JPS62261237A - Pcm transmission system - Google Patents

Abstract

PURPOSE:To eliminate the problem of discontinuous accumulated sum and to prevent the generation of a DC offset by using a just preceding round-off eror as an initial value of an accumulated error after switching so as to apply the succeeding error accumulation when a data selected and compressed alternately is switched from a linear data into a differential data. CONSTITUTION:An accumulator 20 has the following function in addition to the conventional addition accumulation function of round-off error. in switching the data from a quasi-momentary compressed PCM(NI-PCM) into a differential quasi-momentary companding PCM(NI-DPCM) in response to a discrimination signal from a discriminator 4, the round-off error in the NI-PCM data (last sample) just before the switching is latched, and the content of the accumulator is replaced from the accumulated value of the round-off error of the conventional NI-PCM into the latched value at the switching. The accumulator is subjected to zero clear in the switching from the data NI-DPCM into the data Nl-PCM.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is based on PCM (pulse code mod
(pulse code modulation) transmission system and its equipment, in particular ordinary PCM, that is, linear PCM.
Linear data used for CM and D P CM (d1
PCM of a system that alternately switches and selects difference data used for rf'erentralPCM~differencePCi) and provides for transmission, and also includes data compression/expansion of transmission data.
This paper relates to a technique for improving DC component deviation in transmission. In this case, "transmission" is not limited to transmission via wireless or wired communication lines, but simply means transmission in a broad sense, including transmission through modulation/demodulation systems and recording/reproduction systems. The term "transmission line" means a system including a communication/signal line, a modulation/demodulation system, a recording/reproduction system, etc., or a combination thereof.

[Conventional technology]

Simply convert analog signals into A/D (Analog-Digital)
The PCM method for quasi-instantaneous companding of converted PCM data, that is, linear data, is N I-P.
CM (near In5 tantaneous
coIIlpancltngPCM ~ Quasi-instantaneous companding PC
M). On the other hand, P
The Fvi method, that is, the differential quasi-instantaneous companding PCM (hereinafter referred to as rNI-DPCMJ for convenience of explanation) is considered. N1-PCM depends on the level of the original signal.
The S/N is determined. On the other hand, in DPCM, the S/N is determined by the frequency and level of the original signal. Therefore, if the size of the original signal is smaller than the value corresponding to the transmission compression bit length, N1-PCM and N
The S/N is the same for both I-DPCM systems, but when the original signal is larger than the value corresponding to the transmission compression bit length, the S/N differs depending on the frequency between N1-PCM and NI-DPCM. There is a t-th pick-up. That is,
At low frequencies, even if the amplitude of the original signal is large, the value of the difference data is small, and therefore the reduction in information when data is compressed is small, so the S/N of Nl-DPCM is good. However, in this Nl-DPCM, when there is a reduction in information due to compression and the above-mentioned data loss, a deviation occurs due to a DC component. On the other hand, the value of linear data simply corresponds to the amplitude of the original signal. Therefore, if the amplitude of the original signal is small, there will be less information loss when compressing the data, and N
The S/N of l-PCM becomes good. Also, N1-PCM
Since linear data is basically transmitted, there is no DC deviation.

Therefore, we have developed a PCM that utilizes compressed transmission of differential data and can substantially prevent adverse effects such as deviations in the DC component caused by transmission errors, thereby realizing highly efficient PCM transmission with a good S/N ratio. As transmission methods, N1-PCM and Nl-D
A system that transmits a combination of PCM and PCM is being considered.

In such a PCM transmission system, on the transmitting side, linear data and differential data are alternately selected and compressed in accordance with the original data, and are transmitted together with information indicating the selection state. Then, on the receiving side, the received data is expanded, and when differential data is being transmitted, the expanded received data is further integrated and reproduced according to the information indicating the selection state, and linear data is being transmitted. When the received data is expanded, the expanded received data is directly reproduced.

On the other hand, in compressed transmission of PCM data in which transmission data of a predetermined bit length is obtained by giving priority to the upper effective bits of the original data, the transmitting side It has been considered to accumulate the lower truncated bits and include this accumulated data in the compressed data.

In such a system, the truncation bits due to compression are added and accumulated to an accumulator provided on the transmitting side, and when the accumulated value of this accumulator reaches a value corresponding to the transmission direction due to compression, it is included in the transmitted data. be done.

