JP2002351497A - Encoding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoding device which has been made able to suppress increase in quantization noise due to the switching of the kind of an object signal to be encoded in a unit block where encoding is carried out. SOLUTION: The bit rate in encoding is set by unit blocks to be encoded according to whether the kind of the object signal to be encoded in the block is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code for converting a signal on the time axis, which may switch the type of signal for each frame, into a signal on the frequency axis for each block composed of a plurality of frames, and coding the converted signal. The present invention relates to a gasifier.

[0002]

2. Description of the Related Art As a high-efficiency encoding method of an audio signal, a signal on a time axis is converted into a signal on a frequency axis for each frame (predetermined time unit) and divided into a plurality of frequency bands. A transform coding method that encodes each signal, a band division coding method that divides a signal on a time axis into a plurality of frequency bands, and encodes each band, and a band division coding method and a transform coding method. Are known.

In the band division coding system, a signal on the time axis is divided into a plurality of frequency bands by using a filter such as a quadrature mirror filter. In the transform coding method, a discrete Fourier transform (Discrete Fourier Transfo
rm), Discrete Cosine Transfor
m), Modified Discrete Cosin
e Transform) is used to perform spectrum conversion (convert a signal on the time axis into a signal on the frequency axis).

Here, for example, in the case of performing spectrum conversion using modified discrete cosine transform, assuming that the number of sample data in one frame is M, the latter half of 2M sample data which has been spectrum-converted immediately before is M. Is used as the first half of the 2M sample data to be subjected to the spectrum conversion, so that the spectrum conversion is performed for each of the 2M sample data (that is, the sample data for two frames). Has become. By doing so, it is possible to reduce connection distortion between unit blocks to be encoded.

[0005] International Publication No. WO 98/46045.
In the publication of, for example, stereo signals of audio,
In the case of encoding a plurality of signals having a correlation, a technique is disclosed which realizes more efficient encoding by utilizing the correlation between the plurality of signals.

For example, when encoding an L (left) channel signal and an R (right) channel signal that constitute an audio stereo signal, an average of the L channel signal and the R channel signal is obtained. The signal is a signal of the first channel, and a signal obtained by dividing the difference between the signal of the L channel and the signal of the R channel by 2, a signal of the L channel, or a signal of the R channel is a signal of the second channel; The signal of the first channel and the signal of the second channel are separately encoded.

If there is a correlation between the L-channel signal and the R-channel signal, a signal obtained by dividing the difference between the L-channel signal and the R-channel signal by 2 is used as a second-channel signal. On the other hand, if there is no correlation between the signal of the L channel and the signal of the R channel, the signal having the relatively lower signal level of both signals is set as the signal of the second channel. Which of the three signals is set as the signal of the second channel is determined for each frame.

As a result, the level of the signal of the second channel is smaller than that of the signal of the first channel. Therefore, the bit rate for encoding the signal of the second channel is reduced, and a more efficient code is obtained. Can be realized.

[0009]

However, the above two techniques, that is, a technique for reducing connection distortion between unit blocks to be coded, and a method for coding a plurality of correlated signals with higher efficiency. If you try to use a combination of technologies, multiple frames (two frames in the above example)
Is performed as a unit, whereas the signal type may be switched for each frame, so that the signal level changes abruptly in the unit block to be encoded. Since the bit rate assigned to the channel for switching the type is low, there is a problem that quantization noise increases.

Accordingly, the present invention provides an encoding apparatus capable of suppressing an increase in quantization noise caused by switching of the type of a signal to be encoded in a unit block to be encoded. The purpose is to provide.

[0011]

According to the present invention, there is provided a first channel converter for outputting a signal obtained by synthesizing all input signals of a plurality of channels as a signal of a first channel. Means, a signal obtained by synthesizing all input signals of a plurality of channels, or second channel conversion means for outputting input signals of some channels as signals of a second channel, and input signals of each channel Channel conversion control means for setting a signal output by the second channel conversion means for each frame, and signals output from the first and second channel conversion means according to the relationship Encoding means for converting the signal into a signal on the frequency axis for each block composed of a plurality of frames, and encoding the signal. The bit rate for encoding the signal output from the channel conversion means is encoded according to whether or not the type of the signal output from the second channel conversion means is switched in the block to be encoded. A bit rate setting means for setting each block is provided.

