JP2002542522A - Use of gain-adaptive quantization and non-uniform code length for speech coding - Google Patents

Abstract

(57) [Summary] Techniques such as Huffman coding are used to more efficiently represent digital audio signal components that use non-uniform length codes than are represented by other coding techniques that use uniform length codes. obtain. Unfortunately, the coding efficiency that can be achieved with Huffman coding depends on the probability density function of the information to be coded, requiring the Huffman coding process itself, considerable processing and memory resources. The encoding process using gain-adaptive quantization according to the present invention overcomes the drawbacks of Huffman encoding, but can realize the advantage of using non-uniform length codes. In gain-adaptive quantization, the amplitude of the signal component to be encoded is compared to one or more thresholds and placed into classes according to the result of the comparison. The amplitude of the components placed in one of the classes is changed according to the gain factor with respect to the threshold used to classify the components. Preferably, the gain factor may be expressed as a function of only one threshold. Gain-adaptive quantization may be used to encode frequency sub-band signals in a split-band speech coding system. Additional features are disclosed, including cascaded gain-adaptive quantization, intra-frame coding, split spacing and non-overloaded quantizers.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD OF THE INVENTION The present invention relates generally to encoded and decoded signals. The invention can be used advantageously for split-band coding and decoding, where the frequency sub-band signals are separately coded. The invention is particularly useful in perceptual speech coding systems.

BACKGROUND OF THE INVENTION There is a continuing interest in encoding digital audio signals in a manner that imposes a low information capacity requirement on the transmission channel, and storage media still carry the encoded audio signal with a high level of subjective quality. can do. Perceptual coding systems use the process of encoding and quantizing the audio signal in a way that masks the resulting quantization noise or uses larger spectral components in the audio signal to make it inaudible. Thereby attempt to achieve this conflicting purpose. In general, it is advantageous to control the shape and amplitude of the quantization noise spectrum so that it lies just below the psychoacoustic mask threshold of the signal to be encoded.

[0003] Perceptual coding processes apply a bank of analysis filters to the speech signal to obtain a sub-band signal having a bandwidth proportional to the critical band of the human auditory system, and the resulting quantization noise is just the speech. Establishing a quantization step size for quantizing the sub-band signal small enough to be less than or equal to the estimated mask threshold of the signal; quantizing the sub-band signal according to the established quantization step size; It may be performed by a so-called split band encoder that assembles a plurality of codes representing the band signal into an encoded signal. The supplemental perceptual decoding process extracts the code from the coded signal, then recovers the quantized sub-band signal, obtains a non-quantized indication of the quantized sub-band signal, ideally from the original speech signal May be performed by a split-band decoder, which applies a bank of synthesis filters to the non-quantized indication to generate a perceptually indistinguishable speech signal.

[0004] The coding processes in these coding systems often use uniform length codes to represent the quantized signal elements or elements of each subband signal. Unfortunately, the use of uniform length codes imposes a higher information capacity than required. The required information capacity can be reduced by using non-uniform length codes to represent the quantized components of each subband signal.

[0005] One technique for providing non-uniform length codes is Huffman coding of the quantized subband signal components. Typically, the Huffman code table is designed with "training signals" selected to represent the signal to be encoded in the actual application. Huffman coding can provide very good coding gain if the average probability density function (PDF) of the training signal is reasonably close to the PDF of the encoded real signal and the PDF is not flat.

If the PDF of the actual signal to be coded is not close to the average PDF of the training signal, Huffman coding does not achieve coding gain but increases the information capacity requirement of the coded signal and incurs a coding penalty. You may. This problem can be minimized by using multiple codebooks corresponding to different signal PDFs. However, additional storage space is required to store the codebook, and additional processing is required to encode the signal according to each codebook and choose the one that provides the best results.

A block of quantized sub-band signal components can be represented using non-uniform length codes in each sub-band that is independent of any particular PDF of component values, and is efficient with minimal computation and memory resources There remains a need for coding techniques that can be implemented in

DISCLOSURE OF THE INVENTION The objects of the present invention may be realized by using non-uniform length codes to represent quantized signal components, such as subband signal components within respective frequency subbands in a split-band coding system. To provide benefits.

The present invention provides for any particular P value of the component values to achieve good coding gain.
This goal is achieved using techniques that are not dependent on DF and can be performed efficiently with minimal computation and memory resources. In one application, the coding system
The features of the present invention may be advantageously used in connection with other techniques such as Huffman coding.

In accordance with the teachings of one aspect of the present invention, a method for encoding an input signal includes receiving the input signal and generating a sub-band signal block of sub-band signal components representing frequency sub-bands of the input signal. Comparing the magnitude of the components in the sub-band signal block with a certain threshold, arranging each component in two or more classes according to the magnitude of the components, and obtaining a gain factor; Applying the gain factor to components arranged in one of the classes to change the magnitude of some of the components; andquantizing the components of the subband signal block; Assembling into coded signal control information conveying the classification of the components and a non-uniform length code representing the quantized subband signal components. According to the teachings of another aspect of the present invention, a method of decoding an encoded signal comprises receiving the encoded signal, obtaining a control signal and a non-uniform length code therefrom, and converting a frequency subband of the input signal. Obtaining a quantized sub-band signal component from the non-uniform length code; dequantizing the sub-band signal component to obtain a sub-band signal non-quantized component; Applying a gain factor to change the magnitude of some of the components; and generating an output signal in response to the sub-band signal non-quantized components.

[0011] These methods may be embodied in a medium as a program of instructions that can be executed by an apparatus for performing the present invention.

In accordance with the teachings of another aspect of the invention, an apparatus for encoding an input signal comprises an input for receiving the input signal, and a sub-band of a sub-band signal component representing a frequency sub-band of the input signal. An analysis filter having an output for supplying a signal block; comparing the magnitude of the component of the subband signal block with a certain threshold; arranging each component into two or more classes according to the magnitude of the component; A sub-band signal block analyzer connected to the analysis filter, and the gain factor arranged in one of the classes to change the magnitude of some components in the sub-band signal block. A sub-band signal component processor connected to the sub-band signal block analyzer and having a magnitude modified according to the gain factor. A first quantizer connected to the subband signal processor for quantizing components of the subband signal block, and a control for transmitting a non-uniform length code representing the quantized subband signal component and a classification of the component Assemble information into an encoded signal,
A formatter connected to the first quantizer.

According to still another teaching of the present invention in an apparatus for decoding an encoded signal, the apparatus receives the encoded signal, obtains control information and a non-uniform length code therefrom,
A deformatter for obtaining a quantized sub-band signal component from the non-uniform length code; and dequantizing some sub-band signal components of the block according to the control information to obtain a first non-quantized component. A first non-quantizer connected to the deformatter, and a first first one of some of the sub-band signal blocks according to the control information.
A sub-band signal block processor connected to the first non-quantizer for applying a gain factor to change the magnitude of the non-quantized component of the sub-band signal processor; and an input connected to the sub-band signal processor. , A synthesis filter having an output for providing an output signal.

According to the teachings of yet another aspect of the present invention, the medium is (1) a non-uniform length code representing a quantized sub-band signal component, wherein the quantized sub-band signal component is an audio signal. A non-uniform length code corresponding to a sub-band signal block element representing a frequency sub-band, and (2) control information indicating a classification of a quantized sub-band signal component according to the size of the corresponding sub-band signal block element; 3) transmitting an indication of a gain factor related to the size of the quantized sub-band signal component according to the control information.

The various features of the present invention and its preferred embodiments are better understood by referring to the following discussion and accompanying drawings, in which like reference numerals refer to like components in the several figures. obtain. The following discussion and the contents of the drawings are presented by way of example only and are not to be understood as limiting the scope of the present invention.

