JP2638344B2 - Digital data converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital data converter for converting digital data by reducing the number of bits, and more particularly to a digital data converter suitable for converting low-level digital audio data.

[0002]

2. Description of the Related Art Generally, digital audio data stored on a compact disk (CD) or the like is 16 bits.
Consists of bits. A method of recording such 16-bit data on a CD or the like is disclosed in, for example, "Digital Audio" by Takegahara et al. (Corona 1989). On the other hand, some devices for digitally recording an audio signal can record audio data in 16 bits or more. Therefore, when stored as digital audio data of, for example, 20 bits, the audio signal is reproduced and reproduced as a CD.
For example, the data must be converted to 16 bits.

Conventionally, as shown in FIG. 5, a digital data converter used for the above-mentioned purpose transfers digital data read from a storage medium 1 to a shift register 2 and uses the shift register 2 to remove unnecessary lower-order bits. Is configured to be truncated. In FIG. 6, for example, when 6-bit data “001010” is converted into upper 3-bit data “001”, the 6-bit data is shifted rightward, that is, lower by 3 bits in the shift register 2. Top 3 remaining in 2
The bit data "001" is output.

[0004]

However, in the above-mentioned conventional digital data converter, the number of bits of digital data is reduced by truncating the lower-order bit data. Therefore, for example, as shown on the left side of FIG. When converting digital audio data with low
As shown on the right side of FIG. 7, there is a problem that when the data of the significant lower bits is truncated, the audio data becomes inferior in quality. Therefore, in order to prevent the sound quality of the audio data from deteriorating, the recording level must be set high in the recording stage.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a digital data converter capable of preventing loss of important lower-order bit data when converting digital data by reducing the number of bits.

[0006]

In order to achieve the above object, the present invention provides a digital data converter for reducing the number of bits of a series of input digital data and outputting the digital data. Coefficient calculating means for calculating a coefficient for multiplying the input digital data by a value or a minimum value; multiplying means for multiplying the input digital data by a coefficient calculated by the coefficient calculating means; Shift register means for temporarily storing the resulting data; and shifting the multiplication result data stored in the shift register means in the lower direction in accordance with a desired reduced bit number, and outputting the remaining upper bit data. Control means for controlling the shift register, It is subjected.

[0007]

Since the present invention has the above structure, the original digital data is multiplied by a coefficient corresponding to the maximum value or the minimum value of the series of digital data, and the lower-order bit data is truncated. When converting digital data, it is possible to prevent both important upper bit data and lower bit data from being lost.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing one embodiment of a digital data converter according to the present invention, FIG. 2 is a block diagram showing a specific configuration of the digital data converter of FIG. 1, and FIG. FIG. 4 is a flowchart for explaining the operation of the digital data converter, and FIG. 4 is an explanatory diagram showing a conversion result of the digital data converter.

In FIG. 1, the maximum value or the minimum value of the digital data stored in the storage medium 11 is searched in advance by the maximum value / minimum value searching means 12, and then the coefficient calculating means 13 calculates the maximum value or the minimum value from the maximum value or the minimum value. , A coefficient for multiplying the original digital data is calculated and stored in the coefficient register 14. Note that the maximum value minimum value searching means 1
2 and the coefficient calculating means 13 are provided by a CPU 21 as shown in FIG.
Can be realized by the memory 24 and the data output interface 25.

When the number of bits of digital data stored in the storage medium 11 is reduced, the digital data is stored in the data register 15. Then, the coefficient from the coefficient register 14 and the data in the data register 15 are multiplied by the multiplier 16, and the lower bits of the data resulting from the multiplication are discarded by the shift register 17.

In FIG. 2, a CPU (Central Processing Unit) 21 performs digital data conversion processing so that both important upper bit data and lower bit data are not lost as described later. The CPU 21 is also connected via a data bus 22 to a hard disk 23 used as the storage medium 11 in which digital data is stored in advance, a working memory 24 and a data output interface 25. Note that, instead of the hard disk 23, a storage medium such as a magneto-optical disk or a magnetic tape may be used.

The data output interface 25 is connected to the coefficient register 14 for storing coefficients corresponding to the maximum and minimum values of a series of digital data, and the data register 15 for storing digital data. Coefficient stored in the data register 14 and the data register 1
The data stored in 5 is multiplied by the multiplier 16.
The result of the multiplication by the multiplier 16 is transferred to the shift register 17, and the lower bit data is truncated by the shift register 17 to change the number of bits. Here, the series of digital data means a large amount of data such as 3 minutes or 10 minutes for one music in the case of an audio signal, for example. Therefore, the search for the maximum value and the minimum value is performed for each predetermined byte of the data for one piece of music.

Next, the operation of the digital data converter of this embodiment, particularly the operation of the CPU 21, will be described with reference to FIG. The CPU 21 first sets variables max and min for storing the maximum value and the minimum value of a series of digital data, respectively.
Are reset together on the memory 24 (step S
1, S2). In this case, the maximum value variable max is a variable for storing the maximum value of digital data in the positive direction, and the minimum value variable min is a variable for storing the maximum value of digital data in the negative direction. .

