KR20080042696A - Frequency band extending apparatus, frequency band extending method, player apparatus, playing method, program and recording medium - Google Patents

Abstract

A frequency band extending apparatus, a frequency band extending method, a reproducing apparatus, a reproducing method, a program and a recording medium are provided to determine an extending start band of an input signal and extend a frequency band based on plural sub band signals of a lower band side lower than the extending start band, thereby reproducing the input signal with high sound quality. A frequency band extending apparatus(10) comprises an extending controller(11), a band divider(12), a time classifier(13), an envelope estimator(14), a band complementing unit(15), a high frequency band generator(16), a phase regulator(17), and a band synthesizer(18). The extending controller determines an extending start frequency band based on side information related to an input signal. The band divider divides the input signal to sixteen sub band signals. The time classifier provides the envelope estimator with average sample power of four sub bands of a lower band side from sb-4 to sb-1. The envelop estimator provides the band complementing unit with an envelope value of the sub band signal of the low band side from the sb-4 to sb-1 and an envelope value of a sub band of a high band side from sb to 15. The band complementing unit provides the phase regulator with the sub band signal of the high band side from the sb to 15. The phase regulator provides the band synthesizer with the sub band signal of the high band side from the sb to 15. The sb is determined according to the side information, and a frequency band is extended based on the plural sub band signals of the low band side lower than the sb.

Description

Frequency band expanding apparatus and frequency band expanding method, reproducing apparatus and reproducing method, program and recording medium {Frequency band extending apparatus, frequency band extending method, player apparatus, playing method, program and recording medium}

The present invention provides a frequency band expanding apparatus and a frequency band expanding method, a reproducing apparatus and a reproducing method, and a reproducing process for executing a reproducing process on a computer capable of reproducing encoded encoded data with higher sound quality after deleting a signal of a high frequency band. This relates to a recorded recording medium.

Recently, a music delivery service that provides encoded data such as MP3 (International Standard ISO / IEC 11172-3, MPEG Audio Layer 3) has been spreading. Most of these services distribute encoded data with reduced bit rates so that it does not take time to download data.

Low bit rate encoded data is often encoded by deleting components of signals belonging to high frequency bands above about 15 kHz that are difficult to hear in the human ear. As a result, the data has a small file capacity, but when the high frequency band signal is deleted, there is a problem that the actual feeling provided by the original signal is lost and the sound becomes dull.

In order to cope with such a problem, in encoding schemes such as HE-AAC (International Standard ISO / IEC 14496-3, High Efficiency MPEG4 AAC), band extension technology generates signal components belonging to a high frequency band of about 15 kHz or more. As a result, high frequency components close to the original signal are reproduced. Recently, a high frequency component close to the original signal is inputted by a post-processing band extension technique for removing a component of a signal belonging to a high frequency band and decoding the encoded data. Is played.

For example, Japanese Patent Application Publication No. In the technique proposed in JP 2004-184472 (Patent Document 1), a high frequency band is generated by mixing an input signal and a local oscillation signal, and filtered by a passband characteristic corresponding to an encoding method or a genre of music. The band is complemented by adding high frequency components and input signals. Japanese Patent Application Publication No. In the technique presented in JP 2002-175092 (Patent Document 2), the input signal is transformed into the frequency domain by Fourier transform, and the envelope of the high frequency band is estimated from the frequency spectrum of the low frequency band. Therefore, the gain of the frequency spectrum of the low frequency band is adjusted to comply with the envelope.

However, in the technique proposed in Patent Document 1, there is a limit to the kind of pass-pass characteristics of the high pass filter to be learned in advance, so that flexibility in gain adjustment of the high frequency band cannot be obtained. Further, in the technique proposed in Patent Document 2, the input signal is Fourier transformed to obtain the adjusted amplitude in the frequency domain, and as a result, the signal is inverse Fourier transformed to obtain the time domain signal, but this technique is dependent on the Fourier transform field. There is a problem in that time-domain aliasing occurs.

In addition, Japanese Patent No. This problem is avoided by using a band division filter in 3538122 (Patent Document 3). 10 is a block diagram of a reproducing apparatus of the prior art proposed in Patent Document 3. As shown in FIG. In this technique, the input pulse-code modulation (PCM) signal is decomposed into a plurality of subband signals by the band divider 101. The envelope estimator 102 estimates the frequency envelope in units of frames, and the high frequency band generator 103 generates a subband signal belonging to the high frequency band. Finally, the band-extended subband signal is supplied to the band synthesis section 104, and the band-extended PCM signal is output.