Modes for Carrying Out the Invention A. Coding system The present invention is directed to improving the efficiency of representing quantized information, such as speech information, and finds advantageous application in coding systems that use split-band coder and split-band decoder. Embodiments of a split band encoder and a split band decoder incorporating various aspects of the present invention are shown in FIGS. 1 and 2, respectively.

[0017] 1. Encoder a) Analysis Filtering In FIG. 1, analysis filter bank 12 receives an input signal from path 11 and splits the input signal into sub-band signals representing frequency sub-bands of the input signal;
Pass the subband signals along 3 and 23. For clarity of illustration, the embodiments shown in FIGS. 1 and 2 show components with only two subbands. However, it is common for the sub-band encoder and decoder of the perceptual coding system to process more sub-bands having a bandwidth proportional to the critical band of the human auditory system.

The analysis filter bank 12 includes a multilayer filter, a grating filter, and an orthogonal mirror filter (
It can be performed in a wide variety of ways, including various time-domain to frequency-domain block transforms, including QMF), Fourier series transforms, cosine modulation filterbank transforms, and wavelet transforms. In a preferred embodiment, the bank of filters is weighted or modulated by a superposition block of digital audio samples with an analysis window function, and by a specific modified discrete cosine transform (MDCT).
) To the window weighting block. This MD
CT is referred to as a time domain aliasing cancellation (TDAC) transform and
In Proc. Int. Conf. Acoust., Speech, and Signal Proc.
Princen, Johnson and Bradley, "Subband / Transform Coding Using Filter Bank Design Based on Time Domain Aliasing Cancellation," p. 2164. Although the choice of implementation can have a significant effect on the performance of the coding system, the particular implementation of the analysis filterbank is not important in the inventive concept.

The sub-band signals passed along paths 13 and 23 each include sub-band signal components arranged in blocks. In a preferred embodiment, each sub-band signal block is represented in a block-scale format where the components are scaled with respect to magnification. For example, the sub-band signal components may use a block floating point (BFP) format.

For example, if the analysis filter bank 12 is performed by block transformation,
A subband signal is generated by applying a block of input signal samples to the transform to generate a block of transform coefficients, and then grouping one or more adjacent transform coefficients that form the subband signal block. You. For example, if the analysis filter bank 12 is implemented by another type of digital filter, such as QMF, the sub-band signal is converted to generate a series of sub-band signal samples for each frequency sub-band. Generated by applying a series of input signal samples to the filter and then grouping the subband signal samples into blocks. The subband signal components of these two examples are the transform coefficients and the subband signal samples, respectively.

B) Perceptual modeling In a preferred embodiment for the perceptual coding system, the encoder uses a perceptual model to establish a respective quantization step size for quantizing each subband signal. One method of using a perceptual model to adaptively assign bits is shown in FIG. According to this method, step 51 applies a perceptual model to information characterizing the input signal to establish a desired quantization noise spectrum. In many embodiments, this spectral noise level corresponds to the estimated psychoacoustic mask threshold of the input signal. Step 52 establishes an initial proposed quantization step size for quantizing the components of the subband signal block. Step 53 determines the bit allocation required to obtain the proposed quantization step size for all subband signal components. Preferably, the assignment is made for the noise-stretching effect of the synthesis filter of the split-band decoder used to decode the encoded signal. Some methods for making such an assignment are described in Ubale et al., Entitled "Quantization in Perceptual Speech Coders with Compensation for Synthetic Filter Noise Decomposition," filed April 12, 1999. U.S. Patent No. 5,623,577 and U.S. Patent Application Serial No. 09 / 289,865. Both of which are incorporated herein by reference.

Step 54 determines whether the total required allocation differs significantly from the total number of bits available for quantization. If the total allocation is too high, step 55 increases the proposed quantization step size. If the total allocation is too low, step 55 reduces the proposed quantization step size. The process returns to step 53 and repeats until step 54 determines that the total allocation required to obtain the proposed quantization step size is approximately close to the total number of available bits. Then step 5
6 quantizes the sub-band signal components according to the established quantization step size.

C) Gain-Adaptive Quantization Gain-adaptive quantization may be incorporated into the method described above, for example by including various aspects of the invention during step 53. Although the method described above is typical of many perceptual coding systems, it is only one example of a coding process that can be incorporated into the present invention. The invention can be used in coding systems that essentially use any subjective and / or objective criteria to establish a step size for the quantized signal components. For ease of discussion, simplified embodiments will be used herein to describe various aspects of the invention.

The subband signal block for one frequency subband is passed along path 13 to a subband signal analyzer 14. The analyzer 14 compares the magnitude of the subband signal component of each part lock with a threshold and arranges each component into one of two classes according to the magnitude of the component. The control information for transmitting the component classification is passed to the formatter 19. In a preferred embodiment, components having a magnitude less than or equal to the threshold are arranged in a first class. Subband signal analyzer 14 also obtains a gain factor for the next use. As described below, preferably, the value of the gain factor is related to the threshold level in some manner. For example, the threshold may be expressed as a function of the gain factor only. Alternatively, the threshold may be expressed as a function of the gain factor and other considerations.

The sub-band signal components arranged in the first class are passed to a gain element 15.
It applies the gain factor obtained by the sub-band signal analyzer 14 to each component of the first class. The gain change component is then passed to a quantizer 17. Quantizer 17 quantizes the gain modification component according to the first quantization step size and passes the resulting quantized component to formatter 19. In a preferred embodiment,
The first quantization step size is set according to the perceptual model and according to the value of the threshold used by the subband signal analyzer 14.

The sub-band signal components arranged in the first class are passed along path 16 to a quantizer 18. It quantizes these components according to a second quantization step size. The second quantization step size may be equal to the first quantization step size. However, in a preferred embodiment, the second quantization step size is smaller than the first quantization step size.

The sub-band signal block for the second frequency sub-band is passed along path 23 and, in the same manner as described above for the first frequency sub-band, sub-band signal analyzer 24, It is processed by a gain element 25 and quantizers 27 and 28. In a preferred embodiment, the thresholds used for each frequency subband are adaptive and independent of the thresholds used for other frequency subbands.

D) Coded Signal Formatting The formatter 19 assembles control information, which conveys the classification of the components, and a non-uniform length code representing the quantized subband signal components into a coded signal. Transmission media such as modulated communication paths in the spectrum, including up to ultraviolet frequencies,
Alternatively, the encoded signal is passed along a path 20 carried by storage media, including magnetic tapes, magnetic disks and optical disks, that carry information using magnetic or optical recording techniques.

The sign used to represent the quantized component may be the same as the quantized value,
Alternatively, they may be some type of code derived from the quantized values. For example, the code may be obtained directly from a quantizer, or the quantized value may be obtained by some process such as Huffman coding. The quantized value itself can easily be used as a non-uniform length code. This is because a non-uniform number of bits can be assigned to quantized sub-band signal components within a sub-band.

[0030] 2. Decoder a) Encoded Signal Deformatting In FIG. 2, the deformatter 32 receives the encoded signal from the path 31 and converts therefrom a code representing the quantized subband signal components and control information conveying the classification of the components therefrom. obtain. The decoding process may be applied as needed to obtain the quantized components from the code. In a preferred embodiment, the gain modification components are arranged in a first class. For example, deformatter 32 also obtains any information that may be required by any perceptual model or bit allocation process.

B) Gain-Adaptive Dequantization The dequantizer 33 receives the components for one subband signal block arranged in a first class and decompresses them according to a first quantization step size. Dequantize,
The result is passed to the gain element 35. In a preferred embodiment, the first quantization step size is set according to a perceptual model and according to the threshold used to classify the subband signal components.

The gain element 35 applies a gain factor to the non-quantized component received from the non-quantizer 33, and passes the gain change component to the junction 37. Operation of the gain element 35 reverses the gain change provided by the one blowfish ride feature 15. As explained above,
Preferably, this gain factor is related to the threshold used to classify the subband signal components.

