JP3559488B2 - Hierarchical encoding method and decoding method for audio signal - Google Patents

Hierarchical encoding method and decoding method for audio signal Download PDF

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JP3559488B2
JP3559488B2 JP2000037418A JP2000037418A JP3559488B2 JP 3559488 B2 JP3559488 B2 JP 3559488B2 JP 2000037418 A JP2000037418 A JP 2000037418A JP 2000037418 A JP2000037418 A JP 2000037418A JP 3559488 B2 JP3559488 B2 JP 3559488B2
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健弘 守谷
直樹 岩上
岳至 森
明夫 神
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Nippon Telegraph and Telephone Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は音声や楽音信号などの音響信号をできるだけ少ない情報量でディジタル符号化する高能率信号符号化方法及び符号化方法に関するものであり、特にビット列に誤りやフレーム損失があった場合に音声や楽音を再構成できる階層符号化方法及び符号化方法に関する。
【０００２】
【従来の技術】
従来の信号の階層的スケーラブル符号化、復号化法は図１に示されるような構成となっている。
符号器では入力信号ベクトルを量子化するために複数の階層の量子化器と各階層間に誤差信号算出器を備え、最下位の階層の量子化器は入力信号ｘ（ｆ）を入力とし、量子化符号（圧縮ビット列）と逆量子化により再構成した信号ｘ＾（ｆ）を出力し、
第１段の誤差信号算出器は入力信号ｘ（ｆ）とｘ＾（ｆ）の誤差ｄ１（ｆ）（＝ｘ（ｆ）−ｘ＾（ｆ））を出力し、
次の階層の量子化器はｄ１（ｆ）を入力として、その階層の量子化符号と、逆量子化により再構成した信号ｄ１＾（ｆ）を出力し、
第２段の誤差信号算出器は入力信号ｘ（ｆ）とｄ２＾（ｆ）を加えた信号の誤差ｄ２（ｄ２＝ｘ（ｆ）−（ｄ１＾（ｆ）＋ｘ＾（ｆ）））を出力し、
同様に上位の階層変形した誤差を逐次多段階に量子化を行う。
【０００３】
復号器では各階層の量子化符号を逆量子化して信号を再構成し、加え合わせて最終的な信号を再生する。第１段の出力ｙ１（ｆ）、第２段の出力ｙ２（ｆ）と、各階層の量子化誤差をｑ１（ｆ）、ｑ２（ｆ）とすると、

Figure 0003559488
となる。この場合、下位の階層の誤差はすべて上位にフィードバックされ、上層ほど品質の高い信号が再現できる。また上位の階層の信号はなくても、ビットレートに見合った信号が再生でき、これが、スケーラブル符号化の特徴である。しかし、下位の階層のビット列に誤りやフレーム損失があった場合には、出力ｙ２‐（ｆ）はｄ１＾（ｆ）だけとなり
Figure 0003559488
ｘ（ｆ）とは大きな誤差が生じ、上位の階層で救済することは不可能であった。
【０００４】
【発明が解決しようとする課題】
従来の技術で述べた階層的スケーラブル符号化、復号化方法においてはビット列に誤りやフレーム損失があった場合、音声や楽音を再構成することは困難であった。
本発明はネットワークやデコーダの環境にあわせてできるだけ高品質で楽音や音声を伝送することができ、特に伝送ビットに誤りが生じる可能性がある無線伝送に適用して好適な音響信号の階層符号化方法及び符号化方法を提供することを目的としている。
【０００５】
【課題を解決するための手段】
本発明は、上記課題を解決するために階層的な量子化によるビットレートスケーラブル符号化で、階層にまたがる誤差に振幅の制御などの変形を行うことで伝送誤りやパケット消失の影響を軽減するものである。
【０００６】
【発明の実施の形態】
図２は、本発明の実施例の符号器及び復号器における処理を説明するブロック図である。
符号器では入力信号ベクトルを量子化するために最下位の階層の量子化器Ｑ１
は入力信号ｘ（ｆ）をα１倍した信号を入力とし、量子化符号（圧縮ビット列）と逆量子化Ｑ１ −１により再構成した信号〔α１ ｘ（ｆ）〕＾を出力する。ここでα１ は１以下の定数とする。すなわち、第１段の逆量子化では入力信号をそのまま入力として使わずに、変形した信号を使う。ここでは定数倍の例であるが、周波数に依存した係数やフィルタの処理でもよい。
