
            
              j
              =
              1
            
            
              N
              -
              1
            
          
          ⁢
          
            
          
          ⁢
          
            0.5
            ⁢
            
              {
              
                
                  sgn
                  [
                  
                    
                      
                        x
                        ^
                      
                      m
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                      
                      )
                    
                  
                  ]
                
                -
                
                  sgn
                  [
                  
                    
                      
                        x
                        ^
                      
                      m
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                        -
                        1
                      
                      )
                    
                  
                  ]
                
              
              }
            
          
        
      
    
    
      
        (
        14
        )
      
    
  




Herein, N is a positive integer which denotes a number of the sampling signals within the mth voice frame, mL is a margin threshold, and {circumflex over (x)}m is the original voice sampling signal within the mth voice frame. The processing unit 104 may determine whether the original voice sampling signal is the consonant signal according to whether Zm0 is greater than or equal to a preset zero-cross rate by, for example, the following formula:

Zm0≧22  (15)

Herein, the preset zero-cross rate is not limited only to be 22, and its value may also be adjusted based on actual situations in some other embodiments. In addition, the processing unit 104 may also determine whether the original voice sampling signal is the consonant signal according to zero-cross rates Zm+ and Zm− of an energy condition contained in the original voice sampling signal, and the zero-cross rates Zm+ and Zn− may be respectively represented by the following formulas:




  
    
      
        
          Z
          m
          +
        
        =
        
          
            ∑
            
              j
              =
              1
            
            
              N
              -
              1
            
          
          ⁢
          
            
          
          ⁢
          
            0.5
            ⁢
            
              {
              
                
                  sgn
                  [
                  
                    
                      x
                      m
                      +
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                      
                      )
                    
                  
                  ]
                
                -
                
                  sgn
                  [
                  
                    
                      x
                      m
                      +
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                        -
                        1
                      
                      )
                    
                  
                  ]
                
              
              }
            
          
        
      
    
    
      
        (
        16
        )
      
    
  
  
    
      
        
          Z
          m
          -
        
        =
        
          
            ∑
            
              j
              =
              1
            
            
              N
              -
              1
            
          
          ⁢
          
            
          
          ⁢
          
            0.5
            ⁢
            
              {
              
                
                  sgn
                  [
                  
                    
                      x
                      m
                      -
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                      
                      )
                    
                  
                  ]
                
                -
                
                  sgn
                  [
                  
                    
                      x
                      m
                      -
                    
                    ⁡
                    
                      (
                      
                        mL
                        +
                        j
                        -
                        1
                      
                      )
                    
                  
                  ]
                
              
              }
            
          
        
      
    
    
      
        (
        17
        )
      
    
  




Herein, xm+ and xm− may be respectively represented by the following formulas:

xm+(j)={circumflex over (x)}m(j+mL)−αxEm  (18)

xm−(j)={circumflex over (x)}m(j+mL)+αxEm  (19)

In the present embodiment, a value of αx is 0.5, but the invention is not limited thereto. In some other embodiments, said value may also be adjusted based on actual situations. Accordingly, by adjusting a criterion for calculating the zero-cross rate, whether the original voice sampling signal is the consonant signal may be determined more accurately. The processing unit 104 may also determine whether the original voice sampling signal is the consonant signal according to the average zero-cross rate of the voice frames. For instance, in regard to the mth voice frame, whether the original voice sampling signal is the consonant signal may be determined according to an average of zero-cross rates of the closest two voice frames (i.e., (m−1)th and (m−2)th voice frames), and a determination method may be represented as follows.




  
    
      
        
          
            
              Z
              m
              0
            
            +
            
              Z
              
                m
                -
                1
              
              0
            
            +
            
              Z
              
                m
                -
                2
              
              0
            
          
          3
        
        ≥
        34
      
    
    
      
        (
        20
        )
      
    
  
  
    
      
        
          
            
              Z
              m
              +
            
            +
            
              Z
              
                m
                -
                1
              
              +
            
            +
            
              Z
              
                m
                -
                2
              
              +
            
          
          3
        
        ≥
        30
      
    
    
      
        (
        21
        )
      
    
  
  
    
      
        
          
            
              Z
              m
              -
            
            +
            
              Z
              
                m
                -
                1
              
              -
            
            +
            
              Z
              
                m
                -
                2
              
              -
            
          
          3
        
        ≥
        30
      
    
    
