JP2012083790A - Signal processor and signal processing method, program and recording medium, and reproducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency bandwidth expansion device, frequency bandwidth expansion method, a reproducer, and a reproducing method which can reproduce a signal where a high-frequency band is deleted with higher sound quality; a program causing a computer to perform reproduction processing; and a recording medium where the program is recorded.SOLUTION: A frequency bandwidth expansion device comprises: an expansion controller 11 for determining an expansion start bandwidth of an input signal in accordance with side information relating to the input signal; and a bandwidth divider 12 for performing bandwidth division of the input signal into a plurality of sub-band signals. A frequency bandwidth is expanded on the basis of the plurality of the sub-band signals on a lower frequency side than the expansion start bandwidth, among the plurality of the sub-band signals subjected to the bandwidth division by the bandwidth divider 12.

Description

  The present invention relates to a frequency band expansion device, a frequency band expansion method, a reproduction device, a reproduction method, and a reproduction that are optimal for reproducing encoded data encoded by deleting a signal in a high frequency band with higher sound quality. The present invention relates to a program for causing a computer to execute processing and a recording medium on which the program is recorded.

  In recent years, music distribution services that provide encoded data such as MP3 (International Standard ISO / IEC 11172-3, MPEG Audio Layer 3) are becoming widespread. In these services, the distribution of encoded data with a low bit rate is the mainstream so that it does not take time to download.

  In order to reduce the file capacity, encoded data of a low bit rate is often encoded by deleting a signal in a high frequency band of about 15 kHz or higher that is hardly perceived by the human ear. As a result, the file capacity is small, but there is a problem that the presence of the original signal is lost and the sound is muffled by deleting the high frequency band.

  On the other hand, encoding schemes such as HE-AAC (International Standard ISO / IEC 14496-3, High Efficiency MPEG4 AAC) generate a high frequency band of about 15 kHz or more by the band expansion technique and are close to the original signal. The high frequency component is reproduced. Also, in recent years, high frequency frequencies close to the original signal can be obtained by using post-processing band expansion technology that supplements the high frequency band by inputting the signal obtained by decoding the data encoded by deleting the high frequency band signal. The ingredients are reproduced.

  For example, in the technique presented in Patent Document 1, a high-frequency component is generated by mixing an input signal and a local oscillation signal to generate a high-frequency band, and filtering with a passband characteristic according to the encoding method and the genre of music. And the band is complemented by adding the input signal. Further, in the technique presented in Patent Document 2, an input signal is converted into a frequency domain using Fourier transform, an envelope of a high frequency band is estimated from a frequency spectrum of a low frequency band, and the envelope is followed. The frequency spectrum gain in the low frequency band is adjusted and pasted.

JP 2004-184472 A JP 2002-175092 A Japanese Patent No. 3538122

However, in the technique presented in Patent Document 1, the type of passband characteristic of the highpass filter that is learned in advance is limited, and flexibility in gain adjustment in the high frequency band cannot be obtained.
In the method presented in Patent Document 2, a time signal is obtained by performing Fourier transform, adjusting the amplitude in the frequency domain, and performing inverse Fourier transform, but time aliasing depending on the Fourier transform length is performed. There is a problem of getting up.

  In Patent Document 3, these problems are avoided by using a band division filter. FIG. 10 is a block diagram of a conventional reproducing apparatus proposed in Patent Document 3. In FIG. In this method, an input PCM (Pulse-Code Modulation) signal is decomposed into a plurality of subband signals by a band dividing unit 101. Further, the envelope estimation unit 102 estimates the frequency envelope of each frame, and the high frequency generation unit 103 generates a high frequency band sub-band signal. Finally, the band-expanded subband signal is input to the band combining unit 104, and the band-expanded PCM signal is output.

  However, the method of Patent Document 3 has three problems. The first problem is that as a result of processing in units of a certain frame, generation of a high frequency band signal that follows temporal variations in one frame of the input signal is not performed. The second problem is that when an extremely large signal is input, the signal in the high frequency band is also calculated correspondingly, and the output of the band synthesis filter may overflow. The third problem is that in a post-processing band expansion technique for inputting a signal obtained by decoding encoded data and complementing a high frequency band, the start frequency band for band expansion is unknown.

  The present invention has been made in view of these problems, and a frequency band expansion device and a frequency that can reproduce encoded data encoded by deleting a signal in a high frequency band with higher sound quality. It is an object of the present invention to provide a bandwidth expansion method, a playback device and a playback method, a program for causing a computer to execute playback processing, and a recording medium on which the program is recorded.

  In order to solve the above-described problem, a frequency band expanding apparatus according to the present invention includes an expansion control unit that determines an expansion start band of the input signal in the frequency band expanding apparatus that expands the frequency band of the input signal, and the input. Band dividing means for dividing the signal into a plurality of subband signals, and among the plurality of subband signals divided by the band dividing means, a plurality of subband signals on a lower frequency side than the expansion start band Based on the above, the frequency band is expanded.