【０００７】
次に第１段の誤差信号算出器は〔α1 x(f)〕＾と入力信号x(f)との誤差d1(f)
d1(f)＝x(f)−〔α1 x(f)〕＾ （４）
を出力する。
次の階層の量子化器はd1(f)をα2倍した信号を入力として、その階層の量子化符号と、逆量子化により再構成した信号〔α2d1(f)〕＾を出力する。
第２段の誤差信号算出器は〔α 1 x(f) 〕＾ と〔α 2 d 1 (f) 〕＾とを加算器により加算した和信号（〔α 1 x(f) 〕＾＋〔α 2 d 1 (f) 〕＾）と入力信号x(f)との誤差d 2 (f) ＝ x(f) −（〔α 1 x(f) 〕＾＋〔α 2 d 1 (f) 〕＾）を出力し、同様に上位の階層に変形した信号を入力して逐次多段階に量子化を行う。
なお最終階層ではこの変形は必要ない。
【０００８】
復号器では符号誤りやフレーム消失がない場合には各階層の量子化符号を逆量子化して信号を再構成する。
Figure 0003559488
第１段の出力y1(f)に含まれる入力信号の成分はα1 倍となり、また第２段までの出力はy2(f)に含まれる入力信号の成分は（α1＋α2−α1α2 ）倍となる。この結果、q1(f)やq2(f)の量子化誤差が相対的に大きくなり、αを含まない通常の場合よりもＳＮＲは低くなる。
【０００９】
ある階層の量子化符号の誤りや消失があった場合にはその階層の信号を０として信号を再構成する。誤り検出符号が伝送路の情報として入手できる場合はそれを利用すればよく、ない場合はフレーム毎、各階層毎に誤り検出符号をつければよい。たとえば第１階層の情報がないとき、第２階層だけの出力信号y2 -(f)は〔α 2 d1(f)〕＾となる。
Figure 0003559488
これから分かるように、第１階層からの出力がまったくなくてもα2(１−α1)倍された入力信号の成分が第２層の出力に含まれるので、第１階層がない条件で比較すると従来法よりもＳＮＲが高くなる。同様に上位の階層にも入力信号の成分が分散され、加え合わせることで第１階層の欠落をある程度補うことができる。
【００１０】
ここまでの実施例では量子化の入力の変形は定数倍としたが、周波数に依存した処理に拡張することが可能である。
図３は本発明の第２実施例を示している。
図２と類似しているが、信号の変形（ここでは定数倍）を逆量子化による出力信号のあとに行う。第１実施例と同様の効果があるが、複号器側の再生信号が少し異なる。
【００１１】
Figure 0003559488
第２階層の出力は
Figure 0003559488
となる。
【００１２】
第１階層の情報がないとき、第２階層だけの出力信号ｙ２ −（ｆ）はｄ１＾（ｆ）となる。
Figure 0003559488
効果や拡張は第１の実施例と同様であり、二つの実施例を組み合わせることも可能である。この実施例では式（９）のｘ（ｆ）の係数が（２−α１）であるので、通常の第２層の音量が本来より大きくなる。また、式（１０）のように第１層の出力が使えないときは係数が（１−α１）なので音量が低下する。通常の復号器の場合には、どの階層の情報を使うかはあらかじめわかるので、出力に補正定数をかけて音量がもとのｘ（ｆ）となるように修正すればよい。ただし、復号器が国際標準などで固定されてチップ化されているような場合にはこの補正ができないので音量の違いを許容するか、別に音量を修正する必要がある。
【００１３】
【発明の効果】
本発明のスケーラブル符号化ではシステム全体として冗長になるため、同じビット数で比較すると、誤りのない場合の量子化歪みは従来法より大きくなるが、入力信号の成分が各階層に分散され、どこかの階層の情報が消失してもその被害が軽減される。
【図面の簡単な説明】
【図１】従来の階層符号化器及び復号化器の基本構成を示す図。
【図２】本発明の第１実施例における階層符号化器及び復号化器の構成を示す図。
【図３】本発明の第２実施例における階層符号化器及び復号化器の構成を示す図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-efficiency signal encoding method and an encoding method for digitally encoding an audio signal such as a voice or a musical tone signal with a minimum amount of information. The present invention relates to a hierarchical encoding method and an encoding method capable of reconstructing a musical tone.
