Band correcting apparatus

TECHNICAL FIELD The present invention relates to a frequency band correction device, and more particularly, to a signal correction device for correcting the frequency characteristics of a band-limited signal.

Background Art Band correction devices for VoIP (Voice over Internet Protocol) technology that have been widely used in recent years group voice signals into IP (Internet Protocol) packets to integrate voice and data. This integration helps reduce network or communication costs. This advantage has led to the widespread use of this technology.

The traditional public switched telephone network (PSTN) focuses on how to send voice signals. Voice communication uses a frequency band not higher than 3.4kHz, therefore, the network is designed to establish a bandwidth per channel of 3.4kHz. The digital transmission network is based on a 64Kb/s communication unit using a sampling frequency of 8kHz.

On the other hand, with the widespread use of broadband technologies and services in recent years, transmission devices on the network side are now designed to support broadband communications. Moreover, even subscriber lines support broadband networks through asymmetric digital subscriber lines (ADSL) or optical transmission lines, thereby enabling end-to-end broadband voice signal transmission. Currently, higher quality voice communication is required.

However, using existing ordinary user telephones instead of IP dedicated telephones suitable for IP networks, the bandwidth is limited to 4kHz or lower by such as attenuators to set the telephone transmitter and receiver characteristics. Using this existing ordinary user telephone, the voice quality achieved does not exceed the quality that is basically the same as the voice quality generally allowed by the public switched telephone network, even if the transmission line allows frequency band signals higher than 4kHz as in the IP network.

In order to solve this problem and achieve higher voice quality, even if existing telephones use transmission channels such as IP networks that use public broadband signals, such a method is currently being studied, which includes correcting the frequency characteristics of the signals sent and received by the telephone. To expand the voice frequency band.

200480005360.5 At the same time, Japanese Patent Publication JP 2002-82685 discloses a voice frequency band extension device and method, in which if a low-frequency range signal is used to generate a high-frequency range signal that does not exist, the generated voice sounds very much compared with the original voice. unnatural. Moreover, in the frequency range lower than the normal range and in the frequency range higher than the normal range, only a small amount of the speech signal is left. Therefore, the calling party cannot perceive these voice signal components, and therefore, the voice heard by the calling party is only of poor sound quality. In order to improve the sound quality, as a simple method, you can amplify the smaller signals left in each frequency band. However, this simple band expansion is achieved by re-amplifying the lower and higher range components to raise these components to an audible level. Therefore, the amplification of the frequency band components in the audio signal directly leads to the amplification of the amplitude, so that the amplitude will exceed the maximum and minimum limits in digital signal processing.

The conventional operation sequence in the extended frequency band will now be described. As an input signal, a signal limited in the bandwidth range of 300 Hz to 3.4 kHz is supplied to the correction filter. The correction filter responsible for expanding the frequency band has such a characteristic that it does not amplify the frequency band from 300 Hz to 3.4 kHz, that is, the filter has an amplification factor of 1, while amplifying the frequency bands from 0 Hz to 300 Hz and 3.4 kHz to 8 kHz through corresponding amplification characteristics. Through this correction, the correction filter outputs a signal with flat characteristics in the OKHz to 8kHz frequency band.

However, the impulse response, which represents the overall filter characteristics, has an amplification degree of +30dB. Specifically, the amplification level is +40dB only in the range involving high frequencies. Now, suppose i-low is used_oIf you provide a signal whose amplitude does not exceed -27dBmO, the output signal will be limited because its instantaneous value can easily reach the maximum value. If the input signal is an ideal bandwidth-limited signal, no serious problems will occur. However, if there is electrical noise outside the range of 300Hz to 3.4kHz, this noise is also amplified by +30dB to +40dB_oFor example, assuming a base-layer noise level of -50dBm0, the amplified base-layer noise reaches -20dBm0 to -10dBm0_o SUMMARY OF THE INVENTION The object of the present invention is to provide a frequency band correction device, whereby a narrowband signal can be corrected to a wideband signal without over-amplification in the process of digital amplification.

In order to achieve the above-mentioned object, the present invention provides a frequency band correction device, including: a corrector, which receives an input signal restricted in a frequency band, and is configured to correspond to the signal of each restricted frequency band

200480005360.5 The first level corrects the input signal and outputs the corrected signal; a monitor for monitoring whether the signal level of the corrected signal reaches a preset level; and a level adjuster for responding to the signal from the monitor The level information of the circuit adjusts the signal level.

According to the frequency band correction device of the present invention, the signal level of the restricted frequency band is amplified by the corrector, the signal level of the correction signal provided from the monitor is compared with the preset level, and the decision result is provided as level information for adjustment The level adjuster of the signal level. The input signal can be corrected into a wideband signal without reducing the quality of the communication signal due to over-amplification, thereby ensuring high-quality transmission.

The present invention also provides a frequency band correction device, including: a frequency band divider for dividing the frequency spectrum of an input signal into a plurality of restricted frequency bands; a corrector for correcting the signal level of the frequency band obtained by the division to output a correction signal; And an analog converter, used to convert each correction signal into an analog signal.

According to the frequency band correction device of the present invention, the input signal is divided into corresponding signal frequency bands by the frequency band divider, and the obtained signal frequency band is sent to the corrector. The corrector corrects the corresponding frequency band signal obtained at the time of division in terms of signal level. The obtained signals are corrected and combined by an analog converter. In this way, the speech frequency band can be expanded because the naturally occurring sound quality is maintained without the limitation of the boundary of the digital representation, even if the signal is amplified to be close to the boundary of the bit representation by the corrector and combined.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the accompanying drawings, the purpose and features of the present invention will become more apparent from the following detailed description. In the accompanying drawings: FIG. 1 is a schematic block diagram illustrating the structure of a speech band correction device according to the present invention; 2A, 2B, and 2C are graphs that help to understand the frequency band correction of the voice frequency band correction device shown in Figure 1; Figures 3A, 3B, and 3C are helpful to understand the voice frequency band correction device shown in Figure 1 In the frequency band correction, the frequency characteristic curve of the frequency band correction by the coefficient suppression; Figures 4A and 4B are the frequency characteristics of the original voice and the voice limited in the phone bandwidth

200480005360.5 The first curve; Figure 5 is a frequency characteristic curve that helps to understand the bandwidth correction obtained by using the comparative example of the present invention; Figure 6 and Figure 7 are respectively illustrating the first obtained from the voice band correction device of Figure 1 modified And a schematic block diagram of the structure of the second embodiment; Figs. 8A to 8D are graphs of frequency characteristics helpful to understand the frequency band correction of the voice band correction device shown in Fig. 7; Fig. 9 is a diagram illustrating the second embodiment from Fig. 7 Fig. 10 is a schematic block diagram illustrating the structure of the third embodiment obtained by modifying the voice band correction device of Fig. 1; Fig. 11 is a schematic block diagram of the structure obtained by modifying the third embodiment of Fig. 10 Figure 12 is a schematic block diagram of the structure of the fourth embodiment modified from the voice band correction device of Figure 1; Figure 13 is a schematic diagram of the structure of the fifth embodiment modified from the voice band correction device of Figure 1 Block diagram; Fig. 14 is a schematic block diagram of the structure of the sixth embodiment modified from the voice band correction device of Fig. 1.

