JP2834144B2 - Digital recording and playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a digital recording / reproducing apparatus which has a punch-in / out function and can be applied to a digital audio tape recorder or the like which performs oversampling.

[Prior art]

2. Description of the Related Art As a conventional digital recording / reproducing apparatus, an apparatus having a so-called punch-in / out function of rewriting a part of a signal already recorded on a recording medium to a new signal in order to edit a signal is known. Various types of recording media such as a magnetic tape, a magnetic disk, a magneto-optical disk, and a semiconductor memory are used. Here, a digital recording / reproducing apparatus using a magnetic tape will be described. FIG. 3 is a block diagram showing a conventional digital recording / reproducing apparatus having a punch-in / out function. In the figure, reference numeral 1 denotes a magnetic tape transported in the direction of arrow a, 2 denotes a reproducing head for reproducing the magnetic tape 1, 3 Is a reproduction amplifier for amplifying the output of the reproduction head, 4 is a reproduction signal processing circuit which performs signal detection, demodulation, data deinterleaving, error correction, etc. on the output of the reproduction amplifier 3 to form a reproduction signal, and 11 is an analog signal. input terminal, 20 is a low pass filter for aliasing noise removal analog signal is supplied, 21 denotes an a / D converter is driven at twice the sampling frequency f _s of the analog signal band 15 from the reproduction signal processing circuit 4 A first signal switching means for smoothly switching the obtained reproduction signal and the output of the A / D converter 21 at a predetermined timing to form a recording signal. Da 15 have been used. Reference numeral 16 denotes a recording signal processing circuit that performs addition of an error correction code, data interleaving, and modulation on the recording signal obtained from the crossfader 15, and 17 denotes a recording signal processing circuit.
A recording amplifier 18 for amplifying the recording signal processed by the recording amplifier 17 is a recording head for recording the recording signal amplified by the recording amplifier 17 on the magnetic tape 1, and is arranged at a predetermined distance from the reproducing head 2. 22 a D / A converter recording signal obtained from the cross-fader 15 is driven by the supplied sampling frequency f _s, 23 is a low pass filter for aliasing noise removal output of the D / A converter 22 is supplied, 10 Is the low pass filter 23
Output terminal for extracting the output of Next, the operation will be described. When performing insert recording by punch-in, first, the playback mode is set, and the magnetic tape 1 is moved to the playback head 2.
And reproduces the signal from the reproduction amplifier 3 through the reproduction signal processing circuit 4 to become a digital reproduction signal.
At this time, the crossfader 15 has selected the reproduction signal side, and this reproduction signal is supplied to the D / A converter 22 and the low-pass filter 2.
It is obtained as a monitor output from the output terminal 10 through 3.
Next, when a portion of the magnetic tape 1 slightly before the predetermined editing point comes to the reproducing head 2, the recording amplifier 17 is operated to establish the reproducing recording mode. As a result, the recording signal from the crossfader 15 is applied to the recording head 18 through the recording signal processing circuit 16 and the recording amplifier 17, and
Will be recorded. In this case, the magnetic tape 1 is
And the signal reproduced by the reproducing head 2 is applied to the recording head 18 through the reproducing amplifier 3, the reproducing signal processing circuit 4, the crossfader 15, the recording signal processing circuit 16, and the recording amplifier 17. If the time until the reproduction is the same, the reproduced signal can be recorded on the same portion of the magnetic tape 1 again. Next, when the edit point of the magnetic tape 1 comes to the reproducing head 2, the cross fade mode is set, and the cross fader 15 selects the A / D conversion side. Then, the analog signal input from the input terminal 11 becomes a recording signal through a low-pass filter 20, an A / D converter 21, and a crossfader 15, and this recording signal is transmitted to a recording head 18 through a recording signal processing circuit 16 and a recording amplifier 17. By being added, it is recorded from the edit point of the magnetic tape 1. At the time of this recording, the recording signal is obtained as a monitor output from the output terminal 10 through the D / A converter 22 and the low-pass filter 23. When the recording is completed, punch-out is performed and insert recording is completed. The punch-out operation is performed by switching the crossfader 15 from the A / D conversion side to the reproduction signal side, contrary to the punch-in operation. As described above, in the punch-in / out operation,
The signal input from the input terminal 11 is synchronized with the reproduction signal, and there is no time lag on the magnetic tape 1 and the connection between the two signals is smoothly performed. In the digital recording and reproducing apparatus described above, as the sampling frequency f _s of the A / D converter 21 and D / A converter 22, because of the use of twice the frequency of the signal band, as a low-pass filter 20 and 23, In order to remove aliasing noise due to sampling, a filter having an attenuation characteristic that drops sharply at f _s / 2 is required. For this reason, the phase rotation becomes intense in the upper part of the signal band, which causes a problem in the high-frequency transmission characteristics. In order to solve this problem, an oversampling method has been conventionally used. FIG. 4 is a block diagram showing a digital recording / reproducing apparatus using oversampling. In the figure, 1 to 4, 10, 11, 15 to 18 indicate the same parts as in FIG. 12 is a low pass filter the analog signal inputted from the input terminal 11 is applied, which has a moderate attenuation characteristic from f _s 12 until f _s is used. An A / D converter 13 to which the output of the low-pass filter 13 is added is driven at a sampling frequency of 2 _fs . 14 first digital filter for linear decimation of the phase characteristic to bring down the sampling frequency 2f _s of the A / D converter 13 to f _s, 6 is the sampling frequency fs of the recording signal obtained from the cross-fader 15 A second digital filter for linear interpolation with a phase characteristic for increasing to 2 fs, the output of the digital filter 6 is added to 8
It is driven at a sampling frequency of 2fs by a D / A converter. 9
Is a low-pass filter to which the output of the D / A converter 8 is added, and f
from _s / 2 to f _s it is is used in those with moderate attenuation. According to the above configuration, since the low-pass filters 12 and 9 having gentle attenuation characteristics are used, these low-pass filters are used.
The phase rotation of the analog signal passing through 12, 9 is reduced.
In addition, in the A / D converter 13 and the D / A converter 8, the usual 2
Sampling at a double sampling rate is performed. However, the sampling rate is returned to the original sampling rate by the first digital filter 14, and the original sampling rate can be doubled by the second digital filter 6. Fig. 5 shows a linear FIR (Finite Inpulse Re
1 shows a conceptual circuit configuration of a spouse type digital filter. This digital filter can be applied to the first and second digital filters 14 and 6 in FIG. In the figure, 30 is a digital signal input terminal,
31 is a delay element connected to a plurality of stages synchronized with the sampling period of the input digital signal, and 32 is each delay element 31
Each coefficient a ₁ on the output of, a ₂ ··· a _n multiplies the multiplier, 33 adder for adding outputs of the multipliers 32, 34 at the output terminal to the output of the adder 33 is applied is there. The coefficients a ₁ , a ₂ ... _An are symmetrical about the time axis. According to the above configuration, the digital signal inputted from the input terminal 30, while being sequentially delayed by the delay element 31 of the plurality of stages, the coefficients a _1, a ₂ ··· a _n to the output of each delay element 31 The multiplication is performed, and the multiplied values are added, so that a digital output having predetermined filter characteristics can be obtained from the output terminal 34. When the digital recording / reproducing apparatus handles audio signals, the first and second digital filters 14, 6 are required to have an attenuation characteristic of 90 dB or more. In order to realize this, a large number of delay elements 31 are required, and the number of taps becomes 100 or more. In this case, the delay amount on the A / D side and the D / A side is 1 msec or more, which is a range that can be detected by a human.