[0002]
[Prior art]
A conventional hierarchical scalable encoding and decoding method of a signal has a configuration as shown in FIG.
The encoder includes a plurality of layers of quantizers for quantizing the input signal vector and an error signal calculator between each layer. The lowest layer quantizer receives the input signal x (f) as an input, A signal x ＾ (f) reconstructed by a quantization code (compressed bit string) and inverse quantization is output,
The first-stage error signal calculator outputs an error d 1 (f) (= x (f) −x ＾ (f)) between the input signal x (f) and x ＾ (f),
The quantizer of the next layer receives d 1 (f) as an input, and outputs a quantization code of the layer and a signal d 1 ＾ (f) reconstructed by inverse quantization.
The second-stage error signal calculator calculates an error d 2 (d 2 = x (f) − (d 1 ＾ (f) + x ＾ (f) of a signal obtained by adding the input signal x (f) and d 2 ＾ (f). )))
Similarly, the upper hierarchically transformed error is sequentially quantized in multiple stages.
[0003]
The decoder inversely quantizes the quantization code of each layer to reconstruct a signal, and adds the signals to reproduce a final signal. Assuming that the output y 1 (f) of the first stage, the output y 2 (f) of the second stage, and the quantization error of each layer are q 1 (f) and q 2 (f),
Figure 0003559488
It becomes. In this case, errors in lower layers are all fed back to higher layers, and higher layers can reproduce higher quality signals. Further, even if there is no signal of an upper layer, a signal corresponding to the bit rate can be reproduced, which is a feature of the scalable coding. However, if there is an error or a frame loss in the bit sequence of the lower layer, the output y 2- (f) is only d 1 ＾ (f).
Figure 0003559488
A large error occurs with respect to x (f), and it is impossible to rescue at a higher hierarchical level.
[0004]
[Problems to be solved by the invention]
In the hierarchical scalable encoding and decoding methods described in the related art, it is difficult to reconstruct speech or musical sound when a bit string has an error or a frame loss.
INDUSTRIAL APPLICABILITY The present invention can transmit musical sounds and voices with as high quality as possible in accordance with the environment of a network or a decoder, and is particularly suitable for hierarchical transmission of audio signals suitable for wireless transmission in which transmission bits may have errors. It is intended to provide a method and an encoding method.
[0005]
[Means for Solving the Problems]
The present invention solves the above-mentioned problem by bit rate scalable coding by hierarchical quantization, which reduces the influence of transmission errors and packet loss by performing a modification such as amplitude control on errors across layers. It is.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 is a block diagram illustrating processing in the encoder and the decoder according to the embodiment of the present invention.
In the encoder, in order to quantize the input signal vector, the quantizer Q 1 of the lowest hierarchy is used.
As an input was 1 times alpha input signal x (f) signal, and outputs the ^ quantization code reconstructed signal by (compressed bit string) and inverse quantization Q 1 -1 [alpha 1 x (f)]. Here, α 1 is a constant of 1 or less. That is, in the first stage of inverse quantization, a modified signal is used instead of using an input signal as it is as an input. Here, an example of a multiple of a constant is used, but processing of a coefficient or filter depending on frequency may be used.
[0007]
Next, the first-stage error signal calculator calculates an error d 1 (f) between [α 1 x (f)] ＾ and the input signal x (f).
d 1 (f) = x (f) − [α 1 x (f)] ＾ (4)
Is output.
Quantizer following hierarchy as input signal obtained by doubling alpha to d 1 (f), the quantization code of the hierarchy, a signal reconstructed by the inverse quantization [α 2 d 1 (f)] ^ Output.