      
        (
        22
        )
      
    
  




As described in the foregoing embodiments, the processing unit 104 may determine whether the original voice sampling signal is the consonant signal according to at least one of the energies or the zero-cross rates. That is to say, the processing unit 104 may combine use of at least one condition from among the aforementioned formulas to determine whether the original voice sampling signal is the consonant signal. For instance, the processing unit 104 may determine whether all of the formulas (5), (7), (9), (10), (13), (15), (20), (21) and (22) are satisfied at the same time, and determines that the original voice sampling signal corresponding to the target voice frame is the consonant signal only if all of said formulas are satisfied. As another example, the processing unit 104 may also determine whether all of the formulas (5), (7), (9), (11), (12), (13), (15), (20), (21) and (22) are satisfied at the same time, and determines that the original voice sampling signal corresponding to the target voice frame is the consonant signal only if all of said formulas are satisfied.
Referring to FIGS. 2A to 2C, FIGS. 2A to 2C are schematic flowcharts illustrating a speech recognition method according to an embodiment of the invention. In view of the foregoing embodiments, a speech recognition method of the speech recognition apparatus may include the following steps. First of all, a low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band are performed for a voice signal in order to generate a low-pass filter signal, a first band-pass filter signal and a second band-pass filter signal respectively (step S202). Subsequently, the voice signal, the low-pass filter signal, the first band-pass filter signal and the second band-pass filter signal are divided into a plurality of voice frames (step S204). Herein, each of the voice frames includes an N number of sampling signals, and N is a positive integer. Then, energies of the sampling signals in a target voice frame are calculated in order to obtain an energy of an original voice sampling signal, an energy of a low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal (step S206). Thereafter, whether the original voice sampling signal corresponding to the target voice frame is a noise signal is determined according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal (step S208). For example, whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively may be determined. If the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, the original voice sampling signal of the target voice frame is the noise signal.
Thereafter, a ratio value of the energy of the second consonant frequency band signal is calculated according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal, and whether the original voice sampling signal corresponding to the target voice frame is the consonant signal is determined according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal. As shown in FIGS. 2A to 2C, an energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal may first be calculated (step S210). Then, a ratio of the energy of the second consonant frequency band signal to the energy difference value is calculated in order to obtain the ratio value of the energy of the second consonant frequency band signal (step S212). Thereafter, whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio is determined, and whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio are determined (step S214). If the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is not less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal does not fall within the preset energy ratio range, or if the ratio value of the energy of the second consonant frequency band signal is not greater than the second preset ratio, it is determined that the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216).
Otherwise, if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within the preset energy ratio range and the ratio value of the energy of the second consonant frequency band signal is greater than the second preset ratio, a weighted average of the energies of the voice frames having the original voice sampling signals previously determined as the noise signal is calculated in order to obtain a noise signal energy weighted average (step S218). Thereafter, whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average is determined (step S220). Herein, a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal may change with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame. If the energy of the original voice sampling signal corresponding to the target voice frame is not greater than the noise signal energy weighted average, it is determined that the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216).
Otherwise, if the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average, an average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame is calculated in order to obtain a low-pass sampling signal energy ratio average (step S222). Then, whether the low-pass sampling signal energy ratio average is less than a preset average is determined (step S224). If the low-pass sampling signal energy ratio average is not less than the preset average, the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216). Otherwise, if the low-pass sampling signal energy ratio average is less than the preset average, a weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal is then calculated in order to obtain a consonant frequency band signal energy sum weighted average (step S226). Herein, a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame. Then, whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average is then determined (step S228). If the difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is not greater than the consonant frequency band signal energy sum weighted average, the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216).
Otherwise, if the difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average, whether the energy of the original voice sampling signal is greater than or equal to a lower limit value is determined (step S230). If the energy of the original voice sampling signal is not greater than or equal to the lower limit value, the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216). Otherwise, if the energy of the original voice sampling signal is greater than or equal to the lower limit value, a first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal are calculated and an average zero-cross rate of the original voice sampling signals in the target voice frame and the voice frames in front of the target voice frame is calculated in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate (step S232). Herein, the first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value. Then, whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively is then determined (step S234). If all of the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are not greater than or equal to the corresponding preset average zero-cross rates, the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216).
Otherwise, if the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively, whether the second zero-cross rate is greater than or equal to a preset zero-cross rate is then determined (step S236). If the second zero-cross rate is not greater than or equal to the preset zero-cross rate, the original voice sampling signal corresponding to the target voice frame is not the consonant signal (step S216). Otherwise, if the second zero-cross rate is greater than or equal to the preset zero-cross rate, the original voice sampling signal corresponding to the target voice frame is the consonant signal (step S238).
In summary, the invention may combine use of at least one condition from among the aforementioned formulas to determine whether the original voice sampling signal is the consonant signal, so as to improve a recognition accuracy for the consonant signal. For example, whether the original voice sampling signal corresponding to the target voice frame is the consonant signal may be determined according to at least one of the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal. As a result, occurrences of the situation where the original voice sampling signal is mistakenly determined as the consonant signal may be reduced to improve the recognition accuracy for the consonant signal.
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.