With this configuration, it is possible to assign a higher bit rate to each unit block to be encoded when the type of the signal to be encoded in the block is switched than when it is not switched.

[0013] Further, the bit rate for encoding the signal output from the second channel conversion means may be set to a frame rate which has elapsed since the type of the signal output from the second channel conversion means was last switched. It may be configured to be set according to the number.

With this configuration, the signal type is not switched in the unit block to be encoded, but a high bit rate is allocated to a block including a frame in which the signal type is switched from the immediately preceding frame. Can be.

[0015] Further, the bit rate for encoding the signal output from the second channel conversion means may be set according to the type of the signal output from the second channel conversion means. Good.

With this configuration, when encoding a type of signal in which quantization noise greatly affects the degradation of a decoded signal as compared with other types, a high bit rate is set to reduce quantization noise. can do.

The signal output from the second channel conversion means is coded first,
Of the bit rate given in advance for encoding the signal output from the first channel conversion means and the signal output from the second channel conversion means,
A signal output from the first channel converter may be encoded at a bit rate remaining after the signal output from the second channel converter is encoded.

With this configuration, even if the bit rate for encoding a signal whose signal type is likely to be switched in a unit block to be encoded is set to be high, bits that are not used in actual encoding are set. For rates,
It is assigned to the bit rate when encoding other signals.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an encoding apparatus according to an embodiment of the present invention, which encodes audio stereo signals (L (left) channel signal and R (right) channel signal). The L-channel signal and the R-channel signal, which are input signals to the encoding apparatus and are subjected to PCM (Pulse Code Modulation) modulation, are divided into a plurality of frequency bands by a frequency band dividing circuit 1 configured by a quadrature mirror filter or the like. After that, the first channel conversion circuit 2-1 and the second channel conversion circuit 2-
2 and the control circuit 5.

The first channel conversion circuit 2-1 outputs a signal obtained by averaging the L-channel signal and the R-channel signal supplied from the frequency band dividing circuit 1 (that is, (L-channel signal + R-channel signal). ) / 2) is output.
The second channel conversion circuit 2-2 generates a signal obtained by dividing the difference between the L-channel signal and the R-channel signal provided from the frequency band division circuit 1 by two (that is, (L-channel signal−R-channel signal). ) / 2), L channel signal, R
Outputs one of the channel signals. Which signal is output by the second channel conversion circuit 2-2 depends on whether there is a correlation between the L-channel signal and the R-channel signal given from the frequency band division circuit 1, and the magnitude relationship between the two signals. Accordingly, the setting is made by the control circuit 5 for each frame.

More specifically, the L-channel signal and the R-channel signal are as shown in FIGS. 2A and 2B, respectively. If there is a correlation, as shown in FIG.
Since the signal level of (L channel signal−R channel signal) / 2 becomes very small, (L channel signal−R signal)
(Signal of channel) / 2.

On the other hand, the L channel signal and the R channel signal are as shown in FIGS. 4A and 4B, respectively, and there is no correlation between the L channel signal and the R channel signal. In this case, as shown in FIG. 5B, since the signal level of (L channel signal−R channel signal) / 2 does not decrease, the L channel signal and the R channel signal are relatively reduced. The signal level is set so as to output the lower one (the R channel signal in FIG. 4).

Thus, the second channel conversion circuit 2-
2 outputs a signal whose level is as small as possible. Therefore, even if the bit rate when encoding the signal output from the second channel conversion circuit 2-2 is reduced, the quantization noise is not so large. It becomes inconspicuous. Therefore, it is possible to reduce the bit rate assigned to the signal output from the second channel conversion circuit 2-2, and realize more efficient encoding.

The first encoding circuit 3-1 converts a signal output from the first channel conversion circuit 2-1 (hereinafter referred to as an "A channel signal") into two adjacent frames x For each encoded block composed of the #th frame and the x + 1st frame, the signal is converted into a signal on the frequency axis by modified discrete cosine transform, and then encoded at the bit rate set by the control circuit 5, and the code obtained thereby is obtained. A
It is output as the code of the x + 1-th frame of the channel signal.