The second-stage error signal calculator calculates the sum signal obtained by adding [α 1 x (f) ] ＾ and [α 2 d 1 (f) ] ＾ with an adder ([α 1 x (f) ] に よ り + [ α 2 d 1 (f) ] ＾) and the error d 2 (f) = x (f) − ([α 1 x (f) ] ＾ + [α 2 d 1 (f) ]) , And similarly, a signal transformed to a higher layer is input, and quantization is sequentially performed in multiple stages.
This modification is not necessary in the last layer.
[0008]
If there is no code error or frame erasure, the decoder dequantizes the quantization code of each layer and reconstructs a signal.
Figure 0003559488
The component of the input signal included in the output y 1 (f) of the first stage is α 1 times, and the component of the input signal included in the output y 2 (f) is (α 1 + α 2 −) α 1 α 2 ) times. As a result, the quantization errors of q 1 (f) and q 2 (f) become relatively large, and the SNR becomes lower than in a normal case not including α.
[0009]
If there is an error or loss of the quantization code of a certain layer, the signal of that layer is set to 0 and the signal is reconstructed. If the error detection code can be obtained as information on the transmission path, it may be used. If not, the error detection code may be attached to each frame or each layer. In the absence example information of the first layer, the output signal y 2 only the second layer - (f) is the ^ [alpha 2 d 1 (f)].
Figure 0003559488
As can be seen, even if there is no output from the first layer, the component of the input signal multiplied by α 2 (1−α 1 ) is included in the output of the second layer. Then, the SNR becomes higher than in the conventional method. Similarly, the components of the input signal are also distributed to the higher layers, and by adding the components, the lack of the first layer can be compensated to some extent.
[0010]
In the embodiments described above, the modification of the quantization input is made a constant multiple, but it can be extended to a process depending on the frequency.
FIG. 3 shows a second embodiment of the present invention.
Similar to FIG. 2, but the signal transformation (in this case, a constant multiple) is performed after the output signal by inverse quantization. The effect is the same as that of the first embodiment, but the reproduced signal on the decoder side is slightly different.
[0011]
Figure 0003559488
The output of the second layer is
Figure 0003559488
It becomes.
[0012]
When there is no information in the first layer, the output signal y 2 only the second layer - (f) becomes d 1 ^ (f).
Figure 0003559488
The effect and extension are the same as those of the first embodiment, and the two embodiments can be combined. In this embodiment, since the coefficient of x (f) in equation (9) is (2-α 1 ), the normal volume of the second layer is higher than it should be. Further, when the output of the first layer cannot be used as in the equation (10), the volume decreases because the coefficient is (1−α 1 ). In the case of a normal decoder, since it is known in advance which layer of information is to be used, the output may be corrected by multiplying the output by a correction constant so that the volume becomes the original x (f). However, in the case where the decoder is fixed and chipped according to international standards or the like, this correction cannot be performed, so that it is necessary to allow a difference in volume or to separately correct the volume.
[0013]
【The invention's effect】
In the scalable coding of the present invention, since the entire system becomes redundant, when compared with the same number of bits, the quantization distortion in the case where there is no error is larger than that of the conventional method, but the components of the input signal are dispersed in each layer. Even if the information of the hierarchy is lost, the damage is reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a conventional hierarchical encoder and decoder.
FIG. 2 is a diagram showing a configuration of a hierarchical encoder and a decoder in the first embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a hierarchical encoder and a decoder according to a second embodiment of the present invention.

