JP2004138789A - Digital signal coding method, decoding method, encoder, decoder, and programs therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform scalable coding with which reproduced signals from a high quality to a low quality can be obtained and to make large noise not to be generated in a reproduced signal even when reproduction is performed from some coded bit strings. <P>SOLUTION: When the number of effective digits which can be transmitted through a transmission line is M, and there is a bit 1 in digit positions (9 to 15 digit positions) higher than the high order M=8 digit positions from the lowest order digit (least significant bit) in the magnitude part in the digital signal (of Figure A) of sign magnitude format, this program changes altogether bits 0 of the LSB to M=8 of the sample into bits 1, and in Figure A, samples correspond to it except samples S4 and S9 and it makes Figure A to be Figure B and it makes the sign bit string of the most significant bit (MSB) a packet P1 and makes the bit string B1 of the LSB a packet P2 and makes bit strings B2, B3 to B8 which are 2th digit, 3th digit to 8th digit respectively from the lowest order to be packets P3, P4 to P9 respectively and the packets are constituted so that precedence is made lower at order of P1 to P9. Further, at the time of decoding, each bit of 9 to 15 digit positions is set to 0. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is a method of scalably encoding or decoding a digital signal such as an audio signal or an image signal such as sound or music according to required quality, transmission speed, storage capacity, and the like, an encoder, a decoder, and an encoder. Regarding these programs.
[0002]
[Prior art]
As a conventional digital signal encoding and decoding method of this kind, a lossless encoding with a high compression ratio is performed, and the compression ratio of the compression ratio is reduced by reversibly compressing the error signal between the reproduced signal and the original signal. A method of flexibly using both high lossy coding and lossless compression has been proposed (for example, Patent Document 1). For example, Non-Patent Document 1 proposes a method in which this is improved and the scalability of compression can be changed more flexibly. This conventional method will be described with reference to FIG.
[0003]
In the encoder 10, a time series of a digital input signal (hereinafter, referred to as “digital input signal sequence”) is input from an input terminal 100, and the frame division unit 110 converts the digital input signal sequence into, for example, 1024 digital input signals. (Ie, 1024 samples) are sequentially divided into frame units.
In the irreversible compression unit 120, the output of the frame division unit 110 is irreversibly compressed and encoded. This encoding may be performed by any method that can reproduce the original digital input signal to some extent during decoding. For example, if the digital input signal is audio, ITU-T audio coding can be used, if it is music, MPEG or Twin @ VQ can be used, and if it is video, MPEG can be used. In addition, various irreversible quantization methods disclosed in Patent Document 1 can be used. Note that the output of the lossy compression unit 120 is referred to as “lossy compression code I (n)”.
[0004]
In the local decoding unit 130 having the same configuration as the decoding unit corresponding to the irreversible compression unit 120 (that is, the irreversible decompression unit 230), a local reproduction signal is generated from the irreversible compression code I (n). An error signal between the local reproduction signal and the original digital input signal is obtained by a subtractor 140. Usually, the amplitude of this error signal is much smaller than the amplitude of the original digital input signal. Therefore, the amount of information can be reduced by lossless compression encoding of the error signal, rather than by lossless compression encoding of the digital input signal.
In order to increase the efficiency of the lossless compression encoding, the reordering unit 162 reorders the bits of the error signal (that is, the bit string). The error signal is represented by a two's complement representation (each sample is represented by a positive or negative integer). The bit string is converted into a binary code of the polarity code and the absolute value by the polarity absolute value conversion unit 161, and then, the reordering unit 162 converts the bits at the same digit position of each sample from the bits in the frame across the samples. The bit sequence is supplied to the transmission recording unit dividing unit 310, and the bit sequence is divided into data of a transmission unit or a recording unit. Each of the divided transmission recording unit data is losslessly compressed by the lossless compression unit 150, and a header is attached by the packetizing unit 320 so that the divided transmission recording unit data can be reconstructed as one frame at the time of decoding. The packet is output to the output terminal 170 as a packet. For example, as shown in FIG. 2A, each of the 1024 samples S1,..., S1024 of one frame of the error signal is a 16-bit PCM signal, that is, the most significant bit (MSB) has a polarity code, and the other 15 bits have an absolute amplitude value. , Where the MSB side is the upper digit. Each sample S1,..., S1024 constitutes a bit string for one frame of bits at the same digit position, that is, 1024 bits. That is, in this example, 16 bit strings B1,. These bit strings B1,..., B16 are divided into transmission recording units, for example, divided into respective bit strings, each of which is one packet P1,.
[0005]
The packetizer 320 attaches the header 31 to the transmission recording unit data (payload) 32, for example, as shown in FIG. 2B. The header 31 is provided with a packet number 33 composed of, for example, a frame number and a number of transmission recording unit data in the frame, a packet priority order 34 and a data length 35, and a decoding side can reconstruct a digital signal sequence for each frame. Is to be.