The second encoding circuit 3-2 converts the signal output from the second channel conversion circuit 2-2 (hereinafter referred to as "B channel signal") into two adjacent frames x For each encoded block composed of the #th frame and the (x + 1) th frame, the signal is converted into a signal on the frequency axis by a modified discrete cosine transform, and then encoded at the bit rate set by the control circuit 5, and the code obtained thereby is obtained. B
It is output as the code of the x + 1-th frame of the channel signal.

The code string generation circuit 4 generates and outputs a code string as shown in FIG. The code string output from the code string generation circuit 4 is recorded on, for example, a recording medium. FIG. 6 shows an example of a format in which the codes of the A channel and the B channel are stored in a frame having a predetermined bit rate. In the x-th frame of the code string, the code of the x-th frame of the signal of the A channel, the code of the x-th frame of the signal of the B channel, and the channel configuration data are stored in this order from the top. The channel configuration data is B in this frame.
Indicates the type of signal on the channel. In this example,
When the channel configuration data is 1, (L-channel signal-
(R channel signal) / 2, 2 means an L channel signal, and 3 means an R channel signal.

As described above, the control circuit 5 determines whether or not there is a correlation between the L-channel signal and the R-channel signal provided from the frequency band dividing circuit 1 and determines the second channel according to the magnitude relationship between the two signals. The type of signal output from the conversion circuit 2-2 is set, and the operation of each unit is controlled.
Further, the control circuit 5 includes the first encoding circuit 3-1 and the second encoding circuit 3-1.
A bit rate is set for each encoded block of each frame for the encoding circuit 3-2. This operation will be described with reference to the flowchart shown in FIG.

First, it is determined whether or not the channel configuration data of the B channel signal has been switched from the immediately preceding frame in the current frame (S1). If the result of determination in S1 is that the channel configuration data has been switched (S
1 (YES), the value of a frame counter for counting the number of frames that have elapsed since the last switching of the channel configuration data is set to 0 (S2), and then the second
And a bit rate of 96 [kbps] for the encoding circuit 3-2 (that is, a bit rate for encoding a B-channel signal is set to 96 [kbps]).
A bit rate of 32 [kbps] is provisionally set for the first encoding circuit 3-1 (that is, a bit rate for encoding an A-channel signal is provisionally set to 32 [kbps]. (S3). When S3 ends, the process moves to S9 described later.

On the other hand, if the result of determination in S1 is that the channel configuration data has not been switched (NO in S1),
The value of the frame counter is incremented by 1 (S4). The value of the frame counter is limited so as not to exceed a predetermined value. Next, it is determined whether the value of the frame counter is smaller than 2 (S5). As a result of the determination in S5, if the value of the frame counter is smaller than 2 (YES in S5), the process proceeds to S3 described above, while if the value of the frame counter is not smaller than 2 (N in S5).
O) The process proceeds to S6 described below.

In S6, it is determined whether or not the channel configuration data of the current frame is "1". If the result of the determination in S6 is that the channel configuration data is 1 (YES in S6),
A bit rate of 32 [kbps] is set for the second coding circuit 3-2, and a bit rate of 96 [kbps] is provisionally set for the first coding circuit 3-1 ( S
7). On the other hand, if the channel configuration data is not 1 (S6
NO), 48 [kbps] for the second encoding circuit 3-2.
And a bit rate of 80 [kbps] is provisionally set for the first encoding circuit 3-1 (S8). When S7 and S8 are completed, S
Move to 9.

At S9, the second encoding circuit 3-2 causes the B-channel signal to be encoded. Thereby, the second
The coding circuit 3-2 converts a block consisting of the previous frame of the B channel signal and the current frame into a signal on the frequency axis by a modified discrete cosine transform, and then sets the bit set by the control circuit 5. Encode at a rate.

Next, in the encoding process, not all of the assigned bit rates are used.
When the encoding of the B channel signal by the second encoding circuit 3-2 is completed, the difference between the set bit rate and the bit rate used in the actual encoding (that is, the surplus bit rate) is calculated. (S10). Next, the bit rate obtained by adding the bit rate calculated in S10 to the bit rate provisionally set for the first encoding circuit 3-1 is reset (S11).