Claims (4)

音響信号をフレーム単位で符号化する符号化方法であって、
複数の階層の量子化過程と各階層間に誤差信号算出過程を備え、
第１の階層の量子化過程は、まず、入力信号ｘ（ｆ）にあらかじめ設定した１以下の定数α1を乗算することにより変形した信号α1ｘ（ｆ）を生成し、次に、前記変形した信号α1ｘ（ｆ）を量子化して第１の量子化符号を出力し、さらに、前記第１の量子化符号を逆量子化して再構成した信号〔α1ｘ（ｆ）〕＾を出力し、
第１段の誤差信号算出過程は入力信号ｘ（ｆ）と前記第１の階層の量子化過程で再構成した信号〔α1ｘ（ｆ）〕＾との誤差信号ｄ1（ｆ）（＝ｘ（ｆ）−〔α1ｘ（ｆ）〕＾
）を出力し、
第２の階層の量子化過程は、まず、前記第１段の誤差信号算出過程で算出した誤差信号ｄ1（ｆ）にあらかじめ設定した１以下の定数α2を乗算することにより変形した信号α2ｄ1（ｆ）を生成し、次に、前記変形した信号α2ｄ1（ｆ）を量子化して第２の量子化符号を出力し、さらに、前記第２の量子化符号を逆量子化して再構成した信号〔α2ｄ1（ｆ）〕＾を出力し、
第２段の誤差信号算出過程は、第１の階層の量子化過程で再構成した信号〔α1ｘ（ｆ）〕＾と第２の階層の量子化過程で再構成した信号〔α2ｄ1（ｆ）〕＾との和信号（〔α1ｘ（ｆ）〕＾＋〔α2ｄ1（ｆ）〕＾）と入力信号ｘ（ｆ）との誤差信号ｄ2（ｆ）（＝ｘ（ｆ）−（〔α1ｘ（ｆ）〕＾＋〔α2ｄ1（ｆ）〕＾）を出力し、
同様に上位の各階層の量子化過程にその前段の誤差信号算出過程より出力された誤差信号を入力して逐次多段階に量子化を行い、
前記各階層の量子化過程の量子化符号を出力することを特徴とする音響信号の階層符号化方法。An encoding method for encoding an audio signal on a frame basis,
Includes a degree error signal calculation over between a plurality of hierarchies of quantization process and each layer,
Quantization excessive extent of the first hierarchy, first generates a modified signal alpha 1 x (f) is multiplied by the constant alpha 1 of 1 or less which is preset to the input signal x (f), then, The transformed signal α 1 x (f) is quantized to output a first quantized code, and further, the first quantized code is inversely quantized and reconstructed signal [α 1 x (f)] Output ＾
Error signal d 1 and the error signal calculation over enough for the first-stage signal reconstituted with quantization process of the input signal x (f) and said first hierarchical [alpha 1 x (f)] ^ (f) ( = X (f)-[α 1 x (f)] ＾
),
Quantization excessive degree in the second layer, first, a signal deformed by multiplying the error signal d 1 1 following constants alpha 2 set in advance in (f) calculated by the error signal calculation process of the first stage α 2 d 1 (f) is generated, and then the transformed signal α 2 d 1 (f) is quantized to output a second quantized code. Further, the second quantized code is inverted. Output the quantized and reconstructed signal [α 2 d 1 (f)] ＾,
The second stage error signal calculation over enough for the signal [alpha 2 reconstituted with the first reconstructed signal quantization process hierarchy [alpha 1 x (f)] ^ and quantization process in the second layer d 1 (f)]} and an error signal d 2 (f) ([α 1 x (f)]} + [α 2 d 1 (f)]}) and the input signal x (f). = X (f)-([α 1 x (f)] ＾ + [α 2 d 1 (f)] ＾), and
Similarly, the error signal output from the error signal calculation process at the preceding stage is input to the quantization process of each upper layer, and quantization is sequentially performed in multiple stages,
A hierarchical encoding method of an acoustic signal, comprising outputting a quantization code of a quantization process of each layer. 音響信号をフレーム単位で符号化する符号化方法であって、
複数の階層の量子化過程と各階層間に誤差信号算出過程を備え、
第１の階層の量子化過程は入力信号ｘ（ｆ）を入力とし、第１の量子化符号と、逆量子化により再構成した信号ｘ＾（ｆ） を出力し、
第１段の誤差信号算出過程はｘ＾（ｆ）にあらかじめ設定した１以下の定数α1を乗算することにより変形した信号α1ｘ＾（ｆ）を算出し、入力信号ｘ（ｆ）と前記乗算した信号ｘ＾（ｆ）の誤差信号ｄ1（ｆ）（＝ｘ（ｆ）−α1ｘ＾（ｆ））を出力し、
第２の階層の量子化過程は前記第１段の誤差信号算出過程で算出した誤差信号ｄ1（
ｆ）を入力として、第２の量子化符号と、逆量子化により再構成した信号ｄ1＾（ｆ）を出力し、
第２段の誤差信号算出過程は、まず、ｄ1＾（ｆ）にあらかじめ設定した１以下の定数α2を乗算することにより変形した信号α2ｄ1＾（ｆ）を算出し、次に、第１段の誤差信号算出過程で乗算した信号α1ｘ＾（ｆ）と前記第２段の誤差信号算出過程で乗算した信号α2ｄ1＾（ｆ）との和信号（α1ｘ＾（ｆ）＋α2ｄ1＾（ｆ））と入力信号ｘ（ｆ）との誤差信号ｄ2（ｆ）（＝ｘ（ｆ）−（α1ｘ＾（ｆ）＋α2ｄ1＾（ｆ）））を出力し、
