JPH09298467A - Data converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an error from being caused in a decoding operation (e.g. interruption of an output voice signal is not caused) even when there is a relative error caused between a bit rate of input data to a decoder and a sampling rate of output data. SOLUTION: The data converter 1 is provided with an analyzer 3 that analyzes presence of a frame length control code included in compression digital data, a control means 4 that detects an error between an actual content of the control code and a content of the standards and generates a control signal indicating the content to correct the error, and a data processing means 5 processing the control code depending on the control signal, an input speed of compression digital data to the decoder always matchs the processing speed of the decoder by detecting the error between the actual content of the control code and the content on the standards and processing the compression digital data to revise the content of the control code in a way of eliminating the error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data conversion device, and more particularly to a decoding system in which a transfer bit rate of compressed digital data to a decoder and an operation reference frequency of the decoder are set independently of each other. It is suitable to be applied to.

[0002]

2. Description of the Related Art Among various conventionally proposed compression encoding systems, when decoding and outputting compressed digital data, the input bit rate of the compressed digital data to the decoder and the output data There is a device in which the sampling rate (the operation reference frequency of the decoder) can be set independently of each other. In this type of scheme,
Normally, the ratio between the input bit rate of compressed digital data and the sampling rate of output data is kept constant.

[0003]

However, a relative error may occur in the ratio between the input bit rate of the compressed digital data and the sampling rate of the output data.
When the relative error occurs in this way, the operation of the decoding process becomes abnormal. When an abnormality occurs in a normal decoder, after resetting, the compressed digital data that is continuously input is decoded, so that the continuity of the output data is lost when the abnormality occurs. There was an inconvenience.

For example, MPEG1 audio (ISO / IEC
11172-3) Decoders that comply with the compression encoding method,
It has a buffer memory for internal processing, etc., and since this buffer capacity has a certain amount of leeway, even when a relative error occurs, only the amount of that leeway will continue to output decoded speech normally. be able to.

However, when a relative error occurs for a certain amount of time, excess data is input beyond the margin of the buffer memory or the buffer memory is emptied, resulting in a buffer overflow or data shortage abnormality. To do. As a result, the audio data in the section in which such an abnormality has occurred is interrupted, and when used for music, for example, the music is interrupted on the way, which hinders listening to music.

One example of the cause of the relative error in the ratio between the input bit rate of the compressed digital data and the sampling rate of the output data is, for example, that the frame length of the compressed digital data becomes a length according to the standard. There may be an error in the frame length control code itself for adjustment.

For example, in the MPEG audio layer II, one audio frame is formed in 1152 PCM units. Here, the bit rate of the compressed digital data is 224 Kbps, and the sampling frequency during compression is 4
In the case of 4.1 KHz, the number of bits per unit time of the audio frame is 224 K × (1152/4)
4.1K) = 5851.42857 ... (Hereinafter, a normal frame length according to this standard is referred to as FlengthN).

As described above, when the number of bits of an audio frame per unit time is accurately calculated, a number below the decimal point appears, but since the number of bits must be an integer, the decimal part is rounded. In MPEG audio layer II, the length per frame is standardized so that the number of bits is divisible by 8, and in this case,
The two closest values to the above calculated value are 58
48 bits (Hereinafter, frame length A is referred to as FlengthA)
And 5856 bits (hereinafter, the frame length B is referred to as FlengthB).

However, if such rounding is simply performed, an error occurs with respect to the original bit rate, which causes a problem. Therefore, in order to eliminate the apparent difference between the amount of data represented by the rounded frame length and the amount of compressed digital data that is actually input, a frame length control code (dummy data) called padding is used. It is used to adjust the frame length.

That is, layer II of MPEG audio
Then, by assuming that the frame length A has no padding and the frame length B has padding, a plurality of audio frames having both attributes are transmitted at a constant ratio, and are actually transmitted in the long term. The data amount of compressed digital data is matched. In the above example, the ratio between no padding and padding is
Must be 4: 3.

However, if the padding presence / absence ratio itself is incorrect, the input speed of the compressed digital data and the decoding processing speed are different during the actual decoding processing. For example, if all the padding is eliminated, the compressed digital data comes in at a speed higher than the decoding processing speed, resulting in buffer overflow. As a result, as described above, there is a problem that output audio data is interrupted by the reset operation, which hinders listening to music.