DETAILED DESCRIPTION With reference to the drawings, certain preferred embodiments of the present invention will be described in detail.

In these embodiments, the frequency band correction device of the present invention is applied to the voice frequency band correction device 10. Parts or components that are not directly related to the understanding of the present invention are not illustrated in the drawings. The speech band correction device 10 is suitable for monitoring the output of the correction filter and reducing the filter coefficient to control the degree of band expansion so as not to exceed the limits on the maximum and minimum values in the digital signal processing range.

Referring to FIG. 1, the voice band correction device 10 includes a correction filter 12, a coefficient controller 14, and a level detector 16, which are connected to each other as shown. The correction filter 12 is an analog or digital filter, and has a correction function for flattening the frequency characteristics of the voice signal 18 input from a user phone (not shown) over the entire voice frequency band. It should be noted that the voice signal 18 can

200480005360. 5 The first includes signals other than voice, such as fax or image signals. The correction filter 12 is adapted to correct the speech signal 18 to output the corrected speech signal 20 to the level detector 16.

The coefficient controller 14 has a control function so that when the output of the correction filter 12 exceeds a limit value, a control signal 24 is sent to the correction filter 12 for changing the correction filter 12 according to the detection signal 22 provided from the level detector 16. The coefficient. The coefficient controller 14 also has a function of resetting the coefficient to the original or initial coefficient value when the output of the correction filter 12 has become lower than the limit value. The coefficient controller 14 is also adapted to gradually change the coefficient according to how close to the limit value is. Specifically, according to the detection signal 22 output by the level detector 16, the coefficient controller 14 increases the amplification factor of the correction filter to a preset value, and at the same time reduces the amplification factor by the decrement of 1DB. The preset value is selected so as to amplify the input speech signal 18 as a whole by an amplification factor of, for example, 30 dB. However, it should be pointed out that the predetermined amplification factor and the reduction in the amplification factor are not limited to the specific values mentioned above.

The level detector 16 has a function of receiving and monitoring the corrected speech signal 20 of the correction filter 12 to send a detection signal 22 indicating the change state of the corrected output level to the coefficient controller 14. The level detector 16 outputs the corrected speech signal 20 as the output signal 26 of the speech band correction device 10.

Specifically, the level detector 16 that monitors the corrected speech signal 20 verifies whether the output value of the correction filter 12 in the form of a digital signal takes a 16-bit digital limit value, that is, +32768 or -32767. The level detector 16 sends the decision result as a detection signal 22 to the coefficient controller 14.

It should be pointed out that the boundary or threshold value used in the judgment in the currently described embodiment and the following embodiment is not limited to the specific value given above, for example, it may be +16384 or -16384. Any appropriate method can be applied to determine whether these preset values are exceeded, assuming that the correct decision can be given by the methods used.

The operation of the voice band correction device 10 will now be described. The speech signal 18 is limited to a bandwidth range of 300 Hz to 3.4 kHz, as shown in FIG. 2A, and is deteriorated by electrical noise outside this frequency range. The input voice signal 18 is supplied to the correction filter 12, and is initially amplified by the correction filter 12 having the frequency characteristic of the gain shown in FIG. 2B. The amplified corrected speech signal 20 is supplied from the correction filter 12 to the signal shown in FIG. 2C

200480005360.5 The first level detector 16.

The level detector 16 monitors the level of the amplified corrected speech signal 20, and once it detects that the signal level is close to or has exceeded the maximum value, it outputs the detection signal 22 to the coefficient controller 14. For example, the maximum value of 16 bits is 32768. The coefficient controller 14 receives the detection signal 22 from the level detector 16. In this embodiment, the coefficient controller 14 controls to reduce the coefficient value of the correction filter 12 in the corresponding frequency ranges A, B, and C of 0 Hz to 0.3 kHz, 0.3 kHz to 3.4 kHz, and higher than 3.4 kHz. Through this control, the correction filter 12 amplifies the input signal while suppressing the noise level in the input signal, as shown in FIG. 3B.

The correction filter 12 may also be adapted to predict the state of the noise mixed into the input signal 18 to use correspondingly changed coefficient values. Specifically, the amplification factor of the correction filter 12 may have the preset initial characteristics shown in FIG. 2B, and the amplification factors for the frequency ranges A, B, and C illustrated in FIG. 3B are reduced by a reduction of 1DB. It should be pointed out that the initial frequency gain characteristics and the decrement in reducing the amplification factor are not limited to the above cases. Specifically, if the amplification factor is lowered for the high frequency range as shown in FIG. 3C, the frequency characteristic of the original sound may be close to the frequency characteristic of the original sound.

As a comparative example, a conventional voice band correction device is provided with a voice signal 18 as the original sound, having frequency characteristics as shown in FIG. 4A. The bandwidth of this input signal 18 is limited by the telephone in order to obtain a frequency characteristic cut off toward the high frequency range, as shown in FIG. 4B. If the voice band extension device disclosed in Japanese Patent Publication JP2002-82685 is now applied, the low-frequency and high-frequency ranges are excessively amplified, thereby obtaining a voice having the frequency characteristics shown in FIG. 5.

However, with this embodiment, the voice band correction device 10 operates in the manner described above to allow the frequency component level of the input signal 18 to be corrected, thereby expanding the bandwidth of the input signal without excessively amplifying in the process of amplifying, for example, a digital signal. Narrowband input signal, thereby providing a high-quality output signal 26 in the speech signal.

The structure of the first embodiment obtained from the modification of the speech band correction device 10 will now be described. In this text, the same reference numerals are used to denote the same parts or components, and the corresponding description will be omitted for simplicity. Referring to FIG. 6, the voice band correction device 10 is the same as the previous embodiment, except that the amplitude controller 30 is connected to the amplifier 28 to provide an amplitude control signal.

200480005360.5 No. 32, so as to control the amplitude of the signal 34 input to the correction filter 12 from the beginning without controlling the coefficient of the correction filter 12.

