JPH0535612B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a digital signal transmission method for transmitting digital signals such as PCM signals, and more particularly to a block-contained digital signal transmission method for transmitting a plurality of data words in blocks. [Background technology and its problems] In recent years, with the advancement of digital technology, analog signals such as audio signals and video signals are sampled and quantized and encoded, resulting in so-called PCM (pulse code modulation). ) signals are increasingly being transmitted (including recording and playback). In this way, when converting an analog signal into a PCM digital signal and transmitting it, generally speaking, the higher the sampling frequency, the wider the analog signal band that can be transmitted, and the higher the number of quantization bits, the wider the dynamic range. is known to become wider. Therefore, to digitally transmit the original analog signal with high fidelity, that is, over a wide band and a large dynamic range, a high sampling frequency and a large number of quantization bits are required, and the number of bits transmitted per unit time is low. The so-called bit rate increases. However, transmission media (including recording media)
The above-mentioned bit rate is limited by the characteristics of By considering economic efficiency, cost performance, etc. when supplying products, it is important to perform high-quality signal transmission or recording/reproduction at as low a bit rate as possible. By the way, differential PCM methods and adaptive differential PCM methods are known as technologies for transmitting signals with a large dynamic range at relatively low bit rates, but these methods are susceptible to the adverse effects of error propagation phenomena. Furthermore, if an attempt is made to ensure a certain level of error correction capability, redundancy increases and the bit rate reduction effect cannot be effectively obtained. Therefore, in Japanese Patent Application No. 58-97687, etc., the applicant created a block for each word of digital data based on sampled peak value data, etc., and applied common bit compression etc. to all the words in this block. A method is proposed in which adaptive processing is performed and at least the information word of the adaptive processing and the plurality of words of the digital data are transmitted as one block. Adaptive processing using blocks as a unit can be said to be an effective method for expanding the dynamic range because processing can be performed using one piece of adaptive information per block, but if the bit rate falls below 100 Kbit/sec per channel, For example, when the speed increases to about several tens of Kbit/sec, it becomes necessary to increase the adaptive operation to further improve compression efficiency. [Object of the Invention] The present invention further improves the applicant's prior art as described above, and provides a digital signal transmission method that can significantly increase compression efficiency and efficiently expand dynamic range. The purpose is to provide. [Summary of the Invention] The digital signal transmission method according to the present invention is characterized in that the digital signal transmission method digitizes and transmits data based on sampled peak value data of an input signal, and blocks each of a plurality of data words. a mode selection step of selecting one of a plurality of processing modes including at least a differential processing mode for each block; and a mode selection step of selecting one of a plurality of processing modes including at least a differential processing mode; The process includes a step of performing quasi-instantaneous companding processing, and a step of performing non-linear companding processing for each word in the block subjected to the quasi-instantaneous companding processing, and A process that is the inverse operation of the non-linear companding process described above is applied to each word, a process that is the inverse operation of the quasi-instantaneous companding process described above is commonly applied to all words in the block, and the selected mode is This is to perform the inverse process of the above process. [Embodiment] First, the basic principle of the digital signal transmission method according to the present invention will be explained with reference to FIGS. 1 to 5. FIG. 1 is a block circuit diagram showing the basic configuration of a transmitting side (or recording side) encoder used in the digital signal transmission method of the present invention. In FIG. 1, a digital signal input terminal 1 receives a so-called digital signal obtained by sequentially sampling an input signal such as an audio signal or a video signal, and subjecting it to quantization and encoding.
PCM sample peak value data is supplied.
The n words of this input digital data constitute one block, and the maximum absolute value of the n words within this one block is detected by the block maximum value detection circuit 2, and the detected value is detected by the adaptive information generation circuit 3 at the next stage. Adaptive information corresponding to the maximum absolute value within the block, for example, information on the number of bits that can be compressed in common for all words within the block is obtained. In addition, the above 1 from input terminal 1
The digital data of block n words is sent to the block unit adaptive processing circuit 5 via the block memory 4, and is sent to the adaptive information generation circuit 3.
According to the above adaptive information from the block, all n words of one block are commonly subjected to quasi-instantaneous compression. This quasi-instantaneous compression operation will be explained with reference to FIG. FIG. 2 shows the absolute values of the n data words W ₀ , W ₁ , ..., W _o-1 in one block, |W ₀ |, |W ₁
This shows an example of the bit pattern of |, ..., |W _{o-1 |} , and the block maximum absolute value detection circuit 2 shown in FIG. A case is shown in which the maximum absolute value of n words is detected. In addition, in FIG. 2, the bit length of one word is l bits, and the number of "0"s consecutive to the sign bit MSB of the maximum absolute value |W _k | is m, and this m is one block. This is the number of bits that can be compressed in common for all words in the file. This means that for the absolute value of each word in one block, when looking at the bit position where "1" appears for the first time from the MSB to the lower bits, the word where the bit position of this first "1" is closest to the MSB is This is a word with the maximum absolute value, and if m is the number of "0"s placed between the MSB of this maximum absolute value word and the above first "1" bit, then for other words, The number of consecutive “0”s on the lower side is at least m
In other words, m+1 or more "0"s, including the MSB "0" which is the code bit, are consecutively placed on the most significant side of each word. Therefore, the m consecutive "0's" lower than the MSB, which is the sign bit, can be commonly omitted for all words in one block, and the block-based adaptive processing circuit 5 can process the m-bit quasi-instantaneous bits. Compression processing or so-called adaptive processing can be performed. This adaptive processing reduces the bit length to l.
- By transmitting the number m of "0"s omitted above as adaptive information together with the n data words in one block that have become m bits, the receiving side (or playback side) can write the data to the upper side of each data word. The original 1-bit data can be restored by adding the above m number of "0"s. Note that if the original data has positive and negative values and is expressed in two's complement, the above m bits of sign bits "0" or "1" can be removed or added. As for the concrete operations,
On the transmitting side, an m-bit arithmetic left shift or a logical left shift not including the sign bit MSB may be performed, and on the receiving side, an m-bit arithmetic right shift or a so-called sign bit extension operation may be performed. Furthermore, in the present invention, each word within one block that has been subjected to the above-described adaptive processing is subjected to instantaneous compression processing by the word unit adaptive processing circuit 6 of FIG.
This can be done by performing non-linear quantization (re-quantization) based on broken lines as shown in FIG. 3, for example. In other words, in Fig. 3, ^2p types of input data (on the x-axis side) are generally quantized with p bits.
is converted _{into 2} ^pq types of p-q bit data (y-axis side) and output. p
−q bit data y ₁ , y ₂ , . . . correspond to each other. Instant compression (or instantaneous expansion) using such nonlinear requantization first uses a comparator or decoder to determine which section of the polygonal line the input data belongs to, and then performs processing according to the conversion rules for each section. Then, a shift using a shift register and addition of a constant are performed to convert the data into p-q bit data. If the conversion is performed along such a broken line, the lower bits will not be deleted if the value of the input data is small, and the above bits will remain without being deleted if the value is large. When playing this result,
Data with a small value is reproduced exactly to the value before recording, and data with a large value is also reproduced to approximately the value before recording. That is, each section of the polygon line can be compressed (or expanded) without substantially losing any useful information.
It can be performed. FIG. 4 shows an example of a preferred polygonal line in the signal conversion circuit for nonlinear instantaneous compression proposed earlier by the applicant, and converts 10-bit input data into 8
The bit pattern at each corner when converting to bit output data is set as shown in Table 1 below.