The present invention has been made to solve such a problem, and a relative error occurs between the input bit rate of the compressed digital data to the decoder and the sampling rate of the output data from the decoder. Even in such a case, the object is to prevent an abnormality in the decoding operation (for example, to prevent the output audio data from being interrupted).

[0013]

A data conversion apparatus according to the present invention is a bit rate for transferring compressed digital data to a decoder, in which a frame length control code for adjusting at least a frame length is included in a bit stream, In a system in which the operation reference frequency of the decoder is set independently of each other, analysis means for analyzing the presence or absence of a frame length control code included in the compressed digital data for each frame, and analysis by the analysis means Based on the result, the actual content rate of the frame length control code and the content rate determined from the standard of the compressed digital data are compared to detect an error between the two, and the error is corrected. The control means for generating a control signal indicating the content rate, and the control signal generated by the control means. And a Deda processing means for processing the data so as to change the content of the frame length control codes in the compressed digital data.

According to another feature of the present invention, the data processing means has a frame containing a frame length control code and a frame not containing a frame length control code in the compressed digital data according to a control signal generated by the control means. The content ratio of the frame length control code is changed by changing the mixing ratio of

Another feature of the present invention is that the control means controls the actual content rate of the frame length control code contained in the compressed digital data by statistical processing at predetermined time intervals. It is characterized by doing.

Another feature of the present invention is that the compressed digital data includes, in its bit stream, a frame length code for expressing a standard frame length in addition to the frame length control code. The control means obtains a standard content rate of the frame length control code based on the frame length code analyzed by the analyzing means.

Another feature of the present invention is that the frequency ratio between the actual transfer bit rate of the compressed digital data to the decoder and the original frequency of the clock input from the outside is determined from the standard. The control means further comprises a comparing means for detecting an error between the two by comparing with the frequency ratio, and the control means further comprises means for generating a control signal indicating a content rate for correcting the error detected by the comparing means. It is characterized by including.

Another feature of the present invention is a transfer bit rate of compressed digital data to a decoder,
In a system in which the operation reference frequency of the decoder is set independently of each other, the frequency ratio between the actual transfer bit rate of the compressed digital data to the decoder and the original frequency of the clock input from the outside is determined from the standard. Comparison means for detecting an error between the two by comparing with the determined frequency ratio, control means for generating a control signal for correcting the error detected by the comparison means, and control means for generating the control signal Depending on the control signal
Data processing means for processing the data so as to change the content rate of the frame length control code in the compressed digital data.

Another feature of the present invention is that it further comprises means for arbitrarily setting an original frequency, which is a source for generating the operation reference frequency of the decoder, by external control to the control means. Is characterized by.

Since the present invention comprises the above technical means, even if the content rate of the frame length control code contained in the compressed digital data is different from the standard content rate, the actual content rate and the standard content are Error is detected, the compressed digital data is processed by the control signal according to the error and the content ratio of the frame length control code is corrected, and it is adjusted by inserting the frame length control code. The input speed of compressed digital data to the decoder is controlled so as to always match the processing speed of the decoder.

According to another feature of the present invention, the frequency ratio between the actual transfer bit rate of the compressed digital data to the decoder and the original frequency which is the source of the operation reference frequency of the decoder is a standard frequency. Even if the ratio is different from the ratio, the error in the frequency ratio between the two is detected by the comparing means, and the compressed digital data is processed by the control signal according to the error so that the content ratio of the frame length control code is corrected. Therefore, the input speed of the compressed digital data to the decoder is controlled so as to always match the processing speed of the decoder.

Further, according to another feature of the present invention,
For example, by setting the original frequency compliant with various compression encoding methods to the control means by external control, the above-described error is detected corresponding to various compression encoding methods, and the compression code It is possible to generate the operation reference frequency for the decoder to operate without error under the conversion system by the frequency conversion means.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing the overall configuration of a decoding system including the data conversion device according to the present embodiment. Note that, hereinafter, the decoding system shown in FIG. 1 will be described as being based on the MPEG audio layer II.

In FIG. 1, the compressed digital data is supplied to the decoder 2 via the data conversion device 1, and the decoding process is performed here. This decoding process is performed according to a predetermined operation reference clock, and the operation reference clock is given by the frequency converter 7 multiplying the original frequency of the clock input from outside the data conversion device 1 by a predetermined value.