The data length 35 is not required if the data length of the transmission recording unit data 32 is fixed, but the data length differs depending on the packet when the data is compressed by the lossless compression unit 150 or the like.
[0006]
More generally, one packet 30 is formed by adding an error detection code 36 such as a CRC code for detecting whether an error has occurred in the entire packet, and this packet 30 is output to the output terminal 170. You.
The lossless compression unit 150 encodes a bit string (divided data) by entropy coding such as Huffman coding or arithmetic coding using a case where there is a continuous sequence or a case where there is a frequently appearing sequence. Become Universal encoding for reversibly compressing text or the like may be applied.
[0007]
The irreversible compression code I (n) from the irreversible compression unit 120 is also converted into a packet P0 by the packetizing unit 320, the packet P0 is given a first priority, and the lossless compression code I ( The second priority is given to the packet P1 of e), and thereafter, the priority is sequentially lowered as the packet becomes the packet of the lossless compression code I (e) of the bit string at the lower digit position.
The packets P0,..., P16 are transmitted or stored by the output unit 330. In the decoder 20, the packet is received by the input unit 400 or read from the storage unit and input to the depacketizing unit 440 from the input terminal 200. The non-packetizing unit 440 determines whether the packet is error-free or usable if there is an error, determines the priority and the packet number, and determines the lossy compression code I (n) and the lossless compression code. Each required data is sequentially extracted so as to be separated into I (e) and to enable frame reconstruction.
[0008]
The reversible compression code I (e) is reversibly decoded by the reversible decompression unit 210, and each transmission recording unit data is divided by the transmission recording unit integration unit 410 into one bit stream B1,. B16 are integrated so that they can be distinguished, and the integrated data is taken out by the reordering unit 221 one bit at a time from each of the bit strings B1,..., B16, and sequentially converted as a sample string. .., S1024 are obtained, and these are converted into a two's complement representation by a two's complement converter 222 to reproduce an error signal.
[0009]
On the other hand, the irreversible compression code I (n) from the non-packetizing unit 440 is irreversibly decoded by the irreversible decompression unit 230 and decompressed. The adder 240 adds the error signal. If a packet loss has occurred from the packet number, it is detected by the loss detection unit 420, supplied to the loss information correction unit 430, corrected for the loss information, and supplied to the addition unit 240. If no packet loss has occurred, the error signal is immediately supplied to the adder 240. The frame synthesizing unit 250 sequentially connects the input signals and outputs the digital signals to the output terminal 260 as a reproduced digital signal sequence.
[0010]
In accordance with the characteristics of the transmission path, the storage capacity when storing, or the request of the user, only packets with low priority are not output or input. For example, the packets P15 and P16 in FIG. 24A are not output or not input, and the decoder 20 adds two bits of “0” to the lower part of the sample sequence of the sign absolute value reproduced as shown in FIG. 2C. Regenerate the error signal. In this manner, as the required quality is lower, a scalable function can be provided by omitting a larger number of packets in order from a lower priority.
[0011]
Although the error signal is scalable in the above description, the encoder 10 in FIG. 1 omits the irreversible compression unit 120, the irreversible decompression unit 130, and the addition unit, and converts the output of the frame division unit 110 into absolute value conversion. The decoder 20 directly supplies the output of the two's complement converter 222 to the frame synthesizer 250 or the missing information corrector 430 by omitting the irreversible decompressor 230 and the adder 240. Then, the scalable encoding of the input digital signal time series can be performed directly.
[0012]
Non-Patent Document 1 also describes the following as a countermeasure against packet loss. A parameter LPC expressing a spectrum envelope of an error signal for each frame is obtained as a linear prediction coefficient by, for example, linear prediction analysis in a spectrum envelope calculation section 351 in the auxiliary information generation section 350, and an error for each frame is obtained in a power calculation section 352. The average power of the signal is calculated. The linear prediction coefficient LPC and the average power are encoded by the auxiliary information encoding unit 353 at a low bit of, for example, about 30 to 50 bits, to obtain an auxiliary information code. The auxiliary information code is added by the packetizer 320 to a packet having a higher priority, for example, a packet in which transmission recording unit data including a polarity code is stored, or is output as an independent packet. In the decoder 20, the auxiliary information code is separated and supplied to the auxiliary information decoding unit 450 in the non-packetizing unit 440, and the auxiliary information decoding unit 450 calculates a parameter representing the spectral envelope of the error signal of the frame and the average power. After decoding, the spectrum envelope parameter and the average power are supplied to the missing correction unit 430.
[0013]
The processing of the missing information correction unit 430 will be described below.