The amplifier 28 is suitable for changing the amplitude of the input signal 18 and has a function of increasing or decreasing the amplitude of the input signal 18 according to the value of the amplification factor provided from the amplitude controller 30. In order to prevent the maximum and minimum limit values from being exceeded in digital signal processing, in response to the detection signal 22 output by the level detector 16, the amplitude controller 30 controls the amplitude of the amplifier 28 to change. The amplifier 28 also has a function of resetting the amplitude to its original value when the output of the correction filter 12 has become lower than the limit value, and gradually changing the amplitude value according to how close the amplitude is to the limit value. Specifically, as in the previous embodiment, the decision is provided according to whether the output of the correction filter 12 takes the 16-bit digital limit value (+32768 and -32767). The level detector 16 sends the decision result as a detection signal 22 to the amplitude controller 30.

Now, the operation of the voice band correction device 10 of the first embodiment will be described. The speech signal 18 is limited to a bandwidth range of 300 Hz to 3.4 kHz, as shown in FIG. 2A, and the quality is degraded due to noise outside this frequency range. The input speech signal 18 is first amplified by the correction filter 12 having the frequency gain characteristic shown in FIG. 2B. The amplified corrected speech signal 20 is supplied from the correction filter 12 to the level detector 16. The level detector 16 monitors the level of the amplified corrected speech signal 20, and once it detects that the signal level is close to or has exceeded the maximum Value, the detection signal 22 is output to the amplitude controller 30. For example, the maximum value of the 16-bit input signal is 32768. The amplitude controller 30 receives the detection signal 22 from the level detector 16. The amplitude controller 30 controls to reduce the amplitude of the signal passing through the amplifier 28. In the initial state, the amplifier 28 is practically useless and does not change the signal amplitude. In this embodiment, the correction filter 12 has the frequency gain characteristic shown in FIG. 2B and an impulse response gain of 30 dB over the entire frequency. However, this is not to be interpreted as a restrictive way. The amplitude controller 30 can be configured to reduce the gain by the decrement of 1DB in response to the detection signal 22, which is also a non-limiting way. Under this control, the input signal 18 is amplified while suppressing the noise level.

Through this operation, the narrowband signal can be expanded into a wideband signal more naturally, and the filter characteristics can be temporarily fixed. For changes that occur over time, use tools

200480005360.5 The first amplitude controller 30 with simple amplification function, so that the complexity of the software can be solved and its scale can be further reduced.

In the above two embodiments, the output of the correction filter 12 is monitored to control the coefficient of the correction filter 12 or the amplifier 28, thereby preventing the output signal 26 of the speech band correction device from reaching its maximum value. However, if the gain of the correction filter 12 is simply reduced, the level of the 300 Hz to 3.4 kHz frequency band within the input signal 18 is also reduced. Therefore, the sound signal passing through the correction filter 12 is reduced to such an extent that as long as the signal level reaches its maximum value, rapid changes in the sense of reality tend to appear repeatedly. On the other hand, it is a well-known fact that the frequency of the above-mentioned electrical noise is, for example, in the range from 50 Hz to 60 Hz.

The configuration of the second embodiment will now be described in which the voice band correction device is modified

10. In this embodiment, the filter is divided into filter sub-parts to adjust the degree of amplification from one frequency band to another frequency band. To this end, the voice band correction device 10 includes a correction filter 12, a coefficient controller 14, a level detector 16, and an adder 34, which are connected to each other as shown in FIG.

The correction filter 12 includes segment filters 36, 38, and 40 associated with frequency bands A, B, and C, respectively. One filter 36 is a low-pass filter adapted to pass 0 Hz to 300 Hz and cut higher frequency components to amplify signals in the lower frequency range. The other filter 38 is adapted to pass an intermediate frequency band of 300 Hz to 3.4 kHz to limit the frequency band of the input signal, while adjusting the delay of the lower and higher range signals relative to the delay of the intermediate frequency band signal. For example, by simulating during the design of these filters, the magnitude of each delay can be adjusted. The remaining filter 40 is a high-pass filter suitable for passing through the 3.4 kHz to 8 kHz range and cutting lower frequency components while amplifying signals in the higher frequency range. The filters 36, 38, and 40 respectively output the filtered output signals 42, 44, and 46 to the adder 34, and at the same time provide the output signals 42 and 46 to the amplitude measurement circuits 48 and 50.

The level detector 16 includes amplitude measurement circuits 48 and 50. These amplitude measuring circuits 48 and 50 have the functions of monitoring the output of the filters 36 and 40, outputting the measured amplitude signals 52 and 54 and indicating the change state of the corrected output amplitude to the coefficient updating circuits 56 and 58, respectively. In this embodiment, the level detector 16 verifies whether the filter output value in the form of a digital signal takes the limit value represented by a 16-bit number, that is, +32768 or -32767.

200480005360.5 No. However, the limit value used is not limited to the specific value given above, but can be, for example, +16384 or -16384. Any suitable method can be applied to determine whether these preset values are exceeded, assuming the method used Allows the decision whether the desired level has been reached.

The coefficient controller 14 includes coefficient update circuits 56 and 58 and multipliers 60 and 62. The coefficient update circuits 56 and 58 change the coefficients according to the measured amplitude signals 52 and 54 and send the coefficients 64 and 66 to the multipliers 60 and 62, respectively. . The multipliers 60 and 62 are provided with the input signal 18 at one end 68 and 70, and are provided with coefficients 64 and 66 at the other ends 72 and 74, thereby multiplying the input signal 18 with the coefficients 64 and 66 to multiply The results 76 and 78 are output to the correction filter 12.

The coefficient update circuits 56 and 58 do not update the signal in their initial state because the multipliers 60 and 62 basically do not operate in the initial state. The coefficient update circuits 56 and 58 respond to the measured amplitude signals 52 and 54 to change the coefficients 64 and 66 supplied to the multipliers 60 and 62, respectively. Once the over-amplification is measured, the coefficient update circuits 56 and 58 output the amplitude attenuation coefficients to the multipliers 60 and 62, respectively. This coefficient is not greater than 1 and less than 0. The coefficient update circuits 56 and 58 may update the coefficients to reduce the gain by a decrement of 1db for the multipliers 60 and 62, respectively, as long as excessive amplification is confirmed in the measured amplitude signals 52 and 54 output from, for example, the amplitude measurement circuits 48 and 50. However, the coefficient update or gain adjustment is not limited to the above method.

The adder 34 has a function of adding the outputs of the filters 36, 38, and 40 to each other to combine the frequency bands (0 Hz to 300 Hz, 300 Hz to 3.4 kHz, and 3.4 kHz to 8 kHz) obtained by division.