The cumulative value of this accumulator can be included in the transmitted data, for example, by directly adding the cumulative value to the original data before compression, by adding the cumulative value to the compressed data, or by transmitting the cumulative value by compression. One possible method is to increment the transmitted data appropriately when it reaches a value corresponding to the direction, and the value of the accumulator after addition or increment is a value obtained by subtracting the amount equivalent to the addition or increment from the original cumulative value. Become.

In particular, when differential data is compressed and transmitted, the transmitted data is integrated for demodulation on the receiving side, so the accumulation of truncation errors becomes a large DC error. The effect of transmission is significant.

Therefore, it is conceivable to apply this cumulative error prevention method to a PCM transmission method in which the above-described linear data and differential data are alternately selected in accordance with the original data, compressed, and transmitted.

[Problem that the invention seeks to solve]

When applying the above cumulative error prevention method to a PCM transmission method in which the linear data and differential data described above are selected alternately in accordance with the original data, compressed and transmitted,
The following problems arise.

The meaning of the truncation error is different when linear data is compressed and when differential data is compressed. Therefore, the cumulative value held in the accumulator at the time of switching from linear data to differential data or from differential data to linear data is not an appropriate value.

For example, a case will be explained in which the original data is 16-bit data, and this linear data and differential data corresponding to successive differences between the linear data are selected and compressed into 8-bit data at an appropriate time and transmitted.

In FIG. 4, 16-bit original data, ie, linear data, is applied to an input terminal 1, and this linear data is applied to an adder 2, a latch circuit 3, and a discriminator 4. The discriminator 4 discriminates from the linear data whether to compress the linear data or compress the differential data, that is, to transmit by Nl-PCM or by NI-DPCM, according to a predetermined discriminating condition, and outputs a discriminating signal according to the determination. do. This determination is performed in units of predetermined data blocks. The latch circuit 3 latches the input linear data, delays it by one sample period, and supplies it to the multiplier 5 . Multiplier 5 multiplies the data provided from latch circuit 3 by a difference coefficient α corresponding to the output of discriminator 4 and provides the result to adder 2 .

Adder 2 subtracts the output of multiplier 5 from the original data and provides the result to data compressor 6 . A data compressor 6 compresses the output of the adder 2 and sends 8-bit compressed data from an output terminal 7 to a transmission line. In data compression by the data compressor 6, data at bit positions corresponding to 8 bits of the highest significant bits of the maximum value (absolute value) in the data block is extracted for each predetermined data block. When data is compressed by the data compressor 6, the truncation bits accompanying the compression, that is, the data in the lower digits than the 8 bits to be transmitted, are cumulatively added in the accumulator 8, and the cumulative value is 8 bits. When the value corresponds to the transmission orientation, it is included in the transmission data. A discrimination signal indicating the discrimination result of the discriminator 4 is sent to the transmission line via the output terminal 9.

When the value of the difference coefficient α in the multiplier 5 is zero (α
-0), the output of the multiplier 5 is zero and N I -P C
When M transmission is performed and α is 0, Nl-DPC
M transmission. In the case of normal N1-DPCM transmission, it is α-1, and in the present invention, NI-DPCM transmission using incomplete differences where α≠1 is not considered.

Then, at the time of Nl-DPCM transmission, the accumulator 8
Since the truncated bits of the difference data are cumulatively added, the contents of the accumulator 8 always indicate the difference between the original data and the demodulated data demodulated by the receiver.

On the other hand, during N1-PCM transmission, the accumulator 8 cumulatively adds the truncation bits of the linear data, that is, the difference between the original data and the demodulated data. This is the cumulative value of the difference between The cumulative value is sequentially transferred to the transmission data within a plurality of sample periods, but the instantaneous value itself of the value held in the accumulator 8 in this case has no direct relation to the value of the error due to companding.