The frequency converter 7 is based on, for example, two frequency dividers having different frequency division ratios, a phase comparator for obtaining the phase difference between the outputs of the frequency dividers, and the obtained phase difference. And a voltage controlled oscillator (VCO) that changes the oscillation frequency and feeds it back to one of the frequency dividers.

The decoding system shown in FIG. 1 has a transfer bit rate of compressed digital data to the decoder 2 and
The operation reference frequency of the decoder 2 is set independently of each other. In this embodiment,
In order to prevent the inconvenience such as sound interruption described in the conventional example, the ratio of the transfer bit rate and the operation reference frequency is always constant, that is, the input speed of the compressed digital data to the decoder 2. And the processing speed of the decoder 2 always match.

The above-mentioned compressed digital data includes a frame length control code (padding) for adjusting the frame length of the compressed digital data, and M in the bit stream.
It includes a frame length code (information on the bit rate and the sampling frequency at the time of compression) for expressing the frame length on the standard conforming to the layer II of PEG audio.

In the case of layer II of MPEG audio, the above frame length code is included in the bit stream of the compressed digital data, but at least the frame length control code is included in order to apply this embodiment. The frame length code does not necessarily have to be included. However, it is assumed that the frame length is set in some form according to the standard of the compression encoding method to be applied (for example, a certain value is set according to the standard).

Further, the frequency information of the operation reference clock of the decoder 2 may not be included in the bit stream of the compressed digital data, but like the frame length code, it is in some form in the standard of the compression encoding system. It is assumed to be set. That is, for the frequency of the operation reference clock, it is necessary to select a certain multiple of the sampling frequency at the time of compression for the convenience of the decoding system.
The value is defined in the data conversion device 1 or set from the outside.

Further, the original frequency of the clock input from the outside of the data converter 1 to generate the operation reference clock of the decoder 2 is also defined in the data converter 1 or is set from the outside. And

In the following, layer II of MPEG audio is used.
Sampling frequency (hereinafter referred to as Fs) included in the bit stream of compressed digital data conforming to
Is 44.1 KHz, bit rate (hereinafter referred to as BR)
Is 224 Kbps. Further, it is assumed that the multiplication factor (hereinafter, referred to as Dfs) of the operation reference clock required by the decoder 2 is 384 times, and the original frequency (hereinafter, referred to as CLKm) is 13.5 MHz.

As described above, normally, the bit rate of the compressed digital data is adjusted to the standard bit rate by the frame length control code (padding), and the input speed of the compressed digital data to the decoder 2 and the decoder 2 are adjusted. It is designed to always match the processing speed. That is, an audio frame including padding and an audio frame not including padding are transmitted at a constant ratio so that the total bit rate is adjusted according to the standard.

However, an error may occur in the content rate of the frame length control code itself, which may cause an abnormal decoding operation. In the present embodiment, in order to cope with such a case, the analyzer 3, the control means 4, and the data processing means 5 perform the processing described below.

The analyzer 3 analyzes three pieces of information (frame length control code, sampling frequency Fs, bit rate BR) included in the bit stream of the compressed digital data. That is, the analyzer 3 checks the presence or absence of the frame length control code for each audio frame unit, and analyzes the contents of the sampling frequency Fs and the bit rate BR included in the header of the bit stream.

Further, the control means 4, based on the analysis result by the analyzer 3, the ratio (content ratio) in which the frame length control code is actually included in the compressed digital data,
By comparing the sampling frequency Fs and the standard content rate calculated from the bit rate BR, an error between the two is detected, and a control signal for correcting the error is generated.

Then, the data processing means 5 processes the data so as to change the content rate of the frame length control code in the compressed digital data according to the control signal generated by the control means 4. Specifically, in response to the control signal, an audio frame including a frame length control code (hereinafter, a frame of this frame length B is Fra
By changing the mixture ratio of the audio frame not including meB) and the audio frame not including it (hereinafter, the frame of the frame length A is referred to as Frame A), the content ratio of the frame length control code in the compressed digital data is changed. To

That is, by appropriately changing the blending ratio of Frame A and Frame B according to the error rate of the generated error (described later), the input speed of the compressed digital data input to the decoder 2 and the decoder 2 thereof. The decoder 2 operates normally by matching the processing speed of the data input to the decoder. It should be noted that how to change the blending ratio of Frame A and Frame B is determined by the control means 4 by obtaining the value of n from the following equations (1) and (2).