Now, the operation of the second embodiment of the voice band correction device 10 will be described. Refer to Country 8A, when the voice band correction device is provided with an input signal 18 whose bandwidth is limited to the range of 300Hz to 3.4kHz, filters 36, 38, and 40 divide the input signal 18 into 0Hz to 300Hz, 300Hz to 3.4kHz, respectively And the frequency band from 3.4kHz to 8kHz, as shown in China 8A.

The filter 36 sends a low-range signal without high frequency components or a lower sub-band signal (0 Hz to 300 Hz) to the amplitude measurement circuit 48. The amplitude measurement circuit 48 monitors the filtered output signal 42 to output the measured amplitude signal 52 Give the coefficient update circuit 56. Measured

200480005360.5 The first amplitude signal 52 represents the state of amplitude change. When the output signal 42 of the filter 36 exceeds the limit value, the coefficient update circuit 56 controls the coefficient provided to the multiplier 60 in response to the measured amplitude signal 52. Therefore, the signal of this frequency band is controlled by the signal changed by the gain expression coefficient 64.

The filter 38 adapted to adjust the delay of the frequency band signal provided and limited to the bandwidth of 300 Hz to 3.4 kHz delays the frequency band signal relative to the low range and high range signals. The purpose of delaying the signal passing through the filter 38 is to prevent the signal level passing through the filter 38 from being reduced without reducing the realism of the emitted audible sound.

The filter 40 forms a high-range signal without a low-range signal or a higher sub-band signal 46 (3.4 kHz to 8 kHz) as shown in FIG. 8D to send the thus filtered signal to the amplitude measurement circuit 50. The amplitude measurement circuit 50 monitors the filtered output signal 46 to send the measured amplitude signal 54 to the coefficient update circuit 58. The measured amplitude signal 54 indicates the state of the amplitude change. If the output of the filter 40 exceeds the limit value, the coefficient update circuit 58 controls the coefficient 66 to be provided to the multiplier 62 in response to the measured amplitude signal 54.

The correction filter 12 sends the filter outputs 42, 44, and 46 to the adder 34 to combine the frequency bands (0 Hz to 300 Hz, 300 Hz to 3.4 kHz, and 3.4 kHz to 8 kHz) obtained by the division. If the above processing only corrects the low range so that the output signal 26 has an excessively large amplitude, the gain can be reduced. The same is true for the high frequency range. Because the middle range itself is not bandwidth limited, the signal in this range simply passes through without changing the signal level. Therefore, the gain is fixed at 1.0.

When noise reduces the quality of the input signal 18 as shown in FIG. 2A, it is sufficient to reduce the gain of the filters 36 and 40. Because the gain in the middle range is set to 1.0, the volume does not significantly affect the sound. Using ordinary sounds that are only affected by noise to a limited extent, the inputs of filters 36 and 40 are very small, so even if the input is multiplied by the relevant gain value, the signal level with a gain of 1.0 is not exceeded. It is also possible to provide a gain (<1.0) to the amplitude of the original signal according to the amplitude of the output of the filters 36 and 40.

Through this operation, the frequency amplification factor is automatically determined for each frequency range. Unlike the first embodiment, if the background noise suffers from an offset in the frequency characteristics, for example, the noise is only located in the low frequency range, the high range can be expanded without being affected by the noise, therefore,

200480005360. 5 The speech range can be expanded with natural sound quality. The same effect can also be obtained from the high range.

In this embodiment, the level detector 16 is provided on the input side of the adder 34, and includes amplitude measurement circuits 48 and 50. However, the amplitude measurement circuit 48 may also be provided on the output side of the adder 54 as shown in FIG. 9. The amplitude measurement circuit 48 may be adapted to provide the measurement results of the corrected output signal 26 from the adder 34 to the two coefficient update circuits 56 and 58 and transmit the output signal 26 to the output 26 of the speech band correction device 10. This can simplify the corresponding circuit from the level detector 16 in FIG. 7 to a separate amplitude measurement circuit 48.

The structure of the third embodiment obtained from the modification of the speech band correction device 10 will now be described. In the second embodiment, the gain values of the filters 36 and 40 will be widely distributed in the range from the negative value to the positive value thereof, thus causing design difficulties. A configuration that can overcome this difficulty is described according to the third embodiment. The voice band correction device 10 divides the frequency band into a low range and a high range through an FIR (Finite Impulse Response) filter, and uses the filter to process the signal as in the second embodiment to overcome difficulties that would otherwise be encountered in design.

Now, referring to FIG. 10, in addition to the components of the second embodiment, the voice band correction device 10 further includes a band divider 80. The band divider 80 includes a low-pass filter 82, an intermediate filter 84, and a high-pass filter 86, which are interconnected as shown.

The low-pass filter 82 is, for example, an FIR filter for cutting high frequency components in the range from 3.4 kHz to 8 kHz. The intermediate filter 84 is adapted to pass an intermediate frequency of 300 Hz to 3.4 kHz to limit the frequency band of the input signal, while adjusting the delay of the low frequency and high frequency signals relative to the intermediate frequency signal. The delay of the filter 38 can be considered with respect to low-frequency and high-frequency signals, and the intermediate filter 84 can be adjusted, for example, through simulations performed in the process of designing these filters. The high-pass filter 86 is, for example, an FIR filter, and cuts low-frequency components from 0 Hz to 300 Hz. The low-pass filter 82 and the high-pass filter 86 provide the filtered signals 88 and 90 to the multipliers 60 and 62, respectively, while the intermediate filter 84 outputs the filtered signal 92 to the filter 38.

The filter 36 in this embodiment amplifies low frequency signals in the range from 0 Hz to 300 Hz. The filter 38 is suitable for passing the intermediate frequency of 300Hz to 3.4kHz to limit the input signal.

200480005360.5 No. frequency band, while adjusting the delay of low-frequency and high-frequency signals relative to the delay of the intermediate frequency signal. The delay of the filter 38 can be considered to adjust the intermediate filter 84. The filter 40 amplifies the high frequency signal in the range of 3.4 kHz to 8 kHz.

In this embodiment, the amplifier 60 multiplies the output 88 from the low-pass filter 82 and the coefficient 64 from the coefficient update circuit 56 to output the multiplication result 76 to the filter 36. The multiplier 62 multiplies the output 90 of the high-pass filter 86 with the coefficient 66 from the coefficient update circuit 58 to output the multiplication result 78 to the filter 40. Now, the operation of the third embodiment of the speech band correction device 10 will be described. When the speech band correction device 10 is provided with an input signal 18 limited in the bandwidth range of 300 Hz to 3.4 kHz, the low-pass filter 82, the intermediate filter 84, and the high-pass filter 86 divide the input signal into 0 Hz to 300 Hz, 300 Hz to 3.4kHz and 3.4kHz to 8kHz frequency band. A low frequency signal (0 Hz to 300 Hz) without a high frequency signal is amplified by the filter 36 88. The output signal 42 thus amplified is monitored by the amplitude measuring circuit 48. If the output of the filter 36 exceeds the limit value, the coefficient update circuit 56 controls the coefficient 64 provided to the multiplier 60 in response to the measured amplitude signal 52.