However, if the value of the accumulator 8 is left unchanged when switching between N1-PCM and Nl-DPCM8, the contents of the accumulator 8 immediately after switching will have the same meaning in each transmission system (system after switching). As a result, the continuity of cumulative addition is lost, resulting in a DC deviation. This DC shift occurs every time the transmission system is switched, and therefore, under conditions where the switching is performed frequently, it causes further deterioration of the S/N ratio, increase in audible noise, and the like.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a PCM transmission system that compresses and transmits linear data and differential data by alternately selecting them in accordance with the original data, and employing the cumulative error prevention method using the cumulative addition of cut-off bits. In this method, PCM solves the problem of discontinuity of cumulative addition values when switching between linear data and differential data, and can prevent the occurrence of DC deviation.
The goal is to provide a transmission method.

[Means for solving problems]

The present invention achieves the above-mentioned object by alternately switching and selecting linear data corresponding to an analog original signal and differential data corresponding to successive difference values of the linear data, compressing the data, and converting the data into digital transmission data. In addition to obtaining
The transmission data and selection information substantially corresponding to the switching selection are transmitted, the transmission data and selection information are received, the received transmission data is expanded, and the transmission side converts the linear data into data based on the reception selection information. In the PCM transmission method, the expanded data is used as it is when selected, and the expanded data is integrated when differential data is selected on the transmitting side, and then converted into an analog playback signal. On the transmitting side, when the data selected for data compression is switched from linear data to differential data, when the truncation error due to the data compression is accumulated and reflected in the subsequent transmission data generation, the previous This is a PCM transmission system characterized in that, instead of the cumulative value of the truncation error, the immediately preceding truncation error is used as the initial value of the cumulative error after switching for subsequent error accumulation.

〔Example〕

Before specifically describing embodiments of the present invention, the principle of the present invention will first be explained.

For example, from N I -D P CM to N I -P C
When switched to M, the contents of the accumulator, ie the result of cumulative addition in the previous Nl-DPCM, loses meaning. However, in N1-PCM, linear data is compressed, so even if the contents of the accumulator are discarded, that is, cleared to zero, the error based on the zero clearing will not exceed the size of the truncation error due to compression.
There is little actual damage.

However, on the contrary, when switching from N1-PCM to Nl-DPCM, the receiving side performs demodulation by adding the expanded received data of Nl-DPCM to the last demodulated data of N1-PCM. The compression error immediately after switching is the sum of the Nl-PCM compression error and the Nl-DPCM compression error, as shown in FIG.
This results in a large error in excess of the size corresponding to the truncation bit length (corresponding to the compression scale value). This error results in a sudden DC shift in the reproduced signal. Since such an error occurs every time there is a switch from N1-PCM to N1-DPCM, switching of the difference coefficient α, that is, switching between N1-PCM and N1-DPCM occurs frequently. Under such frequency and/or level conditions, the S/N ratio deteriorates and noise increases significantly in terms of audibility.

Therefore, in the present invention, from N I -P CM to N
When switching to l-DPCM, the contents of the accumulator in which the truncation error of the previous NI-PCM has been accumulated are changed to NI-DPCM.
The value is modified to be suitable for PCM demodulation, and the modified contents are used to encode the Nl-DPCM data immediately after switching (data compression and cumulative addition of truncation errors). N1
-The appropriate value for the accumulator immediately after switching from PCM to Nl- and DPCM is Nl-PCM immediately before switching.
The difference between the demodulated data (last sample) and the original data (linear data), that is, the N I - immediately before switching
P Truncation error in CM data (last sample) (
(a single value that is not a cumulative value). This value is the accumulator value when compressing the N1-PCM data (last sample) immediately before switching, and the N1-PCM data one sample before that.
It can also be said to be the difference from the accumulator value when CM data is compressed.

Note that when switching from NI-DP CM to N1-PCM, the value of the accumulator may be cleared to zero as described above.

Therefore, in the first embodiment of the present invention, N1-
When switching from PCM to Nl-DPCM, the N
Latch the truncated difference in the I-P CM data (last sample) and change the contents of the accumulator to the previous N1-PCM when switching from N1-PCM to Nl-DPCM.
Replace the cumulative value of the truncation error of M with the above latched value, and use this corrected content as the initial value to set N I after switching.
- Accumulate the truncated z1 difference of D P CM. And N
When switching from I-D PCM to N1-PCM, the accumulator is cleared to zero.

Therefore, the configuration of the transmitter according to the first embodiment of the present invention is as shown in FIG.