(Error rate) × {(frame length according to blend ratio after change) / (frame length according to blend ratio of input data)} = 1.0 (1) However, frame length according to blend ratio after change Is Frame B
Is defined as n (0 ≦ n ≦ 1), FlengthA × (1-n) + FlengthB × n = 5848 × (1-n) + 5856 × n = 5848 + 8 × n (2)

Next, FIG. 2 is a block diagram showing a more detailed structure of the control means 4. Hereinafter, the operations of the control means 4 and the data processing means 5 will be described in more detail with reference to FIG.

The result of the analysis of the presence or absence of the frame length control code by the analyzer 3 of FIG. 1 is given to the frame length control code monitoring means 41 of FIG. The frame length control code monitoring means 41 obtains the ratio of the frame length control code contained in the actual bit stream by statistical processing for every fixed time (for example, 2 seconds) based on the analysis result.

On the other hand, similarly, in the analyzer 3 of FIG. 1, the frame length code (sampling frequency Fs and bit rate B
The result of analysis regarding R) is given to the frame length control code normal content rate calculating means 42 of FIG. The frame length control code normal content rate calculating means 42 is the analyzer 3 described above.
The ratio of normal frame length control codes determined from the MPEG audio layer II standard is calculated based on the analysis result of the frame length code given by

Frame length control code error judging means 43
Is the actual ratio of the frame length control codes included in the compressed digital data obtained by the frame length control code monitoring means 41 and the normal data calculated by the frame length control code normal content rate calculating means 42. The ratio of the included frame length control code is compared, and the presence or absence of abnormality is determined from the error.

A sampling frequency Fs and a bit rate B are included in the bit stream of the compressed digital data.
In the case of a compression coding method that does not include R, the frame length control code normal content rate calculating means 42 is not necessary, and the content rate determined by the standard of the compression coding method is used as described above. You can make a comparison.

However, due to the relationship between the time divisions in the above statistical processing, the content rate is slightly different from the normal one in the short term, but considering the time divisions before and after,
It may be normal. In such a case, it is not preferable to judge it as an error, and it is necessary to suppress it.

In order to realize this, in the present embodiment, the accumulation of the error of the frame length control code content rate is calculated, and when the accumulated value exceeds a certain threshold, it is judged as an error. That is, FIP0, FIP1, FIP2,
The normal content rate is FIPnorm, the threshold for determining an error is ErrLimit, and the error may be determined when any of the following conditional expressions (3) and (4) is satisfied.

Overflow judgment: sum (FIP0-FIPnorm, FIP1-FIPnorm, FIP2-FIPnorm,…)> ErrLimit (3) Underflow judgment: sum (FIP0-FIPnorm, FIP1-FIPnorm, FIP2-FIPnorm,…) <-ErrLimit (Four)

Here, as a specific example in the case where an error occurs in the content rate of the frame length control code (padding), a case where the padding is included in all the audio frames during the fixed time for which the statistical processing is performed will be described. . When all the padding is present, the number of frames contained in the compressed digital data per second is different from the normal case (no padding: Yes = 4: 3) as follows.

Number of frames included per second in a normal bitstream: 224K / 5851.429 [frame / sec] Number of frames included per second in a bitstream including the above error: 224K / 5856 [frame / sec]

Frame length control code error judging means 43
If an error like this is detected, the expression
The error rate ErrFrame is calculated according to (5). ErrFrame = FlengthB / FlengthN = 5856 / 5851.429 (5) Then, the calculated error rate ErrFrame is supplied to the control signal generation means 44. The control signal generation means 44, based on the supplied error rate ErrFrame, FrameA, FrameB
Mixing ratio (Frame A and Fra in compressed digital data
A control signal for changing the meB content) is generated (specifically, the value of n shown in the above equations (1) and (2) is calculated) and supplied to the data processing means 5.

When an error that all padding exists is generated as described above, FlengthB is shown in Formula (1) (frame length according to the mixture ratio of input data). Therefore, in this case, the ratio n at which Frame B should be included in the compressed digital data after data processing is calculated as in the following equations (6) and (7) based on the above equations (1) and (2). .