The delay is limited by the bandwidth of the intermediate filter 84 to the input signal 92 in the range of 300 Hz to 3.4 kHz to adjust the delay of the output signal 88 of the low-pass filter 82 and the delay of the output signal 90 of the high-pass filter 86 relative to the delay of the intermediate output signal 92 . The purpose of delaying the signal passing through the filter 38 is to prevent the level of the signal passing through the filter 38 from being lowered without reducing the true perception of the audible sound emitted.

The low frequency and high frequency signals (3.4 kHz to 8 kHz) 90 are amplified by the filter 40 and filtered through the filter 86. The amplified output signal 46 is monitored by the Fudo measurement circuit 50. If the output of the filter 40 exceeds the limit value, the coefficient update circuit 58 controls the coefficient 66 provided to the multiplier 62 in response to the measured amplitude signal 54. The correction filter 12 sends the filter outputs 42, 44 and 46 to the adder 34 for summation, thereby combining the frequency bands obtained by the division (0Hz to 300Hz, 300Hz to 3.4kHz and 3.4kHz to 8kHz).

With this embodiment, the three filters 82, 84, and 86 that divide the frequency band are provided separately from the correction filter 12 adapted to correct the filter outputs 88, 90, and 92, respectively, and operate as described above. Therefore, for the correction filter 12, only the positive side gain is usually considered

200480005360. 5 is sufficient, so that the limited number of positive and negative quantization steps can be designed more flexibly to ensure natural signal correction that does not reduce the sound perception.

In this embodiment, the level detector 16 is provided on the input side of the adder 34, and includes amplitude measurement circuits 48 and 50. However, the amplitude measurement circuit 48 shown in FIG. 11 is included on the output side of the adder 34. The amplitude measurement circuit 48 can provide the measurement results of the corrected output signal 26 from the adder 34 to the two coefficient update circuits 56 and 58, and transmit the output signal 26 as the output 26 of the speech band correction device 10. This can transfer the corresponding circuit from The level detector 16 in FIG. 10 is simplified into a single amplitude measurement circuit 48.

Hereinafter, the voice band correction device 10 of the fourth embodiment will be described with reference to FIG. 12 by using the quadrature mirror filter (QMF) used in the ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Recommendation G.722 The input signal 18 is divided into two parts.

ITU-T Recommendation G.722 provides an audio coding system (50Hz to 7kHz) for various high-quality voice signals. The specified coding system uses SB-ADPCM (Subband Adaptive Differential Pulse Code Modulation) at a bit rate of 64kb/s. Using this SB-ADPCM technology, a quadrature mirror filter is used to divide the frequency band into two sub-bands, namely a high range and a low range. The signal in the corresponding frequency band is encoded by ADPCM.

The voice band correction device 10 shown in FIG. 12 basically imitates the configuration of the third embodiment shown in FIG. 8 and further includes a quadrature mirror filter (QMF) unit 94 in this configuration. Specifically, in addition to the band divider 80, the correction filter 12, the coefficient controller 14, and the level detector 16, the voice band correction device 10 further includes a quadrature mirror filter unit 94.

The frequency band divider 80 includes orthogonal mirror filters 96 and 98 connected to each other as shown in the figure. These orthogonal mirror filters 96 and 98 are suitable for dividing the sub-band from 0 Hz to 8 kHz into two sub-bands, namely from 0 Hz to 4 kHz. Linear phase non-recursive digital filter for low sub-band and high sub-band from 4kHz to 8kHz. Sampling the input signal of the filter at 16kHz 18₀The quadrature mirror filters 96 and 98 sample the low-range output signal 100 and the high-range output signal 102 at a sampling frequency of 8 kHz to output the sampled output signal to the correction filter 12.

The correction filter 12 includes a low-range corrector 104 and a high-range corrector 106 interconnected as shown. The low range corrector 104 is, for example, an FIR filter and has an amplification of 0kHz

200480005360. 5 The function of low-range signal to 4kHz. The low-range corrector 104 is preferably a filter that corrects the filter characteristics of the frequency bands A and B in combination, for example, as shown in FIG. 2B. Specifically, this can be achieved by combining the characteristics shown in FIGS. 8B and 8C, which is only an example.

The high-range corrector 106 is also an FIR filter suitable for amplifying high-range signals from 4 kHz to 8 kHz. Preferably, a filter having the characteristics shown in FIG. 8D can be applied to the high-range corrector 106, which is only an example. However, the high-range corrector 106 is not limited to this specific corrector. The low-range corrector 104 and the high-range corrector 106 included in the correction filter 12 respectively provide both the level detector 16 and the QMF unit 94 with output signals 108 and a combination corresponding to the output signals 42 and 44 of FIG. 7 The output signal 110 corresponding to the output signal 46 of FIG. 7 = the level detector 16 includes a low-range amplitude measurement circuit 112 and a high-range amplitude measurement circuit 114. The low-range amplitude measurement circuit 112 has a function of monitoring the output signal 108 of the low-range corrector 104 to output a measured amplitude signal 52 indicating the amplitude change state of the corrected output signal 108. The high-range amplitude measurement circuit 114 includes a function of monitoring the output signal 110 of the high-range corrector 106 to output a measured amplitude signal 54 indicating the amplitude change state of the corrected output signal 110.

In this embodiment, it is checked whether the output value of the low range corrector 104 or the high range corrector 106 in the form of a digital signal takes a 16-bit digital limit value, that is, +32768 or -32767. However, the limit value used is not limited to the specific value given above, and can also be, for example, +16384 or -16384. In this case, it is verified whether one of the threshold values is exceeded. Any suitable method can be used to determine whether these preset values are exceeded, assuming that the method used allows a decision whether the desired level has been reached.

