JPS63209317A - Fir type digital filter in recording and reproducing device - Google Patents

Abstract

PURPOSE:To retard the phase of one signal from the other phase at the time of reproduction and to eliminate the phase difference of signals at the time of recording by switch C, F coefficient groups deciding the filter characteristic in response to the signals of recording/reproduction and L/R channel. CONSTITUTION:In the case of L-channel signal input at the time of recording, a switch circuit 29 is thrown to the position (a). A signal from a terminal 20 is retarded by a shift register 24 and a RAM 25 and multiplied with a C coefficient group from a ROM 27 by a multiplier 26. Moverover, the result is added to a feedback input from an accumulator 31 by an adder 30, fed to a shift register 32 and outputted as an L-channel digital signal. In the case of the R channel signal input, the circuit 29 is thrown to the position (b), the input signal is multiplied with an F coefficient group by a multiplier 26 and outputted as an R channel signal from the register 32. The circuit 29 is thrown at the reproduction oppositely from the recording. Thus, the phase difference of signals is eliminated at the time of recording and the phase of one signal is retarded more than that of the other at the time of reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FIR type digital filter used in an analog-to-digital conversion circuit and a digital-to-analog conversion circuit in a digital recording/reproducing device.

[Summary of the invention]

The present invention provides first and second multiplication coefficient groups that are in an interpolation relationship with each other to provide predetermined filter characteristics, and when recording, the first and second multiplication coefficient groups are applied to the first and second channel signals, respectively. and the second multiplication coefficient group, at the time of playback,
the second channel for the first and second channel signals, respectively.
By using the and first multiplication coefficient group,
Common A/D for first and second channel signals
This eliminates the phase difference between the signals of two channels that occurs when oversampling is performed using a converter and a common D/A converter.

[Conventional technology]

In a recording and reproducing device such as a digital audio recorder using the DAT method, as shown in FIG.
The L-channel analog audio signal SL and the R-channel analog audio signal SR supplied to the input terminals 1.2 are converted into digital audio signals by the common A/D converter 5 through the respective low-pass filters 3.4. That's what I do. In that case, the A/D converter 5
In the above, oversampling is performed at a frequency 2fs which is twice the normal sampling frequency fs, and the signals SL, S, and I are sampled alternately in the order of SL, SR-. Therefore, in order to obtain the sampling rate of 2fS, the A/D converter 5 is supplied with a sampling clock having a frequency of 2fsx2.

The two-channel digital signals obtained from the A/D converter 5 are then supplied to a digital low-pass filter (hereinafter referred to as digital filter) 6, where they are each converted to a sampling rate of a regular frequency fs, and then digitally The signal is supplied to the recording/reproducing circuit 7 and recorded on the magnetic tape.

The R channel digital signal reproduced from the magnetic tape is supplied from the recording/reproducing circuit 7 to the digital filter 6, sampled at a sampling rate of fS, and then supplied to a common D/A converter 8. Here, at a sampling rate of 2f, L, R---
The signals are alternately oversampled in the order of ---------- and converted into analog signals. These analog signals are passed through low-pass filters 9 and 10 to output terminals 11 and 12, respectively.
The original signals St and SR are then extracted.

In such a digital recording/reproducing apparatus, the standard stipulates that during recording, R channel signals should be recorded on a magnetic tape in a state in which they have no phase difference with each other. Incidentally, an invention related to the present invention is disclosed in Japanese Patent Application Laid-open No. 60-24.
No. 2717.

[Problem that the invention seeks to solve]

In the circuit shown in FIG. 6 described above, during recording, the A/D converter 5 samples the H signals alternately and supplies them to the digital filter 6. Start signal processing at the same time. Therefore, as the output of this digital filter 6, the L channel signal is delayed with respect to the R channel signal, and if this is recorded on the magnetic tape as it is, it will deviate from the above-mentioned standard.

Also, during playback, two channels of signals recorded on the magnetic tape with no phase difference from each other are played back, and this playback signal is passed through a digital filter 6 to a D/A converter 8, and is sampled alternately in the order of R. Then, as an output, the L channel signal leads the R channel signal in phase. 2 with such a phase difference
If a channel reproduction signal is applied to a two-channel speaker, the sense of sound localization, three-dimensional effect, etc. will be impaired.

In order to solve the above problem, it is necessary to install two A/D converters and two D/A converters for the L and R2 channel signals.
It would be possible to provide them one by one, but the circuit configuration would be complicated and
It becomes a cost amplifier.

[Means for solving problems]

In the present invention, first and second multiplication coefficient groups that are in an interpolation relationship with each other to provide predetermined filter characteristics are prepared, and at the time of recording, the first multiplication coefficient group is applied to the signal of the first channel. The second multiplication coefficient group is used for the second channel signal, and during playback, the second multiplication coefficient group is used for the first channel signal, and the second multiplication coefficient group is used for the second channel signal. The above first signal
A selection means for using the multiplication coefficient group is provided.