However, three problems arise in the technique proposed in the patent document 3. First, there is a problem that generation of a high frequency band signal due to temporal fluctuation within one frame of the input signal is not performed as a result of the processing performed in units of a certain number of frames. Second, when an extremely large signal is input, the signal of the high frequency band is also calculated very large correspondingly, and the output of the band synthesis filter may overflow. Third, in the post-processing band extension technique in which a signal obtained by decoding the encoded data is input and the high frequency band is complemented, the band starting frequency band for band extension cannot be known.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a frequency band expanding apparatus, a frequency band expanding method, a reproducing apparatus, a reproducing method, and a reproducing process capable of reproducing encoded data with higher sound quality by deleting components of signals belonging to a high frequency band. And a recording medium on which the program is executed by the computer.

In one embodiment of the present invention, there is provided a frequency band expanding apparatus for expanding a frequency band of an input signal. The frequency band expanding apparatus includes expansion control means for determining an extension start band of the input signal, and band dividing means for dividing the input signal into a plurality of sub band signals, wherein the input signal is divided by the band dividing means. A frequency band is enlarged based on a plurality of subband signals on the low side of the band-divided subband signals lower than the extension start band.

In another embodiment of the present invention, a frequency band expanding method for expanding a frequency band of an input signal is provided. The frequency band expansion method includes an expansion control step of determining an extension start band for an input signal according to information related to an input signal, a band division step of dividing the input signal into a plurality of subband signals, and the band division step in the band division step. Input signal is band-divided And a frequency band expanding step of expanding a frequency band on the basis of a plurality of subband signals on the low side of the plurality of subband signals that are lower than the extension start band.

In another embodiment of the present invention, there is provided a reproducing apparatus for reproducing an input signal after band widening the input signal. The playback apparatus includes expansion control means for determining an extension start band for an input signal in accordance with information related to the input signal, and band division means for dividing the input signal into a plurality of subband signals. The input signal is band-divided by A frequency band is enlarged based on a plurality of subband signals on the lower side of the plurality of subband signals than the extension start band.

In another embodiment of the present invention, there is provided a reproducing method of reproducing an input signal after band widening the input signal. The reproduction method includes an extension control step of determining an extension start band for an input signal in accordance with information related to the input signal, and a band division step of dividing the input signal into a plurality of subband signals. The input signal is band-divided by And a frequency band expanding step of expanding a frequency band on the basis of the plurality of sub band signals on the lower side of the plurality of sub band signals than the extension start band.

In another embodiment of the present invention, a program is provided for causing a computer to execute a process of reproducing an input signal after band widening the input signal. The program includes an extended control step of determining an extension start band of an input signal according to the information related to the input signal, and a band division step of dividing the input signal into a plurality of subband signals. The input signal is band-divided by A computer may be provided with a frequency band expanding step in which a frequency band is expanded based on a plurality of sub band signals on a lower side of the plurality of sub band signals than the extension start band.

In another embodiment of the present invention, a recording medium is provided in which a program for causing a computer to execute a process of reproducing an input signal after band-extending the input signal is provided. The program includes an expansion control step of determining an extension start band for the input signal, and a band division step of dividing the input signal into a plurality of subband signals, wherein the input signal is band-divided by the band division step. A computer may be provided with a frequency band expanding step in which a frequency band is expanded based on a plurality of sub band signals on a lower side of the plurality of sub band signals than the extension start band.

According to the embodiment of the present invention, the extended start band of the input signal can be determined, and the frequency band is expanded based on a plurality of subband signals on the lower side of the extended start band. Therefore, the input signal can be reproduced with high sound quality.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. This embodiment allows the input signal to be reproduced in high quality.

1 is a block diagram showing the configuration of the frequency band expanding apparatus 10 according to the present embodiment. The frequency band expanding apparatus 10 includes an expansion control section 11, a band dividing section 12, a time classifying section 13, an envelope estimating section 14, a band complementing section 15, and a high frequency band generating section 16. And a phase adjuster 17 and a band synthesizer 18.

The expansion control unit 11 is supplied with side information such as the type of the encoding scheme, the sampling rate, and the bit rate related to the input signal, and determines the extension start frequency band based on the side information and divides the determined extension start frequency band into bands. Supply to installment 12. Optionally, the side information may be a preset value or an arbitrary user-specified value according to the type of encoding scheme of the input signal.

The band dividing unit 12 divides the input signal into a plurality of sub band signals. As a result, the band dividing unit 12 supplies a plurality of sub band signals (hereinafter, referred to as low band sub band signals) on the lower side of the generated sub band signals to the band combining unit 18 from the extension start frequency band. do. In addition, the band dividing section 12 generates a plurality of sub band signals (hereinafter, referred to as extended low band subband signals) closer to the extended starting frequency band among the plurality of low band subband signals, by the time classifying section 13 and the high frequency band generation. It supplies to the part 16.