FIG. 3 shows the processing procedure. First, a provisional waveform (provisional sample sequence) in a frame is reproduced using only the determined bits input from the two's complement conversion unit 222 (S1). In the reproduction of the provisional waveform, the missing bits are fixed to, for example, 0 or an intermediate value of possible values of the missing bits. For example, if the lower 4 bits are missing, any of the levels from 0 to 15 is a correct value, but is temporarily set to 8 or 7.
[0014]
Next, the spectrum envelope of this provisional waveform is calculated (S2). For example, a spectral envelope can be estimated by performing an all-pole type linear prediction analysis used in voice analysis on a provisional waveform. The estimated spectrum envelope is compared with the spectrum envelope of the error signal transmitted as the auxiliary information, that is, the spectrum envelope decoded by the auxiliary information decoding unit 450, and if the error is within an allowable range, the provisional waveform is output as the output waveform ( The signal is output to the adder 240 as a (corrected error signal waveform) signal (S3).
If the estimated spectrum envelope shape is significantly different from the decoded spectrum envelope shape in step S3, first, the inverse characteristic of the estimated spectrum envelope is given to the provisional waveform (S4). Specifically, the spectrum is flattened by passing the provisional waveform through, for example, an all-pole type linear prediction inverse filter (all-zero type) using the parameter representing the spectrum envelope obtained in step S2 to obtain a flattened signal. I do. Calculate the average power of this flattened signal, calculate the correction amount from this average power and the average power decoded from the auxiliary information decoding unit 450, for example, take the ratio or difference between the two, Amplitude correction is performed on the flattened signal, that is, the flattened signal is multiplied or added by a correction amount to match the decoding power (S5).
[0015]
Next, the spectrum envelope characteristic of auxiliary information is given to the amplitude-corrected flattened signal to correct the spectrum envelope (S6). That is, a spectrum correction waveform is created by passing the power-corrected flattened signal through an all-pole type synthesis filter using the parameter LPC representing the decoded spectrum envelope of the auxiliary information. The spectral envelope of the resulting waveform is close to the original sound.
However, there is a possibility that this spectrum correction waveform is inconsistent with a bit of an already known amplitude, and in that case, it is corrected to a correct value (S7). For example, when the lower 4 bits of the 16-bit precision amplitude value are unknown, there are 16 uncertainties in the possible values of each sample, but the values are corrected to values closest to the spectrum correction waveform. In other words, when the corrected sample value of each sample is out of the possible range, it is corrected to the limit value of the possible range. With this correction, all the bits whose amplitude values are determined coincide, and at the same time, a waveform whose spectral envelope is close to the original sound can be reproduced.
The process after step S2 can be repeated using this corrected waveform as a provisional waveform of step S1.
[0016]
[Patent Document 1]
JP 2001-44847 A (FIG. 1)
[Non-patent document 1]
T. Moriya, 4 other authors, "Lossless, scalable, audiocoder, and quality, enhancement", ICACSP, 2002, # 2440, 2002
[0017]
[Problems to be solved by the invention]
The problem with the conventional method as described above is that when the information bit string is divided into a plurality of packets scalably when transmitting or storing an audio signal, sound can be heard at the highest quality if all the packets are reproduced during reproduction. However, if you try to reproduce a sound of reasonable quality from only some of the packets, the quality of the degraded sound will vary depending on the nature of the target signal, and in some cases it will produce very hard-to-hear loud noises It is to be.
[0018]
For example, when a part of the waveform of the input original signal is a 16-bit PCM signal as shown in FIG. 4A, and when the lower 6 bits of each packet are not input to the decoder 20, the reproduced signal is as shown in FIG. The lower 6 bits are set to "0", and the envelope waveforms of the samples S4 to S7 have a gentle mountain shape as shown in FIG. 4C, but do not input each packet of the lower 7 bits to the decoder 20. In this case, the reproduced signal has the lower 7 bits of each sample set to "0" as shown in FIG. 4D, and the envelope waveforms of the samples S4 to S7 have a pulse shape as shown in FIG. It becomes.
[0019]
[Means for Solving the Problems]
(1) According to the encoding method of the present invention, an input digital signal is divided into frames, and a code sequence straddling each code sample in a code absolute value representation of a digital signal is formed into a packet for each frame. For each digit number in the absolute value and / or for each of a plurality of consecutive digit numbers, a bit sequence straddling the sample of the bit is set as a packet, and a high priority is given to the packet of the code sequence. The lower the priority is given to the packet, which is lower than the packet of the code string and the larger the digit number, the output is given.
(2) Preferably, the required number of digits to be output is determined in the above item (1), and if there is a bit 1 in the upper digit of the required digit portion from the lower order in the absolute value of each sample, the required digit number All bits of the portion are set to 1, and then, the packet of the bit string is generated only for the necessary number of digits portion.
