JPS63272116A - Band limiting circuit - Google Patents

Abstract

PURPOSE:To widely decrease the number of delay elements and arithmetic steps obtained by multiplying and adding, to miniaturize a circuit and to expand the function of a system as a whole, by making a filter part into a cyclic filter. CONSTITUTION:A sixth cyclic filter part 22 has 11 delaying elements together with an input delaying element 23 and an output delaying element 24, and a signal is band-limited by 15 times of multiplying and adding. A signal band- limited by a sixth cyclic filter part 23 is inputted from the output delaying element 24 of the sixth cyclic filter part 22 through a decimeter part 2 to sample down a signal to 16:1 and a 10th cyclic filter part 26. The 10th cyclic filter part 26 has 16 delaying elements together with an output delaying element 27 of the 10th cyclic filter part 26 and the signal is band-limited by 25 times of multiplying and adding. Thus, the signal band-limited by the 10th cyclic filter part 26 is outputted from the output delaying element 27 of the 10th cyclic filter part 26 through an output terminal 28.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a band limiting circuit for linear predictive analysis.

(Prior Art) Conventionally, this type of band-limiting circuit has been designed to reduce the aliasing error of linear prediction coefficients, which is one of the features of an audio signal, so that the delay within the passband is constant. Used to limit frequency bands. FIG. 2 is a block diagram showing a conventional band limiting circuit. A conventional band limiting circuit includes a filter section 11 that limits the frequency band of a signal.
゜12, ... IM and a decimator section 21゜22, -2 that reduces the sampling rate of the signal between each filter section
It consists of N (however, N=M-1). By the way, in the conventional band-limiting circuit, the filter sections 11, 12, . . . -IM are constructed of a symmetric acyclic type.

(Problem to be Solved by the Invention) However, in the band-limiting circuit having the above configuration, since an acyclic filter is used in the filter section, due to the nature of the acyclic filter, it is necessary to filter the filter in order to obtain the desired frequency characteristics. It is necessary to increase the order, and there are problems of an increase in the number of delay elements and an increase in the number of calculation steps. Such problems cause an increase in the amount of hardware and an increase in the occupation rate during a predetermined calculation step, which limits the functions of the entire system incorporating the band limiting circuit.

The present invention solves the above-mentioned problems, and aims to provide a band limiting circuit for linear predictive analysis, which has frequency band limiting capability equal to or higher than that of the conventional one, and which has a small number of delay elements and a small number of calculation steps. .

(Means for Solving the Problems) In order to solve the problems in library records, the present invention includes a filter section,
In a band limiting circuit for linear prediction that limits a frequency band so that a delay is constant within a passband, the filter section is a recursive filter, and the filter section is a recursive filter. It is something.

(Operation) According to the present invention, since the band limiting circuit is configured as described above, the technical means operates as follows. Due to its nature, the recursive filter constituting the filter section requires fewer delay elements and fewer calculation steps for multiplication and addition than conventional non-recursive filters.

Therefore, the problems of the prior art described above can be solved.

(Embodiment) FIG.
It is an ivy diagram. In the figure, 21 is an input terminal, 22 is a 6th order recursive filter section, and 23 is a 6th order recursive filter section 2.
2 is a manual delay element of 2, 24 is an output delay element of the 6th order recursive filter 22, 25 is a decimator section that downsamples the signal to 16:1, 26 is an 1O order recursive filter section,
27 is an output delay element of the 10th-order cyclic filter 24; 28
is the output terminal.

Next, the operation will be explained.

First, a human input signal is input from the input terminal 21 to the input delay element 23 of the sixth-order recursive filter section 22 . 6
The next recursive filter section 22 has 11 delay elements including an input delay element 23 and an output delay element 24, and band-limits the signal by performing 15 multiplications and additions. 6th order recursive filter section 2
The signal band-limited by 3 is input from the output delay element 24 of the 6th order cyclic filter section 22 to the 100th order cyclic filter 26 via the decimator section 2 which downsamples the signal at a ratio of 16:1. The 100th order cyclic filter 26 has 16 delay elements including the output delay element 27 of the 100th order cyclic filter 26, and limits the band of the signal by multiplying and adding 25 times. The signal band-limited by the 100th order cyclic filter 26 is output from the output delay element 27 of the 100th order cyclic filter 26 via an output terminal 28. In this embodiment, the output delay element 24 of the 6th order cyclic filter section 23 has the function of being the first of 6 delay elements for circulating the output sample of the 6th order cyclic filter section 23 to the input side, 1
Manual delay element of 00th order cyclic filter 26 (not shown)
The output delay element 27 of the 100th order cyclic filter 26 has the function of the first of the 10 delay elements for circulating the output sample of the 10th order cyclic filter 26 to the input terminal. have.

In this way, in this embodiment, the sixth-order cyclic filter sections 23 and 10
The total number of delay elements of the zero-order cyclic filter 26 is 27, and the total number of calculation steps by multiplication and addition is 40. In order to achieve the same band-limiting characteristics as in this example using an acyclic filter configuration in a conventional band-limiting circuit, the total number of delay elements must be 106, and the total number of calculation steps by multiplication and addition must be 105. be. Therefore, compared to the conventional band limiting circuit, the number of delay elements in the band limiting circuit of this embodiment is approximately 1/I, and the number of calculation steps is approximately 275, which significantly reduces both the amount of hardware and the number of calculation steps. This makes it possible to expand other functions in terms of hardware and calculations.

In the above embodiment, the filter section was explained using two 6th-order and 10th-order cyclic filter sections and one decimator section.
It is clear that the order and number of stages can be varied depending on the required band-limiting characteristics.

(Effects of the Invention) As described in detail above, according to the present invention, by employing a recursive filter in the filter section, the number of delay elements and the number of calculation steps due to multiplication and addition can be significantly reduced. This makes it possible to reduce the size of the circuit and expand the functionality of the entire system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional band limiting circuit. 21--Input terminal, 22-6th-order cyclic filter section, 23--Manual delay element, 24.27--Input delay element, 25--Decimeter section, 26-10th-order cyclic filter Part, 28-... Output terminal.

Claims (1)

[Claims] In a band limiting circuit for linear prediction that limits a frequency band so that a delay is constant within a passband, the circuit consisting of a filter section and a decimator section that reduces the sampling rate connected in multiple stages alternately. . A band-limiting circuit, wherein the filter section is a recursive filter.