The subband signal components not arranged in the first class are passed to the non-quantizer 34. It dequantizes these components according to a second quantization step size,
The result is passed to the junction 37. The second quantization step size may be equal to the first quantization step size. However, in a preferred embodiment, the second quantization step size is smaller than the first quantization step size.

The junction 37 fuses the gain modified unquantized component received from the gain element 35 with the unquantized component received from the dequantizer 36 and the resulting subband signal block along path 38 To the synthesis filter bank 39.

The quantized components in the subband signal block for the second frequency subband are:
The resulting subband signal block processed by the dequantizers 43 and 44, the gain element 45, and the confluence 47 and along the path 48 in the same manner as described above for the first frequency subband. This is passed to the synthesis filter bank 39.

C) Synthesis Filtering The synthesis filterbank 39 may be implemented in a wide variety of ways complementary to the above-described methods for implementing the analysis filterbank 12. The output signals are provided on paths 38 and 48.
Are generated along path 40 in response to blocks of subband signal components received from.

B. Function 1. Sub-band signal component classification a) Simplified threshold function The effect of gain-adaptive quantization can be evaluated in FIG. It shows the virtual blocks 111, 112 and 113 of the subband signal components. In the example shown,
Each subband signal block includes eight components, numbered from 1 to 8.
Each component is represented by a vertical line, and the magnitude of each component is represented by the height of the respective line. For example, component 1 of block 111 has a magnitude slightly greater than the value 0.25, as shown on the ordinate axis of the graph.

Line 102 represents the threshold at the 0.50 level. Each component of block 111 can be arranged into one of two classes by comparing the magnitude of each component to its threshold. Components having a magnitude less than or equal to the threshold are arranged in a first class. The remaining components are arranged in a second class. Alternatively, by arranging components having a magnitude strictly less than the threshold into the first class, slightly different results can be obtained if the components are classified. For ease of discussion, a threshold comparison according to the first example is envisaged and will be specifically mentioned here.

The components of block 112 are obtained by applying two gain factors to each lock 111 component arranged in the first class. For example, a magnitude of component 1 of block 112 slightly greater than 0.500 is obtained by multiplying the magnitude of component 1 of block 111 by a gain factor equal to two. Conversely, the magnitude of component 2 of block 112 is equal to the magnitude of component 2 of block 111. This is because this component is arranged in the second class and is not changed by the gain factor.

Line 104 represents the threshold at the 0.25 level. Each component of block 111 may also be arranged in one of two classes by comparing the magnitude of each component to this threshold and arranging components having a size less than or equal to the threshold into a first class. Good. The remaining components are arranged in a second class.

The components of block 113 are obtained by applying a gain factor of 4 to each block 111 component arranged in the first class. For example, the magnitude of component 3 of block 113, which is approximately 0.44, is obtained by multiplying the magnitude of component 3 of block 111, which is approximately 0.11, by a gain factor equal to 4. Conversely, the magnitude of component 1 of block 113 is equal to the magnitude of component 1 of block 111. This is because this component is arranged in the second class and is not changed by the gain factor. The threshold may be expressed as a function of the gain factor only. As shown by these two examples, the threshold may be expressed as: Th = 1 / G (1)
Where Th = threshold and G = gain rate.

B) Alternative Threshold Function Unfortunately, the threshold obtained from Equation 1 may be too large. This is because, when changed by the gain factor G, a sub-band signal component having a magnitude slightly smaller than the threshold Th may overload the quantizer. If the quantization error for that value exceeds half the quantization step size, the value is said to overload the quantizer. For a symmetric quantizer having a uniform quantization step size that quantizes values in the range of approximately -1 to +1, a positive region that overloads the quantizer is expressed as: Q _OL > Q _MAX + ΔQ / 2 (2a
Also, the negative region that overloads the quantizer can be expressed as: Q _OL <−Q _MAX −ΔQ / 2 (2b
Where Q _OL = value that overloads the quantizer; Q _MAX = maximum positive quantization value; ΔQ = quantization step size.

For a b-bit symmetric mid-thread sine quantizer with a uniform quantization step size that quantizes values in the approximate range of −1 to +1, the maximum positive quantization value Q _MAX is 1-2 ^{1 − b} , the quantization step size ΔQ is equal to 21 ^-b ,
1/2 of the quantization step size is equal to 2- ^b . Equation 2 for positive overload values
a can be rewritten as follows: Q _OL > 1-2 ^1−b +2 ^−b = 1-2 ^−b (3a) Also, equation 2b for negative overload values is: It can be rewritten: Q _OL <− (1-2 ^1−b ) −2 ^−b = −1 + 2 ^−b (
3b)

Line 100 in FIG. 4 represents the boundary of the positive overload value for a 3-bit symmetric mid-thread sine quantizer. The negative range of this quantizer is not shown. Maximum positive quantized value for this quantizer is 0.75 = ^{(1-2 1-3),} 1/2 of the quantization step size is 0.125 ^{= 2 -3;} it Therefore, the boundary of positive overload values for this quantizer is 0.875 = ^{(1-2 -3).} The boundary of the negative overload value is
-0.875.

Component 5 of block 111 has a magnitude slightly smaller than the threshold at 0.500. If a gain factor equal to 2 is applied to this component, the resulting magnitude will cross the quantizer overload boundary. A similar problem occurs with component 6 when a threshold equal to 0.250 is used with a gain factor equal to 4.

A positive threshold that avoids overload and optimally maps the region of the first class of positive component values into the positive range of the quantizer can be expressed as: Th = Q _OL / G (4a)
The negative threshold can be expressed as: Th = −Q _OL / G (4b)

Throughout the remainder of this discussion, only the positive threshold will be discussed. This simplicity does not lose any universality. This is because the operation of comparing the magnitude of the component with the positive threshold is equivalent to the other operation of comparing the amplitude of the component with the positive and negative thresholds.

For the b-bit symmetric mid-thread sine quantizer described above, the threshold function of Equation 4A can be rewritten as: Th = (1-2− ^b ) / G (5)

The effect of gain-adaptive quantization using this alternative threshold is shown in FIG. The figure shows the virtual blocks 121, 122, 123 and 124 of the subband signal components.
Is shown. In the example shown, each sub-band signal block includes eight components numbered from one to eight. Its magnitude is represented by the length of each vertical line. Lines 102 and 104 represent thresholds for a 3-bit minimum mid-threaded sine quantizer for gain factors equal to 2 and 4, respectively. Line 100 represents the boundary of the positive overload value for this quantizer.

The components of the sub-band signal block 122 may be obtained by comparing the magnitude of the components of the block 121 with the threshold 102 and applying a gain of G = 2 to the components having a magnitude below the threshold. . Similarly, the component of the sub-band signal block 123 is
The magnitude of the component of block 121 may be obtained by comparing the magnitude of the component to threshold value 104 and applying a gain of G = 4 to components having a magnitude less than or equal to this threshold value. The components of the subband signal block 124 may be obtained using the cascade technique described below. Unlike the example shown in FIG. 4 due to the first threshold described above, the gain modification component shown in FIG. 5 does not cross the quantizer overload boundary.

On the other hand, an alternative threshold according to equation 5 is desirable. This is because it avoids quantization overload for small magnitude components of the first class and optimally loads the quantizer. On the other hand, this threshold may not be desirable in some embodiments for finding the optimal quantization step size. Because the threshold is
This is because it cannot be determined until the quantization step size is established. In embodiments that adapt the quantization step size by allocating bits, the quantization step size cannot be established until the bit allocation b of each subband signal block is known. This disadvantage is explained in detail below.