  The frequency band expansion method according to the present invention is a frequency band expansion method for expanding a frequency band of an input signal, an expansion control step for determining an expansion start band of the input signal, and a plurality of subband signals. The frequency band is expanded on the basis of a plurality of subband signals lower than the expansion start band among the plurality of subband signals divided in the band dividing step. And a frequency band expanding step.

  The reproduction apparatus according to the present invention further comprises an expansion control means for determining an expansion start band of the input signal and a band division of the input signal into a plurality of subband signals. Band dividing means for expanding the frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals divided by the band dividing means. It is a feature.

  The reproduction method according to the present invention is a reproduction method for reproducing an input signal after expanding the band, and an expansion control step for determining an expansion start band of the input signal, and dividing the input signal into a plurality of subband signals. And a frequency band expansion for expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals divided in the band dividing step. And a process.

  According to another aspect of the present invention, there is provided a program for causing a computer to execute a process of reproducing an input signal after expanding the band, and an expansion control step for determining an expansion start band of the input signal; The frequency band is expanded based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals divided in the band dividing process. And a frequency band expanding step.

  The recording medium according to the present invention includes an expansion control step for determining an expansion start band of the input signal in a recording medium recorded with a program for causing a computer to execute a process of reproducing the input signal after band expansion, A band dividing step of dividing the input signal into a plurality of subband signals, and a plurality of subband signals lower than the expansion start band among the plurality of subband signals divided in the band dividing step. And a frequency band expansion step for expanding the frequency band based on the above.

  The frequency band expanding apparatus according to the present invention is a frequency band expanding apparatus that expands a frequency band of an input signal, an expansion control unit that determines an expansion start band of the input signal according to information about the input signal, and Band division means for dividing the input signal into a plurality of subband signals, and among the plurality of subband signals lower than the expansion start band divided by the band division means, continuous to the expansion start band. A transient detection means for transiently detecting a predetermined number of subband signals in the time direction, and group division for dividing the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection means And a predetermined number of subband signals based on an average value of group power for each group divided by the group dividing means. A power average value calculating means for calculating an average value of-and an envelope estimating means for extrapolating an envelope straight line of a plurality of subband signals equal to or larger than the expansion start band starting from the average value calculated by the power average value calculating means Band complement means for complementing a plurality of subband signals that are equal to or greater than the expansion start band based on the envelope straight line, a plurality of subband signals that are lower than the expansion start band, and a plurality that are equal to or greater than the expansion start band Based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided by the band dividing means. It is characterized by expanding the frequency band.

  According to the present invention, since the expansion start band of the input signal is determined and the frequency band is expanded based on the plurality of subband signals on the lower frequency side than the expansion start band, the input signal has higher sound quality. Can be played.

It is a block diagram which shows the structure of the frequency band expansion apparatus in this Embodiment. It is a figure which shows the relationship between side information and the expansion start frequency band sb. It is a figure which shows the frequency amplitude characteristic in case code | symbol degradation is severe. It is a flowchart which shows the flow of a process of the determination of the subband of transient detection. It is a schematic diagram which shows the mode of the envelope reference value by the difference in an average method. It is a flowchart which shows the flow of a process of calculation of the envelope reference value by a weighted average. It is a flowchart which shows the flow of a process of a restriction | limiting of an envelope reference value. It is a schematic diagram which shows the mode of a restriction | limiting of an envelope reference value. It is a schematic diagram which shows the mode of the phase adjustment of the subband signal of a low frequency side, and the subband signal of a high frequency side. It is a block diagram which shows the structure of the frequency band expansion apparatus of a conventional method.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, the input signal is reproduced with higher sound quality.

  FIG. 1 is a block diagram illustrating a configuration of a frequency band expansion device 10 according to the present embodiment. The frequency band expansion device 10 includes an expansion control unit 11, a band division unit 12, a time classification unit 13, an envelope estimation unit 14, a band complement unit 15, a high frequency generation unit 16, and a phase adjustment unit 17. And a band synthesizing unit 18.

  The expansion control unit 11 inputs side information regarding the input signal, such as the type of encoding method, the sampling rate, and the bit rate, determines the expansion start frequency band based on this side information, and supplies it to the band dividing unit 12. Note that the side information may be a value set in advance according to the type of encoding method of the input signal, or may be an arbitrary value set by the user.

  The band dividing unit 12 divides the input signal into a plurality of subband signals. Then, among the generated subband signals, a plurality of subband signals (hereinafter referred to as low band side subband signals) lower than the expansion start frequency band are transmitted to the band synthesizing unit 18 and the low band side subband signals are also transmitted. Among the band signals, a plurality of subband signals on the side close to the expansion start frequency band (hereinafter referred to as “expanded low band side subband signals”) are supplied to the time classification unit 13 and the high band generation unit 16.