The time classifying unit 13 performs transient detection in the time direction of the extended low pass subband signal, groups the extended low pass subband signal in the time direction, generates an average sample power for each group of the extended low pass subband signal, This average sample power is supplied to the envelope estimation unit 14.

The envelope estimation unit 14 obtains group power for each group from the sum of the average sample powers generated by the time classifying unit 13, and calculates an average value of the group powers of the entire extended low-band subband signal. Based on the average value of the group powers, the envelope value of the subband on the higher frequency side than the extended frequency band is estimated, and the estimated envelope value is supplied to the band complementer 15.

The band complementer 15 calculates a gain adjustment value from the envelope of the high band subband and the low band subband to the extended low band subband signal to the high band subband signal, and calculates the calculated gain adjustment high frequency. Supply to the band generation unit 16.

The high frequency band generation unit 16 multiplies the gain adjustment value of the high band subband signal by the extended low band subband signal to generate a high band subband signal, and the generated high band subband signal is converted into a phase adjuster ( 17).

The phase adjuster 17 changes the phase of the high band side subband signal generated by the high frequency band generator 16 and supplies the band combiner 18 with the subband signal whose phase on the high band side is changed.

The band combining section 18 band synthesizes the high band subband signal supplied from the phase adjusting section 17 and the low band subband signal supplied from the band dividing section, and outputs the resulting band-expanded signal.

By using side information related to the input signal in this way, the extension start frequency band for band extension can be determined with high precision. Further, since the subband signal on the higher side than the extended start frequency band is generated based on the extended low band subband signal closer to the extended start frequency band, the frequency band can be expanded to higher quality. In addition, overflow can be prevented by changing the phase of the generated high band subband signal.

Hereinafter, each component of the above-mentioned frequency band expanding apparatus will be described in detail.

Extended control

The expansion control unit 11 determines the expansion start frequency band based on side information related to the input signal. This side information includes the type of encoding scheme, the sampling rate, the bit rate, and the like. Optionally, the side information may be a preset value or any user specified value according to the type of the encoding scheme of the input signal.

In general, the frequency band of the input signal has a correlation with various side information such as the type of the encoding scheme, the sampling rate, and the bit rate. Therefore, in this embodiment, the side information is used to estimate the frequency band of the input signal, and to determine the extended start frequency band sb to complement the frequency band. The determined extended start frequency band sb is supplied to the band divider 12.

2 is a diagram illustrating a relationship between side information and an extended start frequency band sb. As shown in Fig. 2, the frequency band belonging to the input signal is divided into 16 subbands, and the extended starting frequency band sb (sb is arbitrary from 0 to 15 depending on the encoding method, the sampling rate and the bit rate). Is determined). For example, when the encoding method of side information is B, the sampling rate is 44100 Hz, and the bit rate is 64-96 kbps, the extended start frequency band sb is determined to be nine. Elements for determining side information include stereo / mono, CBR / VBR, and the like.

treason Division

The band divider 12 divides the input signal x (n) into 16 subband signals x (ib, n). (Ib = 0 to 15, where the greater the id, the higher band the subband signal. Of the 16 subband signals x (ib, n) from subband 0 to subband sb-1 before one subband of the extended start frequency band (hereinafter, referred to as sb). The subband signal x (ib, n) belonging to the subband of the region is supplied to the band combining section 18, and the subband signal x (ib, n belonging to the subband from sb-4 to sb-1. ) Is supplied to the time classifying section 13 and the high frequency band generating section 16.

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

time Classification

The time classifying section 13 classifies signals into different groups each time to detect transients in the time direction, such as rising or falling of the sound, and complements the high frequency bands for each group. Sound deterioration can be prevented even for a natural sound signal having a state and having a difference in gain and frequency characteristics. On the other hand, in the technique proposed in Patent Document 3, frame processing is performed, and processing is performed on a frame-by-frame basis to supplement the high frequency band. In other words, the complementation is performed without separating the acoustic signal of the natural system and without considering the time variation. This causes the sound quality deterioration.

ㆍ Calculation of time division and power envelope

The low-band subband signals x (ib, n) from sb-4 to sb-1 supplied from the band dividing section 12 are used as inputs. Each subband signal (x (ib, n)) is divided into sixteen, which is a unit called a slot. The average sample power per power (ib (is, islot)) is calculated for each slot, and the number of samples in each slot is set to eight.