[0052] 2. Quantization Preferably, the quantization step size of the quantizer used to quantize the components of the subband signal block is adapted according to the gain factor for that block. In one embodiment described above using a process similar to that shown in FIG. 3, a number of bits b are allocated to each component in the subband signal block, and then the quantization step size or bit allocation is Each component is adapted according to the gain factor selected for that block. For this embodiment, the gain factor is
It is selected from four possible values representing gains of 1, 2, 4 and 8. The components in the block are quantized using a symmetric mid-thread sine quantizer.

Larger magnitude components that are not arranged in the first class and that are not gain modified are assigned the same number b of bits so that they are assigned without the benefit of the present invention. In an alternative embodiment using split interval quantization shown below, the bit allocation for these larger magnitude components may be reduced for some gain factors.

The smaller magnitude components that are arranged in the first class and that are gain modified are assigned more bits according to the values shown in Table I.

[0055]

[Table 1]

A gain factor equal to one for a particular subband signal block indicates that the gain modification function of the present invention does not apply to that block. Therefore, the same number b of bits is assigned to each component such that it is assigned without the benefit of the present invention. The use of a gain factor G = 2, 4 and 8 for a particular subband signal block benefits from the reduced allocation of 1, 2, and 3 bits for each smaller magnitude component of that subband block, respectively. Can potentially be provided.

The assignments shown in Table I are subject to the restriction that the number of bits assigned to each component cannot be less than one. For example, if the bit allocation process that allocates b = 3 bits to a particular subband signal block and gain factor G = 8 is selected for that block, then the bit allocation for the smaller magnitude components is , Table I
Will be reduced to one bit rather than zero bits. The intentional effect of the gain changes and adjustments to the bit allocation is to essentially preserve the same signal-to-quantization noise ratio with fewer bits. If desired, one embodiment may avoid selecting any gain factors that do not reduce the number of allocated bits.

[0058] 3. Control Information As described above, subband signal analyzer 14 provides control information to formatter 19 for assembly into an encoded signal. This control information conveys the classification for each component in the subband signal block. This control information may be included in the encoded signal in various ways.

One way to include the control information is to embed the bit sequence of each subband signal block, where one bit corresponds to each component in the block, into the encoded signal.
A bit set to one value, eg, a value of 1, indicates that the corresponding component is not a gain changing component, and a bit set to another value, which in this example is a value of 0, indicates that the corresponding component has a gain changing component. Indicates a component. Another way to include the control information is to embed a special "escape code" in the coded signal immediately before each component that has been gained or otherwise not gain changed.

In the preferred embodiment described above using a symmetric mid-thread sine quantizer,
Each large magnitude component that is not a gain change is preceded by an escape code equal to the unused quantization value. For example, the quantized value for a 3-bit two's complement sine quantizer may be from a minimum of -0.750 represented by a 3-bit binary sequence b'101 to +0 represented by a binary sequence b'011. .75. -1
. The binary sequence b'100 corresponding to 000 is not used for quantization, but is available for use as control information. Similarly, the unused binary sequence for 4-bit two's complement sine quantization is b'1000.

In the sub-band signal block 121 shown in FIG.
It is a component of a large size exceeding. If this threshold is used for a gain factor G = 2, the bit allocation for all small magnitude components arranged in the first class is b-1 as shown above in Table I. . For example, if the bit allocation process allocates b = 4 bits to each component of block 121, the allocation of each subband signal component is reduced to 3 = (b-1) bits and the 3-bit quantizer is small. Used to quantize magnitude components. In this example, components 4 and 5
Each large magnitude component is quantized by a 4-bit quantizer and is identified by an unused binary sequence of the 3-bit quantizer or control information equal to b'100. This control information for each large-sized component can be conveniently assembled into the coded signal immediately preceding the respective large-sized component.

It can be instructive to point out that the present invention does not provide benefits in the examples discussed in the previous paragraph. The cost or overhead required to convey control information, which in this example is 6 bits, is equal to the number of bits saved by reducing the bit allocation for small size components. In the above example, block 1
If only one component of 21 was a large component, the invention reduces the number of bits required to carry this block by four. Seven bits are saved by the reduced allocation to seven smaller components, and only three bits are required to convey control information for one larger component.

This last example ignores one additional aspect. Two bits are required for each subband signal block in this exemplary embodiment to convey what four gain factors are used for that block. As mentioned above, a gain factor equal to 1 may be used to indicate that features of the present invention do not apply for a particular subband signal block.

The present invention does not typically provide the benefit of quantizing sub-band signal blocks having four or fewer components. In a perceptual coding system that generates a subband signal having a bandwidth proportional to the critical bandwidth of the human auditory system, the number of components of the subband signal block for the low frequency subband is small, perhaps one component per block. However, the number of components for each subband signal block increases as the subband frequency increases. As a result, in the preferred embodiment, the processing required to implement the features of the present invention may be limited to wider subbands.
An additional piece of control information may be embedded in the coded signal to indicate the lowest frequency subband where gain-adaptive quantization is used. The encoder can adaptively select this subband according to the input signal characteristics. This technology is
Gain-Prevents the need to provide control information for subbands without adaptive quantization.

[0065] 4. Decoder Features A decoder incorporating the features of the present invention may adapt the quantization step size of its quantizer in essentially any manner. For example, a decoder that is used for decoding a coded signal generated by an encoder in the above embodiment uses adaptive bit allocation to set a quantization step size. You may.
The decoder may operate in a so-called forward adaptive system. In that system,
The bit allocation may be obtained directly from the encoded signal. It may operate with a so-called backward adaptive system. In that system, the bit allocation may be obtained by repeating the same allocation process used for the encoder. Or,
It may operate in a mixture of the two systems. The assignment values obtained in this way are referred to as "conventional" bit assignments.

The decoder obtains control information from the coded signal to identify the gain factor and the classification of the components of each subband signal block. Continuing with the above example, the control information conveying the gain factor G = 1 does not use the gain-adaptation feature and the conventional bit allocation b dequantizes the components of that particular subband signal block. To be used. For other gain factor values, the conventional bit allocation for a block, b, is used to determine the value of the "escape code" or control information that identifies the large magnitude component. In the example given above, the gain factor G = 2 and b =
The assignment of 4 is a binary sequence in which the control information has a length equal to 3 = (b-1) bits
b'100. The presence of this control information in the encoded signal indicates that a large magnitude component will immediately follow.

The bit allocation for each gain modification component has been adjusted as described above and is shown in Table I. Dequantization is performed with an appropriate quantization step size, and the gain change component is multiplied by a gain factor that is a replica of the gain factor used to perform the gain change in the encoder. For example, when a component having a small size has a gain factor G =
2, the decoder adds a reciprocal gain G = 0.5 to the corresponding unquantized component.
Apply

C. Additional Features In addition to the variations described above, some alternatives are discussed below.

1. Additional Classification According to one alternative, the magnitudes of the components of the subband signal block are compared to two or more thresholds and arranged into two or more classes. For example, in FIG.
The magnitude of each component of one can be compared to thresholds 102 and 104 and arranged in one of three classes. Gain factors are obtained for two of the classes and can be applied to the appropriate components. For example, a gain factor G = 4 may be applied to components having a magnitude less than or equal to the threshold 104, and a gain factor G = 2 may be applied to components having a magnitude less than the threshold 102 but greater than the threshold 104. . Alternatively, a gain factor G = 2 may be applied to all components having a magnitude less than or equal to the threshold 102, and a gain factor G = 2 may be applied to components having a magnitude less than or equal to the threshold 104.

2. Cascade Operation The gain change process described above may be performed multiple times before quantization. FIG. 6 is a block diagram illustrating one embodiment of two gain stages in a cascade. In this embodiment, the sub-band signal analyzer 61 compares the size of the sub-band signal block with a first threshold and arranges its components into one of two classes. Gain element 62
Applies a first gain factor to components arranged in one of the classes. The first gain factor value is related to a first threshold value.