## Claims

1. A speech recognition apparatus, comprising:
a low-pass filter and a band-pass filter, the low-pass filter and the band-pass filter respectively performing a low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band for a voice signal in order_to generate a low-pass filter signal, a first band-pass filter signal and a second band-pass filter signal respectively; and
a central processing unit, coupled to the low-pass filter and the band-pass filter, and dividing the voice signal, the low-pass filter signal, the first band-pass filter signal and the second band-pass filter signal into a plurality of voice frames, wherein each of the voice frames comprises an N number of sampling signals, N is a positive integer, wherein the central processing unit calculates energies of the sampling signals in a target voice frame in order to obtain an energy of an original voice sampling signal, an energy of a low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal, calculates a ratio value of the energy of the second consonant frequency band signal according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal, and determines whether the original voice sampling signal corresponding to the target voice frame is a consonant signal according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal.

2. The speech recognition apparatus of claim 1, wherein the central processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is a noise signal according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal.

3. The speech recognition apparatus of claim 2, wherein the central processing unit further determines whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively, and if the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, determines the original voice sampling signal of the target voice frame as the noise signal.

4. The speech recognition apparatus of claim 1, wherein the central processing unit further calculates an energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal, and calculates a ratio of the energy of the second consonant frequency band signal to the energy difference value in order to obtain the ratio value of the energy of the second consonant frequency band signal.

5. The speech recognition apparatus of claim 4, wherein the central processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio, and according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio.

6. The speech recognition apparatus of claim 5, wherein if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within the preset energy ratio range and the ratio value of the energy of the second consonant frequency band signal is greater than the second preset ratio, the central processing unit further calculates a weighted average of the energies of the voice frames having the original voice sampling signals previously determined as the noise signal in order to obtain a noise signal energy weighted average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average.

7. The speech recognition apparatus of claim 6, wherein a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame.

8. The speech recognition apparatus of claim 6, wherein the central processing unit further calculates an average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame in order to obtain a low-pass sampling signal energy ratio average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the low-pass sampling signal energy ratio average is less than a preset average.

9. The speech recognition apparatus of claim 8, wherein the central processing unit further calculates a weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal in order to obtain a consonant frequency band signal energy sum weighted average, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average.

10. The speech recognition apparatus of claim 9, wherein a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame.

11. The speech recognition apparatus of claim 9, wherein the central processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal is greater than or equal to a lower limit value.

12. The speech recognition apparatus of claim 11, wherein the central processing unit further calculates a first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal and calculates an average zero-cross rate of the original voice sampling signals in the target voice frame and a plurality of the voice frames in front of the target voice frame in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate, and determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively, wherein the first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value.

13. The speech recognition apparatus of claim 12, wherein the central processing unit further determines whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the second zero-cross rate is greater than or equal to a preset zero-cross rate.

14. A speech recognition method, comprising:
performing a low-pass filtering and a band-pass filtering of a first consonant frequency band and a second consonant frequency band for a voice signal in order to generate a low-pass filter signal, a first band-pass filter signal and a second band-pass filter signal respectively;
dividing the voice signal, the low-pass filter signal, the first band-pass filter signal and the second band-pass filter signal into a plurality of voice frames, wherein each of the voice frames comprises an N number of sampling signals, and N is a positive integer;
calculating energies of the sampling signals in a target voice frame in order to obtain an energy of an original voice sampling signal, an energy of the low-pass sampling signal, an energy of a first consonant frequency band signal and an energy of a second consonant frequency band signal;
calculating a ratio value of the energy of the second consonant frequency band signal according to the energy of the second consonant frequency band signal, the energy of the original voice sampling signal and the energy of the low-pass sampling signal; and
determining whether the original voice sampling signal corresponding to the target voice frame is a consonant signal according to at least one of a ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal and the ratio value of the energy of the second consonant frequency band signal.