Then, the first encoding circuit 3-1 causes the A-channel signal to be encoded (S12). As a result, the first encoding circuit 3-1 converts the block consisting of the previous frame of the A channel signal and the current frame into a signal on the frequency axis by the modified discrete cosine transform, and then controls the control circuit 5 Encoding at the bit rate set by. The above processing of S1 to S12 is performed for each frame.

With the above configuration, for example, an L-channel signal and an R-channel signal as shown in FIGS. 8A and 8B are input, and as a result, an A-channel signal and a B-channel signal Are (c) in FIG. 8, respectively.
As shown in (d), the channel configuration data of the B-channel signal is 1 in both the (N-1) th frame and the Nth frame which form the coding block of the Nth frame, and the type of the B channel signal Are not switched in the coding block, so that the bit rate for coding the B channel signal in the coding block of the Nth frame is 32.
Set to [kbps].

On the other hand, in the N-th frame and the N + 1-th frame which form the coding block of the (N + 1) -th frame, B
The channel configuration data of the channel signal is 1, 3 respectively.
Since the type of the signal of the B channel is switched in the coding block, the bit rate for coding the signal of the B channel in the coding block of the (N + 1) th frame is 9
It is set to 6 [kbps].

As described above, in the present embodiment, the bit rate for encoding the B-channel signal is set higher in the coded block in which the type of the B-channel signal is switched in the block than in the non-switched block. Therefore, it is possible to suppress an increase in quantization noise caused by switching of the type of the signal of the B channel.

Here, in the second channel conversion circuit 3-2, when the channel configuration data is switched, the signal level is prevented from suddenly changing at the joint between the immediately preceding frame and the switched frame. In some cases, the last sample data of the previous frame and the first few sample data of the switched frame are corrected so that both frames are smoothly connected. In this case,
Although the channel configuration data is the same between the frame in which the channel configuration data is switched and the next frame,
In the former frame, the sample data is modified, and there is a concern that quantization noise may increase at a low bit rate.

However, in the present embodiment, S in FIG.
When the number of frames that have elapsed since the last switching of the channel configuration data is 1 by the processing in step 5, in other words, in the coding block composed of the frame in which the channel configuration data has switched and the next frame, the B channel Is set to a high bit rate when encoding the signal. Therefore, even if the sample data is modified as described above, it is possible to suppress an increase in quantization noise due to switching of the signal type. If the sample data is not corrected as described above, the determination threshold value in S5 may be set to 1, or S5 may be deleted.

When the channel configuration data is 1 (ie, when the B channel signal is (L channel signal−R channel signal) / 2), the decoded L channel signal and R channel The degree of signal degradation is determined by the quantization noise of both the A-channel signal and the B-channel signal, but when the channel configuration data is other than 1 (that is, the B-channel signal is the L-channel signal or In the case of an R channel signal), the degree of deterioration of the decoded L channel signal or R channel signal depends only on the quantization noise of the B channel signal. For this reason,
When the B channel signal is encoded at the same bit rate when the channel configuration data is 1 and when the channel configuration data is other than 1, when the L channel signal and the R channel signal are decoded, the channel of the B channel signal is decoded. Deterioration is noticeable in portions where the configuration data is other than 1.

On the other hand, in the present embodiment, S in FIG.
By the processing of 6 to S8, the bit rate at the time of encoding the signal of the B channel is made higher when the channel configuration data is other than 1 than when it is 1, so the above-described problem occurs. Can be prevented.

In this embodiment, even if the bit rate for encoding the B channel signal is set high by the processing of S10 and S11 in FIG. 7, the bit rate not used in the actual encoding is set. Is assigned to the bit rate used to encode the signal of the first channel, so that encoding can be performed more efficiently.

As an embodiment of the present invention, only the case where the input signal has two channels and the unit block to be encoded is two frames has been described, but the case where the input signal has three or more channels, The present invention can be applied to a case where a unit block to be encoded is three frames or more.

[0043]

As described above, according to the coding apparatus of the present invention, the type of signal to be coded in each unit block to be coded is switched according to whether or not the type of the signal to be coded in the block is switched. Since the bit rate is set, a higher bit rate is assigned when the signal is switched than when the signal is not switched, so that an increase in quantization noise due to the signal type switching can be suppressed.