Grouping by transient detection

In the subband on the low side from sb-4 to sb-1, the average sample power (ib (is, islot)) is compared in the time direction (before and after along the time axis) for all 16 slots, rising and falling Transient detection is performed to detect this. The term overdetection refers to the detection of a position where the average sample power exhibits a large variation in time direction.

The ratio of the average sample power (power (ib, islot-1)) between the slot under search and the slot before the slot is calculated, and when the ratio is 16 times or more, it is judged as an increase, and the ratio is 1/16. If it is less than (= 0.0625) times, it is determined to fall and temporarily forms a group from the slot in which the transient was detected in the past to the next slot of the slot in which the current transient is detected.

When rising or falling is detected in any subband ib, it is assumed that rising and falling are detected in all subbands on the low side from sb-4 to sb-1.

As a result, since the grouping is performed by following the time variation, it is possible to generate a high frequency band component closer to the acoustic signal of the natural system, so that high sound quality can be calculated.

In the present embodiment, the subband signals (x (ib, n) on the low-side side from sb-4 to sb-1 supplied from the band dividing unit are each divided into 16 in the time direction, and the unit is divided into slots. However, the number of divisions in the time direction is not limited. In addition, although one slot contains 8 samples, the number of divisions in the time direction and the number of samples in one slot are not limited. In addition, when the ratio for transient detection is 16 times or more, it is judged as rising, and when the ratio is 1/16 (= 0.0625) times or less, it is determined as falling, and the rise and fall in response to the number of band divisions, the number of divisions in the time direction, etc. The threshold for detection can be changed.

• Determination of the subband to detect the transient

In grouping encoded signals with code degradation, the accuracy of time variation depends on the degradation state of the subband signal on the low-band side of the object to be subjected to transient detection. 3 is a diagram illustrating frequency amplitude characteristics in the case of severe code degradation. As shown in Fig. 3, when the code degradation (a) is intense, it is shown as a hole on the frequency axis, and the time classifying section 13 interprets the hole as a signal attenuation state so that a transient portion exists in the original signal. There is a problem of detecting a faulty transient even in a place where it is not. As a result, the sound quality deteriorates because the accuracy of grouping is lowered, and the amount of calculation is increased by such transient detection.

For these problems, in this embodiment, the maximum value of the average sample power is compared for each subband, and it is determined whether or not it is a subband required for transient detection. Thereafter, actual transient detection is performed. In addition, the transient detection is not performed in order to prevent an increase in the amount of calculation due to time fluctuations in the unacceptable range in the case where all the subbands are extremely minute signals.

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

In steps S41 to S43, in each of the four subband signals on the low side from sb-4 to sb-1, the maximum value (power (ib, islot)) of the average sample power of all 16 slots is retrieved. This maximum value is set to the representative value max power (ib) of the subband.

In step S44, the maximum value among four representative values (max power (ib) (ib = sb-4, sb-3, sb-2, sb-1) obtained in each of the four subbands on the low side is determined. The branch subband is set to the parent subband pb, and the rest is set to the child subbands cb (0), cb (1), and cb (2). The representative value of the parent band is set as max power (pb) (step S45).

If it is determined in step S46 that the representative value max power (pb) of the parent subband is equal to a level of -80 [dBFs] or more based on the 16-bit full scale criterion, the process proceeds to step S47. .

On the other hand, when the representative value (max power (pb)) of the parent subband is equivalent to a level smaller than -80 [dBFs] based on a 16-bit full scale criterion, the time due to the transient detection for the four bands on the low side No direction grouping is done. This means that there is no subband (step S48). As a result, the transient detection of the minute signal is not performed, and it is possible to prevent an unnecessary increase in the calculation amount.

In step S47, it is determined that max power (ib) is equal to or greater than -80 [dBFs], and any child subband cb (m) with respect to the representative value max power (pb) of the parent subband pb. If the representative value (max power (cb (m))) is smaller than 0.0015625 times, the process proceeds to step S49, where no transient detection is performed for this subband.

On the other hand, max power (ib) is greater than or equal to -80 [dBFs], and the representative value max of any child subband cb (m) with respect to the representative value max power (pb) of the parent subband pb. If power (cb (m)) is a value of 0.0015625 times or more, the process proceeds to step S50 where transient detection is performed for this subband. The subband for transient detection also includes a parent subband pb.

As a result, high quality sound can be reproduced by preventing the error detection of the time fluctuation due to code degradation and reproducing the time envelope close to the natural sound signal. The average sample power (ib, islot) of the four subbands ib on the low pass side from sb-4 to sb-1 generated by the time classifying unit 13 is supplied to the envelope estimating unit 14.

