JPS6386910A - Dynamic range compressing circuit - Google Patents

Abstract

PURPOSE:To execute a compression control of a dynamic range with sufficient accuracy by simple constitution, by detecting a sample value corresponding to a level component exceeding the prescribed level of an analog data by a level detecting means, multiplying a digital data by a prescribed coefficient in accordance with its count value, and controlling an attenuation quantity of the analog data. CONSTITUTION:An output of an OR gate 14 is supplied to a counter 16. The counter 16 counts within the level detection time T, the number of times by which a level of an analog audio signal goes to a state exceeding a prescribed level with respect to an output of the OR gate 14. In a ROM 17, a coefficient table in which a prescribed attenuation ratio epsilon is stored in advance is formed in an address designated by a count value of the counter 16. Therefore, from the address designated by the count value of the counter 16, a coefficient having the prescribed attenuation ration epsilon is outputted to a multiplying circuit 18. Therefore, the multiplying circuit 18 multiplies the inputted coefficient and an input digital data, and the input digital data is attenuated by a prescribed quantity and outputted, the dynamic range compression quantity is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of a dynamic range compression circuit that adjusts the amount of compression of the dynamic range of a digitized audio signal.

(Prior Art) As is well known, in the field of audio equipment, in order to achieve as high density and high fidelity recording and playback as possible, Oti, T.M.
Digital recording and reproducing systems, which convert numbers into digital data using PCM (Zrus code modulation) technology, record it on a recording medium such as a disk or magnetic tape, and play it back, have become widespread.
Compact discs are now mainstream.

One of the characteristics of this type of digital recording and playback system is
One of them is the wide dynamic range. That is, while the dynamic range of conventional analog record players and magnetic tape recorders is generally about 60 dB, the dynamic range of compact discs has been dramatically improved to over 90 dB.

Here, under the proper listening environment, it is dynamic.

Having a wide clean range is very effective, but in noisy environments, such as when listening in a car or as BGM (Paper Grand Music), it may be difficult to This causes the inconvenience that the number of intervals υ of the voice becomes difficult. Furthermore, when attempting to record from a compact disc or the like onto an analog tape recorder, a problem arises in consistency of dynamic range. Therefore, in order to solve such problems, dynamic range compression circuits have been conventionally used.

FIG. 5 shows such a conventional dynamic range compression circuit. In other words, this circuit detects the level amount of an input signal for a certain period of time using the level detection circuit 11, and uses the detected level amount. By controlling the attenuation circuit 12 accordingly, the input signal is attenuated and outputted.

In this case, the input level iVrml is generally expressed as follows, where the effective value of the input signal νi and the level detection time are T. Also, the calculation using the above formula is generally complicated.

Level detection using the average values v and f of the input levels has also been considered, as shown in FIG.

Here, the average value of digital data obtained by digitizing an audio signal is obtained by cumulatively adding the absolute values of sample values up to a certain period of time (0 to T), and dividing this by the number of samples within a certain period of time. It will be done. In other words, it becomes .

By the way, when performing the calculation shown in equation (1) above, for example, when the level detection time T is 1 second and the sampling interval τ is 1 second,
/44.1kHz, sample value is 16 bits.

If we cumulatively add the input signals whose effective value is 70% of the maximum level at
An accumulative adder of 0, 30, or more bits is required.

In this case, normally the sample value does not require precision of 16 bits, so even if the sample value is compressed to, for example, 8 bits, it will be 28-1 x 0.7 x 44100 = 22 out of 3.9 x 10'.
2, and a 22-bit cumulative adder is required.

(Problems to be Solved by the Invention) As described above, the conventional dynamic range compression circuit has a problem in that the cumulative adder has a large number of bits and the configuration becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and provides an extremely good dynamic range compression circuit that has a simple configuration and can perform level detection with sufficient accuracy to perform dynamic range compression control. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) In other words, the dynamic range compression circuit according to the present invention converts analog data into analog-to-digital conversion among each sample value of digital data. A sample value corresponding to a level component higher than a predetermined level of the data is detected, and the digital data is multiplied by a predetermined coefficient according to the count value obtained by counting the number of detections within a certain period of time to control the amount of narrowing of the analog data. This is how it was done.

(Function) According to the above configuration, a sample value corresponding to a level component higher than a predetermined level of analog data is detected from among each sample value of digital data, and the number of detections is counted within a certain period of time. Since the attenuation of analog data is controlled according to the quant value,
It is possible to perform arithmetic processing with a slightly smaller number of bits than before, simplifying the configuration, and performs level detection with sufficient accuracy for practical use to control compression of the dynamic range. It is something that you will be able to do.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In Figure 1, 16-bit digital data obtained by digitizing an analog audio signal is
When entered, if positive.

In other words, if the MSB (signal bit) is 10'', the selector 13 directly selects the OR gate circuit 14.
guided by. Also, if the input digital data is negative,
In other words, the MSB (Signal Bi).