[0020]
(3) In the above item (1) or (2), preferably, the code string and each of the above-mentioned bit strings are each subjected to lossless compression encoding, and then formed into a packet.
(4) In any of the above items (1) to (3), preferably, the original signal is irreversibly compressed and coded to generate a irreversibly compressed code, and the irreversible compressed code is given priority over packets in the above-mentioned code sequence. , And locally decodes the irreversible compression code, and sets an error signal between the obtained locally decoded signal and the original signal as the digital signal.
(5) According to the decoding method of the present invention, a code string is obtained from a packet of an input code string, a bit string is obtained from each of a plurality of packets of the input bit string, and each bit of the bit string is used. Reproduce the least significant digit position with the highest priority, reproduce the positions after the second digit from the bottom in the order of priority, reproduce the absolute value of each sample, and determine the most significant digit position of each sample. Reproducing with the corresponding code of the above-mentioned code string, if there are any digit positions that are not reproduced between the reproduced code and the absolute value of each of the samples, all these digit positions are reproduced with bit 0 and the code is reproduced. Reproduce the digital signal of the absolute value representation.
[0021]
(6) In the item (5), preferably, the number of reproduction digits of the absolute value in the digital signal represented by the sign absolute value is determined, and the reproduction of the absolute value of the sample from each of the bit strings is determined from the least significant digit position. Perform only the number of digits to be played.
(7) In the above item (5), preferably, the number of reproduced digits of the absolute value in the digital signal represented by the sign absolute value is determined, and the determined number of reproduced digits from the least significant digit in the absolute value of the reproduced sample is determined. If there is a bit 1 in the upper digit from the position, all bits 0 in the absolute value of the reproduced sample are changed to bit 1, and then, from the least significant digit of the reproduced sample, the determined reproduction digit position and All digit positions with the sign bit of the most significant digit are reproduced to bit 0.
[0022]
(8) In any one of the above items (5) to (7), preferably, the code sequence and the bit sequence are generated by losslessly decoding a lossy compression code in a corresponding packet.
(9) In any one of the above items (5) to (8), preferably, a lossy compression code is irreversibly decoded from the input packet to generate a decoded signal, and the reproduced code absolute value representation digital signal is The digital signal is converted into a digital signal in a complement representation to generate an error signal, and the error signal and the decoded signal are added to reproduce the digital signal.
[0023]
(10) According to the encoder of the present invention, a frame dividing section for dividing an input digital signal for each frame, an effective digit determining section for determining the number of significant digits to be output, and each of the digital signal in the sign absolute value representation If the absolute value of the sample contains bit 1 from the least significant digit to the significant digit position determined above, bit 0 from the least significant digit to the significant digit position of the sample is replaced with bit 1. A maximum value conversion unit to be converted; a code string for the digital signal for each frame, in which code bits are formed across samples; bits from the least significant digit to the digit position of the number of significant digits are digit numbers or a plurality of consecutive digits; A reordering unit that converts a sample into a bit string that spans a sample for each number, and generates a packet having a high priority including the code string, including the bit string, Lower than packet, and includes a packetizing unit to generate a respective packet with a higher priority as the least significant digit.
(11) According to the decoder of the present invention, means for obtaining a code string and a plurality of bit strings from a plurality of input packets, and reproducing the most significant digit position of each sample with each code bit of the code string, For each bit, as the corresponding packet priority of the bit string is higher, the lower digit position of each sample is reproduced to reproduce the absolute value, and the reordering unit, the reproduced code bit of each sample, and the reproduced absolute value And a zero padding section for reproducing each digit position between bits with a bit to reproduce a digital signal represented by a sign absolute value.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 5 shows an embodiment of an encoder and a decoder according to the present invention. In this embodiment, a lossy compression code and a lossless compression code are used, and portions corresponding to those in FIG. 1 are denoted by the same reference numerals.
Coding
In the encoder 10, the digital signal is divided into frames, irreversibly compressed and encoded, an error signal between the local decoded signal and the input digital signal is generated, converted into an error signal in a sign absolute value expression, and further converted by the reordering unit 162. It is converted into a code string of code bits and a bit string for each digit position, is divided in units of transmission recording, is losslessly compressed by the lossless compression unit 150, and is packetized by the packetization unit 320.
[0025]
In this case, the priority of the packet is different from that of the conventional encoder shown in FIG. As shown in FIG. 6A, the packet containing the lossy compression code I (n) is the highest priority packet P0, and the packet containing the lossless compression code I (C) of the code string is the next highest priority packet. Up to the priority packet P1, the packet is the same as the conventional one, but the next-highest second priority packet P2 includes the lossless compression code I (B1) of the column B1 of the least significant bit (LSB). The next third priority packet P3 is a packet including the lossless compression code I (B2) of the second lowest bit sequence B2. Hereinafter, the priority of the packet of the lossless compression code of the bit string at the upper digit position is set lower. In FIG. 6A, the number of bits of the sample is 16, and the number of samples of the frame is originally large, for example, 1024, but is set to 12 for the sake of illustration.
