JPS5979651A - Method and apparatus for transmitting signal - Google Patents

Abstract

PURPOSE:To obtain superior SN and a distortion characteristic by the small number of bits by dividing a representative value of each block obtained by dividing a PCM code in each fixed period by the difference value of an original signal, then transmitting the compressed value together with the representative value. CONSTITUTION:An A/D converter 1 converts an analog signal AS into a digital signal OP and an RAM 2 stores the digital signal OP. A maximum/minimum detecting circuit 3 detects the maximum and minimum values in the block. A block level calculating circuit 4 finds out a center value BL in the block and a difference detecting circuit 8 finds out the difference value between the center value BL and an original signal. A width detecting circuit 5 detects the variation width in one block and a scale value generating circuit 6 reads out a scale value corresponding to the variation width from a scale reference storage circuit 7 and generates a scale value SL. The difference value is compressed at a data compressing circuit 9 on the basis of the scale value, and synthesized at a synthesizing circuit 10 and the center value BL, and transmitted.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention digitizes analog signals to create a transmission path,
The present invention relates to a signal transmission system that is applied to a transmission system such as a demodulation system or a recording/reproduction system, receives a transmission signal from the transmission system, and converts it back into an analog signal.The present invention also relates to a signal transmission system that is used directly to implement the system.

[Technical background of the invention]

Analog signals are digitized by PCM (Hals code modulation) and transmitted by a transmission system (in this case, "transmission")
means not only transmission through transmission lines, but also modulation/demodulation systems, recording/
``Transmission'' in a broad sense includes passing through a reproduction system, etc. Therefore, ``1 transmission system'' also refers to a ``transmission system'' in a broad sense, including modulation/demodulation systems, recording/reproduction systems, etc. ), PCM transmission is performed to receive this signal and convert it back into an analog signal.

Although this PCM transmission system has many advantages, the generation of quantization noise accompanying digital encoding is unavoidable.

In order to reduce the influence of this quantization noise, it is necessary to increase the number of bits of the transmitted code, that is, the data length.

However, if the data length of the transmission code is increased, for example in a recording/reproduction system, reading errors will increase due to the increase in recording density, or recording errors may be caused by moving the recording medium at high speed to avoid this. This has the disadvantage of shortening the time. Further, in general transmission systems, problems arise, such as the need to widen the bandwidth of the transmission system as the amount of transmitted information increases.

Therefore, there is a need to be able to transmit PCM codes with a smaller number of bits than before, and there is a need for so-called D
PCM (differential PCM) and ADPCM (adaptive differential PCM)
Low bit rate encoding methods such as CM) have been proposed.

However, these conventional low bit rate encoding systems such as DPCM and ADPCM simply transmit the difference between samples1, so if an error occurs for some reason on the receiving side, this error will be transmitted from then on. This results in accumulation, and this becomes a serious problem, especially when receiving (reproducing) information from the middle of a series of transmitted information, as the absolute level of the original information cannot be reproduced.

[Purpose of the invention]

The present invention provides a signal transmission method and a signal transmission method that can improve the transmission of PCM codes using transmission codes with a small number of bits, and can obtain sufficiently good S/N ratio and distortion characteristics without substantially accumulating errors. The purpose is to provide a receiving device that can be used directly for its implementation.

[Summary of the invention]

The first invention according to the present invention is a "method" invention, in which an original PCM code is divided into blocks each having a scheduled time, a block level representing the sample values of the entire block is obtained, and this block level is and the original P in each block
At the same time as detecting the difference value with the CM code, find the maximum value of the above difference values in the block, and based on this maximum value, all the difference values in the block are PCM codes with fewer bits than the original PCM code. The above difference value is divided and compressed to obtain a transmission PCM code so that it can be represented by a code, and this transmission PCM code is
In addition to transmitting the M code, the scale information corresponding to the coefficient value of the division compression and the block level information are transmitted once for each block, and these transmission signals are received, and the received transmission PCM code is received. The method is characterized in that a reproduced difference value PCM code is obtained by decompression and restoration using multiplication according to scale information, and a reproduced PCM code is obtained by adding a block level based on received block level information to the reproduced difference value PCM code. Signal transmission system The second invention according to the present invention is an invention of an "apparatus" directly used for carrying out the above-mentioned first invention (6), in which each entire block of the original PCM code divided into blocks each having a scheduled time is block level information corresponding to the block level of each block representing the Sansol value of , a transmission PCM code obtained by dividing and compressing the difference value between this block level and the original PCM code in each block, and the coefficient value of the above division compression. In a receiving apparatus that receives a transmission signal from a transmission system and obtains a reproduced PCM code corresponding to the original PCM code, the reception and transmission PCM
a restoring means for expanding and restoring the reproduced difference value PCM code corresponding to the difference value by performing multiplication processing on the code according to reception scale information; The receiving device is characterized by comprising an adding means for adding block levels to obtain a reproduced PCM code.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