15. The speech recognition method of claim 14, further comprising:
determining whether the original voice sampling signal corresponding to the target voice frame is a noise signal according to a ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, a ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and a ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal.

16. The speech recognition method of claim 15, further comprising:
determining whether the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within corresponding preset ratio ranges respectively; and
if the ratio of the energy of the first consonant frequency band signal to the energy of the second consonant frequency band signal, the ratio of the energy of the first consonant frequency band signal to the energy of the original voice sampling signal and the ratio of the energy of the second consonant frequency band signal to the energy of the original voice sampling signal fall within the corresponding preset ratio ranges respectively, determining the original voice sampling signal of the target voice frame as the noise signal.

17. The speech recognition method of claim 14, further comprising:
calculating an energy difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal; and
calculating a ratio of the energy of the second consonant frequency band signal to the energy difference value in order to obtain the ratio value of the energy of the second consonant frequency band signal.

18. The speech recognition method of claim 17, further comprising:
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than a first preset ratio, and according to whether the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within a preset energy ratio range and whether the ratio value of the energy of the second consonant frequency band signal is greater than a second preset ratio.

19. The speech recognition method of claim 18, wherein if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal is less than the first preset ratio, or if the ratio of the energy of the low-pass sampling signal to the energy of the original voice sampling signal falls within the preset energy ratio range and the ratio value of the energy of the second consonant frequency band signal is greater than the second preset ratio, the speech recognition method further comprises:
calculating a weighted average of the energies of the original voice sampling signals previously determined as the noise signal in order to obtain a noise signal energy weighted average; and
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal corresponding to the target voice frame is greater than the noise signal energy weighted average.

20. The speech recognition method of claim 19, wherein a weighted value corresponding to each of the voice frames having the original voice sampling signals determined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signals determined as the noise signal to the target voice frame.

21. The speech recognition method of claim 19, further comprising:
calculating an average of ratios of the energies of the low-pass sampling signal to the energies of the original voice sampling signal corresponding to the target voice frame and the voice frames in front of the target voice frame in order to obtain a low-pass sampling signal energy ratio average; and
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the low-pass sampling signal energy ratio average is less than a preset average.

22. The speech recognition method of claim 21, further comprising:
calculating a weighted average of a sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to the voice frames having the original voice sampling signal previously determined as the noise signal in order to obtain a consonant frequency band signal energy sum weighted average; and
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether a difference value of the energy of the original voice sampling signal minus the energy of the low-pass sampling signal corresponding to the target voice frame is greater than the consonant frequency band signal energy sum weighted average.

23. The speech recognition method of claim 22, wherein a weighted value of the sum of the energies of the first consonant frequency band signals and the energies of the second consonant frequency band signals corresponding to each of the voice frames having the original voice sampling signal deten lined as the noise signal changes with different lengths of an interval from each of the voice frames having the original voice sampling signal determined as the noise signal to the target voice frame.

24. The speech recognition method of claim 22, further comprising:
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the energy of the original voice sampling signal is greater than or equal to a lower limit value.

25. The speech recognition method of claim 24, further comprising:
calculating a first zero-cross rate, a second zero-cross rate and a third zero-cross rate of the original voice sampling signal and calculating an average zero-cross rate of the original voice sampling signals in the target voice frame and the voice frames in front of the target voice frame in order to obtain a first average zero-cross rate, a second average zero-cross rate and a third average zero-cross rate, wherein the first zero-cross rate, the second zero-cross rate and the third zero-cross rate are frequencies of the original voice sampling signal in the target voice frame for crossing a first preset value, a second preset value and a third preset value respectively, and the second preset value is less than the first preset value and greater than the third preset value; and
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the first average zero-cross rate, the second zero-cross rate and the third zero-cross rate are greater than or equal to corresponding preset average zero-cross rates respectively.

26. The speech recognition method of claim 25, further comprising:
determining whether the original voice sampling signal corresponding to the target voice frame is the consonant signal according to whether the second zero-cross rate is greater than or equal to a preset zero-cross rate.