In Fig. 1, input terminal 1, adder 2, latch circuit 3
, discriminator 4, multiplier 5, data compressor 6, output terminal 7,
and output terminal 9 are the same as in FIG. 4, so
Detailed explanation of these will be omitted.

The accumulator 20 has the same function as the accumulator 8 in FIG. 4, that is, the function of adding and accumulating truncation errors.

This function has been added. In response to the discrimination signal output from the discriminator 4, when switching from N1-PCM to Nl-DPCM, switching in N1-PCM data (last sample) immediately before switching from N1-PCM to Nl-DPCM is performed. Latch the error and convert from N1-PCM to NI-D
When switching to PCM, the contents of the accumulator are changed to the previous N.
1-Replace the cumulative value of the PCM truncation error with the latched value. And from Nl-DPCM to N1-PCM
When switching to , the accumulator is cleared to zero.

Specifically, the accumulator 20 is configured as shown in FIG. 2, for example. The truncation error output from the data compressor 6 is provided to an adder 21 and a latch 22. The addition result output from the adder 21 is sent to the selector 23
is input. Data delayed by one sample by the latch 22 is also provided to the selector 23 . The selector 23 selects either the output of the adder 21 or the value latched by the latch 22. The data selected by the selector 23 is latched by the latch 24. The data latched by the latch 24 and delayed by one sample is provided to the adder 21, where it is added to the truncation error provided from the data compressor 6. The operation of the selector 23 and the latch 24 is controlled by the control unit 2 which responds to the discrimination signal output from the discriminator 4.
5 at a predetermined timing. Adder 2J
The result of addition is the accumulated value in this accumulator 20, and is given to the data compressor 6, and if there is a value that falls within the transmission foil, it is included in the compressed data.

That is, when Nl-PCM is being transmitted, the ° selector 23 selects the addition result of the adder 21 by the operation of the control unit 25 in response to the discrimination signal, and this value is delayed by one sample in the latch 24. and is applied to the adder 21. In the adder 21, the newly inputted truncation error data is added to the addition result of one sample before, and cumulative addition of the truncation error is performed.

When the N1-PCM transmission is switched to the NI-DPCkl transmission, the discrimination signal of the discriminator 4 changes, and the control unit 25 that responds to this changes the selector 23, which selects the output of the latch 22, that is, 1 The sample-delayed truncation error is selected, and a latch command is further given to the latch 24 by the control unit 25, so that the truncation error one sample before is latched by the latch 24. This is adder 2
1 is added to the truncation error of NI-DPCM immediately after switching. Thereafter, under the control of the control unit 25, the selector 23
The output of adder 21 is selected, latched by latch 24, and subjected to addition. In this way, from now on, this accumulator 20 receives N1-PCM transmission until it is switched to N1-PCM transmission.
The truncation error of l-DPCM is accumulated.

Next, when the transmission is switched to N1-PCM transmission, the control section 25 responds to the output of the discriminator 4, gives a clear command to the latch 24, and the contents held in the latch 24 are cleared to zero. Therefore, in the adder 21, N1-PCM immediately after switching
Zero is added to the truncation error. Thereafter, under the control of the control unit 25, the selector 23 selects the output of the adder 21, which is latched by the latch 24 and subjected to addition.

In this way, from now on, in this accumulator 20, NI-D
The N1-PCM truncation error is accumulated until switching to PCM transmission.

In this way, even when switching between N1-PCM and N1-DPCM is performed, the continuity of cumulative addition is maintained. As a result, even if both systems are switched alternately, there is no error greater than that due to truncation, and DC shifts, S/N deterioration, etc. caused by switching the transmission system are effectively prevented.

Next, the second embodiment of the present invention provides at least N1-PC
A demodulator that performs demodulation equivalent to that on the receiving side during the M transmission period is provided, and the difference between the demodulated data immediately before switching obtained by this demodulator and the current linear data is calculated and used as the N I after switching.
-D P Set as the initial value of CM truncation error accumulation. Then, when switching from NI-DPCM to NI-PCM, the accumulator is cleared to zero.

The configuration of such a second embodiment of the present invention is shown in FIG.