同様に上位の各階層の量子化過程にその前段の誤差信号算出過程より出力された誤差信号を入力して逐次多段階に量子化を行い、
前記各階層の量子化過程の量子化符号を出力することを特徴とする音響信号の階層符号化方法。An encoding method for encoding an audio signal on a frame basis,
Includes a degree error signal calculation over between a plurality of hierarchies of quantization process and each layer,
Quantization excessive extent of the first hierarchy receives the input signal x (f), and outputs a first quantization code, signal was reconstructed by the inverse quantization x ^ a (f),
The error signal calculation over enough for the first stage to calculate the deformed signal α 1 x ^ (f) by multiplying x ^ 1 following constants alpha 1 set in advance (f), the input signal x (f) And an error signal d 1 (f) (= x (f) −α 1 x ＾ (f)) of the multiplied signal x ＾ (f) is output,
Error signal d 1 quantization excessive degree in the second layer is calculated by the error signal calculation process of the first stage (
f), and outputs a second quantized code and a signal d 1 ＾ (f) reconstructed by inverse quantization,
The error signal calculation over enough for the second stage, first, calculates a deformed signals α 2 d 1 ^ (f) by multiplying d 1 ^ (f) 1 following constants alpha 2 set in advance to, the following And the sum signal (α 1 ) of the signal α 1 x ＾ (f) multiplied in the error signal calculation process of the first stage and the signal α 2 d 1 ＾ (f) multiplied in the error signal calculation process of the second stage An error signal d 2 (f) (= x (f) − (α 1 x ＾ (f) + α 2 d 1 }) between x ＾ (f) + α 2 d 1 (f)) and the input signal x (f). (F))) and output
Similarly, the error signal output from the error signal calculation process at the preceding stage is input to the quantization process of each upper layer, and quantization is sequentially performed in multiple stages,
A hierarchical encoding method of an acoustic signal, comprising outputting a quantization code of a quantization process of each layer. 音響信号をフレーム単位で復号化する方法であって、
請求項１または２に記載の音響信号の階層符号化方法で生成された各階層の量子化符号と量子化符号に対する誤り検出符号を入力し、
各階層の量子化符号を逆量子化して逆量子化信号を出力する逆量子化過程と、
誤り検出符号に基づき各階層の量子化符号の誤りの有無を検出し、誤りが検出されない量子化符号に対する逆量子化信号を加算して音響信号を再構成する過程を備えたことを特徴とする音響信号の階層復号化方法。A method for decoding an audio signal on a frame basis,
An input of a quantization code of each layer and an error detection code corresponding to the quantization code generated by the layer coding method of the audio signal according to claim 1 or 2,
A dequantization process of dequantizing the quantization code of each layer and outputting a dequantized signal;
Detecting a presence or absence of an error in the quantization code of each layer based on the error detection code, adding a dequantized signal to the quantization code in which no error is detected, and reconstructing an acoustic signal. Hierarchical decoding method for audio signals. 請求項３に記載の音響信号の階層復号化方法において、
上記音響信号を再構成する過程より出力された音響信号に補正定数をかけて音量を修正する過程を備えたことを特徴とする音響信号の階層復号化方法。The hierarchical decoding method of an acoustic signal according to claim 3,
A hierarchical decoding method of an audio signal, comprising a step of applying a correction constant to an audio signal output from the step of reconstructing the audio signal to correct the volume.
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