[Problems to be solved by the invention]

Since the conventional digital recording / reproducing apparatus is configured as described above, when performing the punch-in / out operation, the delay time of the first and second digital filters 14 and 6 becomes a problem. That is, in FIG. 4, at the time of punch-in / out, a connection point between a recorded signal and a new signal is set on a predetermined edit point on the magnetic tape 1 due to a delay time of the first digital filter 14. It will shift later. Also, the monitor output obtained from the output terminal 10 is delayed by the delay time of the second digital filter 6. In the case of recording music, etc., there is a case where a performance is performed in accordance with the monitor sound while monitoring the reproduced sound by the monitor output, and insert recording is performed at a predetermined timing. In such a case, if the monitor output is delayed, ,
There has been a problem that accurate insert recording cannot be performed. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. Even when punch-in / out is performed while performing oversampling using a digital filter, the editing point does not shift and the monitor output is also reduced. It is an object of the present invention to obtain a digital recording / reproducing apparatus without delay.

[Means for Solving the Problems]

A digital recording / reproducing apparatus according to the present invention has a total delay time of the first and second digital filters, and delays an input reproduced signal by a first delay means. A recording signal is generated by the first signal switching means from the output of the first digital filter and the output of the first digital filter, and the signal switching timing is set to the delay time of the first digital filter from the signal switching timing of the first signal switching means. The output of the A / D converter and the signal obtained by passing the reproduced signal through the second digital filter are supplied to the D / A converter by the second signal switching means which is advanced by an amount corresponding to that.