ErrFrame × {(FlengthA + 8 × n) / FlengthB} = 1.0 (6) That is, n = {(FlengthB / ErrFrame) −FlengthA} / 8 = {(5856 / (5856 / 5851.429)) − 5848} / 8 ≈ 3/7 (7)

As described above, since all the frames included in the actual compressed digital data are Frame B,
In this case, 4/7 of all the frames included in the compressed digital data are Frame B (frames with padding)
The data is processed so as to be converted from a frame to a frame A (frame without padding) so that the input speed of the compressed digital data to the decoder 2 and the processing speed of the decoder 2 are matched, and the decoder 2 operates normally. You can

It should be noted that side effects caused by changing the padding should be dealt with at the same time.
Specifically, in the case of MPEG audio, C included in the header of the bit stream of compressed digital data
When the protection protection for discriminating a data error by the RC (Cyclic Redundancy Check) code is enabled, the CRC code value is changed. In addition, unnecessary data is deleted or empty data is added in response to the change of the actual frame length.

As described above, according to the present embodiment, even if the actual ratio of padding included in the bit stream of the compressed digital data is different from the standard ratio, the compressed digital data It is possible to make the input speed to the decoder 2 and the processing speed of the decoder 2 always coincide with each other, and it is possible to prevent abnormality in the decoding operation.

The above-described embodiment is an example in which there is no error in at least the input speed and the original frequency of the compressed digital data input from the outside of the data converter 1 (at least there is no error in the frequency ratio of both). Met. However, this frequency ratio can also deviate from the normal ratio.

For example, the normal ratio between the transfer bit rate BR of compressed digital data and the original frequency CLKm is BR / CLKm = 224 KHz / 13.5 MHz, while the bit rate BR 'different from the standard (for example, 219 Kbps). Compressed digital data is transferred at the original frequency CLKm '(for example, 13.
When a clock is input at 2 MHz), the frequency ratio is BR '/ CLKm' = 219 KHz / 13.2 MHz.

As described above, even if an error occurs in the transfer bit rate of the compressed digital data itself or an error occurs in the original frequency of the clock of the external input, an error occurs in the padding content rate. Similarly to the case, the decoder 2 may operate abnormally due to the accumulation of errors. Therefore, in the present embodiment, in order to cope with such a case,
As shown in FIG. 1, comparison means 6 is provided.

The comparison means 6 compares the frequency ratio when no error has occurred with the frequency ratio when an error has occurred, and detects the error. That is, the comparison means 6
Is a normal bit rate BR and an erroneous bit rate B
It is not possible to detect the absolute deviation from R'or the absolute deviation between the normal original frequency CLKm and the incorrect original frequency CLKm ', but it is possible to detect the deviation between the normal frequency ratio and the error frequency ratio. it can.

In this case, as shown in FIG. 2, the control means 4 receives the above comparison result in the comparison means 6 in the ratio error judgment means 45 and judges whether or not an error relating to the frequency ratio has occurred. . As the method for determining the presence / absence of a frequency ratio error, similar to the method for determining the presence / absence of a padding content rate error described above, an error is determined when the sum of the errors detected at regular time intervals exceeds a certain value. You can do it.

When it is determined that the frequency ratio error as described above has occurred, the ratio error determination means 45
The error rate ErrFreq is calculated according to the following equation (8). ErrFreq = (BR '/ CLKm') / (BR / CLKm) = (219K / 13.2M) / (224K / 13.5M) (8) Then, the calculated error rate ErrFreq is supplied to the control signal generating means 44.

The control signal generating means 44 generates a control signal for changing the blending ratio of Frame A and Frame B based on the supplied error rate ErrFreq (Frame B is included according to equations (1) and (2)). Calculate the value of the ratio n) and supply it to the data processing means 5. If a frequency ratio error occurs as in this example, there is no error in the padding content rate itself, so the value shown in equation (1) (frame length according to the mixing ratio of the input data) is FlengthN.

Therefore, in this case, the ratio n at which Frame B should be included in the compressed digital data after data processing is n.
Is calculated by the following equations (9) and (10). ErrFreq × {(FlengthA + 8 × n) / FlengthN} = 1.0 (9) That is, n = {(FlengthN / ErrFreq) −FlengthA} / 8 = {5851.429 / [(219K / 13.2M) / (224K / 13.5M) )]-5848} / 8 = 0.50284 (10)

On the other hand, the ratio of Frame B contained in the compressed digital data before data processing is 0.42857 (= 3/7)
Therefore, in this case, 0.07427 (= 0.50284-0.42857) of all frames included in the compressed digital data is converted to Fra
By processing the data so as to convert from meA (frame without padding) to FrameB (frame with padding), the above-mentioned inconvenience can be avoided.