  The time classifying unit 13 performs transient detection in the time direction of the expanded low-frequency subband signal, performs grouping in the time direction of the expanded low-frequency subband signal, and groups the expanded low-frequency subband signal An average sample power for each is generated and supplied to the envelope estimation unit 14.

  The envelope estimation unit 14 obtains the group power for each group from the sum of the average sample powers generated by the time classification unit 13, and calculates the average value of the group power of the entire extended low-frequency subband signal. Then, using the average value of the group power as a starting point, the envelope value of the subband higher than the expanded frequency band is estimated from the extrapolation by the linear line, and supplied to the band complementing unit 15.

  The band complementation unit 15 calculates a gain adjustment value from the expanded low band side subband signal to the high band side subband signal from the envelope value of the high band side subband and the envelope value of the low band side subband. To the high frequency generator 16.

  The high frequency band generation unit 16 multiplies the enlarged low band side subband signal by the gain adjustment value of the high frequency side subband to generate a high frequency side subband signal and supplies the generated high frequency band subband signal to the phase adjustment unit 17.

  The phase adjustment unit 17 shifts the phase of the high-frequency side subband signal generated by the high-frequency generation unit 16 and supplies it to the band synthesis unit 18.

  The band synthesizing unit 18 band-synthesizes the high-frequency side subband signal supplied from the phase adjusting unit 17 and the low-frequency side subband signal supplied from the band dividing unit, and outputs a band-enlarged signal. .

  As described above, by using the side information regarding the input signal, the expansion start frequency band to be expanded can be determined with high accuracy. In addition, since the subband signal on the higher frequency side than the expansion start frequency band is generated based on the expanded low frequency side subband signal close to the expansion start frequency band, the frequency band can be expanded with higher sound quality. Moreover, overflow can be prevented by shifting the phase of the generated high-frequency subband signal.

  Hereinafter, each component of the above-described frequency band expansion device will be described in more detail.

(Expansion control unit)
The expansion control unit 11 determines the expansion start frequency band based on the side information regarding the input signal. Examples of the side information include the type of encoding method, sampling rate, bit rate, and the like. Note that the side information may be a value set in advance according to the type of encoding method of the input signal, or may be an arbitrary value set by the user.

  Since the frequency band of the input signal generally has a correlation with various side information such as the type of encoding method, sampling rate, and bit rate, this side information is used in this embodiment. The frequency band of the input signal is estimated, and the expansion start frequency band sb for complementing the frequency band is determined. The determined expansion start frequency band sb is supplied to the band dividing unit 12.

  FIG. 2 is a diagram illustrating a relationship between the side information and the expansion start frequency band sb. The example shown in FIG. 2 shows a case where the frequency band of the input signal is divided into 16 parts, and the expansion start frequency band sb (sb is 0 or more and 15 or more) according to the encoding method, sampling rate, and bit rate. The following arbitrary constants) are determined. For example, when the side information is the encoding method B, the sampling rate is 44100 Hz, and the bit rate is 64-96 kbps, the expansion start frequency band sb is determined to be 9. In addition to the above, factors that determine side information may include differences between Stereo / Mono and CBR / VBR.

(Band division unit)
The band dividing unit 12 divides the input signal x (n) into 16 subband signals x (ib, n) (ib = 0 to 15, where the larger ib indicates the higher frequency subband signal. ). Of these 16 subband signals x (ib, n), subband signals x (ib, n) from 0 to the previous (sb-1) of the expansion start frequency band (hereinafter referred to as sb). n) is supplied to the band synthesizing unit 18 and the subband signals x (ib, n) from sb-4 to sb-1 are supplied to the time classifying unit 13 and the high frequency generating unit 16.

  In this embodiment, the input signal x (n) is described as being divided into 16 subband signals x (ib, n), but the number of subband divisions is not limited to this.

(Time classification part)
The time classifying unit 13 classifies as a separate group every time transient detection in the time direction such as the rise and fall of the sound is performed, and supplements the high frequency band for each group. As a result, sound quality deterioration can be prevented even in a natural acoustic signal having a non-steady part and a steady part and having a difference in gain and frequency characteristics. On the other hand, the technique described in Patent Document 3 performs frame processing, performs processing in units of frames, and complements a high frequency band. In other words, since natural acoustic signals are not separated and complementation is performed without considering temporal fluctuations, sound quality is deteriorated.

Calculation of time division and power envelope The subband signal x (ib, n) on the low frequency side from sb-4 to sb-1 supplied from the band division unit 12 is input. Each subband signal x (ib, n) is divided into 16 in the time direction, and one unit is defined as a slot. Then, an average sample power power (ib, islot) per sample is calculated for each slot from the subband signal x (ib, n). At this time, the number of samples per slot is 8.