[Action]

The shift of the edit point and the delay of the monitor output based on the delay time of the first and second digital filters are corrected by the first and second signal switching means and the reproduction signal delay circuit in the present invention.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 1 to 4, 6, 8 to 18 correspond to the same reference numerals in FIGS. 3 and 4, and a description thereof will be omitted. Reference numeral 5 denotes a delay circuit for delaying the reproduction signal obtained from the reproduction signal processing circuit 4 and supplying the delayed signal to the crossfader 15. The first digital filter 14 has a first delay time τ ₁ and a second digital filter 6 Has a delay time τ ₁ + τ _{2 in} total with the second delay time τ ₂ . Reference numeral 7 denotes second signal switching means for switching between the reproduction signal and the output of the A / D converter 13. In this embodiment, a cross fader 7 is used. Note that the cross fader 15 is used as the first signal switching means 15. 19 denotes an input terminal of the timing signal for operating the cross-fader 15, 7, 20 is a delay circuit to add to the cross-fader 15 by delaying the timing signal by _one the first delay time tau. FIG. 2 is a timing chart of signals at points 1 to 3 in FIG. Next, the operation will be described. When performing punch, firstly, in the reproduction mode, the reproduction signal obtained to the point from the reproduction signal processing circuit 4 while being double the sampling rate in the second digital filter 6, delayed by tau _1, the cross from point It is applied to a D / A converter 8 via a fader 7. As a result, a monitor output is obtained at the point. Next, when the recording amplifier 17 is operated slightly before the edit point to enter the reproduction / recording mode, the reproduction signal at the point is delayed by τ ₁ + τ ₂ by the delay circuit 5, and the recording signal processing circuit is passed from the point via the crossfader 15. The recording medium is recorded on the magnetic tape 1 by being added to the recording head 18 via the recording amplifier 17. In this case, the time required for the magnetic tape 1 to travel from the reproducing head to the recording head 18 and the delay time of the signal path from the reproducing head 2 to the recording head 18 via the delay circuit 5, the crossfader 15 and the like are matched. Thus, the reproduced signal is recorded on the same portion on the magnetic tape 1. Next, when the edit point comes to the reproducing head 2, the input terminal 11 (
Analog signal input from the point)
The signal is converted into a digital signal through the A / D converter 13. This digital signal is applied to the crossfader 7 from a point, is returned to the original sampling rate by the first digital filter 14, and is applied to the crossfader 15 from the point after being delayed by τ ₁ . At this time, the input terminal
The crossfader 7 first performs the signal switching operation smoothly by the timing signal input from 19 (point), and then the crossfader 15 performs the signal switching operation by the timing signal at the point delayed by τ _{1 in the} delay circuit 20. Is performed smoothly. According to the above description, as shown in FIG.
At the input side of 15, points, points, and points are synchronized at the same time, whereby the editing operation by the crossfader 15 is performed with the editing timing in accordance with the input of the analog signal, and the first and second digital Editing without influence of the delay time of the filters 14 and 6 is performed. The monitor output during insert recording is input terminal 11, low-pass filter
12, the A / D converter 13, the crossfader 7, the D / A converter 8, the low-pass filter 9, and the output terminal 10, so that a large delay element such as the first and second digital filters 14, 6 is provided. And monitor output without delay. In the above embodiment, the sampling frequency of the oversampling is 2 fs, but may be 4 _fs , 8 _{fs, and} so on. Although the crossfaders 15 and 7 are used as the first and second signal switching means, other switches may be used as long as abnormal signals do not occur at the time of signal switching and signals can be switched smoothly. Good.

【The invention's effect】

As described above, according to the present invention, the first signal switching means for switching from the reproduction signal to the analog input signal at the time of insert recording, and the second signal switching means for switching from the monitor output of the reproduction signal to the monitor output of the analog input signal Since the delay circuit having the same delay amount as the delay time of the first and second digital filters for performing oversampling is provided, the editing point by punch-in / out can be set while performing oversampling. There is an effect that a monitor with no shift and no delay in monitor output can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a timing chart showing signal timing in each section of the apparatus, and FIG. 3 is a block diagram showing a conventional digital / recording / reproducing apparatus. Figure, 4th
FIG. 5 is a block diagram of the same apparatus with an oversampling method added thereto, and FIG. 5 is a circuit configuration diagram of an FIR digital filter. 4 is a reproduction signal processing circuit, 5 is a delay circuit, 6 is a second digital filter, 7 is a crossfader, 8 is a D / A converter, 13 is an A / D converter, 14 is a first digital filter,
5 is a crossfader, 16 is a recording signal processing circuit, and 20 is a delay circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] A first digital filter is provided on an output side of an A / D converter, and a second digital filter is provided on an input side of a D / A converter, wherein the A / D converter and the D / A converter are provided. A digital recording / reproducing apparatus for performing oversampling and having a punch-in / out function in a converter, comprising: a delay time that is a sum of delay times of the first and second digital filters; First delay means for delaying the reproduced signal, first signal switching means for generating a recording signal from the output of the first delay means and the output of the first digital filter, and the A / D converter The output of the signal and the signal obtained by passing the reproduced signal through the second digital filter are supplied to the D / A converter, and the signal switching timing is determined by the signal switching timing of the first signal switching means. Digital recording and reproducing apparatus characterized by comprising a second signal switching means to advance by the delay time of said first digital filter.