In the case of the example described above, the error rate ErrFra
Since both me and ErrFreq are values close to 1.0, the problem could be avoided, but if the error rate of the generated error is far from 1.0, the problem may not be avoided. is there. In this case, the following two methods can be considered. One is a method of stopping the reproduction of the sound because it deviates from the controllable range, and the other is a method of making a sound for some time even if the sound is not a normal sound.

The former method of stopping the reproduction of the sound can be realized by the control means 4 outputting a reproduction stop signal to the decoder 2. Alternatively, it can be realized by sending an MPEG audio data frame containing silent data to the decoder 2 instead of the data frame to be reproduced.

Here, a point to be noted when stopping the sound reproduction is to lengthen the sound reproduction stop time to some extent (time in seconds). The reason is that if the sound reproduction stop time is extremely short, sound reproduction and stop are repeated in a short time so that the sound output from the speaker (not shown) sounds like a "machine gun" sound. turn into. This is very unpleasant to the ears and may have an adverse effect on the speaker itself, and it is necessary to suppress it.

On the other hand, when the sound reproduction is not stopped as in the latter method, in MPEG audio, a certain data frame itself is duplicated and reproduced or deleted to be output from the decoder 2. Although the data is different from the original data, it is possible to suppress the influence on the sound quality as compared with the case where an error occurs.

Further, in this embodiment, as shown in FIGS. 1 and 2, the original frequency of the original clock for generating the operation reference clock of the decoder 2 is controlled by the external control of the data converter 1 (for example, manually). Means for setting the control means 4 are also provided.

Thus, for example, by setting an original frequency based on a compression encoding method other than MPEG audio, error detection is performed corresponding to various compression encoding methods, and under that compression encoding method. Frame length control code (padding) so that the decoder 2 operates without error
Can be processed. That is, it is possible to easily use one control means 4 by adapting it to a plurality of purposes.

In this case, the original frequency set by the external control is given to the normal frequency ratio calculating means 46 shown in FIG. The normal frequency ratio calculating means 46 uses the set original frequency and the standard transfer bit rate analyzed by the analyzer 3 (the bit rate of the compressed digital data by the corresponding compression encoding method) to determine the compression code. A normal frequency ratio is calculated when an error does not occur in the coding method.

Then, the ratio error judging means 45 calculates the error rate ErrFreq based on the calculation result of the normal frequency ratio calculating means 46 in the same manner as the above equation (8), and the calculated error rate ErrFreq is calculated. Supply to. The control signal generation means 44 generates a control signal for changing the mixture ratio of Frame A and Frame B based on the supplied error rate ErrFreq, and supplies it to the data processing means 5.

In the embodiment described above, as shown in FIG. 1, means for controlling the frequency of the operation reference clock of the decoder by observing the error of the padding content rate, the transfer bit rate of the compressed digital data. Means for controlling the frequency of the operation reference clock by observing an error in the ratio between the operation reference clock and the original frequency, and means for controlling the frequency of the operation reference clock by arbitrarily setting the original frequency by external control. Although all are included, it is possible to apply each independently or in any combination.

Although the layer II of MPEG audio is taken as an example of the compression encoding method, the present invention is not limited to this. For example, any compression encoding method such as MPEG1 or MPEG2 for image compression, AC-3, etc. may be applied as long as the bit length of the compressed digital data includes at least the frame length control code. You can

[0074]

As described above, the present invention analyzes the content rate of the frame length control code contained in the compressed digital data and compares the analyzed actual content rate with the standard content rate. By detecting the error between the two, the data is processed to change the content rate of the frame length control code so as to eliminate the error, so that the frame length control code of the compressed digital data Even if the content rate is different from the standard content rate, the compressed digital data is processed so that the content rate is correct,
It can be supplied to the decoder so that the input speed of the compressed digital data to the decoder and the processing speed of the decoder always match.

Therefore, even if a relative error occurs between the input bit rate of the compressed digital data to the decoder and the sampling rate of the output data due to an error in the content rate of the frame length control code, no abnormality occurs in the decoding operation. Thus, it is possible to prevent the inconvenience that the continuity of the output data is lost. For example, MP
When the compressed digital data of EG audio is used, it is possible to eliminate the interruption of the reproduced voice.