The sub-band signal analyzer 64 compares the magnitude of the gain modifying component or the remaining components in the block with a second threshold and arranges the components into one of two classes.
Gain element 65 applies the second gain factor to the components arranged in one of the classes. The second gain factor value is associated with a second threshold value. If the second threshold is less than or equal to the first threshold, subband signal analyzer 64 need not analyze components arranged in classes because analyzer 61 has a magnitude greater than the first threshold.

The subband signal block components are quantized 67 and 68 in a manner similar to that described above.
Is quantized by

In FIG. 5, the components of sub-band signal block 124 are a succession of gain stages where sub-band signal analyzer 61 and gain element 62 apply a gain factor G = 2 to components having a magnitude less than or equal to threshold value 102. The sub-band signal analyzer 64 and the gain element 65 may apply a gain factor G = 2 to the gain-modifying component having a magnitude that is still less than or equal to the threshold value 102. For example, components 1-3 and 6-8 of block 121 are modified by a gain factor G = 2 in the first stage producing the provisional result shown in block 122. Components 1, 3, 7 and 8 are modified in the second stage by a gain factor G = 2 to obtain the result shown in block 124.

In embodiments using cascaded gain stages, appropriate control information should be provided to the encoded signal so that the decoder can perform a complementary set of cascaded gain stages.

[0075] 3. Optimized Bit Allocation There are several possible schemes for applying gain-adaptive quantization. One simple scheme is to analyze the components of the sub-band signal block, respectively, by starting with a first threshold and an associated first gain factor G = 2, and gain according to the first threshold and the first gain factor. Determine whether adaptive quantization results in reduced bit allocation requirements. If not, the analysis stops and no gain-adaptive quantization is performed. If so, the analysis indicates that the second threshold and the associated second gain factor G =
Continue with 4. If the use of the second threshold and the associated gain factor does not result in a reduction in bit allocation, gain adaptive quantization is performed using the first threshold and the first gain factor. If the use of the second threshold and the second gain factor results in a decrease, the analysis continues at the third threshold and the associated third gain factor G = 8. This process continues until the use of a threshold and the associated gain factor does not result in a reduction in bit allocation, or all combinations of the threshold and the associated gain factor are considered.

Another strategy is to calculate the cost and benefit provided by each possible threshold and the associated gain rate, and optimize the choice of gain rate by using the threshold and gain rate that yield the largest total benefit. Investigate that In the above example, the total benefit for a particular threshold and the associated gain factor is the overall benefit less the cost. The overall benefit is the number of bits saved by reducing the bit allocation for small magnitude components that are gain modified. Cost is the number of bits required to convey control information for a large component that is not gain changed.

One way in which this preferred scheme can be implemented is shown in the following program fragment.
This program fragment is represented in pseudo-code using a syntax that includes certain syntactic features of the C, FORTRAN, and BASIC programming languages. This program fragment and the other programs shown here are not intended to be source code portions suitable for compilation, but are provided to convey a few aspects of possible implementations.

Gain (X, N, b) {Th2 = (1-2 ^ (-b)) / gf [1]; // Initialize threshold of gain factor G = 2 Th4 = Th2 / 2; // Th8 = Th4 / 2; // gain factor G = 8... N2 = n4 = n8 = 0; // initialize counter for (k = 1 to N) {/ / For each component k, CompMag = Abs (X [k]); // get component size if (CompMag> Th2) n2 = n2 + 1; // count components above Th2 else if (CompMag > Th4) n4 = n4 + 1; // count components between Th4 and Th2 else if (CompMag> Th8) n8 = n8 + 1 // count components between Th8 and Th4} n24 = n2 + n4; // Number of large components above Th4 n248 = n24 + n8; // Number of large components above Th8 benefit2 = Min (b-1, 1); // Small saved by using G = 2 Bits per component benefit4 = Min (b-1, 2); // small bits per component saved by using G = 4 benefit8 = Min (b-1, 3); // G = 8 Using Bits per small component saved by net [0] = 0; // Total profit without gain change net [1] = (N-n2) * benefit2-n2 * (b-benefit2); // G = 2 Total profit to use net [2] = (N-n24) * benefit4-n24 * (b-benefit4); // Total profit using G = 4 net [3] = (N-n248) * benefit8-n248 * (b -benefit8); // Total profit using G = 8 j = IndexMax (net [j], j = 0 to 3); // Get index of maximum profit Gain = gf [j]; // Get gain rate }

The function Gain is an array X of subband signal block components, the number N of components of the block,
And the conventional bit allocation b for the block of components. The first part of the function uses a calculation according to Equation 5 shown above to initialize a variable Th2 to represent a threshold associated with a gain factor G = 2 obtained from array gf. In this example, the gain factors gf [1], gf [2] and gf [3] are equal to G = 2, 4 and 8, respectively. The following statement initializes variables for the thresholds associated with gain factors G = 4 and 8. Next, the counters used to determine the number of large components in the various classes are 0
Is initialized to

The for-loop statement calls the function Abs to obtain the magnitude for each subband signal block component of array X, and compares the magnitude of the component to that threshold only at the highest threshold. For example, if the magnitude is greater than the threshold Th2, the variable n2 is increased by one. At the end of the for-loop, the variable n2 includes the number of components having a size greater than the threshold Th2, the variable n4 includes the number of components having a size greater than the threshold Th4 but less than or equal to the threshold Th2, and the variable n8 includes , The number of components having a size larger than the threshold Th8 but equal to or smaller than the threshold Th4.

The two sentences immediately following the for-loop calculate the total number of components above their respective thresholds. The number of the variable n24 indicates the number of components having a size larger than the threshold Th4, and the variable n248 indicates the number of components having a size larger than the threshold Th8.

The next third sentence computes the benefit for each small magnitude component to use each gain factor. This benefit may be as much as 1, 2 or 3 bits per component as shown above in Table I, but since the assignment to each component is limited to a minimum of 1 bit, The benefit is also limited to only b-1 bits per component. For example,
The number of variables benefit2 represents the number of bits per component of small magnitude saved by using the gain factor G = 2. As shown in Table I, the benefits may be as many as one bit. However, the benefits are also slightly limited to the conventional bit allocation b-1. The calculation of this benefit is provided by using the function Min which yields the minimum of the two values b-1 and 1.

The net profit is then calculated and assigned to the elements of the array net. Element n
et [0] represents the net benefit without gain-adaptive quantization being zero. Gain factor G
Net profit using = 2 is obtained by multiplying the appropriate profit benefit2 for each small-sized component by the appropriate number of small-sized components (N-n2) and reducing the cost by net [1]
Assigned to. It is the number n2 of large components, multiplied by the length of the unused quantization value used for control information. This length is the bit length of the small magnitude component, which may be obtained from the conventional bit allocation b, which is reduced by the bits saved for each small magnitude component. For example, the bit length of the small-sized component when the gain factor G = 2 is the quantity (b-benefit2). Similar calculations are performed to assign net benefits using gain factors G = 4 and 8 to variables net [2] and net [3], respectively.

The function IndexMax is called to get the array index j for the largest net benefit of the array net. This index is used to get the appropriate gain factor from the gf array reduced by the function Gain.

[0085] 4. Improved Efficiency Using Simplified Threshold Function It has been described above that various features of the present invention can be incorporated into the perceptual bit allocation process, as shown in FIG. In particular, these features may be performed at step 53. Step 53 is performed in a loop that iteratively determines a proposed bit allocation that quantizes the components of each subband signal block to be encoded. For this reason,
The efficiency of the operation performed in step 53 is very important.

The process described above for the function Gain, which determines the optimal gain factor for each block, is relatively inefficient. This is because it must count the number of subband signal block components arranged in various classes. Component counts must be calculated during each iteration. This is because the threshold obtained according to equation 5 cannot be calculated until the proposed bit allocation b for each iteration is known.