[0026]
All packets are output, for example, in descending order of priority, and the original digital signal can be reproduced by decoding using all the packets. When the number of packets to be output is reduced in accordance with the capacity of the transmission path, the capacity of the storage unit, and other requirements of the user, the output is not performed in order of decreasing priority. When a part of the packet is not output as described above, the following is preferably performed.
When an effective digit determining unit 340 is provided and the line capacity of the transmission path for outputting the packet, the storage capacity of the storage unit for storing the packet, the quality required by the user, and the like are input to the effective digit determining unit 340, these are determined in advance. The number of significant digits M is determined based on the relationship between the request parameter and the number of significant digits that may be output. Up to the packet corresponding to each bit string of each significant digit number M including the least significant digit, for example, when M = 8, the packets P2 to P9 are separated from the packets P0 and P1 as shown in FIG. 6A. The packetizer 320 is controlled to output the packet.
[0027]
More preferably, a maximum value conversion unit 360 is provided between the polarity absolute value conversion unit 161 and the reordering unit 162. In the maximum value conversion unit 360, the effective value including the least significant digit in the absolute value portion of each sample is included. It is checked whether or not the upper digit 12 bits “1” exist from the upper digit position of the number of digits M, and if it exists, the bit 0 in the M digits including the least significant digit of the sample is changed to the bit 1. For example, in the case of the PCM digital signal shown in FIG. 6A, only samples S4 and S9 where the bit 1 does not exist in the absolute value part of the digit higher than the M = 8 digit position from the lower digit are other than the M + 1 digit position. Since bit 1 exists in the absolute value of, the bit 0 in the digit position below the M digit position in the samples S1 to S3, S5 to S8, and S10 to S12 is changed to bit 1 as shown in FIG. 6B.
[0028]
The code absolute value expression error signal thus changed is supplied to the reordering unit 162, and the same processing as before is performed. However, only the code string of the code bits and the bit strings B1 to B8 at the lower 1 to 8 digit positions are provided. Are generated, and packets P1, P2 to P9 and P0 of these lossless compression codes I (C), I (B1) to I (B8) are output. The priority order of the packets is P0, P1, P2,..., P9.
As described above, only the number of significant digits M is output from the least significant bit of the error signal. However, by changing the bit 0 to the bit 1, the actual absolute value of the sample is changed from M = 8 bits when the bit is not changed. The values are close to each other, and accordingly, the quality of the reproduced signal is good.
[0029]
Decryption
In the decoder 20, the input packet is depacketized by the depacketizing unit 440, the irreversible code I (n) of the packet P0 is supplied to the irreversible decompression unit 230, and the packets P1, P2,. Are reversibly decompressed by a reversible decompression unit 210, and are integrated into a code sequence and respective bit sequences B1, B2,... By a transmission recording unit integration unit 410. The reordering unit 221 reproduces the most significant digit position of each sample with each code bit of the code string, reproduces the least significant digit position of each sample with each bit of the bit string B1, and sets each sample bit with each bit of the bit string B2. , The second digit from the least significant digit is reproduced, and similarly, the upper digit position is sequentially reproduced from the lower digit of each sample. Note that information on which digit position each reversibly expanded bit string corresponds to is added to the packet in advance, or it can be sequentially known from the packet number priority order number.
[0030]
The reordering unit 221 reproduces each sample as described above. However, when all the packets are not input, there is a digit position that is not reproduced in the absolute value portion of each sample. In such a case, all the digit positions that have not been reproduced by the zero padding part 460 are reproduced to bit 0. For example, as shown in FIG. 6B, when the number of significant digits M in the encoder 10 is M = 8 and the maximum value conversion is performed, packets P1 to P9 are input to the decoder 40, and the decoder 40 shown in FIG. As described above, the sign bit is reproduced in the most significant digit by the packet P0 by the packets P1 to P9, the digit positions from the least significant digit to the eighth digit are reproduced by the packets P2 to P9, and the ninth to the fifteenth digit from the least significant digit. The seven positions up to are all reproduced to bit 0 by the zero padding 460. If the conversion by the maximum value conversion unit 360 is not performed in the encoder 10 and M = 8, the code bits in FIG. 6A and the state from the least significant digit position to the eighth digit are reordered by the reordering unit 221. , And all the digit positions from the ninth digit to the fifteenth digit are reproduced by the zero padding part 460 to all bits 0 as in FIG. 7A.