If ``g'' is ``1'', the selector 13 selects the two's complement converted data by the complement generating circuit 15 as ORr.
-) lead to circuit 14t/C.

Therefore, when the data shown in Figure 2 is supplied as input digital data, the selector outputs the absolute value of the input digital data in 16 bits as shown in Figure 3. It will be done.

The 16-bit absolute value data outputted from the selector 13 is logically summed by the upper 7 bits excluding the MSB (signal bit) by the OR gate circuit 14. In this way, as shown in FIG. 4, the sampling timing to.

tIIk! +iS It, , t, , t, data at H level is output from the OR date circuit 14.

In other words, the fact that an H level signal is output from the OR gate circuit 14 means that the logical sum of the remaining bits after discarding the lower 8 bits of the 16-bit data obtained from the selector 13 has become "1". This means that values below 2-1=255 are ignored, and input digital data with a value greater than that is supplied. 9 M, sample values of digital data corresponding to level components of the analog audio signal equal to or higher than the predetermined level Dth are detected. In this case, Dth=256.

Here, the output of the OR f-) circuit 14 is supplied to a 17-bit counter 16. This counter 16 is cleared by a clear noculus that is supplied at intervals of the level detection time T shown in FIG. The number of times the level exceeds a predetermined level is counted within the level detection time T.

Therefore, in the example shown in FIG. 4, the counter 16 is
It will count up to 7.

The count value of the counter 16 is supplied as address data to a read-only storage device (hereinafter referred to as ROM) 17tlC1. This ROM 17 has a coefficient table in which a predetermined damping ratio g (Q≦e≦1) is stored in advance at an address specified by the count value of the counter 16. Therefore, a coefficient having a predetermined attenuation ratio C is output to the multiplication circuit 18 from the address specified by the count value of the counter 16.

Then, the multiplication circuit 18 multiplies the input coefficient by the input digital data, and the input digital data is reduced by a predetermined amount and output, and the dynamic range compression amount is controlled here. It is something.

Therefore, according to the configuration of the above embodiment, the amount of dynamic range compression can be controlled by digital processing of a maximum of 17 bits, so it can be realized with a simpler configuration than the conventional one. That is, the level detection time T is 1 second, and the sampling interval is 1/
Even if it is 44.1 kHz, the count value is at most 8820
0, and a 17-bit counter of 16 is sufficient for use.
Complement generation circuit 15° selector 13 and OR r-) circuit 1
Even if 4th grade is included, there will be 30 pits and 22 pits like in the past.
Compared to using a bit cumulative adder, the circuit scale can be significantly reduced.

Here, a description will be given of replacing the level component of the input digital data as the count value of the counter 16. For the sake of simplicity, we will consider analog quantities here. That is, if the input signal V is 1=AslInωt (where A is a constant and ω=2πf), then the integral value 2 in the interval from 0 to π/2ω is as follows. Also, in the interval from 0 to π/2ω, the input signal v1 is Dth(
A≧Dth) greater time→, ha.

becomes. Therefore, the count value cannot be said to be a linear reflection of the average value, which is the level amount.

If the coefficients stored in the ROM 17 are set in consideration of this nonlinearity, it is possible to perform level detection with sufficient accuracy for practical use and to perform dynamic range compression control.

Further, in the above embodiment, the absolute value of the input digital data is taken, but the present invention is not limited to this, and it goes without saying that, for example, only the positive or negative polarity components of the input digital data may be extracted.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be practiced by modifying the plant without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, it is possible to provide an extremely good dynamic range compression circuit that has a simple configuration and can perform level detection with sufficient accuracy to perform dynamic range compression control. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the dynamic range compression circuit according to the present invention, FIGS. 2 to 4 are diagrams for explaining the operation of the same embodiment, and FIG. FIG. 2 is a block configuration diagram showing a range compression circuit. 11... Level detection circuit, 12... Attenuation circuit, 13
... Selector, 14... OR gate circuit, 15...
・Complement generation circuit, 16...Counter, 17...RO
M, 18...multiplication circuit. Applicant's agent Patent attorney Takehiko Suzue Director Black 1) Yu Akira Display of the subject Patent application No. 1983-231891 Name of Akira Relationship with the person who corrects the dynamic range compression circuit Patent applicant (307) Toshiba Corporation (1 person) embedding

Claims (1)

[Claims] A level detection means for detecting a sample value corresponding to a level component of a predetermined level or higher of the analog data among each sample value of digital data obtained by analog-to-digital conversion of the analog data, and a constant number of detections by the level detection means. It comprises a counting means for counting within a time, and an attenuation amount control means for controlling the attenuation amount of the analog data by multiplying the digital data by a predetermined coefficient according to the count value of the counting means, A dynamic range compression circuit configured to compress a dynamic range.