In contrast to the threshold obtained according to equation 5, the threshold obtained according to equation 1 is less accurate but can be calculated before the proposed bit allocation b is known. This allows the threshold and component count to be calculated outside the iteration. In the method shown in FIG. 3, the thresholds Th1, Th2 and Th3 and the component counts n2, n24 and n2
48 may be calculated in step 52, for example.

An alternative version of the above-mentioned function Gain that can be used in this embodiment is shown in the following program fragment:

Gain2 (XN) {benefit2 = Min (b-1, 1); // Bit per small component saved by using G = 2 benefit4 = Min (b-1, 2); // G = 4 bits per small component saved by using = benefit8 = Min (b-1, 3); // bits per small component saved by using G = 8 net [0] = 0; / / Net profit without change net [l] = (N-n2) * benefit2-n2 * (b-benefit2); // Net profit using G = 2 net [2] = (N-n24) * benefit4- n24 * (b-benefit4); // Net profit using G = 4 net [3] = (N-n248) * benefit8-n248 * (b-benefit8); // Net profit using G = 8 j = IndexMax (net [j], j = 0 to 3); // Get index of maximum profit Gain = gf [i]; // Get gain rate}

The statement of the function Gain2 is exactly the same as the corresponding statement of the above-mentioned function Gain which calculates the net profit for each gain factor and selects the optimal gain factor.

[0091] 5. Quantization Functions a) Split Interval Function The quantization accuracy of large magnitude components can be improved by using a split interval quantization function that quantizes input values in two discrete intervals.

Line 105 in FIG. 7 is a graph of a function representing the end-to-end effect of a 3-bit symmetric mid-thread sine quantizer and a supplemental non-quantizer. The values along the x axis are
Represents input values to the quantizer, values along the q (x) axis represent corresponding output values obtained from the non-quantizer. Lines 100 and 109 represent the boundaries of the positive and negative overload values for this quantizer, respectively. Lines 102 and 108 represent positive and negative thresholds, respectively, for a gain factor G = 2 according to Equation 1 and as shown in FIG.
Lines 104 and 107 represent the positive and negative thresholds for gain factor G = 4, respectively.

In FIG. 1, if the sub-band signal analyzer 14 classifies the sub-band signal block components according to the threshold 102, it is known that the magnitudes of the components supplied to the quantizer 18 are all larger than the threshold 102. . In other words, quantizer 18 is not used to quantize any values falling between thresholds 108 and 102. This lack represents utilization under the quantizer.

The use below this can be overcome by using a quantizer that performs a split interval quantization function. Various split interval functions are possible. FIG.
Figure 4 is a graph of a function representing the edge-to-edge effect of one split interval 3-bit sine quantization and supplemental non-quantization. Line 101 represents a positive function and line 10
6 represents a negative function.

The function shown in FIG. 8 has eight quantization levels as compared to the function shown in FIG. 7, which has only seven quantization levels. Additional quantization levels are obtained by using the above level corresponding to -1 for the mid-thread quantization function.

B) Non-Overloaded Quantizer A 3-bit quantizer and a supplementary non-quantizer that implement the function shown in FIG.
It is preferred to quantize values within the division interval from -1.0 to about -0.5 and from about +0.5 to +1.0. Because the quantizer is
This is because the load cannot be overloaded. As explained above, if a certain value of the quantization error exceeds one half of the quantization step size, that value overloads the quantizer. In the example shown in FIG. 8, the non-quantizer output is -0.9375
, -0.8125, -0.6875, -0.5625, +0.5625, +0.
Defined as values equal to 6875, +0.8125 and +0.9375, the quantization step size is equal to 0.125. The magnitude of the quantization error for all values in the above-mentioned division interval is 0.062, which is equal to 1/2 of the quantization step size.
Not greater than 5. Such a quantizer is referred to herein as a "non-overloaded quantizer". Because it is immune to overloading.

A non-overloaded signal and split interval quantizer for essentially any quantization step size is achieved by a quantizer “decision point” appropriately spaced within the interval of the quantized values. It may be implemented by performing a quantization function with the quantizer output bounded. Generally speaking, the decision points are separated from each other by a distance d, and the decision points closest to each end of the input value interval are separated from each end by an amount d. This spacing, when used in a supplemental dequantizer, is equally spaced apart from each other by a particular quantization step size, and is の of this particular quantization step size.
Is provided to a quantizer that provides a quantized output having a maximum quantization error equal to:

C) Mapping Function The split interval quantizer may be implemented in various ways. The particular implementation is not important. One implementation shown in FIG. 9A includes a mapping transform 72 cascaded by a quantizer 74. A mapping transform 72 receives the input values from path 71, maps these input values to appropriate intervals, and passes the mapped values to quantizer 73 along path 73. If quantizer 74 is an asymmetric mid-thread sine quantizer, the mapping function represented by lines 80 and 81 shown in FIG. According to this mapping function, values in the interval from -1.0 to -0.5 are linearly mapped to the interval from -1.0-1 / 2? Q to -1/2? Q. Here, ΔQ is the quantization step size of the quantizer 74,
The value in the interval from +0.5 to +1.0 is from -1 / 2ΔQ to +1.0
Linearly mapped to intervals up to -1 / 2ΔQ. In this example, large magnitude components cannot have a value exactly equal to either -0.5 or +0.5. This is because components having these values are classified as components having a small size. For this reason, the mapping transformation 72 does not map the input value exactly to -1 / 2ΔQ. However, it may map input values arbitrarily close to or on either side of -1 / 2ΔQ.

The effect of this mapping is shown in FIGS. 9B and 9C. In FIG. 9B, mapping transformation 72 is shown mapping input points 82 and 84 to mapping points 86 and 88, respectively. In FIG. 9C, which shows a function representing the end-to-end effect of a 3-bit symmetric mid-thread sine quantizer and a supplemental dequantizer, mapping points 86 and 88 are quantizers having a value of -1 / 2ΔQ. It is shown that it is on either side of decision point 87.

The supplemental split interval dequantizer may be implemented by a symmetric mid-thread sine dequantizer that is complementary to the quantizer 74 followed by a mapping transform that is the inverse of the mapping transform 72. .

D) Combining Function In the above example, gain-adaptive quantization with gain factor G = 2 is used to quantize the components of the subband signal where the conventional bit allocation b is equal to 3 bits. . As described above with respect to Table I, three bits are used to quantize the large magnitude component bits and 2 = (b-1) bits quantize the small magnitude gain modification component. Used to Preferably, a quantizer that performs the quantization function of FIG. 8 is used to quantize large magnitude components.

[0102] A 2-bit symmetric mid-thread sine quantizer and supplemental dequantizer implementing the execution function 111 shown in FIG. 10 may be used for small magnitude gain changing components. The function 111 as shown takes into account the scaling and descaling effects of the gain factor G = 2 used for the quantizer and the dequantizer, respectively. The output values of the non-quantizer are −0.3333..., 0.0 and +0.3
333... And the quantization determination points are -0.1666.
1666...

The composition of the functions for the large and small magnitude components is shown in FIG.

E) Alternative segmentation interval functions The use of segmentation interval quantizers at a gain factor G = 2 and at a threshold of or about 0.500 provides an improvement in quantization resolution of about one bit. The improved resolution may be used to preserve the quantization resolution of large components while reducing the bit allocation to these components by one bit. In the example above,
A 2-bit quantizer can be used to quantize both large and small magnitude components. The synthesis of the quantization functions performed by the two quantizers is
As shown in FIG. Quantizers that perform quantization functions 112 and 113 can be used to quantize large magnitude components having positive and negative amplitudes, respectively, and quantizers that perform quantization function 111 , Can be used to quantize components of small magnitude.

The use of a split interval quantization function with a larger gain factor and a smaller threshold does not provide full bits of improved quantization resolution. Therefore, the bit allocation is
It cannot be reduced without sacrificing quantization resolution. In a preferred embodiment,
The bit allocation b for large mantissas is reduced by one bit for blocks that are gain-adapted quantized using a gain factor G = 2.