In FIG. 3, the same parts as in FIG. 1 are designated by the same reference numerals. In this case, a demodulator 30 is provided which receives the outputs of the data compressor 6 and the discriminator 4 and performs demodulation equivalent to that on the receiving side at least during N1-PCM transmission, and the output of the demodulator 30 is fed to the adder 31. It will be done. This adder 3
0 takes the difference between the original linear data input from the input terminal 1 and the output of the demodulator 30, and supplies it to the latch 32. Data delayed by one sample by the latch 32 is input to the accumulator 33. This accumulator 3
3, when transmitting Nl-PCM, the normal cumulative addition of truncation errors is performed, and when switching from Nl-PCM to NI-DPCM, the value given from the latch 32, that is, the demodulated data one sample before and the original linear The cumulative value is replaced with the difference from the data, and when sending NI-DPCM, the normal cumulative addition of the truncation error is performed, and the Nl-DPCM
When switching from N1-PCM to N1-PCM, the cumulative value is cleared to zero.

Even in this case, substantially the same results as in the first embodiment can be obtained.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof.

For example, when switching from N1-PCM to Nl-DPCM, find the difference between the cumulative value at that time and the cumulative value one sample before, and use this as the initial value of the cumulative value after switching. This is similar to the first embodiment described above.

〔Effect of the invention〕

According to the present invention, in the PCM transmission method, linear data and differential data are alternately selected in accordance with the original data, compressed and transmitted, and adopts the cumulative error prevention method using the cumulative addition of cut-off bits. , it is possible to provide a PCM transmission system that can solve the problem of discontinuity of cumulative addition values when switching between linear data and differential data, and can prevent the occurrence of DC deviation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of the present invention, FIG. 2 is a schematic block diagram showing the configuration of main parts of the same embodiment in detail, and FIG. 4 and 5 are a block diagram and an explanatory diagram, respectively, for explaining the problem to be solved by the present invention. 2, 21.31... Adder, 3.22.24.32.
... Latch, 4... Discriminator, 5... Multiplier, 6...
・Data compressor, 20°33...Accumulator, 2
3...Selector, 25...Control unit, 30...Demodulator. Applicant's agent Patent attorney Takehiko Suzue Figure 3

Claims (5)

[Claims] (1) Alternately switching and selecting linear data corresponding to the analog original signal and difference data corresponding to successive difference values of the linear data based on the analog original signal or a signal obtained from the analog original signal, and In addition to compressing data to a compressed bit length to obtain digital transmission data,
The transmission data and selection information substantially corresponding to the switching selection are transmitted, the transmission data and selection information are received, the received transmission data is data-expanded, and the linear data is converted on the transmission side based on the reception selection information. In the PCM transmission method, the expanded data is sent as is if it is selected, and the expanded data is integrated and converted to an analog playback signal if differential data is selected on the transmitting side. At the same time, the truncation error due to the data compression is accumulated and reflected in subsequent transmission data generation, and when the data selected for data compression is switched from linear data to differential data, the previous truncation error is A PCM transmission system characterized in that, instead of the accumulated value of the cut-off error, the immediately preceding cut-off error is used as the initial value of the accumulated error after switching for subsequent error accumulation. (2) In the PCM transmission method described in claim 1, when the selected data to be subjected to data compression is switched from differential data to linear data, the cumulative value of the previous truncation error is cleared to zero. A PCM transmission method characterized in that errors are accumulated afterward. (3) In the PCM transmission system according to claim 1, at least during the linear data transmission period, the transmitting side performs demodulation equivalent to that on the receiving side, and the immediately preceding demodulated data and original data obtained by this demodulation A PCM transmission method characterized in that the difference between the data and the data is calculated to obtain the last truncation error when the selected data to be subjected to data compression is switched from linear data to differential data. (4) In the PCM transmission method according to claim 1, the cumulative value of the immediately preceding sample during data compression is held at least during the linear data transmission period, and the cumulative value of the last sample of the linear data is compressed. and the cumulative value of the immediately preceding sample during data compression to obtain the immediately preceding truncation error when the selected data to be subjected to data compression is switched from linear data to differential data. Characteristic PCM transmission method. (5) In the PCM transmission method according to claim 1, the truncation error at the time of data compression of the last sample of linear data is held, and the data selected for data compression is a difference from the linear data. A PCM transmission method characterized by using the truncation error immediately before switching to data.