The coefficient controller 14 includes a low-range gain controller 116 and a high-range gain controller 118. Neither the low-range gain controller 116 nor the high-range gain controller 118 performs control in the initial state. The low-range gain controller 116 has filter characteristics in which the characteristics of FIGS. 8B and 8C are combined with each other. If the output signal 108 of the low range corrector 104 exceeds the limit value, the low range gain controller 116 controls to reduce the amplitude correction value 120 by 1DB in response to the measured amplitude signal 52, thereby outputting a result signal. This system can be adapted to reduce only the component shown in Fig. 8B by 1DB. The filter characteristics are not limited to Figure 8B and Figure 8C

200480005360.5 The combination of characteristics shown in the first.

The high range corrector 106 has the filter characteristics shown in FIG. 8D. If the output signal of the high range corrector 106 exceeds the limit value, the high range gain controller 118 controls in response to the measured amplitude signal 54 to reduce the amplitude correction value 122 to be provided to the high range corrector 106 by 1DB, thereby outputting the result signal. This is just an example for explanation.

The QMF unit 94 includes quadrature mirror filters 124 and 126. These quadrature mirror filters 124 and 126 are linear phase non-recursive digital filters that interpolate the low-frequency range and high-frequency range not shown in the SB-ADPCM decoder. The output is used to convert 8kHz sampling signals 108 and 110 into 16kHz sampling signals 128 and 130. The speech band correction device 10 finally combines the output signals 128 and 130 of the QMF unit 94 with each other to generate an output signal 26 sampled at a frequency of 16 kHz.

Although not shown, an amplitude measuring circuit 48 may be provided downstream of the summation. The amplitude measurement circuit 48 may be adapted to provide measurement results to the two coefficient update units 56 and 58 and transmit the output signal 26 as the device output 26. This can simplify the corresponding circuit from the level detector 16 in FIG. 10 to a separate amplitude measurement circuit 48.

The operation of the fourth embodiment of the speech band correction device 10 will now be described. The input signal 18 in the frequency band of 0 Hz to 8 kHz sampled at 16 kHz is supplied to the band divider 80. This band divider 80 limits the input through the quadrature mirror filter 96 The high-frequency range of the signal 18 is supplied to the low-range corrector 104 as a signal in a frequency band of 0 Hz to 4 kHz sampled at a frequency of 8 kHz. The sample signal 100 is amplified by the low range corrector 104.

The amplified signal 108 is monitored by the low-range amplitude measurement circuit 112. This low-range amplitude measurement circuit 112 outputs the measured amplitude signal 52 to the low-range gain controller 116. Specifically, if the output signal 108 of the low-range corrector 104 exceeds the limit value, the low-range gain controller 116 controls the amplitude correction value 120 in response to the provided measurement amplitude signal 52 and outputs it to the low-range corrector 104. The output signal 108 of the low-range corrector 104 is passed through the quadrature mirror filter 124 to interpolate the output of the unillustrated low-range SB-ADPCM decoder to convert the 8 kHz sampling signal into a 16 kHz sampling signal. The quadrature mirror filter 124 sends out an output signal 128 sampled at a frequency of 16 kHz.

Apply the same operation to the high frequency band. More specifically, the 16kHz frequency is pumped

200480005360.5 The first input signal 16 in the frequency band of 0 Hz to 8 kHz is provided to the quadrature mirror filter 9 & the quadrature mirror filter 98 limits the low frequency band of the input signal 18 to output the signal 102 in the range of 4 Hz to 8 kHz sampled at 8 kHz to the high range Correction unit 106. The output signal 102 is amplified by the high-range corrector 106.

The amplified signal 110 is monitored by the high-range amplitude measurement circuit 114. The high-range amplitude measurement circuit 114 outputs the measured amplitude signal 54 to the high-range gain controller 118. Specifically, if the output signal 110 of the high-range corrector 106 exceeds the limit value , The high-range gain controller 118 responds to the measured amplitude signal 54 to control the amplitude correction value 122 to the high-range corrector 106. The output signal 110 of the high-range corrector 106 is interpolated by the quadrature mirror filter 126 as shown in the figure. The output of the high-range SB-ADPCM decoder shown is to convert the 8kHz sampled signal into a 16kHz sampled signal. The quadrature mirror filter 126 emits an output signal 130 sampled at a frequency of 16 kHz.

In addition, a filter may be provided between the quadrature mirror filter 96 and the low-range corrector 104 to correct the sub-bands in the range of 0 Hz to 340 Hz output by the filter 96 through the low-range corrector 104, while the range of 340 Hz to 4 kHz is not corrected. Output in the case of this subband. The specific operation in this case is the same as that of the second embodiment.

Through this operation, it is possible to expand the voice band by using a quadrature mirror filter instead of a band divider having a frequency division filter. Specifically, in applications where the transmission channel transmits signals dedicated to broadband applications, the sound quality of the output signal processed by the conventional telephone can be improved. Moreover, since frequency correction is performed for the low-range and high-range components separately, by expanding the sound quality of a conventional telephone set into a natural voice frequency band, even when it is necessary to use a quadrature mirror filter such as ITU-T Recommendation G.722 to comply with In the case of this standard, high-quality voice signal transmission can also be achieved.

The configuration of the fifth embodiment of the voice band correction device 10 will now be described. The present embodiment has basically the same configuration as the third embodiment shown in FIG. 10, and is characterized in that the coefficient controller 14 and the level detector 16 are absent. The voice band correction device 10 includes a band divider 80, a correction filter 12, and a D/A conversion unit 132, which are interconnected as shown in FIG.

In a manner similar to the third modified embodiment, the band splitter 80 includes a low-pass filter (LPF) 82, an intermediate filter (BPF) 84, and a high-pass filter (HPF) 86, the same

200480005360. 5 The first time correction filter 12 includes three filters 36, 38, and 40. The correction filter 12 adjusts the amplification gain according to the value provided in the digital signal processing, and amplifies the amplitude to the maximum value of the digital signal, for example. The D/A conversion unit 132 is composed of D/A converters 134, 136, and 138 for converting the three output signals (digital signals) 42, 44, and 46 received from the correction filter 12 into corresponding analog signals.

Now, the operation of the fifth embodiment of the voice band correction device 10 will be described. When the input signal 18 whose frequency band is limited to 300 Hz to 3.4 kHz is provided, the input signal 18 is divided into 0 Hz to 300 Hz, 300 Hz to 3.4 kHz, and 3.4 kHz to 8 kHz through the low-pass filter 82, the intermediate filter 84 and the high-pass filter 86 The sub-bands. The output signal 88 (0 Hz to 300 Hz) of the low-pass filter 82 is amplified by the filter 36. The amplified signal 42 is converted into a corresponding analog signal 140 by the D/A converter 134. The output signal 92 of the intermediate filter 84 is delayed by the filter 38 to adjust the delay of the low-pass filter 82 and the high-pass filter 86 with respect to the delay of the output signal 92. The output signal 44 is converted into a corresponding analog signal 142 by the D/A converter 136. The output signal 90 of the high-pass filter 86 is amplified by the filter 40 (3.4 kHz to 8 kHz). The amplified signal 46 is converted into an analog signal 144 by the D/A converter 138.