[0031]
The sample reproduced by the zero padding unit 460 is converted into a two's complement digital signal by a two's complement conversion unit 222 to reproduce an error signal, and this is added to the lossy decoded signal from the lossy expansion unit 230 and the addition unit 240. Then, reproduced frame digital signals are sequentially connected in the frame synthesizing section 250.
The decoder 20 is provided with a desired digit determining section 470, and when the user specifies and inputs a desired quality to the desired digit determining section 470, the desired digit corresponding to the input is determined in accordance with a predetermined relationship between the quality and the desired number of digits. The number of digits L is output and input to the depacketizing unit 440. The depacketizing unit 440 can reproduce each digit position from the least significant digit in each sample to the upper L (desired number of digits) including it. As described above, it is also possible to select a packet from the input packets and supply the data to the reversible decompression unit 210. If the input packet is originally limited by the number of significant digits M in the encoder 10, L ≦ M.
[0032]
When the number of reproduction digits is limited by the desired number of digits, a maximum value conversion unit 480 may be provided between the reordering unit 221 and the zero padding unit 460. In this case, all the input packets are decoded, and all bits or sign bits of each sample generated by the reordering unit 221 and the least significant digit position to the Mth (in this case, L <M) digit The bit at the position is examined by the maximum value converter 480 to determine whether there is a bit 1 at a digit position higher than the Lth digit from the lower order (excluding the most significant code bit position). All bits 0 between the least significant digit position and the Lth digit position are changed to bit 1, and the sign bit and the bits from the least significant digit position to the Lth digit position are output to the zero padding unit 460 for each sample.
[0033]
For example, as shown in FIG. 6B, when a packet that is limited by the number of significant digits M = 8 in the encoder 10 and has undergone the maximum value conversion is input, the reordering unit 221 selects the ninth from the bottom in FIG. If the desired number of digits L = 7 in the state where the respective bits from the first digit to the fifteenth digit are not reproduced, only S4 is a sample in which bit 1 does not exist at the upper digit position from the least significant L = 7th digit. Samples S1 to S3, S5 to S8, and S10 to S12 all have bit 1 from the least significant digit position to the Mth-eighth digit position, and only sample S9 has bits from the least significant digit position to the Lth digit position. Is changed to 1 and the sign bit of each sample and each bit from the least significant position to the Lth 7th digit position are supplied by the zero padding part 460, and each bit from the 8th digit position to the 15th digit position Is reproduced to 0 and becomes as shown in FIG. 7B
[0034]
As described above, since the error signal is a packet having a higher priority in the lower digits, a packet having a lower priority is not decoded according to the line capacity of the transmission path, the storage capacity of the storage unit, and the quality required by the user. However, a certain level of quality is maintained without generating large noise in the reproduction error signal. In particular, when the maximum value converters 360 and 480 are provided, the fluctuation of the reproduced signal due to the omission of the packet can be reduced, and the generation of noise can be further suppressed.
Also in the present invention, in the encoder 10, the lossy compression unit 120, the local decoding unit 130, and the subtraction unit 140 are omitted in FIG. 5, and the output of the frame division unit 110 is subjected to polar absolute value conversion as indicated by a broken line 11. You may make it supply directly to the part 161. In that case, in the decoder 20, the irreversible decompression unit 230 and the addition unit 240 may be omitted, and the output of the two's complement conversion unit 222 may be directly supplied to the frame synthesis unit 250 as indicated by the broken line 21.
The lossless compression unit 150 may be omitted from the encoder 10 in FIG. 5 as indicated by the broken line 12, and the lossless decompression unit 210 may be omitted from the decoder 20 as indicated by the broken line 22.
[0035]
Application examples and modifications
Since the present invention has scalability as described above, for example, when a packet is distributed from a transmitting side to a receiving side, the packet P0 is always transmitted, but the packets PC, PM, P2,. Accordingly, distribution can be performed while sequentially changing the bit rate. At this time, packets with high priority are sent with priority, and if the transmission rate is insufficient, packets with low priority are discarded and not transmitted, or if the delay time is within the allowable range, the priority is lowered. To be transmitted later. When the bit rate that can be transmitted on the transmission line at that time is input to the significant digit determination unit 340 as indicated by a broken line on the encoder 10 side in FIG. 5, it is determined how many packets of the priority order may be transmitted. , From the packet P0 to the packet of the determined order can be output from the output unit 330.