-Grouping by transient detection In the subbands on the low frequency side from sb-4 to sb-1, the average sample power power (ib, islot) is set in the temporal direction (along the time axis) for all 16 slots. Compare with before and after) and perform transient detection of rise and fall. The transient detection here refers to detecting a portion where the average sample power has a large variation in the time direction.

  The ratio (ratio) between the slot being searched and the average sample power power (ib, islot-1) one slot before is calculated, and the ratio rises when the ratio is 16 times or more, and 1/16 (= 0.0625) ) When the time is equal to or less than double, the period from the slot that has been transiently detected in the past to the slot next to the slot that has been transiently detected in the past is defined as one group.

  When rising or falling is detected in a certain subband ib, it is assumed that transient detection has been performed in all the subbands on the low frequency side from sb-4 to sb-1.

  As a result, grouping is performed in consideration of time fluctuations, and it is possible to create a high frequency band component closer to a natural acoustic signal and to improve the sound quality.

  In this embodiment, the subband signals x (ib, n) on the low frequency side from sb-4 to sb-1 supplied from the band dividing unit are each divided into 16 in the time direction, and one unit thereof is divided. Although it is a slot, the number of divisions in the time direction is not limited. Further, although eight samples are used as slots, the number of divisions in the time direction and the number of samples in one slot are not limited. Also, when the ratio for transient detection is 16 times or more, it rises, and when it is 1/16 (= 0.0625) times or less, it falls, but depending on the number of band divisions and the number of divisions in the time direction, etc. The threshold value for detection of rising edge or falling edge may be changed to 16 or 1/16 (= 0.0625).

-Determination of transient detection target subbands In the grouping of encoded signals accompanied by code degradation, the accuracy of temporal fluctuations depends on the degradation of subband signals on the low frequency side to be subjected to transient detection. FIG. 3 is a diagram showing frequency amplitude characteristics when code deterioration is severe. As shown in FIG. 3, when the code deterioration a is severe, it can be seen as a phenomenon in which a hole is formed in the frequency axis, and the time classification unit 13 interprets the hole as a signal attenuation part, and even in a place where there is no transient part in the original signal. There is a problem that transient detection is performed. As a result, not only the sound quality deterioration due to the reduction in grouping accuracy, but also the amount of calculation due to transient detection is increased.

  Therefore, in the present embodiment, it is determined whether or not the subband is necessary for transient detection by using a comparison of the maximum values of the average sample power for each subband, and then actual transient detection is performed. . Even when all subbands are extremely minute signals, transient detection is not performed in order to prevent an increase in the amount of calculation due to picking up temporal fluctuations in a range that does not affect the sense of hearing.

  FIG. 4 is a flowchart showing a flow of processing for determining a target subband for transient detection.

  In steps S41 to S43, the maximum value is searched for among the average sample power power (ib, islot) of all 16 slots in the four subbands on the low frequency side from sb-4 to sb-1, Is the representative value max power (ib) of the subband.

  In step S44, the maximum value among the four representative values max power (ib) (ib = sb-4, sb-3, sb-2, sb-1) obtained in the four subbands on the low frequency side. A subband having a parent subband pb and the remaining subbands cb (0), cb (1), and cb (2). The representative value of the parent subband is set to max power (pb) (step S45).

  In step S46, if the representative value max power (pb) of the parent subband is a level equal to or higher than −80 [dBFs] based on the 16-bit full scale, the process proceeds to step S47.

  On the other hand, when the representative value max power (pb) of the parent subband is a level smaller than −80 [dBFs] based on the 16-bit full scale, no grouping in the time direction by transient detection is performed in all four bands on the low frequency side. . That is, there is no target subband (step S48). As a result, it is possible to prevent an unnecessary increase in the amount of calculation without performing transient detection of minute signals.

  In step S47, max power (ib) is −80 [dBBFs] or more and the representative value max power (cb () of a child subband cb (m) is compared with the representative value max power (pb) of the parent subband pb. If m)) is less than 0.0015625, the process proceeds to step S49, and no transient detection is performed in this subband.

  On the other hand, max power (ib) is −80 [dBBFs] or more, and the representative value max power (cb (m)) of the child subband cb (m) is smaller than the representative value max power (pb) of the parent subband pb. If the value is greater than 0.0015625, the process proceeds to step S50, and transient detection is performed in this subband. The target subband for transient detection includes the parent subband pb.

  As a result, it is possible to improve the sound quality by preventing erroneous detection of time fluctuation due to code deterioration and reproducing a time envelope closer to a natural acoustic signal. The average sample power power (ib, islot) of the four subbands ib on the low frequency side from sb-4 to sb-1 generated by the time classification unit 13 is supplied to the envelope estimation unit 14.