Sum the outputs 140, 142, and 144 of the D/A converters 134, 136, and 138, and combine the divided frequency bands (0 Hz to 300 Hz, 300 Hz to 3.4 kHz, and 3.4 kHz to 8 kHz). With this combination, the voice band correction device 10 performs correction to expand the frequency band of the band-limited input signal 18 to a wideband to output the resultant signal as the output signal 26.

Therefore, based on the assumption that the input signal has been pre-divided into the low frequency band, the intermediate frequency band, and the high frequency band by the frequency band divider 80 and the amplitude is corrected in each divided frequency band, this embodiment divides the signals 88, 92, and 90 after the frequency bands are divided. The amplitude of is amplified to the maximum value of the digital signal within the digital signal processing range of the correction filter 12, and then the digital signal is converted into an analog signal, and the signals of the corresponding frequency band are added together. This method becomes possible by taking advantage of the fact that there is no limitation of the summation value in the analog signal processing domain. Because the summation is performed in the analog signal domain without the upper limit of the summation, the speech frequency band can be amplified, even when the amplitude becomes very large due to the summation, while maintaining the sound quality without the limitation of digital summation.

200480005360. 5 Now, the configuration of the sixth embodiment will be described. It applies the fifth embodiment to the voice band correction device 10, using the ITU-T Recommendation G.722 described in conjunction with the fourth embodiment. Refer to Figure 14, Voice Band The correction device 10 includes a band splitter 80, a correction filter 12, a quadrature mirror filter 124, a phase compensator 146, a D/A conversion unit 132, and a frequency shifter 148.

Band splitter 80 includes quadrature mirror filters 96 and 98 interconnected as shown. These quadrature mirror filters 96 and 98 are linear phase non-recursive digital filters, which are suitable for dividing the frequency band of the input signal 18 from 0 Hz to 8 kHz into two parts, namely the low sub-band from 0 Hz to 4 kHz and the high sub-band from 4 kHz to 8 kHz. frequency band. The input signal of the filter is sampled at a frequency of 16 kHz. 18. Quadrature mirror filters 96 and 98 use a frequency of 8 kHz to sample the low-range output signal 100 and the high-range output signal 102 to output the sampled signal.

The correction filter 12 includes a low-range corrector 104 and a high-range corrector 106 interconnected as shown. The low-range corrector 104 has a specific frequency characteristic that combines the frequency characteristics of FIGS. 8B and 8C with each other. The high range corrector 106 may have the filter characteristics shown in FIG. 8D. The low range corrector 104 and the high range corrector 106 output the corresponding output signals 108 and 110 amplified according to the input value to the quadrature mirror filter 124 and the D/A converter 138.

The quadrature mirror filter 124 may be suitable for sending, for example, frequency components of 0 Hz to 340 kHz of the provided output signal 108 to the phase compensator 146, while outputting frequency components of 340 Hz to 4 kHz without correction. This facilitates the design of the correction filter 12, which is the same as the second embodiment. The quadrature mirror filter 124 sends the output signal 128 to the phase compensator 146=Because the low-range signal, specifically 0Hz to 4kHz, has been obtained, in order to reduce the equipment scale, the quadrature mirror filter 124 can be omitted. The high range corrects only the consistency of phase or delay on the channel. The reason is that the quadrature mirror filter 124 is responsible for the conversion from the 0 Hz to 4 kHz signal to the 0 Hz to 4 kHz signal, and therefore does not perform substantial frequency conversion.

The phase compensator 146 compensates, for example, the phase, if the phase delay on the high-range signal 152 is caused by the frequency shifter 148 due to the frequency offset, etc. This frequency offset will be described later. If the delay or phase change due to the frequency offset is not caused, the frequency offset can be omitted. As the phase compensator 146, it is preferable to use a delay register. If so

200480005360.5 In order to compensate for delay and phase change, there is no restriction on the phase compensator 146. The phase compensator 146 outputs the output signal 150 of the phase management to the D/A converter 134.

The D/A conversion unit 132 includes D/A converters 134 for the low frequency range and the high frequency range, respectively, which are interconnected as shown. The D/A converter 138 converts the output signal 110 from the high range corrector 106 into an analog signal 144, and then sends it to the frequency shifter 148. The frequency shifter 148 frequency shifts the analog signal 144. Because the signal processing through the quadrature mirror filter is equivalent to the frequency shift from the 4kHz to 8kHz signal component in the signal sampled at the 16kHz frequency to the lower frequency side, processing is performed to finally restore the signal to the higher of 4kHz to 8kHz Frequency side. The voice band correction device 10 combines the output signals 140 and 152 from the D/A converter 134 and the frequency shift unit 148 with each other to output a combined output signal 26.

The operation of the sixth embodiment of the voice band correction device 10 will now be described. The input signal 18 in the frequency band of 0 Hz to 8 kHz sampled at a frequency of 16 kHz is supplied to the quadrature mirror filters 96 and 98. The input signal 18 has a high frequency range limited by the quadrature mirror filter 96. The quadrature mirror filter 96 samples the signal in the frequency range of 0 Hz to 4 kHz using a frequency of 8 kHz, thereby sending the output signal 100 to the low range corrector 104. The output signal 100 is amplified by the low range corrector 104.

The signal 108 amplified in the present embodiment is provided to the quadrature mirror filter 124. The filter 124 sends the signal 128 in the frequency bands of 0 Hz to 340 Hz and 340 Hz to 4 kHz to the phase compensator 146, and at the same time, the phase compensator 146 sends the signal 128 to the phase compensator 146. In the case of correction, the signal in the frequency range of 340Hz to 4kHz is output. However, a delay adjuster, not shown, is provided to adjust the delay in the signal in the frequency bands of 0 Hz to 340 Hz and 340 Hz to 4 kHz.

If the frequency offset of the higher sub-band signal has caused a phase delay, etc., the phase compensator 146 phase compensates the amplified and band-limited signal 128. It should be noted that it has been used for simulation in the design stage, for example. The condition of the phase delay. The phase compensator 146 preferably operates in this manner in response to the condition being met. The D/A converter 134 converts the lower sub-band signal 150 obtained by combining the phase compensation signal and the signal in the 340 Hz to 4 kHz frequency band into a corresponding analog signal.