[0036]
On the receiving side, packets are received almost in real time, and if all packets created at the time of encoding on the transmitting side are sent, decoding using lossless encoding and decoding using irreversible encoding are performed using all of them. By adding the output PCM signal, the completely undistorted sound can be reproduced as an output. Also, when only a part of the packet is received, it is possible to reproduce with a certain quality. The receiving side adjusts the amount of packets to be used for actual playback from the received packets according to the purpose, and plays back only some of the packets with priority to the one with the highest priority. You can also lower or increase the quality. For example, the receiving side can intentionally lower the quality so that it can be used for trial listening or a free service, and if the quality is improved, the present service or a paid service can be performed. For example, a desired digit determination unit 470 is also provided on the decoder 20 side, and when a user inputs an instruction to this unit, it is determined how many packets of the priority order according to the instruction are to be decoded and received by the input unit 400. The packets from P0 to the determined packet are supplied to the depacketizing unit 440.
[0037]
In addition, a packet having a high priority is transmitted to a receiving side as soon as possible on the transmitting side, and the receiving side reproduces the sound in real time or without waiting so long even if the transmission capacity of the line is small, and stores it in the storage section 500. (FIG. 5), and after many packets arrive over a long period of time, they can be reproduced again together with the previously arrived packets to listen to high-quality sound.
If a remote user wants to quickly search for sound data stored in a data center, such as a broadcast program or data stored in a library, search only the high-priority packet part from the same database. High quality sound can be reproduced by searching for a desired sound and then receiving the low priority packets over time. In addition, the transmission side restricts the distribution packets according to the priority order, so that the quality that can be used by the user can be restricted.
[0038]
If a multicast router is used, it is possible to distribute packets to each user in the order of priority from the highest priority to the bit rate corresponding to the request according to the request level of each user.
In addition, each packet of the encoded scalable code bit string is stored in a storage device (storage unit) such as a hard disk or a semiconductor memory. It is also possible to take out a lot of packets and perform book use or paid service, or take out all the packets over time and use them for high-quality services and high-priced services such as broadcasting and education.
[0039]
In the above description, the irreversible compression code and the lossless compression code are used. However, these application examples can be applied to a case where only the lossless compression code is used. In that case, the packet with the highest priority is the PC. As can be understood from the above description, the inputs of the effective digit determining unit 340 and the desired digit determining unit 470 are the bit rate, the required quality of the user, the purpose of the user (search, trial listening, pay, etc.), and the like. , The priority order is determined in advance.
As shown by a broken line in FIG. 5, a supplementary information generation unit 350 is provided, and a supplementary information code such as spectrum LPC and power is added to a packet PC or PM having a high priority, or is output as an independent packet and decoded. The device is provided with a missing information correcting unit 430 and an auxiliary information decoding unit 450, and for example, as described with reference to FIG. 3, a missing packet can be corrected using the decoded auxiliary information.
[0040]
The encoder 10 and the decoder 20 shown in FIG. 5 can be made to function by executing an encoding program and a decoding program by a computer, respectively. In these cases, an encoding program and a decoding program are downloaded to a program memory of the computer from a CD-ROM, a flexible magnetic disk, or the like, or are used through a communication line.
The present invention is applicable not only to audio signal encoding and decoding but also to image signals. In this specification, packets in one frame are intentionally removed in order to adjust the amount of information, so that all the packets in one frame are not input to the decoder, or an exchange station due to traffic congestion in a communication network, etc. In the case of packet loss based on not sending out some packets, or transmission path failure, failure of recording / reproducing device, etc., there is an error in the further input packet, the transmission recording unit data cannot be decoded, A case where the packet cannot be used is generically referred to as a packet loss.
[0041]
【The invention's effect】
According to the present invention, it is possible to perform scalable encoding that enables reproduction from signals of the same quality as the original signal to signals of various quality levels, and furthermore, the absolute value of the sample is given higher priority in the lower order. No significant noise is generated even when the data is reproduced from the encoded bit string of the section.
[Brief description of the drawings]
FIG. 1 is a diagram showing a functional configuration of a conventional digital signal encoder and decoder.
2A is a diagram for explaining a process of a reordering unit 162 of the encoder 10, FIG. 2B is a diagram showing an example of a packet format, and FIG. 2C is a diagram for explaining a process of a reordering unit 221 of the decoder 20. FIG.
FIG. 3 is a flowchart showing a processing example of a missing information correction unit 430 of the decoder 20;
4A is a diagram showing an example of an original PCM signal, FIG. 4B is a diagram showing a reproduced PCM signal in which all lower 6 bits are set to “0”, FIG. 4C is a diagram showing a partial waveform envelope, and FIG. FIG. 7 is a diagram showing a reproduced PCM signal in which all the lower 7 bits of 4A are set to “0”, and FIG.
FIG. 5 is a diagram showing a functional configuration example of each embodiment of an encoder and a decoder according to the present invention.