In the present embodiment, the transient detection is not performed on the subband in which the ratio for transient detection is smaller than 0.0015625 times, but the threshold value for transient detection is changed to 0.0015625 corresponding to the number of band divisions, the number of divisions in the time direction, and the like. Also good.

Envelope Estimator

The envelope estimation unit 14 first obtains the group power for each group from the sum of the average sample powers (powe r (ib, islot)) generated by the time classifying unit 13, and sb-4 to sb-1. The average value of the group powers of the subbands on the low side is calculated. Then, the envelope value of the high band subband from sb to 15 is estimated by the external insertion based on a linear straight line starting from the average value of the group power of the subband of the low band side. When the linear straight line of an envelope value is represented by ax + b, the reference point b is obtained by calculation of the envelope reference value by the weighted average mentioned later, and the inclination a is obtained by the envelope inclination value a'le 'mentioned later.

ㆍ Calculation of group power

The envelope estimation unit 14 takes as input the average sample power (ib, islot) of the four subbands ib on the low side from sb-4 to sb-1 supplied from the time classifying unit 13. . In each subband ib, the sum of the average sample power power (ib, islot) as the number of slots nslot (ig) present in each group is calculated for each group, and ig represents the current group. The sum is set as a group power (tpow (ig, ib)) of up to 16 groups.

ㆍ Calculation of envelope standard value by weighted average

From the group power tpow (ig, ib) in each group obtained by equation (4), the average value of the entire low-band subband signal from sb-4 to sb-1 is obtained. Here, by assigning a greater weight to a subband close to sb using a weighted average to obtain an average value, in this embodiment, the low-side envelope can be more smoothly connected to the high-side envelope.

5 (a) and 5 (b) are schematic diagrams showing envelope reference values based on different average methods, respectively. Here, as shown in Figs. 5A and 5B, the group power tpow (sb-1, ig) of the subband sb-1 proximate to sb is the group power of the remaining subbands. The difference that results from other averaging methods for small cases compared to

Using an average with an even weight, it is later calculated from the average because of the effect of the magnitude of the group power tpow (ib, ig) of the remaining three subbands away from sb, as shown in FIG. The reference point b is calculated with a large value. As a result, the sub band sb-1 and the sub band sb are not smoothly connected, and sound quality deterioration occurs.

Meanwhile, in the present embodiment, as shown in FIG. 5 (b), the frequency envelope can be smoothly connected by allocating a larger weight to a subband close to sb and calculating an average.

6 is a flowchart showing the flow of processing for calculating the envelope reference value based on the weighted average. In steps S61 to S63, the group power tpow (ig, ib) of each of the four subbands on the low side from sb-4 to sb-1 is calculated. Then, in order to obtain the weighted average value (w＿aｖg (ig)) for the group power tpow (ig, ib) in order from the subband closest to sb, for example, at a ratio of 8: 4: 2: 1 ( Step S64) A weighted average is performed (step S65).

Subsequently, the group power of the subband sb is estimated using the weighted average value w \ aigg (ig) obtained from the four subband signals on the low side from sb-4 to sb-1. This value is the same as the reference value b, and is called the envelope reference value (fen_ (ig)). In this embodiment, this value is determined by multiplying the user specified envelope criterion adjustment value b_le \. That is, the envelope criterion is not uniquely determined, but a user controllable envelope criterion adjustment function is provided.

In the embodiment of the present invention, the envelope criterion adjustment value b'le 'is in the range of 0.25 or more and 1.0 or less and can be arbitrarily set by the user. In the embodiment of the present invention, the envelope criterion adjustment value b＿le＿ is set to 0.5 as a recommended value based on the frequency envelope obtained by statistical analysis of general music data. However, the range of the envelope reference adjustment value b ＿le 수 may be changed in correspondence to the number of band divisions and the extended starting frequency band sb.

ㆍ Restriction of envelope standard

The envelope reference value (fenｖ (ig)) is extremely large depending on the weighted average value (w＿aｖg (ig) or extended intensity (e＿leｖ), and is a band-synthesized output signal that is the result of synthesizing the subband signal by the band synthesizer. May overflow. In view of such a situation, in the embodiment of the present invention, the overflow of the output signal can be prevented by applying a limiter so as not to receive an extremely large value for the envelope reference value fen_ (ig).

7 is a flowchart showing the flow of processing for limiting the envelope reference value. 8 (a) and 8 (b) are schematic diagrams showing how the envelope reference value is limited.

If it is determined in step S71 that the envelope reference value fen_ (ig) is greater than the threshold value 6 [dBFs] (= 16384_2 * nslot (ig)), the process proceeds to step S72. As shown in 8 (b), it is forcibly attenuated to the same level as the threshold.