  In the present embodiment, transient detection is not performed if the ratio for transient detection is a subband having a value smaller than 0.0015625 times. However, depending on the number of band divisions and the number of divisions in the time direction, You may change 0.0015625 which is a threshold value for transient detection.

(Envelope estimation part)
The envelope estimation unit 14 first obtains the group power for each group from the sum of the average sample power power (ib, islot) generated by the time classification unit 13, and the low frequency side from sb-4 to sb-1 The average value of the group power of the subbands is calculated. Further, the envelope value of the subband on the high frequency side from sb to 15 is estimated from the extrapolation by the linear line, starting from the average value of the group power of the subband on the low frequency side. When the primary line of the envelope value is represented by ax + b, the reference point b is calculated by calculation of an envelope reference value by a weighted average described later, and the inclination a is determined by the envelope inclination value a_lev described later.

Calculation of group power The envelope estimation unit 14 receives the average sample power power (ib, islot) of the four subbands ib on the low frequency side from sb-4 to sb-1 supplied from the time classification unit 13. . In each subband ib, the total of the average sample power power (ib, islot) for the number of slots nslot (ig) present in each group is calculated for each group, and is calculated as group power tpow (ib, ig). To do. ig refers to the current group, which is 16 at the maximum.

・ Calculation of envelope reference value by weighted average
From the group power tpow (ib, ig) in each group obtained by the equation (4), the average value of the entire subband on the low frequency side from sb-4 to sb-1 is obtained. Here, when averaging is performed, a weighted average is used, and weights are given to subbands close to sb so that the frequency envelopes on the low frequency side and the high frequency side are smoothly connected.

  FIG. 5 is a schematic diagram showing an envelope reference value according to a difference in average method. Here, the difference in the averaging method will be described in the case where the group power tpow (sb-1, ig) of the subband sb-1 close to sb is smaller than the remaining subbands as shown in FIG.

  If an average value with an equal weight is used, as shown in FIG. 5 (A), it is calculated from the average value later from the influence of the group power tpow (ib, ig) of the remaining three subbands far from sb. The calculated reference point b is greatly calculated. As a result, the sub-band of sb-1 and the sub-band of sb are not smoothly connected, resulting in sound quality degradation.

  On the other hand, in the present embodiment, as shown in FIG. 5B, the average is calculated by assigning a large weight to the subbands close to sb, so that the frequency envelope can be smoothly connected.

FIG. 6 is a flowchart showing a flow of processing for calculating an envelope reference value by a weighted average.
In steps S61 to S63, group powers tpow (ib, ig) of the four sub-bands on the low frequency side from sb-4 to sb-1 are calculated. Then, a weighted average value w_avg (ig) is calculated for the group power tpow (ib, ig) in the order of, for example, 8: 4: 2: 1 from the subband closest to sb (step S64). A value w_avg (ig) is obtained (step S65).

  Subsequently, the group power of the subband sb is estimated using the weighted average value w_avg (ig) obtained from the four subbands on the low frequency side from sb-4 to sb-1. This value is equal to the reference value b and is called an envelope reference value fenv (ig). In the present embodiment, it is determined by multiplication with the connection reference adjustment value b_lev by the user. That is, the envelope reference value is not uniquely determined, but the user has an envelope reference adjustment function.

  Here, the envelope reference adjustment value b_lev is in the range of 0.25 to 1.0, and can be arbitrarily set by the user. In the present embodiment, the envelope reference adjustment value b_lev is set to 0.5 as a recommended value from a statistical frequency envelope of general music data, but the range of the envelope reference adjustment value b_lev is divided into bands. It may be changed according to the number, the expansion start frequency band sb, and the like.

・ Limit of envelope reference value
The envelope reference value fenv (ig) becomes an extremely large value depending on the weighted average value w_avg (ig) or the expansion strength e_lev, and the band synthesis output signal overflows as a result of synthesizing the subband signals in the band synthesis unit. there is a possibility. Therefore, in the present embodiment, an overflow of the output signal is prevented by applying a limiter so as not to take an extremely large value with respect to the envelope reference value fenv (ig).

  FIG. 7 is a flowchart showing a flow of the process of restricting the envelope reference value. FIG. 8 is a schematic diagram showing how the envelope reference value is restricted.

  In step S71, when the envelope reference value fenv (ig) is larger than the threshold −6 [dBFs] (= 16384 ^ 2 * nslot (ig)), the process proceeds to step S72, and the same as the threshold as shown in FIG. Force decay to level.

  On the other hand, when the envelope reference value fenv (ig) is equal to or smaller than the threshold value −6 [dBFs] (= 16384 ^ 2 * nslot (ig)) in step S71, the process proceeds to step S73, as shown in FIG. The envelope reference value fenv (ig) is used as it is.

  In the present embodiment, the threshold for limiting the envelope reference value fenv (ig) is set to −6 [dBFs], but may be changed according to the number of band divisions, the expansion start frequency band sb, and the like.

