JPS6190531A - Time axis converter of audio signal - Google Patents

Abstract

PURPOSE:To obtain a circuit with high S/N with simple constitution without characteristic deterioration by making the ratio of a time constant of a de- emphasis circuit to a time constant of a pre-emphasis circuit nearly equal to the converting ratio of a time axis converting circuit. CONSTITUTION:The time axis expanding device 40 is constituted by connecting a pre-emphasis circuit 41 and a de-emphasis circuit 42 before and after a conven tional time axis expanding device. The emphasis band of the circuit 41 is set nearly equal to the emphasis band of a de-emphasis circuit 25 and the pre- emphasis circuit 21 of a recording/reproducing device 20. Further, a time con stant tau41 of the circuit 41 is set equal to a time constant tau21 of the circuit 21 and the time constant tau42 of the circuit 42 is formed to be the relation of tau42/tau25=Ke>1, where Ke is a time expanding ratio of the expansion circuit 32 and tau25 is the time constant of the circuit 25. Since the effective band width of the devices 20, 40 is matched in this way, the output signal S/N of the device 40 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an audio signal time base conversion device.

[Conventional technology]

In a pay television system, time axis conversion and scrambling of the audio signal is performed on the transmitter side, and the receiver 1! ill
! 1, ie, on the system power μ side, there is a system that restores the back door 1d by descrambling and time change.

First, audio signal processing of the Intub system, which is one of this type of systems, will be explained with reference to FIGS. 3 to 5.

FIG. 3 shows an example of the configuration of the audio signal processing devices on the transmitting side and the receiving side of the isotsub system. In FIG. has. The original audio signal is sent from the input terminal (1) to the processing device α11.
The output signal of the processing device t1α is supplied to the output terminal (2;
Sent from・ .

(2) and (2) are a recording/reproducing device and a time axis expansion device on the receiving side, respectively; the recording/reproducing device has a pre-emphasis circuit, a recording/reproducing means (to), a level compression circuit;
Level expansion circuit (24) and de-emphasis circuit (c)
, and the end of the time axis expansion device is a descrambling circuit CII.
J and a time axis expansion circuit C. - The recording and reproducing means is the audio signal system of the VTR, which includes a recording amplifier, a recording head, a reproducing head, and a reproducing amplifier. (
3) is the input terminal of the receiving 1g signal, and (4) is the output terminal of the reproduced signal.

On the transmitting side, the original audio signal is sent to an A/D (not shown).
A converter digitizes the signal using a 22.05 kHz sampling signal, and the 14777-code is defined as one block. The length of the l block is 66.98 m5. As shown in FIG. 4A, four block signals Bl to B
4 form one set, and each block signal 81-B4 becomes a time-compressed block signal C1-C4, respectively, as shown in FIG. 4B, by a time-base compression circuit a1J.

In this case, the time compression ratio Kc is 100/11g. The four compressed block signals C1 to C4 are rearranged in a scramble circuit (Iz) as shown in FIG. 4C.

Scramble circuit (lz output is D/A (not shown)
It is converted into an analog signal by a converter and sent out from the terminal (2). For the sake of simplicity, in the following description, descriptions of Al1) conversion and D/A conversion accompanying time axis processing will be omitted.

Furthermore, a timing signal T is inserted into the gaps between the blocks C1 to C4 caused by time compression in order to absorb jitter caused by the recording/reproducing means. A burst sine wave of about 1.2 kHz is used as the timing signal.

The received signal is sent from the input terminal (3) to the pre-emphasis circuit.
After the high-frequency components are amplified, the signal is level-compressed with appropriate characteristics in a level compression circuit, and then supplied to a recording/reproducing means and recorded on a tape. The recording frequency range is 20Hz to 1QkHz2°, and the tape running speed is, for example, 2cm/S. The output of the recording/reproducing means is level-expanded in a level expansion circuit (24), and then its high frequency components are suppressed in a de-emphasis circuit (24). The time constants iτ21 +τ25 of these pre-emphasis circuit QIJ and de-emphasis circuit (c) are the same, for example, 75 μs and 15p8 Kff, respectively.
6o? x:,':y7shi,;<IPiIuUl) +
8, a level compression circuit 4, and a level expansion circuit 2 are used to improve the S/N'P distortion of the reproduced signal, and usually have complementary characteristics.

The output 1g of the recording/reproducing means 4 is a descrambling circuit 3υ
, the time axis is rearranged in the opposite order to that shown in FIGS. This time expansion rate Ke and the time compression rate Kc of the time compression circuit aD on the transmission side are in a reciprocal relationship with each other. will be restored.

The time axis expansion circuit G3 is well known and includes, for example, two switches q, G!, as shown in FIG. 8 and 2 memory t
, 3a, and (c), and the input signal is sent to one memory (b) via a switch Q at a write clock frequency r.
At the same time, the signal written to the other memory is read out via the switch (g) at the read clock frequency a.
It is read at fr (< fw). The time expansion rate Ke of this circuit 621 is expressed as the following equation (11).

Ke = fw/fr) 1''... (1) This writing and reading is performed alternately for 3M on both the memos Vu4I and W, and both switches ■ and (G) are also turned off. Note that f( )fw, the circuit of FIG. 5 performs a time compression operation.

[Problem that the invention seeks to solve]

In the above-mentioned signal processing system, since the recording and reproducing device f has a pre-emphasis circuit (211), a de-emphasis circuit, and a sys circuit (29), the maximum output level (MOL) that can be extracted from the recording and reproducing device is It decreases as the frequency increases, and its effective spectral bandwidth becomes narrower.