On the other hand, when it is determined in step S71 that the envelope reference value fen_ (ig) is equal to or less than the threshold value-6 [dBFs] (= 16384_2 * nslot (ig)), the process proceeds to step S73. As shown in Fig. 8A, the envelope criterion value fen_ (ig) is directly used.

In the embodiment of the present invention, the threshold for limiting the envelope reference value (fen_ (ig)) is set to -6 [dBFs]. Optionally, the threshold may be changed in correspondence with the number of band divisions, extended start frequency band sb, or the like.

ㆍ Determine the envelope of the high 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 (tilt) a. The inclination a is determined by the envelope inclination value a'le '. In the embodiment of the present invention, the inclination is not uniquely determined, but a user controllable envelope inclination adjustment function is provided.

(a _- lev : envelope slope)

In the embodiment of the present invention, the envelope inclination value (a＿leｖ) is in the range of 0.25 or more and 1.0 or less, and can be arbitrarily set by the user. In the embodiment of the present invention, the envelope inclination (a＿leｖ) is set to 0.5 as a recommended value based on the frequency envelope obtained by statistically analyzing general music data, but the range of the envelope inclination (a＿leｖ) is the number of band divisions and expansion. The change may be made corresponding to the start frequency band sb or the like.

The envelope value (enｖ (ib, ig)) in the subband on the low side has the same meaning as the group power tpow (ib, ig), and the group power of the extended band on the low side is set as the envelope value on the low side. .

Envelopment values (en ｖ (ib, ig)) of the low-band subband signals from sb-4 to sb-1 supplied from the time classifying section 13 obtained by the above-described processing, and the high-band side from sb to 15 Envelopes en ｖ (ib, ig) of sub bands of are supplied to the band complementer 15.

treason Complement

The band complementing section 15 adjusts the gain of the low-band subband signal from sb-4 to sb-1, and compensates for the high-band subband signal from sb to 15. The mapping pattern of each pair of subbands is uniquely determined by sb.

Sb − in which the envelope values en ｖ (ib, ig) for each of the high-band subbands from sb supplied by the envelope estimation unit 14 to 15 are divided, and the source signal of the subband ib is present. By taking the square root of the divider obtained by the envelope (enｖ (sb＿map (ib), ig)) for each of the low-band subbands (sb＿map (ib)) from 4 to sb-1, Gain adjustment coefficients (gain (ib, ig)) of the subband on the high frequency side from sb to 15 are obtained.

Then, the gain adjustment coefficients gain (ib, ig) of the subband on the high band side from sb to 15 obtained by equation (12) are supplied to the high frequency band generation section 16.

High Frequency Band Generation Department

The high frequency band generation section 16 receives the subband signal x (ib, n) on the low-side side from sb-4 to sb-1 supplied from the band dividing section 12, and further includes a band complementing section. The gain adjustment coefficient gain (ib, ig) of the subband on the high frequency side from sb supplied at (15) to 15 is input. The gain adjustment coefficient (gain (ib) of the low band subband signal (x (sb_map (ib), n)) from sb-4 to sb-1 serving as the source signal and the high band subband from sb to 15 , ig)) to obtain the high-band subband signal x (ib, n) from sb to 15.

Then, the high band side subband signal x (i b, n) from sb to 15 obtained in the formula (13) is supplied to the phase adjuster 17.

Phase adjuster

By the way, the subband signal x (ib, n) on the high frequency side from sb to 15 supplied from the band complementer 15 is the four subband signals x on the low side side from sb-4 to sb-1. (sb_m ap (ib), n)). Therefore, the peak of the time domain signal appears at the same timing in the subband signal on the low side and the subband signal on the high side. When all subbands are added to each other by band synthesis at a point having a peak having the same timing, an overflow of the band synthesis output signal may occur.

In view of the above, in order to prevent the overflow, the phase adjusting unit 17 changes the peaks of the low band subband signal and the high band subband signal and inputs them to the band combining unit 18.

9 is a schematic diagram showing phase adjustment of a subband signal on the low side and a subband signal on the high side. Here, the high band subband signal (x (ib, n)) from sb to 15 is moved backward by four samples along the time axis. That is, in this embodiment, the subband signal x (ib, n) is delayed in the time direction within the range which cannot be listened to by using the backward time masking characteristic observed in the human auditory system.

Although the delay is performed with four samples here, the delay of four samples may be changed in correspondence to the number of band divisions, the extended start frequency band sb, the sampling frequency, and the like.