・ Determining the envelope value on the high frequency side
The envelope value env (ib, ig) of the subband on the high frequency side from sb to 15 is calculated by multiplying the envelope reference value fenv (ig) by the slope a. The inclination a is determined by the envelope inclination value a_lev. In the present embodiment, the inclination is not uniquely determined, but the envelope inclination adjustment function by the user is provided.

  Here, the envelope inclination value a_lev is in the range of 0.25 to 1.0, and can be arbitrarily set by the user. In the present embodiment, the envelope slope value a_lev is set to 0.5 as a recommended value based on the statistical envelope of general music data. You may change according to the start frequency band sb.

  The envelope value env (ib, ig) in the low band subband is synonymous with the group power tpow (ib, ig), and the group power in the low band expansion band is the low band envelope value.

  The low-frequency envelope value env (ib, ig) supplied from the time classification unit 13 from sb-4 to sb-1, and the high-frequency envelope value env from sb to 15 obtained by the above processing. (ib, ig) is supplied to the band complementer 15.

(Bandwidth complement)
The band complementing unit 15 adjusts the gain of the subband signals on the low frequency side from sb-4 to sb-1, and complements the subband signals on the high frequency side from sb to 15. The mapping pattern of the paired subbands is uniquely determined by sb.

  The low-frequency range from sb-4 to sb-1 in which the high-frequency envelope value env (ib, ig) supplied from the envelope estimation unit 14 and the source signal of the subband ib are present By taking the square root of the division with the envelope value env (sb_map (ib), ig) of the side subband sb_map (ib), the gain adjustment coefficient gain ( ib, ig).

  Then, the gain adjustment coefficient gain (ib, ig) of the high frequency side subband from sb to 15 obtained by the equation (12) is supplied to the high frequency generator 16.

(High-frequency generator)
The high frequency band generating unit 16 receives the subband signals x (ib, n) on the low frequency side from sb-4 to sb-1 supplied from the band dividing unit 12 and supplied from the band complementing unit 15. Also, the gain adjustment coefficient gain (ib, ig) of the subband on the high frequency side from sb to 15 is input. The subband signal x (sb_map (ib), n) on the low frequency side from sb-4 to sb-1 is converted to the gain adjustment coefficient gain (ib, ig) of the subband on the high frequency side from sb to 15. ) To obtain subband signals x (ib, n) on the high frequency side from sb to 15.

  Then, the subband signal x (ib, n) on the high frequency side from sb to 15 obtained by the equation (13) is supplied to the phase adjustment unit 17.

(Phase adjuster)
By the way, the high-frequency subband signals x (ib, n) from sb to 15 supplied from the band complementer 15 are four subband signals x ((sb-4 to sb-1) on the low frequency side. Since it is generated by sb_map (ib), n), the peak of the time signal also appears at the same timing in the low frequency side subband signal and the high frequency side subband signal. If all subbands are added together by band synthesis at the same timing peak, the band synthesis output signal may overflow.

  Therefore, in order to prevent overflow, the phase adjustment unit 17 shifts the peaks of the low-frequency side subband signal and the high-frequency side subband signal and inputs them to the band synthesis unit 18.

  FIG. 9 is a schematic diagram illustrating a state of phase adjustment between the low-frequency side subband signal and the high-frequency side subband signal. Here, the subband signal x (ib, n) on the high frequency side from sb to 15 is shifted back four samples on the time axis. That is, in the present embodiment, the subband signal x (ib, n) is delayed in the time direction within the range where it cannot be perceived using the backward masking characteristic of human hearing.

  Here, the delay of 4 samples is performed, but the delay of 4 samples may be changed according to the number of band divisions, the expansion start frequency band sb, the sampling frequency, and the like.

  The phase adjustment unit 17 supplies the subband signal x (ib, n) on the high frequency side from sb to 15 obtained by the sample shift to the band synthesis unit 18.

(Band synthesis unit)
The band synthesizing unit 18 includes a subband signal x (ib, n) on the high frequency side from sb to 15 supplied from the phase adjusting unit 17 and a low signal from 0 to sb-1 supplied from the band dividing unit 12. The band-side subband signal x (ib, n) is band-synthesized by the filter bank to obtain a band-synthesized output signal y (n).