Since the bit rate is set according to the number of frames that have elapsed since the last change of the signal type, the signal type does not change within the unit block to be encoded, but the signal type is changed from the immediately preceding frame. Even when assigning a high bit rate to a block that includes a frame in which the signal type is switched, and correcting the data so that when the signal type is switched, the data is smoothly connected to the immediately preceding frame. It is possible to prevent an increase in quantization noise due to switching of the signal type.

Since the bit rate is set for each unit block to be coded according to the type of the signal to be coded in the block, the quantization noise of the decoded signal is smaller than that of other types. When encoding signals of a type that greatly affects degradation, setting a high bit rate and reducing quantization noise may cause a problem that the degradation of the decoded signal will be partially noticeable. Can be prevented.

Further, even if the bit rate for encoding a signal whose signal type is likely to be switched in a unit block to be encoded is set to a high value, the bit rate not used in the actual encoding is determined. Is assigned to the bit rate used when encoding other signals, so that encoding can be performed more efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram of an encoding device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of waveforms of an L-channel signal and an R-channel signal.

3 shows (L channel signal + R channel signal) / 2 and (L channel signal−R channel signal) corresponding to the waveforms of the L channel signal and the R channel signal shown in FIG. 2; It is a figure which shows the waveform of) / 2.

FIG. 4 is a diagram showing another example of waveforms of an L channel signal and an R channel signal.

5 shows (L channel signal + R channel signal) / 2 and (L channel signal−R channel signal) corresponding to the waveforms of the L channel signal and the R channel signal shown in FIG. It is a figure which shows the waveform of) / 2.

FIG. 6 is a diagram for describing a code string generated by a code string generation circuit.

FIG. 7 is a flowchart of a process of setting a bit rate for each encoded block.

FIG. 8 is a diagram showing an example of waveforms of an L-channel signal and an R-channel signal, and corresponding waveforms of an A-channel signal and a B-channel signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frequency band division circuit 2-1 1st channel conversion circuit 2-2 2nd channel conversion circuit 3-1 1st encoding circuit 3-2 2nd encoding circuit 4 Code train generation circuit 5 Control circuit

Claims (6)

[Claims] A first channel conversion unit that outputs a signal obtained by combining all input signals of a plurality of channels as a signal of a first channel; and a first channel conversion unit that combines all input signals of a plurality of channels. Signal or the input signal of some channels
A second channel conversion unit that outputs a signal of a channel, a channel conversion control unit that sets a signal output by the second channel conversion unit for each frame according to a relationship between input signals of the respective channels, Encoding means for converting signals output from the first channel conversion means and the second channel conversion means into signals on the frequency axis for each block comprising a plurality of frames, and then encoding the signals; In the apparatus, a bit rate at the time of encoding a signal output from the second channel conversion unit is set to determine whether a type of a signal output from the second channel conversion unit is switched in a block to be encoded. And a bit rate setting means for setting each of the blocks to be encoded in accordance with the following. 2. A case in which a bit rate at the time of encoding a signal output from the second channel converter is changed in a type of a signal output from the second channel converter within a block to be encoded. 2. The encoding apparatus according to claim 1, wherein the setting is made higher than that in a case where switching is not performed. 3. A bit rate for encoding a signal output from the second channel conversion means, the frame rate having passed since the type of signal output from the second channel conversion means was last switched. 3. The encoding device according to claim 1, wherein the encoding device is set according to the number. 4. A bit rate for encoding a signal output from the second channel conversion means is set according to a type of a signal output from the second channel conversion means. Any one of claims 1 to 3
An encoding device according to any one of the preceding claims. 5. A signal output from the second channel conversion means, which is coded first, and a signal output from the first channel conversion means and the second channel. Among the bit rates given in advance for encoding the signal output from the conversion means, the first bit rate is the remaining bit rate after the signal output from the second channel conversion means is encoded. The encoding device according to any one of claims 1 to 4, wherein a signal output from the channel conversion unit is encoded. 6. The encoding apparatus according to claim 1, wherein the input signals of the plurality of channels are audio stereo signals.