The phase adjuster 17 supplies the high band side subband signal x (ib, n) from sb to 15 obtained by sample-shifting to the band synthesizer 18.

treason Synthesis section

The band combiner 18 is a high band subband signal x (ib, n) from sb to 15 supplied from the phase adjuster 17 and from 0 to sb-1 supplied from the band divider 12. The low-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 embodiment of the present invention, sb is determined according to the side information, and then the frequency band is expanded based on a plurality of subband signals on the lower side of sb. Therefore, the signal from which the signal component belonging to the high frequency band is deleted can be reproduced with high sound quality. In addition, the code degradation of the subband signal on the low pass side from sb-4 to sb-1 is detected, and the transient detection of the subband signal on the low pass side from sb-4 to sb-1 is performed according to the degradation detection result. . Therefore, it is possible to prevent the calculation amount of the transient detection from increasing. In addition, the frequency bands on the low side and the high side can be smoothly connected by allocating the weight envelope close to the high side to the low band subband signals from sb-4 to sb-1. In addition, by performing band combining by applying a limiter to the envelope reference value calculated from the subband signals on the low-band side from sb-4 to sb-1, the overflow of the band combining output signal can be prevented. In addition, the phase of the plurality of subband signals belonging to the subbands sb to 15 in response to the plurality of subband signals from 0 to sb-1 may be changed to prevent the overflow of the band synthesis output signal. have.

This invention is not limited only to the above-mentioned embodiment, Of course, various changes are possible without deviating from the summary of this invention. In the embodiment of the present invention, a frequency band expansion apparatus for processing a signal after decoding processing has been described as an example. Optionally, the present invention is also applicable to a playback apparatus provided with decoding means. In addition, although demonstrated as a hardware structure in the above-mentioned embodiment, this invention is not limited to this. The present invention may be realized by executing a computer program by a CPU (Central Processing Unit) to perform any processing. In this case, the computer program may be provided to be recorded on the recording medium, and may be provided by transmission via the Internet or other transmission medium.

The present invention includes the contents related to Japanese Patent Application (JP 2006-304501) filed November 9, 2006 at the Japan Patent Office.

1 is a block diagram showing the configuration of a frequency band expanding apparatus according to an embodiment of the present invention.

2 is a diagram illustrating a relationship between side information and an extended start frequency band "sb".

3 is a diagram illustrating frequency amplitude characteristics in the case of severe code degradation.

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

5 (a) and 5 (b) are schematic diagrams showing envelope reference values based on different average techniques, respectively.

6 is a flowchart showing the flow of processing for calculating the envelope reference value based on the weighted average.

7 is a flowchart showing the flow of processing for limiting the envelope reference value.

8 (a) and 8 (b) are schematic diagrams showing that the envelope reference value is limited, respectively.

Fig. 9 is a schematic diagram showing phase adjustment of the subband signal on the low side and the subband signal on the high side.

Fig. 10 is a block diagram showing the construction of a frequency band expanding apparatus of the prior art.

[Explanation of symbols on the main parts of the drawings]

10: frequency band expansion device 11: expansion control unit

12: band divider 13: time classifier

14: envelope estimation unit 15: band complement

16: high frequency band generation section 17: phase adjustment section

18: band synthesis section

Claims (18)