First, the analog signal As is converted into, for example, a 16-bit PCM code, and this is used as the original PCM code OP. This original PC
The M code OP is divided into blocks each having a scheduled time. In FIG. 1, seven blocks B1 to B7 are shown. In this case, the number of samples in the pot blocks B1 to B7 is 20.

Next, representative values of each of the 20 samples in each block B1 to B'7 are obtained and set as block levels BLJ to BL7. It is desirable that these block levels BLJ to BL7 be the average value or median value of the samples within each block B1 to B7 as shown in the figure, but they may be rough values, and in some cases, the minimum value within the block may be set as the maximum value. It may be a value, or the value of the first sample in the block may be used as is. However, it may be a value close to these values; in short, it may be an approximate value of each sample in the block obtained from □ using a predetermined method, that is, a representative value representing the value of each sample in the block. These block levels BLI to BL7 are transmitted once for each block.

Furthermore, the difference value between each block rail BLJ to BL7 and the original PCM code OP of each sample is determined.

This difference value is transmitted using a PCM code having fewer bits than the original PCM code op, for example, 8 bits.

However, if the difference value is 8 bits, which is an unbearably large value, only the upper 8 bits of the effective bits of the PCM code of the difference value are extracted. (to be divided by) transmit. At this time, the number of lower bits n that is truncated is also transmitted once for each block as a scale value. 8-bit data compressed according to the need to transmit the above-mentioned difference value,
This PCM code is called a transmission PCM code.

Therefore, the above-mentioned transmission PCM code and the block level and scale value are transmitted once per block.

9- On the other hand, on the receiving side, the received transmission PCM code is bit-shifted (that is, multiplied by 2n) according to the received scale value, and decompressed and restored to obtain a reproduced difference value PCM code. Then, the received block level is added to the reproduced difference value PCM code between OP and OP to obtain a reproduced PCM code corresponding to the original PCM code OP. If this reproduced PCM code is converted into an analog signal, it becomes an analog signal corresponding to the original analog signal As.

By transmitting in this manner, the transmitted PCM code can have a very short data length, that is, a code with a very small number of bits.

In other words, in conventional general PCM transmission systems (not DPCM, etc.), for example, the original 16-bit PCM code OP was used as the transmission code, so a large number of bits had to be transmitted. . In contrast, in this embodiment, the difference value between the block level within a block as shown in FIG. 1 is data compressed according to IIK and transmitted as a transmission PCM code, so that only a small number of bits can be transmitted.

Moreover, in the case of this embodiment, the lower the frequency of the original analog signal AS, the smaller the difference value within the block, and therefore the number of bits to be truncated when creating the transmission PCM code is reduced (in some cases, all heat may be lost). ) has the advantage of

In other words, when transmitting a low frequency, the scale value becomes small and highly accurate transmission is performed.

Since quantization noise is more audibly detectable as the reproduction frequency is lower, the above-mentioned characteristics can be said to be extremely excellent and desirable in practice.

In addition, in conventional DPCM, etc., only the difference value from the previous sample data is transmitted, so if an error occurs on the receiving side or if the data is received in the middle of transmission, the errors will accumulate and the reception will not be normal. However, in the method of this embodiment, refresh is actually performed for each block, so that errors are unlikely to accumulate.

That is, since the block level and scale value are transmitted once for each block, the accumulation of errors disappears for each block.

Furthermore, the difference value of the PCM code becomes larger as the frequency of the analog signal becomes higher, and in conventional DPCM etc.
It had the disadvantage that the maximum clipping level (the maximum amplitude that can be transmitted) decreases as the frequency increases. In this example, the maximum clipping level is limited by the frequency because data division compression is used to transmit the data of the difference value from the block level, and the scale information corresponding to the coefficient value is transmitted. Not done. This is due to the fact that when the frequency of the analog signal is low, as already explained, the scale value becomes smaller and the accuracy becomes higher, so the quantization noise automatically decreases for low-frequency and low-level signals, and this increases the auditory sense. Above all, very favorable regeneration takes place.