  As described above, in the present embodiment, sb is determined according to side information, and the frequency band is expanded based on a plurality of subband signals lower than sb. The deleted signal can be reproduced with higher sound quality. Further, code deterioration of the subband signals on the low frequency side from sb-4 to sb-1 is detected, and transient detection of the subband signals on the low frequency side from sb-4 to sb-1 is detected according to the detection result. Therefore, an increase in the amount of calculation at the time of transient detection can be prevented. Also, the frequency envelopes on the low frequency side and the high frequency side are smoothly connected by weighting the low frequency side subband signals from sb-4 to sb-1 to the high frequency side and averaging the frequency envelopes. Can do. In addition, by applying band synthesis to the envelope reference value calculated from the low-frequency subband signals from sb-4 to sb-1, band overflow can be prevented. Further, by performing band synthesis by shifting the phase of the plurality of subband signals on the low frequency side from 0 to sb-1 and the phase of the plurality of subband signals from sb to 15, the overflow of the band synthesis output signal is prevented. be able to.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, the frequency band expansion device that processes a signal after decoding processing has been described as an example, but the present invention can also be applied to a playback device that includes decoding means. In the above-described embodiment, the hardware configuration has been described. However, the present invention is not limited to this, and arbitrary processing may be realized by causing a CPU (Central Processing Unit) to execute a computer program. Is possible. In this case, the computer program can be provided by being recorded on a recording medium, or can be provided by being transmitted via the Internet or another transmission medium.

  According to the present invention, since the expansion start band of the input signal is determined and the frequency band is expanded based on the plurality of subband signals on the lower frequency side than the expansion start band, the input signal has higher sound quality. Can be played.

DESCRIPTION OF SYMBOLS 10 Frequency band expansion apparatus, 11 Expansion control part, 12 Band division | segmentation part, 13 Time classification | category part, 14 Envelope estimation part, 15 Band complementation part, 16 High band production | generation part, 17 Phase adjustment part, 18 Band synthesis | combination part

The present invention relates to a signal processing apparatus and a signal processing method that are optimal for reproducing encoded data obtained by deleting a signal in a high frequency band with higher sound quality, a program for causing a computer to execute signal processing, and The present invention relates to a recording medium on which the program is recorded and a playback apparatus .

The present invention has been made in view of these problems, and a signal processing apparatus and signal processing capable of reproducing encoded data encoded by deleting a signal in a high frequency band with higher sound quality. It is an object to provide a method , a program for causing a computer to execute signal processing, a recording medium on which the program is recorded, and a playback device .

In order to solve the above-described problem, a signal processing apparatus according to the present invention includes an expansion control unit that determines an expansion start band of a frequency band of an input signal, and band division that band-divides the input signal into a plurality of subband signals. And a predetermined number of subband signals continuous to the expansion start band among a plurality of subband signals lower than the expansion start band divided by the band dividing means in the time direction, respectively. Transient detection means, group classification means for classifying the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection means, and a plurality of bands divided by the band division means Frequency expansion means for expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the subband signals .

An information processing method according to the present invention includes an expansion control step for determining an expansion start band of a frequency band of an input signal, a band division step for band-dividing the input signal into a plurality of subband signals, and the band division step. A transient detection step of transiently detecting a predetermined number of subband signals continuous to the expansion start band in the time direction among a plurality of subband signals lower than the expansion start band divided in band at A group classification step of classifying the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection step; and a plurality of subband signals band-divided in the band division step , that having a frequency expansion step of expanding the frequency band based on a plurality of sub-band signals of low-frequency side than the extension start band.

The reproduction apparatus according to the present invention further comprises an expansion control means for determining an expansion start band of the input signal and a band division of the input signal into a plurality of subband signals. And a predetermined number of subband signals continuous to the expansion start band among the plurality of subband signals lower than the expansion start band divided by the band dividing means in the time direction. The band is divided by the band detection means, the group detection means for classifying the predetermined number of subband signals into a plurality of groups in the time direction based on the transient detection result in the transient detection means, and the band division means. more of the subband signals, the frequency expansion unit to expand the frequency band based on a plurality of sub-band signals of low-frequency side than the extension start band was Equipped with a.

In addition, the program according to the present invention provides a computer with an expansion control step for determining an expansion start band of a frequency band of an input signal, a band division step for dividing the input signal into a plurality of subband signals, and the band division. A transient detection step of transiently detecting, in the time direction, a predetermined number of subband signals continuous to the expansion start band among a plurality of subband signals lower than the expansion start band divided in the step; A group classification step of classifying the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection step; and a plurality of subband signals band-divided in the band division step Of these, the frequency expansion process for expanding the frequency band based on a plurality of subband signals lower than the expansion start band is performed. A gram.

In addition, the recording medium according to the present invention provides a computer with an expansion control step for determining an expansion start band of a frequency band of an input signal, a band division step for dividing the input signal into a plurality of subband signals, and the band A transient detection step of transiently detecting, in the time direction, a predetermined number of subband signals continuous to the expansion start band among a plurality of subband signals lower than the expansion start band divided in the division step A group classification step of classifying the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection step, and a plurality of subband signals band-divided in the band division step A frequency expansion process for expanding a frequency band based on a plurality of subband signals lower than the expansion start band. A recording medium in which the ram is recorded.