〔Effect of the invention〕

According to the digital signal transmission method according to the present invention, one of a plurality of processing modes including a differential processing mode is selected for each block, and quasi-instantaneous companding processing is performed for each block. By performing nonlinear instantaneous companding processing on each word in the processed block, compression efficiency is greatly increased and the dynamic range expansion effect is large, making it possible to transmit signals with a large dynamic range using a small number of bits. It becomes possible.

[Brief explanation of the drawing]

Figure 1 is a block circuit diagram showing an example of the basic configuration of an encoder to explain the basic principle of the present invention, Figure 2 is a diagram showing an example of the bit pattern of the absolute value of each word in the block, and Figure 3 is a diagram showing an example of the bit pattern of the absolute value of each word in the block. A graph showing a general form of a broken line used in broken line compression as an example of nonlinear instantaneous compression, FIG. 4 is a graph showing a preferred specific example of the above broken line, and FIG. 5 is a diagram showing an example of the structure of words within one block. , FIG. 6 is a block circuit diagram showing an example of the circuit configuration of an encoder used in a specific embodiment of the present invention, and FIG. 7A is a general, differential,
Graphs showing the frequency characteristics of each dynamic range in the PCM mode and summation PCM mode, FIG. Graph to explain change, No. 9
This figure is a block circuit diagram showing an example of the circuit configuration of a decoder that operates symmetrically to the encoder of FIG. 6. 1, 31... Input terminal, 2... Maximum absolute value detection circuit in block, 3... Adaptive information generation circuit, 4, 37... Block memory, 5, 43...
Block unit adaptive processing circuit, 6, 44...
...word unit adaptive processing circuit, 7, 33,
52, 56...Multiplexer, 8, 39...Output terminal, 34...Maximum value detection comparison circuit within block, 35...Difference processing circuit, 36...Integration processing circuit, 41...Mode selection adaptive information calculation circuit , 42...Mode switching processing circuit, 46...Error feedback circuit section, 53...Word unit adaptive processing circuit, 54...Block unit adaptive processing circuit, 55...Mode switching processing circuit.

Claims (1)

[Scope of Claims] 1. In a digital signal transmission method for digitizing and transmitting data based on sampled peak value data of an input signal, each block is divided into a plurality of data words, and at least a differential processing mode is applied to each of these blocks. a mode selection step of selecting one of a plurality of processing modes including; a step of performing a common quasi-instantaneous companding process on all words in the block that have been processed in the selected mode; and performing a non-linear companding process on each word in the block subjected to the quasi-instantaneous companding process, and performing the non-linear companding process on each word in the block of the transmitted signal. A process that is the reverse operation of the above-mentioned quasi-instantaneous companding process is performed in common on all words in the block, and a process that is the reverse operation of the process of the selected mode is performed. A digital signal transmission method.