Next, a second embodiment of the present invention will be described.

This embodiment is an example in which a specific transmission device or apparatus is constructed using the present invention.

First, the transmitting device will be explained.

FIG. 2 shows the configuration of the transmitting device in this embodiment. This configuration is an example of a configuration that is considered to be the easiest to understand the present invention.

As shown in FIG. 2, the analog signal As is A/1) converted by an A/b (Analog-to-Digital) converter 1 into an original PCM code op of a sufficient number of bits, for example 16 bits. This original PCM code OP is stored in a storage means, for example, R
It is applied to AM (random access memory) 2 and temporarily stored in RAM 2 during calculation of block level and scale values, which will be explained next. During this time, the maximum and minimum values within one block are detected by the maximum and minimum detection circuit 3 from the original PCM code OP, and the professional Frepel calculation circuit 4 uses the calculation ((maximum value + minimum value)/2). The average of the maximum value and minimum value within the diblock, that is, the median value within the block is determined, and this is set as the block level BL. In addition, the width detection circuit 5 detects the variation width of the sample data within one block by the calculation (maximum value - minimum value),
This is given to the scale value generation circuit 6 (13-). In the scale reference storage circuit 7, appropriate scale values corresponding to various values of the above-mentioned variation range are stored in the form of a table or the like. The scale value generation circuit 6 compares the change width given from the width detection circuit 5 with the contents stored in the scale reference storage circuit 7, and outputs a scale value SL corresponding to the change width. Once the block level calculation circuit 4 has determined the block level BL, the difference detection circuit 8 has determined the block level BL.
A difference value between the original PCM code OP read from AM 2 and the sample data in the block is detected and provided to the data compression circuit 9 as a difference value PCM code DP. Since the difference value PCM code DP between the two and It is output from the data compression circuit 9 as a transmission PCM code TD of a small number of bits, for example, 8 bits. Otherwise, since it is a large value, the upper 8 bits of the effective bits are given priority and the lower effective bits are truncated. The data is output from the data compression circuit 9 as an 8-bit transmission PCM code TP. The compression operation in the data compression circuit 9 is performed based on the scale value output from the scale value generation circuit 6. The output of this data compression circuit 9 is sent to a TP synthesis circuit 10 for each processor
It is combined with each block level BL and scale value SL, and output to the transmission system.

Next, the receiving device will be explained.

FIG. 3 shows the configuration of the receiving device in this embodiment.

In FIG. 3, the transmission signal received from the transmission system is scaled [8L] in the separation circuit 11.

Block level BL and transmission PCM code TP are separated. The transmission PCM code TP is given to the data restoration circuit 12 along with the scale value SL, and is expanded and restored according to the scale value 8L, for example, by bit shift or bit shift + complementation for the truncated data, and corresponds to the original difference value PCM code DP. Playback difference value PC
It is output as M code DP'. This playback difference value PC
The M code D P' is added to the block level BL in the adder circuit 13 and the reproduction PC corresponding to the original PCM code OP is generated.
M code PP is obtained.

This reproduced PCM code PP is converted into an analog signal by a D/A (digital-to-analog) converter 14 and output as a reproduced analog signal AS'.

Note that the scale value SL and block level BL in the above
The number of bits of the transmitted data is small, but since it is transmitted once per block, even if the number of bits increases somewhat, it can be processed without any practical problem. (For example, if the data is 16 bits, it may be sent as two 8-bit words.) If the block level BLO value becomes significantly large, the quantization step of the block level BL itself may be changed to send data with a smaller number of bits. You may do something like this.

Further, in the above description, the data of the differential value PCM code DP is compressed simply by truncating the lower significant bits, but various other methods can be considered as data compression methods.

For example, dividing by a divisor such that the maximum possible value of the number of bits of the transmission PCM code TP is obtained by dividing the maximum value of the difference value PCM code DP, and transmitting this result as the transmission PCM code TP, The divisor at that time may be used as scale information. In addition, when the lower significant bits are truncated, the truncated value is accumulated in an accumulator, etc. without being discarded, and the result of the accumulation is used to carry up (carry) and down (plow) within the transmission digit. Born,
The accuracy may be improved.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

For example, FIG. 4 shows the configuration of another embodiment of the transmission device according to the present invention. In this case, a RAM 15 is added after the difference detection circuit 8 in FIG. Instead, the scale value is determined from the output difference value PCM code DP of the difference detection circuit 8. Therefore, the width detection circuit 5 shown in FIG. Scale reference storage circuit 7. The scale value generation circuit 6 is removed, and a new scale value generation circuit 16 is provided at 17-.