The non-quantization function provided at the decoder should complement the quantization function used at the decoder.

6. Intra-frame coding The term “code interest block” is used herein to refer to coding information that represents all of the subband signal blocks for the frequency subbands beyond the useful bandwidth of the input signal. Some coding systems assemble multiple coded signal blocks into larger units. It is referred to herein as a frame of the encoded signal. Frame structures are useful in many applications that share information beyond coded signal blocks, thereby reducing information overhead, and facilitating synchronization signals such as audio and video signals. Various issues regarding encoded audio information into frames for audio / video applications are disclosed in US Patent Application No. PCT / US98 / 20751, filed October 17, 1998, which is hereby incorporated by reference. You.

The features of gain-adaptive quantization described above may be applied to groups of sub-band signal blocks in different coded signal blocks. This aspect may be advantageously used, for example, in applications that group coded signal blocks into frames.
This technique essentially groups the components of a number of subband signal blocks within a frame, classifies the components, and applies a gain factor to this group of components as described above. This so-called intra-frame coding technique may share control information between blocks in the frame. The particular grouping of the coded signal block is not important for performing this technique.

E. Implementation The present invention is directed to a variety of software including software in a general purpose computer system or any other device that includes a more specialized configuration such as a digital signal processor (DSP) circuit connected to a configuration similar to that found on a general purpose computer. It may be implemented in various ways. FIG. 13 is a block diagram of an apparatus 90 that may be used to implement various aspects of the invention. DSP 92 provides computing resources. RAM
93 is a system random access memory (RAM). ROM 94 represents some form of fixed storage, such as a read-only memory (ROM), that stores the programs necessary to operate device 90 and perform various aspects of the invention. The I / O control 95 represents an interface circuit for transmitting and receiving an audio signal via the communication channel 96. Analog / digital and digital / analog converters may be included in the I / O control 95 as desired to receive and / or transmit analog audio signals. In the embodiment shown, all major components connect to a bus 91, which may represent one or more physical buses. However, a bus scheme is not required to implement the present invention.

In an embodiment implemented on a general-purpose computer system, it interacts with devices such as a keyboard, mouse and display to control a storage device having a storage medium such as a magnetic tape, disk, or optical medium. Additional components may be included. The storage medium may be used to record a program of instructions for an operating system, utilities, and applications, and may include program embodiments that perform various aspects of the present invention.

The functions required to carry out the various aspects of the present invention are independent logical elements,
It can be implemented by components that are implemented in a wide variety of ways, including the ASICs and / or program control processors described above. The manner in which these components are implemented is not critical to the present invention.

The software implementation of the present invention can be implemented on a variety of machine-readable media, such as a bar-band or modulated communication path, or a magnetic tape, magnetic disk, and optical disk through a spectrum that includes ultrasonic to ultraviolet frequencies. Can be transmitted by storage media, including those that convey information using essentially any magnetic or optical recording technology. Various aspects may also be implemented in computer systems by processing circuits such as ASICs, general purpose integrated circuits, microprocessors controlled by programs implemented in various forms of read only memory (ROM) or RAM, and other technologies. It can be implemented with 90 different components.

[Brief description of the drawings]

FIG. 1 is a block diagram of a split-band coder that incorporates gain-adaptive quantization.

FIG. 2 is a block diagram of a split-band decoder that incorporates gain-adaptive quantization.

FIG. 3 is a flowchart showing steps of a repetitive bit allocation process.

FIG. 4 is a diagram illustrating an effect of applying a gain to a virtual block and a component of a subband signal component.

FIG. 5 is a diagram illustrating an effect of applying a gain to a virtual block and a component of a subband signal component.

FIG. 6 is a block diagram of a cascaded gain stage for gain-adaptive quantization.

FIG. 7 is a diagram of a quantization function.

FIG. 8 is a diagram of a quantization function.

FIG. 9 illustrates how a split interval quantization function can be performed using a mapping function transform.

FIG. 10 is a diagram of a quantization function.

FIG. 11 is a diagram of a quantization function.

FIG. 12 is a diagram of a quantization function.

FIG. 13 is a block diagram of an apparatus that may be used to implement various aspects of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR , HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventor Robinson, Charles Quito United States, 94103, California, San Francisco, Potrero Avenue 100 (72) Inventor Truman, Michael Meade United States, 94103, California, San Francisco, Potrero Avenue 100 F term (reference 5D045 DA20 5J064 AA02 BA16 BB12 BC01 BC11 BC16 BC25 BC26 BD01 5K041 CC01 DD01 EE02 [Continued from Summary] The functions described below are disclosed.

Claims (42)