Further, according to another feature of the present invention, an error between the actual frequency ratio between the bit rate of the compressed digital data transferred to the decoder and the original frequency of the external input clock and the standard frequency ratio is detected. However, since the data is processed to change the content rate of the frame length control code so as to eliminate the error, the frequency ratio between the transfer bit rate and the original frequency is different from the standard frequency ratio. Even in such a case, the compressed digital data can be processed so as to correct the content rate according to the error and supplied to the decoder, and the input speed of the compressed digital data to the decoder and the processing speed of the decoder are It can always be a match.

Therefore, even if an error occurs in the frequency ratio, it is possible to prevent an abnormality in the decoding operation and prevent the disadvantage that the continuity of the output data is lost. For example, when the compressed digital data of MPEG audio is targeted, it is possible to eliminate the break in the reproduced voice.

Further, according to another feature of the present invention,
Since a means for arbitrarily setting the original frequency that is the source of generating the operation reference frequency of the decoder to the control means by external control is provided, for example, the original frequency complying with various compression encoding methods is controlled by the control means. Is set by external control to detect the above-mentioned error corresponding to various compression encoding methods, and the operation reference frequency for the decoder to operate without error under the compression encoding method. Can be generated, and one control means can be easily adapted and used for a plurality of compression coding schemes.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an overall configuration of a decoding system including a data conversion device according to an embodiment.

FIG. 2 is a block diagram showing a more detailed configuration of a control means 4 shown in FIG.

[Explanation of symbols]

 1 data converter 2 decoder 3 analyzer 4 control means 5 data processing means 6 comparing means 7 frequency converter 41 frame length control code monitoring means 42 frame length control code normal content rate calculation means 43 frame length control code error judgment means 44 control Signal generation means 45 Ratio error determination means 46 Normal frequency ratio calculation means

Claims (7)

[Claims] 1. A transfer bit rate of compressed digital data containing a frame length control code for adjusting a frame length in a bit stream to a decoder and an operation reference frequency of the decoder are independent of each other. In the set system, the analysis means for analyzing the presence or absence of the frame length control code contained in the compressed digital data for each frame, and the actual operation of the frame length control code based on the analysis result by the analysis means. Control means for detecting an error between the two by comparing the content rate of the compressed digital data with the content rate determined from the standard of the compressed digital data, and generating a control signal indicating the content rate for correcting the error. And the frame length in the compressed digital data according to the control signal generated by the control means. A data conversion device, comprising: a data processing unit that processes data so as to change the content rate of a control code. 2. The data processing means changes the blending ratio of a frame containing a frame length control code and a frame not containing the frame length control code in the compressed digital data according to a control signal generated by the control means. A data conversion device, characterized in that the content rate of the frame length control code is changed. 3. The control means controls to obtain the actual content rate of the frame length control code contained in the compressed digital data by statistical processing at every predetermined time. The data converter described in 1. 4. The compressed digital data includes, in its bit stream, a frame length code for expressing a standard frame length in addition to the frame length control code, and the control means is the analysis means. 2. The data conversion apparatus according to claim 1, wherein the content rate in the standard of the frame length control code is obtained based on the frame length code analyzed by. 5. The frequency ratio between the actual transfer bit rate of the compressed digital data to the decoder and the original frequency of the clock input from the outside is compared with the frequency ratio determined from the standard to obtain both. A comparison means is further provided for detecting an error, and the control means further comprises means for generating a control signal indicating a content rate for correcting the error detected by the comparison means. ~ Any one of 4
The data conversion device according to item. 6. In a system in which a transfer bit rate of compressed digital data to a decoder and an operation reference frequency of the decoder are set independently of each other, the actual transfer bit rate of the compressed digital data to the decoder and the external The frequency ratio with the original frequency of the clock input from is compared with the frequency ratio determined from the standard, comparing means for detecting the error between the two, and the error detected by the comparing means is corrected. And a data processing unit for processing the data so as to change the content rate of the frame length control code in the compressed digital data according to the control signal generated by the control unit. A data conversion device comprising: 7. The apparatus further comprises means for arbitrarily setting an original frequency, which is a source for generating an operation reference frequency of the decoder, by external control to the control means. The data converter according to any one of 1.