There are various other configurations of the transmitter that can be considered, but the key is to find the block level for each block and obtain the difference from the signal.
It is sufficient to transmit this difference value according to the scale value and to transmit the information on the block level and scale value once per block.

In addition, various methods can be considered for determining and transmitting the block level BL, ranging from a method to obtain it accurately to a method to obtain an approximate value. can be realized. The most appropriate method for determining the block level BL is to use the average value as the original PCM code o
The block level BL itself is calculated with a precision of p (16 bits in the example) and is transmitted as is, but the block level BL itself may also be set by truncating the lower bits and transmitted. It is also possible to send only the information. Of course, since the block level BL is a representative value within a block, it is not limited to an average value, but may be an approximate value.

Furthermore, the method for decompressing and restoring compressed data on the receiving side is not simply a method of shifting digits according to the scale value of the binary data, but may also be a method of accurate multiplication using a multiplier. The method must also be consistent with the data compression method on the sending side.
Furthermore, various error correction methods, synchronization methods,
It goes without saying that interleaving, scrambling, and various digital modulation methods may be used in combination.

〔Effect of the invention〕

According to the present invention, PC
It is possible to provide a signal transmission system that transmits M codes and obtains sufficiently good φ ratio and distortion characteristics without substantially accumulating errors, and a receiving apparatus that can be directly used in its implementation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining a first embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing the configuration of a second embodiment of the present invention, and FIG. 4 is a schematic diagram for explaining a first embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a transmitting side in another embodiment. 1...A/I) converter, 2.15...RAM, J.
...Maximum/minimum detection circuit, 4...Block level calculation circuit, 5...Width detection circuit, 6.16...Scale value generation circuit, 7...Scale reference storage circuit, 8...Difference detection Circuit, 9... Data compression circuit, 10... Synthesis circuit, 11... Separation circuit, 12... Restoration circuit, 13.
... Adder circuit, 14... converter.

Claims (3)

[Claims] (1) Divide the original PCM code into blocks of scheduled time, find a block level that represents the sample values of each block, and combine this block level with the original PCM code in each block.
At the same time as detecting the difference value with the CM code, find the maximum value of the above difference values in the block, and based on this maximum value, all the difference values in the block are PCM codes with fewer bits than the original PCM code. Divide and compress the above difference value by a value of 1 or more to obtain a transmission PCM code so that it can be represented by a code,
In addition to transmitting this transmission PCM code, the above-mentioned block level information is transmitted once for each block as scale information corresponding to the coefficient value of the division compression, and these transmission signals are received to convert the received transmission PCM code. , the reproduction difference value P is expanded and restored using multiplication according to the received scale information.
A signal transmission method characterized in that a CM code is obtained, and a block level based on received block level information is added to the reproduced difference value PCM code 1- to obtain a reproduced PCM code. (2) Divisional compression of differential value PCM codes is performed by giving priority to the upper effective bits of the data and extracting the expected number of bits, and when the number of effective bits is large, the lower effective bits are truncated, and this number of truncated bits is 2. The signal transmission system according to claim 1, wherein the scale information is used and the expansion and restoration of the received and transmitted PCM code is performed using a bit shift of data based on the scale information. (3) Professional and Frepel information corresponding to the block level for each block representing the sample values of the entire block of the original PCM code divided into blocks of scheduled time, and the original PCM code in this block level and each block. A transmission signal consisting of a transmission PCM code obtained by dividing and compressing the difference value between the above and the original PCM code by a value of 1 or more, and scale information for each block corresponding to the coefficient value of the above division compression is received from the transmission system, and the above original PCM code is A receiving device that obtains a reproduced PCM code corresponding to the received transmission PCM code performs multiplication processing according to the reception scale information to obtain a reproduced difference value P corresponding to the above-mentioned difference value.
A reception device characterized by comprising a restoring means for expanding and restoring a CM code, and an addition means for adding a block level based on received block level information to the reproduced difference value PCM code obtained by this means to obtain a reproduced PCM code. Device.