In the frequency band expanding apparatus for expanding the frequency band of the input signal, Expansion control means for determining an extension start band of the input signal; Band dividing means for dividing the input signal into a plurality of sub band signals, And a frequency band is enlarged on the basis of a plurality of subband signals on the lower side of the plurality of subband signals in which the input signal is band-divided by the band dividing means, which is lower than the extended start band. The method of claim 1, And a band synthesizing means for synthesizing the plurality of subband signals on the lower side of the extended start band and the plurality of subband signals on the extended start band or more. The method of claim 2, And said band synthesizing means synthesizes by varying the phases of a plurality of subband signals on a lower side of said extended start band and a plurality of subband signals above said extended start band. The method of claim 1, And the expansion control means determines the expansion start band for the input signal using information related to the input signal as side information. The method of claim 1, Transient for detecting in the time direction a predetermined number of subband signals continuous to the extension start band from among a plurality of subband signals on the lower side of the extension start band where the input signal is band-divided by the band dividing means ( Vi) detection means; And group dividing means for dividing the predetermined number of subband signals into a plurality of groups in a time direction on the basis of the result of transient detection in the transient detecting means. The method of claim 4, wherein Power average value calculating means for calculating an average value of powers of the predetermined number of subband signals based on an average value of group powers of groups in which the predetermined number of subband signals are divided by the group dividing means; An envelope estimation stage that extrapolates envelope straight lines of a plurality of subband signals above the extended start band, starting from the average value calculated by the power average value calculating means; And band complementary means for complementing a plurality of subband signals of the extended start band or more based on the envelope straight line. The method of claim 4, wherein And said transient detecting means detects code degradation of said predetermined number of subband signals and performs overdetection of said predetermined number of subband signals in accordance with a result of said code degradation detection. The method of claim 4, wherein And the power average value calculating means calculates an average value of the powers of the predetermined number of subband signals by applying a weight to the predetermined number of subband signals close to a high frequency side. The method of claim 5, And the envelope estimating means extrapolates an envelope straight line using a threshold value as a starting point when the average value calculated by the power average value calculating means is larger than a threshold value. In the frequency band expansion method for expanding the frequency band of the input signal, An extended control step of determining an extended start band for the input signal according to information related to the input signal; A band dividing step of dividing the input signal into a plurality of sub band signals; The input signal is band-divided in the band division step And a frequency band expanding step of expanding a frequency band on the basis of a plurality of subband signals on a lower side of the plurality of subband signals that are lower than the extension start band. A reproduction apparatus for reproducing an input signal after extending an input signal in a band, Expansion control means for determining an expansion start band for an input signal according to the information related to the input signal; Band dividing means for dividing the input signal into a plurality of sub band signals, The input signal is band-divided by the band dividing means. And a frequency band is expanded on the basis of the plurality of sub band signals on the lower side of the plurality of sub band signals than the extension start band. The method of claim 11, And the input signal is a signal obtained by decoding the encoded encoded data. In the reproducing method of reproducing the input signal after extending the input signal, An extension control step of determining an extension start band for an input signal according to the information related to the input signal; A band dividing step of dividing the input signal into a plurality of sub band signals, The input signal is band-divided by the band dividing step. And a frequency band expanding step of expanding a frequency band on the basis of a plurality of sub band signals on a lower side of the plurality of sub band signals than the extension start band. A program for causing a computer to execute a process of reproducing an input signal after extending an input signal, An extension control step of determining an extension start band for an input signal according to the information related to the input signal; A band dividing step of dividing the input signal into a plurality of sub band signals, The input signal is band-divided by the band dividing step. And a computer executing a frequency band expanding step in which a frequency band is expanded based on a plurality of sub band signals on a lower side of the plurality of sub band signals than the extension start band. A recording medium having recorded thereon a program for causing a computer to execute a process of reproducing an input signal after widening the input signal. An extension control step of determining an extension start band for the input signal; A band dividing step of dividing the input signal into a plurality of sub band signals, The input signal is band-divided by the band dividing step. A recording medium having recorded thereon a program for causing a computer to perform a frequency band expanding step of expanding a frequency band based on a plurality of sub band signals on the lower side of the plurality of sub band signals from the extended start band. In the frequency band expanding apparatus for expanding the frequency band of the input signal, Expansion control means for determining an extension start band of the input signal in accordance with information associated with the input signal; Band dividing means for dividing the input signal into a plurality of sub band signals; Transient for detecting in the time direction a predetermined number of subband signals continuous to the extension start band from among a plurality of subband signals on the lower side of the extension start band where the input signal is band-divided by the band dividing means ( Iii) detection means, Group dividing means for dividing the predetermined number of subband signals into a plurality of groups in a time direction based on a result of transient detection in the transient detecting means; Power average value calculating means for calculating an average value of powers of the predetermined number of subband signals based on an average value of group powers of the groups in which the predetermined number of subband signals are divided by the group dividing means; Envelope estimating means for extrapolating envelope straight lines of a plurality of subband signals above the extended start band from the average value calculated by the power average value calculating means; Band complementary means for complementing a plurality of subband signals of the extended start band or more based on the envelope straight line; A band synthesizing means for synthesizing a plurality of subband signals on the lower side of the extension start band and a plurality of subband signals of the extension start band or more, And a frequency band is enlarged on the basis of a plurality of subband signals on a lower side of the plurality of subband signals in which the input signal is band-divided by the band dividing unit, which is lower than the extension start band. In the frequency band expanding apparatus for expanding the frequency band of the input signal, An extension controller for determining an extension start band of the input signal; A band divider for dividing the input signal into a plurality of sub band signals, And a frequency band is enlarged based on a plurality of subband signals on a lower side of the plurality of subband signals in which the input signal is band-divided by the band divider based on a lower subband signal lower than the extension start band. A reproduction apparatus for reproducing an input signal after extending an input signal in a band, An expansion controller for determining an extension start band of the input signal according to the information related to the input signal; A band divider for dividing the input signal into a plurality of sub band signals, And a frequency band is enlarged based on a plurality of sub band signals on the lower side of the plurality of sub band signals in which the input signal is band-divided by the band divider based on the plurality of sub band signals on the lower side of the extended start band.

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