[Effect]

By simply switching the first and second multiplication coefficient groups that define the filter characteristics of the digital filter according to the recording/playback and L/R channels, the phase difference between the signals of the two channels output from the digital filter can be adjusted during recording. In addition, during reproduction, the phase of the signal of one channel of the signal output from the digital filter to the D/A converter can be delayed from the phase of the signal of the other channel.

〔Example〕

FIG. 1 conceptually shows an FIR type digital filter according to the present invention, in which an L channel or R channel input digital signal S1 supplied to an input terminal 20 sequentially passes through delay elements 21 connected in series in N stages. do. The delay time of each delay element 21 has one sampling period of oversampling 1/2 f sc.

The outputs of each delay element 21 are multiplied by predetermined multiplication coefficients in a coefficient multiplier 22 and weighted, and then combined and added in an adder 23 to produce an output signal S. It is closed and taken out. This output signal S. has a predetermined low-pass filter characteristic for the input signal S1. Each of the coefficient multipliers 22 has coefficients 0, C1, Cz ------CN-z, CM-1, respectively.
C coefficient group and coefficients F + and F z '−””” respectively.
-'-'-'F There are two types of coefficients, the F coefficient group of N, and one of the first and second coefficient groups is selected and used.

In this embodiment, the input signal S is used during recording.

When the input signal S1 is an L channel signal, the C coefficient group is used, and when the input signal S1 is an R channel signal, the F coefficient group is used. Further, during reproduction, the F coefficient group is used in the opposite manner to that during recording, that is, when the input signal St is an L channel signal, the F coefficient group is used, and when the input signal S is an R channel signal, the C coefficient group is used.

FIG. 2 shows the impulse response characteristic of the digital filter of FIG. 1.

This response characteristic shows the temporal change in the output signal S0 when an impulse is applied to the input terminal 20. That is, the impulse is sequentially delayed by each delay element 21, and then a predetermined weight is applied to each delayed output by a coefficient unit 22, and then sequentially outputted through an adder 23.

The arrows shown at each sampling point (output time point of each delay element 21) on this impulse response characteristic curve are impulses having a thickness and a height corresponding to the coefficients of the coefficient unit 22.

Therefore, as mentioned above, during recording, the A/D in Figure 6
Since the digital filter 6 simultaneously starts signal processing for the signals supplied from the converter 5 in the order of R, the L channel signal lags behind the R channel signal as an output of the digital filter 6. This delay amount is 1/2 of the sampling period of 2f in the A/D converter 5 at the previous stage, that is, the normal sampling period Ts ("1
/f5) becomes T, /4. Therefore, the digital filter 6 only needs to correct the R channel signal so that it lags the L channel signal by T,/4. For this purpose, a digital filter 6 for the R channel is required.
The curve of the impulse response characteristic of the digital filter 6 for the L channel is
It is sufficient to delay the phase by s/4.

Figure 3 shows the impulse response characteristics of a digital filter based on the above principle, where the curve R indicated by a circle and a solid line indicates the characteristics of the digital filter for the R channel, and the curve L indicated by an x mark and a dotted line indicates the characteristics of the digital filter for the L channel. The characteristics of the digital filter are shown below. And curve R is curve L
It is delayed by T,/4. The size and height of the impulses indicated by "○" and "×" are determined such that "○" is determined by the F coefficient group, and "×" is determined by the C coefficient group. In FIG. 2, the coefficients of the C and F coefficient groups are arranged alternately. In the present invention, every other sampling point in FIG. 2 is selected and divided into two C and F coefficient groups, and each coefficient group is used for the R channel. Therefore, the coefficients of the C and F coefficient groups shown in FIG. 3 are arranged in such a way as to interpolate each other with respect to the characteristics shown in FIG. Note that signal processing is started simultaneously for the L and R channel signals, and the sampling rate of 2 fs from the A/D converter 5 is f.

1 surrounded by a dotted line to convert to a sampling rate of
The delayed data is not actually output.

In the figure, only two representative locations are surrounded by dotted lines.

Next, during playback, the two channels of signals recorded on the magnetic tape with no phase difference are sent to the D/A converter 8, and when they are sampled alternately in the order of R, the output is the R channel. signal is T than the L channel signal.
, /4 will be delayed.

Therefore, the digital filter 6 only needs to correct the L channel signal so that it lags the R channel signal by Ts/4. For this purpose, the curve of the impulse response characteristic of the digital filter 6 for the R channel is
It is sufficient to delay the phase by T s /4 from the curve of the impulse response characteristic of the digital filter 6 for the channel.