However, the time axis conversion device C (■ indicates the M of the high frequency region of the input signal
Although the OL decreases, that is, the effective spectrum bandwidth decreases, the efficiency is poor (,
Furthermore, there was a problem in that the S/N of the restored signal did not reach 59 dB, which was insufficient due to switching noise associated with time axis conversion.

It is possible to obtain a sufficient S/N of 7ft using a digital (PGM) circuit with a long word length, but the circuit would be sloppy and the equipment would be difficult to use. A problem arises in that the value becomes 7tJ.

In view of the above, an object of the present invention is to achieve high S/S with a simple configuration.
An object of the present invention is to provide an N time axis conversion device.

[Means for solving problems]

The present invention relates to a recording and reproducing device to which an audio signal is supplied via a pre-emphasis circuit Qll, a time axis converting device for converting the time axis of a neutral signal of this recording and reproducing means [231], and this time axis converting circuit. The de-emphasis circuit (43) is supplied with the output of the de-emphasis circuit (43), and the ratio of the time constant of the de-emphasis circuit (43) to the time constant of the pre-emphasis circuit Qυ is approximately equal to the conversion ratio of the time axis conversion device Qυ. It is a time axis conversion device.

[Effect]

According to the present invention, it is possible to make the effective bandwidth of the recording/reproducing means reduced by emphasis and the effective bandwidth of the time axis conversion circuit equal to each other.

〔Example〕

Hereinafter, an embodiment of an audio signal time axis conversion device according to the present invention will be described with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention. In Fig. 1, parts corresponding to Fig. 3 are denoted by the same reference numerals.
Breaking glare t'/f14.

In FIG. 1, 140 is a time axis expansion device, and a pre-emphasis circuit (4υ) and a de-emphasis circuit (421
It is configured by connecting. The emphasis band of the electronic fax circuit is set to be approximately equal to the emphasis band of the pre-emphasis circuit (2B) and de-emphasis circuit (c) of the recording/reproducing device (2).

Also, a time axis stretching device! , the time constant τ4 of the pre-emphasis circuit CD of 11 is set equal to the time constant τ21 of the pre-emphasis circuit QD of the recording/reproducing device 1:1,
The time constant τ42 of the de-emphasis circuit (to) is set to satisfy the following equation (2) with respect to the time constant τ25 of the de-emphasis circuit (to) of the recording/reproducing device (2), where Ke is the time expansion rate of the expansion circuit C321. Set.

f4z/fzs = Ke > 1 - (2
) In this way, the effective bandwidths of the recording/reproducing device 4 and the time axis expansion device t41 are matched, so that the switching noise accompanying the time axis conversion is reduced, and the output terminal (4)
The time hat Okinagasou that appears! 87N of the output signal of 141 is an improvement of 5-IQ dB times compared to the conventional device.

Next, with reference to FIG. 2, another embodiment of the audio signal time base conversion device according to the present invention will be described.

FIG. 2 shows the configuration of another embodiment of the present invention. In FIG. 2, parts corresponding to those in FIG. 1 and FIG. 3 are given the same reference numerals, and redundant explanation will be omitted. Further, in FIG. 2, illustration of the transmitting side processing device is omitted.

In FIG. 2, ``■'' is a time axis expansion device. In addition, the pre-emphasis circuit O and the de-emphasis circuit (5) shown in Figure 42 are inserted.
The characteristics of a are set to be the same as those of the pre-emphasis circuit 421 and the de-emphasis circuit +421 shown in FIG. Further, a level compression circuit +2 and a q level expansion circuit 4 may be inserted before and after the recording/reproducing i stage (c), if necessary.

In the above explanation, the scrambling circuit u21 and the descrambling circuit 3υ are included in relation to the isotube system, but if the signal processing is only time axis conversion, these circuits (13, C1υ) are of course unnecessary. It is.

In addition, although the above-mentioned embodiments performed time axis expansion, those skilled in the art will easily understand that the same effects can be obtained even if the time axis is compressed. It is a place where

〔Effect of the invention〕

As described in detail above, according to the present invention, the effective bandwidth of the time axis conversion device is adjusted to 5K to match the reduction in effective bandwidth due to the emphasis of the recording/reproducing means, so that the present invention has a simple configuration.
There is no characteristic deterioration (, high 87H time axis conversion times -' obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of an audio signal time axis converting device according to the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a conventional time axis converting device. A block diagram showing an example, and FIGS. 4 and 5 are a diagram and a block diagram for explaining the conventional example shown in FIG. 3.
゜(II) is the time pressure circuit, +zn, is the current, (5v
is Brienfu 7 cis circuit, +23N! recording and reproducing means;
1251 + +421! 53 is a hardenphasis circuit, and +32 is a time axis expansion circuit. Figure 1 Figure 5

Claims (1)

[Claims] A recording and reproducing means to which an audio signal is supplied via a pre-emphasis circuit, a time axis converting circuit for converting the time axis of an output signal of the recording and reproducing means, and a de-emphasis circuit to which the output of the time axis converting circuit is supplied. 1. A time base conversion device for an audio signal, characterized in that a ratio of a time constant of the de-emphasis circuit to a time constant of the pre-emphasis circuit is approximately equal to a conversion ratio of the time base conversion circuit.