Next, one digital data is read from the hard disk 23 and stored in the memory 24 (step S3), and the digital data and the variable for the maximum value are read.
The maximum value is compared and stored in the area of the maximum value variable max (step S4). Similarly, the digital data is compared with the minimum value variable min, and the smaller one is stored in the area of the minimum value variable min. (Step S5), the processing shown in steps S3 to S5 is performed for all data, and a maximum value variable max and a minimum value variable min are obtained (step S6).

In the following steps S7 to S10, coefficients are calculated. First, the absolute values of the variable max for the maximum value and the variable min for the minimum value are compared (step S7). If the absolute value of the variable max for the maximum value is larger, the "positive value represented by the original number of bits" Is obtained by dividing the “maximum value of” by the maximum value variable max (step S8). On the other hand, when the absolute value of the minimum value variable min is larger, the negative maximum value represented by the original number of bits is obtained. The value is divided by the minimum value variable min to obtain a quotient (step S9). Then, the quotient is stored in the coefficient register 26 (step S10).

[0016] Here, "the maximum positive value represented by the original number of bits", as the number of original bits is n, a 2 ^n-1 -1, for example, in the case of 16-bit, 2 ^16-1 -1 (= 3276)
7). The “negative maximum value represented by the original number of bits” is −2 ⁿ⁻¹ , and in the case of 16 bits, −2 ¹⁶⁻¹
(= −32768). That is, step S10
The quotient (coefficient) stored in the coefficient register is "1" when the maximum amplitude of the audio signal is large, and increases as the maximum amplitude decreases.

In subsequent steps S11 to S13, digital data is converted by the quotient. First, one piece of data is taken out from the hard disk 23 and stored in the data register 15 (step S11). Next, the coefficient of the coefficient register 14 and the data of the data register 15 are given to the multiplier 16, and the result of the multiplication is given to the shift register. 17 (step S12). Then, the shift register 17
As a result, the data is shifted rightward, that is, in the lower direction by the number of reduced bits, and the remaining upper bit data is extracted.

That is, as shown in FIG. 4, for example, when converting low-level 6-bit data into 3-bit data, if the coefficient is "2", the original data is first doubled by the multiplier 16. Therefore, even if the lower 3 bits of the 6-bit data resulting from the multiplication are truncated, the loss of important lower bits can be prevented. That is, in the conventional method shown in FIG. 7, the values of each data after being converted into 3 bits are all the same, whereas in the present invention, the difference in the values remains after the conversion. In this case, the coefficient “2” is calculated so that the higher-order bit data of the original data is not lost due to overflow due to multiplication.

Therefore, according to the above embodiment, when digital audio data of, for example, 16 bits or more is converted and stored on a 16-bit compact disc, it is not necessary to increase the level at the time of recording. There is no deterioration in sound quality. In the above embodiment, steps S1 to S10 in FIG. 3 constitute a coefficient calculation means, steps S11 and S12 constitute a multiplication means, and step S13 constitutes a control means.

[0020]

As is apparent from the above description, according to the present invention, the input digital data is multiplied by a coefficient corresponding to the maximum value or the minimum value of the series of input digital data, and the lower bit data is obtained. When converting the digital data by being truncated and thus reducing the number of bits, it is possible to prevent both important upper bit data and lower bit data from being lost.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing one embodiment of a digital data converter according to the present invention.

FIG. 2 is a block diagram showing a specific configuration of the digital data converter of FIG.

FIG. 3 is a flowchart for explaining the operation of the digital data converter of FIG. 2;

FIG. 4 is an explanatory diagram showing a conversion result of the digital data converter.

FIG. 5 is a functional block diagram showing a conventional digital data converter.

FIG. 6 is an explanatory diagram showing the operation of the digital data converter of FIG.

FIG. 7 is an explanatory diagram showing a conversion result of the digital data conversion device of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Storage medium 12 Maximum value minimum value search means 13 Coefficient calculation means 14 Coefficient register 15 Data register 16 Multiplier 17 Shift register 21 CPU (Central processing unit) 22 Data bus 23 Hard disk 24 Memory 25 Data output interface

Claims (1)

(57) [Claims] 1. A digital data converter for reducing the number of bits of a series of input digital data and outputting the digital data, comprising: a coefficient for multiplying the input digital data by a maximum value or a minimum value of the series of input digital data. A coefficient calculating means for calculating the coefficient; a multiplying means for multiplying the input digital data by a coefficient calculated by the coefficient calculating means; a shift register means for temporarily storing data of a result of the multiplication by the multiplying means; The multiplication result data stored in the shift register means is shifted in a lower direction according to the decreasing bit number,
Control means for controlling the shift register so as to output the remaining higher-order bit data.