Figure 4 shows the impulse response characteristics of a digital filter based on the above principle, where the curve L indicated by a circle is L.
The characteristic of the digital filter for the channel is shown, and the curve R indicated by the X mark shows the characteristic of the digital filter for the R channel. The curve L is delayed from the curve R by T,/4. The size and height of the impulse indicated by each “○, ×” is determined by the C coefficient group, and “×
” is determined by the F coefficient group. These C
, F coefficients are arranged so as to interpolate each other with respect to the characteristics shown in FIG. Incidentally, in order to convert the signal at the sampling rate of fs from the digital filter 6 to the sampling rate of 2f, . is inserted and supplied to the digital filter 6.

FIG. 5 shows a specific embodiment of the digital filter 6, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In FIG. 5, 20 is an input terminal to which a digital signal is supplied, 24 is a shift register that sequentially receives digital signals from the input terminal 20, 25 is a RAM for writing and reading the contents of the shift register 24, and 26 is a RAM.
The output of 25 is supplied as data to one input side of the multiplier, and 27 and 28 are ROMs in which multiplication coefficient groups are stored in advance.For example, ROM27 has a C coefficient group, and ROM28 has a F coefficient group. It has a group of coefficients. 29 is RO
A switch circuit for switching the output of M27.28,
During recording, during D/A conversion of the L channel, it is connected to the contact a side and receives the C coefficient group from the ROM 27, and during D/A conversion of the R channel, it is switched to the contact side and the RO
The F coefficients from M2B are each fed to the other input of the multiplier 26. Further, during reproduction, contacts a and b are switched in the opposite direction to that during recording.

30 is an adder that adds the multiplication output of the multiplier 26, and 31 is an accumulator that latches the result of the adder 30. A part of the output of the accumulator 31 is fed back to the adder 30 and sequentially output from the multiplier 26. is added to the multiplication output of 32 is a shift register to which the output of the accumulator 31 is supplied, and 33 is an output terminal taken out from the shift register 32.

Next, the operation of the circuit with the above configuration will be explained.

During recording, when the L channel signal is input, the switch circuit 29 is connected to the contact a side, and the digital signal supplied from the input terminal 20 is input to the shift register 24 and the R channel.
AM25 sequentially delays the predetermined amount and supplies it to the multiplier 26, where the corresponding multiplication coefficients 0 and CI from the ROM 27
, Ct'-'-... are sequentially multiplied. Then, the multiplication output of the multiplier 26 is sequentially supplied to the adder 30 and added to the previous multiplication output, that is, the feedback input from the accumulator 31. When this addition output is repeated, the output of the accumulator 31 is shifted. The signal is supplied to a register 32, and the contents of this shift register 32 are taken out to an output terminal 33 as a desired L-channel digital signal.

Also, when inputting the R channel signal, the switch circuit 2
9 is switched to the contact side, and the digital signal from the input terminal 20 is transferred to the shift register 24 and RAM 25 as described above.
are sequentially delayed by a predetermined amount to the multiplier 26, where the corresponding multiplication coefficients F I, F z from the ROM 28 are
'---------'- is sequentially multiplied. Then, the multiplication output of the multiplier 26 is sequentially supplied to the adder 30 and added to the feedback input from the accumulator 31, and when this addition operation is repeated, the output of the accumulator 31 is supplied to the shift register 32, The content is the desired R
The signal is taken out to the output terminal 33 as a digital signal of the channel.

Further, during reproduction, the switch circuit 29 is switched in the opposite manner to that described above, and the same operation as described above is performed.

〔Effect of the invention〕

According to the present invention, by simply switching the C and F coefficient groups that define the filter characteristics of the digital filter according to the recording/reproducing and L/R channel signals, the two-channel signal output from the digital filter can be changed during recording. In addition, during reproduction, the phase of the signal of one channel of the signal output from the digital filter to the D/A converter can be delayed from the phase of the signal of the other channel.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an impulse response characteristic diagram of a digital filter, FIG. 3 is an impulse response characteristic diagram for the R channel during recording, and FIG. 4 is a diagram during reproduction. An impulse response characteristic diagram for the R channel, FIG. 5 is a block diagram showing a specific configuration of a digital filter, and FIG. 6 is a block diagram showing a conventional example. In addition, in the symbols used in the drawings, 21------------- Delay element 22
−−−−−−−−−1−−−Coefficient unit 23−・−・−−−
−−−−−−−−−−−Adder 27.28−1−−−
--ROM 29--1----1-------This is a switch circuit.

Claims (1)

[Claims] In a recording and reproducing device for recording and reproducing digital signals of first and second channels, first and second groups of multiplication coefficients that are interpolated with each other in order to have predetermined filter characteristics are prepared. However, when recording,
The first multiplication coefficient group is used for the first channel signal, the second multiplication coefficient group is used for the second channel signal, and during playback, the first multiplication coefficient group is used for the first channel signal. An FIR type digital filter in a recording/reproducing apparatus, characterized in that the second multiplication coefficient group is used and the first multiplication coefficient group is used for a second channel signal.