6A is a diagram for explaining packetization and its priority in the present invention, and FIG. 6B is a diagram for explaining processing of a maximum value conversion unit 360 in the encoder of FIG. 5;
7A is a diagram for explaining a process of a reordering unit 221 and a zero padding unit 460 in the decoder 20 of FIG. 5, and FIG. 7B is a diagram for explaining a process of a maximum value conversion unit 360 in the decoder. FIG.

Claims (13)

Split the input digital signal into frames,
A code string straddling the sample of each code in the code absolute value representation of the digital signal for each frame is defined as a packet,
For each digit number and / or for a plurality of consecutive digit numbers in the absolute value of the digital signal, a bit string straddling the bit sample is formed as a packet,
A digital signal code, wherein a higher priority is given to a packet of the code string, and a lower priority is given to a packet of the bit string as the packet is lower than the packet of the code string and the digit number is larger, and the digital signal is output. Method. Determine the required number of digits to output,
In the absolute value of each sample, if there is a bit 1 in the upper digit of the required digit part from the lower bit, all bits in the required digit part are set to 1,
2. The digital signal encoding method according to claim 1, further comprising generating a packet of the bit string only for the required number of digits. 3. The digital signal encoding method according to claim 1, wherein the code string and the bit strings are each subjected to lossless compression encoding and then converted into a packet. Lossless compression encoding of the original signal to generate a lossy compression code, this lossy compression code is set to a packet having a higher priority than the packet of the code string, and the lossy compression code is locally decoded. 4. The digital signal encoding method according to claim 1, wherein an error signal between a local decoded signal and the original signal is used as the digital signal. A code string is obtained from the packet of the input code string,
A bit string is obtained from each of a plurality of packets of the input bit string,
Using the bits of the above bit string, the least significant digit position of the packet having the highest priority is reproduced, and the positions after the second digit from the lower order in the order of priority are reproduced to reproduce the absolute value of each sample. Then, the most significant digit position of each of these samples is reproduced by the corresponding code of the above code string,
If there is a digit position that has not been reproduced between the reproduced code and the absolute value of each of the samples, it is necessary to reproduce all of these digit positions with bit 0 to reproduce the digital signal represented by the sign absolute value. Characteristic digital signal decoding method. Determine the number of digits of the absolute value to be reproduced in the digital signal represented by the sign absolute value,
6. The digital signal decoding method according to claim 5, wherein the reproduction of the absolute value of the sample from each of the bit strings is performed by the determined number of reproduced digits from the least significant digit position. Determine the number of digits of the absolute value to be reproduced in the digital signal represented by the sign absolute value,
If there is a bit 1 in the absolute value of the reproduced sample from the least significant digit to a digit higher than the determined number of reproduced digits, the bit from the least significant digit in the absolute value of the reproduced sample to the number of reproduced digits is determined. Change all bit 0 between bits to bit 1,
6. The digital signal decoding method according to claim 5, wherein all digit positions from the least significant digit to the reproduced digit number position and the code bit of the most significant digit are reproduced to bit 0. 8. The digital signal decoding method according to claim 5, wherein the code string and the bit strings are generated by losslessly decoding a lossless compression code in a corresponding packet. Lossless decoding of the lossy compression code from the input packet to generate a decoded signal,
The reproduced sign absolute value representation digital signal is converted into a two's complement representation digital signal to generate an error signal,
9. The digital signal decoding method according to claim 5, wherein a digital signal is reproduced by adding the error signal and the decoded signal. A frame division unit for dividing the input digital signal for each frame;
A significant digit determining unit for determining the number of significant digits to be output;
In the absolute value of each sample in the sign absolute value representation of the digital signal, if there is a bit 1 above the digit position of the determined number of significant digits from the least significant digit, the significant digit from the least significant digit of the sample A maximum value converter for converting bit 0 up to several positions into bit 1;
A bit sequence in which the digital signal is a code sequence straddling a sample for each of the frames and a bit is straddled from a least significant digit to a digit position of the effective digit, the bit being a digit number or a plurality of consecutive digit numbers. If you want to convert to
A packetization unit that generates a packet with the higher priority including the code sequence, includes the bit sequence, is lower than the packet of the code sequence, and generates each packet with a higher priority as the least significant digit,
A digital signal encoder comprising: Means for obtaining a code string and a plurality of bit strings from a plurality of input packets;
Reproduce the most significant digit position of each sample with each code bit of the above code string, and reproduce the lower digit position of each sample as the corresponding packet priority of that bit string becomes higher with each bit of each of the above bit strings. If you play the
A digital signal decoder comprising: a zero padding unit for reproducing each digit position between the reproduced sign bit and the reproduced absolute value of each sample with a bit to reproduce a digital signal represented by a sign absolute value. . An encoding program for causing a computer to execute each process of the digital signal encoding method according to claim 1. A decoding program for causing a computer to execute each process of the digital signal decoding method according to claim 5.

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