[Claims] 1. A method for encoding an input signal, comprising: receiving the input signal and generating a subband signal block of a subband signal component representing a frequency subband of the input signal; Comparing the magnitudes of the components in the signal block with a threshold value, arranging each component in two or more classes according to the magnitudes of the components, and obtaining a gain factor; Applying the gain factor to components arranged in one of the classes to change the magnitude, quantizing the components of the subband signal block, and a code transmitting a classification of the components. Assembling into non-uniform length codes representing quantized signal control information and the quantized subband signal components. 2. Assembling control information into a coded signal indicating a quantized sub-band signal component having a size unchanged according to the gain factor, wherein the control information is used to represent the quantized sub-band signal component. 2. The method of claim 1, wherein the method is carried by one or more spare codes. 3. The method according to claim 1, further comprising the step of obtaining the threshold value from a function that depends on a gain factor but does not depend on a quantization step size of the quantization component. 4. The method according to claim 1, further comprising the step of obtaining the threshold value from a function dependent on a gain factor and a quantization step size of a quantization component. 5. The adaptively varying the quantization step size for each component in the subband signal block according to the class in which the component is arranged by adaptively assigning bits to the component. And obtaining the gain factor such that the number of bits allocated to the component having the changed size is reduced while maintaining the respective quantization step size. Item 5. The method according to any one of Items 1 to 4. 6. The method according to claim 1, further comprising the step of quantizing components arranged in one of said classes according to a division interval quantization function. 7. A method of arranging each component into one of three or more classes according to the size of the component, comprising: obtaining one or more additional gain factors associated with each class; 7. A method according to any of the preceding claims, comprising applying each of the additional gain factors to components arranged in respective classes. 8. comparing at least some component magnitudes in the subband signal block with a second threshold, arranging each component into one of two or more second classes according to the magnitude of the component; Obtaining a second gain factor; and changing the magnitude of some components in the sub-band signal block;
Applying the second gain factor to components arranged in one of the second classes, wherein the non-uniform length code is changed according to the gain factor and the second gain factor. A method according to any of the preceding claims, characterized in that such quantization components are represented. 9. The method according to claim 1, wherein at least some of said components are quantized using one or more non-overloaded quantizers. 10. A method for decoding a coded signal, comprising: receiving the coded signal, obtaining a control signal and a non-uniform length code therefrom, and representing a quantized subband signal representing a frequency subband of the input signal Obtaining a component from the non-uniform length code; dequantizing the sub-band signal component to obtain a sub-band signal non-quantized component; To change the
Applying a gain factor; and generating an output signal in response to the sub-band signal non-quantized component. 11. A coded signal representing a quantized sub-band signal component having a magnitude that does not change according to the gain factor is conveyed by one or more spare codes that are not used to represent the quantized sub-band signal component. The method according to claim 10, wherein control information is obtained. 12. The method according to claim 10, further comprising the step of: dequantizing some of the quantized components in said subband signal block according to a dequantization function which complements a division interval quantization function. The described method. 13. The method according to claim 10, further comprising the step of applying a second gain factor to change some magnitudes of non-quantized components according to the control information. the method of. 14. The method of claim 10, wherein at least some of the quantized components are dequantized using one or more dequantizers that complement each non-overloaded quantizer. The method according to any of the above. 15. An apparatus for encoding an input signal, comprising: an input for receiving the input signal; and an output for providing a subband signal block of a subband signal component representing a frequency subband of the input signal. An analysis filter having the following components: comparing the component size of the sub-band signal block with a certain threshold, arranging each component in two or more classes according to the component size, and obtaining a gain factor; A sub-band signal block analyzer, the sub-band signal block applying the gain factor to components arranged in one of the classes to change the magnitude of some components in the sub-band signal block. A subband signal component processor coupled to the analyzer; and a subband signal block having a magnitude modified according to the gain factor. A first quantizer connected to the sub-band signal processor for quantizing a component; and a non-uniform length code representing a quantized sub-band signal component and control information for transmitting a classification of the component to a coded signal. Assembling, the formatter being connected to the first quantizer. 16. The apparatus according to claim 16, further comprising a second quantizer connected to said sub-band signal block analyzer for quantizing components arranged in one of said classes according to a division interval quantization function. The device according to claim 15. 17. The formatter assembles control information into a coded signal indicating a quantized subband signal component having a size unchanged according to the gain factor, wherein the control information represents the quantized subband signal component. 17. Apparatus according to claim 15 or 16, characterized in that it is carried by one or more spare codes which are not used for such purposes. 18. The threshold value is obtained from a function that depends on a gain factor but does not depend on a quantization step size of the quantization component.
An apparatus according to any one of claims 7 to 10. 19. The apparatus according to claim 15, wherein said threshold value is obtained from a function depending on a gain factor and a quantization step size of a quantization component. 20. Adaptively varying the respective quantization step size for each component in the subband signal block according to the class in which the component is arranged by adaptively assigning bits to the component. 20. The method of claim 15, wherein the gain factor is obtained such that the number of bits allocated to the component having the changed size is reduced while maintaining the respective quantization step sizes.
An apparatus according to any one of the above. 21. Arranging each component into one of three or more classes according to the size of the component, obtaining one or more additional gain factors associated with each class, and arranging each of the associated classes. 21. Apparatus according to any of claims 15 to 20, wherein each of the additional gain factors is applied to a component to be determined. 22. The sub-band signal block analyzer compares the magnitude of at least some of the components in the sub-band signal block with a second threshold and determines each component according to a magnitude of the component by two or more second magnitude signals. And obtaining a second gain factor, wherein the sub-band signal component processor is adapted to resize the second component to change the magnitude of some components in the sub-band signal block. Applying the second gain factor to components arranged in one of a class, wherein the non-uniform length code represents a quantized component that is modified by the gain factor and the second gain factor. Apparatus according to any of claims 15 to 21, characterized in that: 23. The apparatus according to claim 15, wherein at least some of the components are quantized using one or more non-overloaded quantizers. 24. An apparatus for decoding an encoded signal, comprising: receiving the encoded signal, obtaining control information and a non-uniform length code therefrom, and obtaining a quantized subband signal component from the non-uniform length code. A formatter; a first dequantizer coupled to the deformatter for dequantizing some subband signal components of the block according to the control information to obtain a first dequantized component; Applying a gain factor to change the magnitude of some first non-quantized components of the sub-band signal block according to the control information, the sub-band connected to the first non-quantizer An apparatus comprising: a signal block processor; and a synthesis filter having an input connected to the sub-band signal processor and an output for providing an output signal. 25. Connect to the deformatter for dequantizing other subband signal components in a block according to a non-quantization function that supplements a split interval quantization function to obtain a second non-quantized component. 25. The apparatus of claim 24, further comprising a second non-quantizer, wherein the synthesis filter has an input connected to the second non-quantizer. 26. The method according to claim 26, wherein the deformatter obtains control information from a coded signal indicating a quantized subband signal component having a size that is not changed according to the gain factor. 26. Apparatus according to claim 24 or claim 25, carried by one or more spare codes not used to represent. 27. The apparatus of claim 24, wherein the sub-band signal block processor applies a second gain factor to change some magnitude of the unquantized component according to the control information. An apparatus according to any one of the above. 28. The method of claim 24, wherein at least some of the quantized components are dequantized using one or more dequantizers that complement each non-overloaded quantizer. An apparatus according to any of the preceding claims. 29. A computer program product embodied in a machine-readable medium, the computer program product being executable by the machine to perform a method for encoding an input signal. Including program instructions, the method comprising: receiving the input signal and generating a subband signal block of a subband signal component representing a frequency subband of the input signal; and a magnitude of the component in the subband signal block. Comparing the magnitude with a certain threshold value, arranging each component in two or more classes according to the magnitude of the component, and obtaining a gain factor, and changing the magnitude of some components of the subband signal block, Applying the gain factor to components arranged in one of the classes; and the components of the subband signal block Step a computer program product characterized by having the steps of: assembling the non-uniform length code representing a coded signal control information and the quantized subband signal components to transmit the classification of the components to be quantized. 30. Assembling control information into a coded signal indicating a quantized sub-band signal component having a size not changed according to the gain factor, wherein the control information includes:
30. The computer program product of claim 29, carried by one or more spare codes not used to represent quantized subband signal components. 31. The computer program product according to claim 29, further comprising the step of obtaining the threshold value from a function that depends on a gain factor but does not depend on a quantization step size of the quantization component. 32. The computer program product according to claim 29, further comprising the step of obtaining the threshold from a function dependent on a gain factor and a quantization step size of a quantization component. 33. Adaptably varying the respective quantization step size for each component in the subband signal block according to the class in which the component is arranged by adaptively assigning bits to the component. And obtaining the gain factor such that the number of bits allocated to the component having the changed size is reduced while maintaining the respective quantization step size. 33. A computer program product according to any one of items 29 to 32. 34. The computer program product according to claim 29, further comprising the step of quantizing components arranged in one of the classes according to a division interval quantization function. 35. The computer program product according to claim 1, wherein each component is arranged into one of three or more classes according to the size of the component. A computer program product, comprising: obtaining additional gain factors; and applying each of the additional gain factors to components arranged in the associated respective classes. 36. comparing the magnitude of at least some components in the sub-band signal block with a second threshold, arranging each component into one of two or more second classes according to the magnitude of the component; Obtaining a second gain factor; and changing the magnitude of some components in the subband signal block,
Applying the second gain factor to components arranged in one of the second classes, wherein the non-uniform length code is changed according to the gain factor and the second gain factor. A computer program product according to any of claims 29 to 35, characterized in that such a quantization component is represented. 37. The computer program product according to claim 29, wherein at least some of the components are quantized using one or more non-overloaded quantizers. 38. A computer program product readable by a device embodying a program of instructions to be executed by the device to perform a method of decoding an encoded signal, the method comprising: Receiving a coded signal, obtaining a control signal and a non-uniform length code therefrom, and obtaining a quantized sub-band signal component representing a frequency sub-band of the input signal from the non-uniform length code; Dequantizing the sub-band signal component to obtain a component; and, according to the control information, changing some magnitude of the non-quantized component:
A computer program product, comprising: applying a gain factor; and generating an output signal in response to the sub-band signal non-quantized component. 39. A coded signal representing a quantized subband signal component having a magnitude that does not change according to the gain factor is conveyed by one or more spare codes that are not used to represent the quantized subband signal component. 39. The computer program product according to claim 38, wherein control information is obtained. 40. The method according to claim 38, further comprising the step of: dequantizing some of the quantized components in said subband signal block according to a nonquantized function complementary to a split interval quantization function. Computer program product as described. 41. The method according to claim 38, further comprising the step of applying a second gain factor to change some magnitude of the non-quantized component according to the control information. Computer program products. 42. The method of claim 38, wherein at least some of the quantized components are dequantized using one or more dequantizers that complement each non-overloaded quantizer. Computer program product according to any of the above.