For higher sub-band signals, the frequency of 0Hz to 8kHz sampled at 16kHz

The input signal 18 in the first rate range of 200480005360.5 has a lower sub-band signal limited by the QMF 98. The quadrature mirror filter 98 uses a frequency of 8kHz to sample the signal in the frequency range of 4kHz to 8kHz to send the sampled signal 102 to the high-range corrector 106. In this high-range correction unit 106, the output signal 102 is amplified according to the input value. Numerical value.

This amplified signal 110 is converted into an analog signal 144 by the D/A converter 138, which is frequency shifted by the frequency shifter 148. The sum is reset to the high-range output signal 152 and the low-range output signal 140 of the original frequency band, and is sent as the output signal 26 of the speech band correction device 10.

Through this operation, even if the input signal is amplified to the maximum value in the form of a digital signal in each frequency range, and then the summation is performed in the analog signal domain, there is no upper limit of the summation in the analog signal domain, so this can be amplified. The voice frequency band, while maintaining the natural sound quality without the limitation of digital summation, even if the amplitude becomes very large due to the addition and combination.

Using the above-mentioned configuration of the voice band correction device 10, the signal level of the frequency band of interest is amplified by the correction filter 12, and the level detector 16 compares the electrical level of the output signal from the correction filter 12 supplied to the level detector 16. Level and the corresponding predetermined level, the detection signal obtained by the detection is provided to the coefficient controller 14, the coefficient controller 14 adjusts the signal level in a control manner, and the control signal 24 is provided to the correction filter 12. In this way, the input signal 18 is corrected into a wideband signal without performing excessive amplification of the input signal 18 that causes a reduction in the quality of the communication signal, thereby ensuring high-quality transmission.

By providing the amplifier 28 and the amplitude controller 30 as a level adjuster to adjust the level of the input signal 18 to be supplied to the correction filter 12, the wideband signal thus corrected can be provided as a high-quality signal. Furthermore, by providing a low-range filter 36, a delay-only intermediate filter 38, and a high-range filter 40 as the correction filter 12, by providing amplitude measurement circuits 48 and 50 in the level detector 16, and eliminating the band limit input The coefficient update circuits 56 and 58 related to the filter of the frequency band signal of the signal 18 and the multipliers 60 and 62, that is, the low-range filter 36 and the high-range filter 40, are further provided with an adder 34, which can be used without affecting other frequency bands. In this case, the speech frequency band is expanded, so it has natural sound quality, even if the noise is in a specific frequency band. Moreover, with the configuration including the amplitude measurement unit 48 downstream, the provision of a single amplitude measurement unit 48 downstream of the adder 34 is sufficient

200480005360.5 This helps reduce the number of components.

Providing a band divider 80 on the input side of the coefficient controller 14 allows the three quadrature mirror filters 82, 84, and 86 to divide the input signal into corresponding frequency bands, and the correction filter with the correction filter outputs 88, 92, and 90 The device 12 is separated. This makes it sufficient to consider only the positive gain of the corresponding filter within the correction filter 12, thereby facilitating the design. The number of quantization steps can be made finer to support natural signal correction without reducing the real feeling of the sound. Among the combination of the quadrature mirror filters 82, 84, and 86, the filter 84 is provided with a signal of a frequency band other than the restricted frequency band of the band-limited input signal 18 that is delayed by a delay value equal to the delay of the correction filter 12 The function to ensure flexibility in system configuration.

By providing the quadrature mirror filter unit 94 for sampling the output signals 108 and 110 at a sampling frequency different from the sampling frequency applied to the output of the correction filter 12, it is possible to output a signal that complies with the provisions of ITU-T Recommendation G.722 signal.

Also, using the illustrated voice band correction device of the present invention, in which the input signal is divided into corresponding frequency bands by the band divider 80 to send the resultant signal to the correction filter 12, for each frequency band obtained by the division to pass the correction The filter 12 corrects the signal level, and the D/A conversion unit 132 converts the corrected signal into an analog signal, and then combines them together. It is possible to expand the voice frequency band while maintaining the natural sound quality without being restricted, such as restrictions imposed by the digital representation boundary, even if the signal is amplified by the correction filter 12 to be close to the bit representation boundary in the digital signal technology.

Specifically, the low-pass filter 82 and the high-pass filter 86 of the band divider 80 are provided with a delay equivalent to the delay caused by the filtering of the signal band other than the limited band of the band-limited input signal to the low-pass filter 82 and the high-pass filter 86 of the band divider 80, and by providing The delay effective for the processing delay caused by the filter 38 is given to the intermediate filter 84, which can divide the function of the correction filter 12, and it is enough to consider only the positive gain when designing the correction filter 12, thereby facilitating the design. The number of quantization steps can be made finer to allow natural signal correction without reducing the real feel of the sound.

Even if the input signal is amplified to the maximum value in the form of a digital signal in each frequency range, and then the summation is performed in the form of an analog signal, there is no upper limit of the summation, thereby expanding the speech frequency band, even if the amplitude is caused by the addition combination In the case of becoming very large, the natural voice quality without the limitation of digital summation is maintained at the same time.

200480005360.5 In the correction filter 12, the input frequency band signal is amplified by the filters 36 and 40, while the filter 38 provides a delay equivalent to the signal delay of the frequency band excluding the limited frequency band of the input signal, so that even in each frequency range Amplify the input signal to the maximum value in the form of a digital signal, and then perform the summation in the form of an analog signal, where there is no upper limit on the summation. Therefore, the speech frequency band can be expanded, even when the amplitude becomes very large due to the addition combination, while maintaining the natural sound quality without the limitation of digital summation.

By providing quadrature image filters 96 and 98 in the band splitter 80 for dividing into low range and high range, in accordance with ITU-T Recommendation G.722, by providing a low range corrector 104 and high range in the correction filter 12 The range corrector 106, by using the frequency shifter 148 to shift the frequency of the output signal 144 of the D/A converter 138 to the original frequency band, that is, toward the higher sub-band, the lower and higher sub-band signals can be combined together In order to provide a standard-compliant output signal as a high-quality signal.

In this regard, a quadrature mirror filter 124 is provided downstream of the low range corrector 104 to allow further band division processing. Moreover, by shifting the frequency of the output signal 128 of the quadrature mirror filter 124 to adjust the phase or delay accordingly in the phase compensator 146, it is possible to provide high-quality voice in compliance with standards without degrading the quality of the communication signal.

The entire disclosure of Japanese Patent Application JP2003-50832 filed on February 27, 2003, including the disclosure, claims, drawings, and abstract, is hereby incorporated by reference in its entirety.

Although the present invention has been described with reference to specific embodiments, it is not limited by these embodiments. It will be understood that those skilled in the art can change or modify these embodiments without departing from the scope and spirit of the present invention.

200480005360.5