Claims (16)

In the frequency band expansion device that expands the frequency band of the input signal,
Expansion control means for determining an expansion start band of the input signal;
Band dividing means for dividing the input signal into a plurality of subband signals,
A frequency band expanding apparatus that expands a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided by the band dividing unit. 2. The frequency band according to claim 1, further comprising: a band synthesizing unit that synthesizes a plurality of subband signals lower than the expansion start band and a plurality of subband signals greater than or equal to the expansion start band. Enlarging device.   The band synthesizing unit performs band synthesis by shifting a phase of a plurality of subband signals lower than the expansion start band and a phase of a plurality of subband signals equal to or greater than the expansion start band. Item 3. The frequency band expanding device according to Item 2. 2. The frequency band expanding apparatus according to claim 1, wherein the expansion control means comprises: determining an expansion start band of the input signal based on information relating to the input signal. Transient detection for transiently detecting, in the time direction, a predetermined number of subband signals continuous to the expansion start band among a plurality of subband signals lower than the expansion start band divided by the band dividing means. Means,
The frequency band expanding apparatus according to claim 1, further comprising group dividing means for dividing the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection means. Power average value calculating means for calculating the average value of the power of the predetermined number of subband signals based on the average value of group power for each group divided by the group dividing means;
Envelope estimation means for extrapolating envelope straight lines of a plurality of subband signals equal to or larger than the expansion start band starting from the average value calculated by the power average value calculation means;
6. The frequency band expanding apparatus according to claim 5, further comprising: band complementing means for complementing a plurality of subband signals equal to or greater than the expansion start band based on the envelope straight line.   6. The frequency band expansion according to claim 5, wherein the transient detection means detects code deterioration of the predetermined number of subband signals and transiently detects the predetermined number of subband signals according to the detection result. apparatus.   7. The frequency according to claim 6, wherein the power average value calculating means calculates the average power value of the predetermined number of subband signals by weighting the predetermined number of subband signals to a high frequency side. Bandwidth expansion device.   7. The frequency band expanding apparatus according to claim 6, wherein the envelope estimation means extrapolates an envelope straight line starting from the threshold value when the average value calculated by the power average value calculation means is larger than the threshold value. In the frequency band expansion method for expanding the frequency band of the input signal,
An expansion control step for determining an expansion start band of the input signal;
A band dividing step of dividing the input signal into a plurality of subband signals;
A frequency band expanding step of expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided in the band dividing step. A characteristic frequency band expansion method. In a playback device that plays back an input signal after expanding the band,
Expansion control means for determining an expansion start band of the input signal;
Band dividing means for dividing the input signal into a plurality of subband signals,
A reproduction apparatus that expands a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals that are band-divided by the band dividing means.   The playback apparatus according to claim 11, wherein the input signal is a signal obtained by decoding encoded encoded data. In a playback method for playing an input signal after expanding the band,
An expansion control step for determining an expansion start band of the input signal;
A band dividing step of dividing the input signal into a plurality of subband signals;
A frequency band expanding step of expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided in the band dividing step. A characteristic reproduction method. In a program for causing a computer to execute a process of reproducing an input signal after expanding the band,
An expansion control step for determining an expansion start band of the input signal;
A band dividing step of dividing the input signal into a plurality of subband signals;
A frequency band expanding step of expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided in the band dividing step. A featured program. In a recording medium recorded with a program for causing a computer to execute a process of reproducing an input signal after expanding the band,
An expansion control step for determining an expansion start band of the input signal;
A band dividing step of dividing the input signal into a plurality of subband signals;
A frequency band expanding step of expanding a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided in the band dividing step. A characteristic recording medium. In the frequency band expansion device that expands the frequency band of the input signal,
Expansion control means for determining an expansion start band of the input signal in accordance with information on the input signal;
Band dividing means for dividing the input signal into a plurality of subband signals;
Transient detection for transiently detecting, in the time direction, a predetermined number of subband signals continuous to the expansion start band among a plurality of subband signals lower than the expansion start band divided by the band dividing means. Means,
Group dividing means for dividing the predetermined number of subband signals into a plurality of groups in the time direction based on a transient detection result in the transient detection means;
Power average value calculating means for calculating the average value of the power of the predetermined number of subband signals based on the average value of group power for each group divided by the group dividing means;
Envelope estimation means for extrapolating envelope straight lines of a plurality of subband signals equal to or larger than the expansion start band starting from the average value calculated by the power average value calculation means;
Band complementing means for complementing a plurality of subband signals equal to or greater than the expansion start band based on the envelope straight line;
Band combining means for combining the plurality of subband signals lower than the expansion start band and the plurality of subband signals greater than or equal to the expansion start band,
A frequency band expanding apparatus that expands a frequency band based on a plurality of subband signals lower than the expansion start band among the plurality of subband signals band-divided by the band dividing unit.

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