JPS6369068A - Processing circuit for digital audio signal - Google Patents

Abstract

PURPOSE:To achieve high sound quality of reproduction by changing over an output mode at a digital data step. CONSTITUTION:A reading RF signal is copied by a PCM decoder 1, and outputted as L and R serial data (SD). The SD is supplied to a data separating circuit 6, synchronized to a control signal from a decoder 1, separated to L-SD and R-SD, supplied to a data selector 7, and from a controller 8 as a control signal, respective signals of a squelch (S)L and a squelch (S)R are supplied. The signals are outputted as the Lch and Rch data of the combination designated by the (S)L and (S)R from a selector 7. Audio data from the selector 7 are converted to an analog signal by D/A converters 2L and 2R and thereafter, outputted from output terminals 5L and 5R through LPF3L and 3R as the audio signal of Lch and Rch. Consequently, since the output mode of the sound is changed over at a digital data step, the high sound quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital audio signal processing circuit.

1 and 1 Normal video discs are recorded with video signals and audio signals modulated by frequency (FM), but in recent years, audio signals have been digitized using a predetermined digital modulation method and made into pulse train signals. Video discs, so-called video discs with digital audio, have been developed and commercialized using a method of recording a video signal and an audio signal by superimposing them on each FM modulated signal (see Japanese Patent Application Laid-open No. 171011/1983). According to this video disc with digital audio, in addition to high-quality video, it is possible to obtain two channels of Hi-Fi sound.

In such a playback device for a video disc with digital audio, when the demodulated digital audio output is, for example, audio multiplexing, the L (left) channel is Japanese and the R (right) channel is a foreign language, as shown in FIG. As shown, the demodulated digital output demodulated by PCM decoder 1 is converted to D/A (
The digital/analog) converters 2L and 2R convert the R channel analog audio signal to the L channel, respectively.
Analog switches 4L and 4 for mode switching operate independently of each other via PF (low pass filter) 3L and 3R.
R, and these switches 4L and 4R supply L,
An operation is performed in which the audio output from the R channel output terminals 5[, 5R is switched to one of three output modes: Japanese and foreign languages, Japanese only, and foreign languages only (Japanese Patent Application Laid-Open No. 1983-1989-1). (See Publication No. 194439).

However, in the conventional device described above, the mode switching by the mode changeover switches 4m and 4R is performed in the analog stage, which tends to cause deterioration of sound quality and deterioration of separation (L, R separation). There is a drawback that the use of the SN ratio tends to deteriorate.

1. Further improvements and 1. The present invention has been made to eliminate the drawbacks of the conventional ones as described above. By switching the output mode at the digital data stage, it is possible to produce high-quality audio with excellent separation and SN ratio. An object of the present invention is to provide a digital audio signal processing circuit that can obtain signals.

The digital audio signal processing circuit according to the present invention comprises two
The system separates channel audio serial data into data for each channel, converts each separated data into two-channel data in a combination specified by a predetermined control signal, and converts each channel data into an analog audio signal. ing.

Tomo-5-1 DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention,
In the figure, parts equivalent to those in FIG. 6 are designated by the same reference numerals.

A read RF (high frequency) signal read from a recording medium (not shown) is demodulated by a PCM decoder 1 and output as R serial data. Further, the R serial data is supplied to a data separation circuit 6, where it is separated into serial data and R serial data in synchronization with the control signal supplied from the PCM decoder 1. This separated data is supplied to the data selector 7. The data selector 7 is supplied with squelch and squelch R signals as control signals from the controller 8.

The data selector 7 has a squelch L at a high level (hereinafter referred to as 1).
1 H”) and the squelch R is at a low level (hereinafter referred to as
(denoted as “L”), and the R channel
Data is output when squelch L is "L II" and squelch R is "H", L data is transmitted as the R channel, and data is transmitted when squelch L and squelch R are both °L.
L data and R data are output as channels, respectively. Note that when squelch is performed and squelch R is both "°H", no data is output from any channel.

That is, from the data selector 7, the separated lch
, RCh data is squelched and output as a combination of Lch and Rch data specified by squelch R. Each audio data output from the data selector 7 is converted into analog data by D/A converters 2L and 2R, and then sent to output terminals 5L and 5R via LPFs 3L and 3R.
It is output as an R channel audio signal.

In this way, when the demodulated digital audio output is, for example, audio multiplexing, the output mode of the audio output from the output terminals 5L and 5R (Japanese and foreign language, Japanese only, and foreign language only) can be switched. By performing this at the digital data stage, there is no adverse effect on sound quality or separation, so it is possible to reproduce audio signals with high sound quality and an excellent S/N ratio. Note that the data separation circuit 6 may basically be any circuit that can separate data.

FIG. 2 is a block diagram showing an embodiment in which a four-times oversampling digital filter, for example, is used as the data separation circuit 6. In the figure, parts equivalent to those in FIG. 1 are designated by the same reference numerals.

In the figure, an Lch data enable signal, an Rch data enable signal, and a latch signal are supplied from a PCM decoder 1 to a quadruple oversampling digital filter 9 along with LR serial data. As is clear from FIG. 3 showing its basic circuit configuration, the 4x oversampling digital filter 9 consists of filter circuits 9m and 9R for two channels, and inputs LR serial data as shown in FIG. 4(a). 1-ch for
Rch enable signals (b) and (c) are “L” respectively.
”, each data is distributed to each filter circuit 91.9H. Also, the timing is set so that each distributed data is simultaneously output by a latch signal. In other words, the data is distributed to each filter circuit 91.9H. For example, L channel enable signal from PCM decoder 1,
By simply supplying the Rch enable signal and the latch signal, Lch and Rch data can be easily separated.

In this way, by using the 4x oversampling digital filter 9 as the data separation circuit 6, in addition to the unique effects of the filter, data separation can be performed using the same circuit without using a dedicated circuit for data separation. Since both can be performed simultaneously, advantages can be obtained in terms of cost and circuit space. The specific effects of the 4x oversampling digital filter 9 will be explained below.

If a 4x oversampling digital filter 9 is inserted before the D/A converters 2L and 2R as shown in FIG.
176.4K)-1z, which is twice as high as 176.4K)-1z, so that when the sampling frequency
．． 1 to +-12,88°2K)-1z, and 132.3
The sampling noise spectrum that was centered at KHz disappears and rises to a point centered at 176.4 KHz, so the signal spectrum centered at each of the above frequencies remains as a digital signal. become. As a result, the characteristics of LPF'3L and 3R provided after the D/A converters 2L and 2R are as shown in FIG.
It has a gentle cut-off characteristic, [, PF3L.

The specifications required for 3R become easier, and the group delay time becomes smaller within the band, resulting in better phase characteristics, which further improves sound quality.

In the above embodiment, a case was explained in which a 4 times oversampling digital filter was used as the data separation circuit 6, but it is also possible to use a 2 times oversampling digital filter, for example, and as in the case of the above embodiment. , data can be separated simultaneously using the same circuit. However, it is better to use a four-fold filter than a two-fold filter because the circuits of the LPFs 3L and 3R can be configured more simply, and this is advantageous in terms of the S/N ratio, distortion rate, etc.

11 Rikyō 1 As explained above, according to the present invention, by switching the output mode at the digital data stage, there is no adverse effect on sound quality, separation, etc., so it is possible to achieve high sound quality and an excellent signal-to-noise ratio. This makes it possible to play back audio signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an embodiment in which a 4x oversampling digital filter is used as the data separation circuit in FIG. 1, and FIG. Figure 2 is a block diagram showing the basic circuit configuration of the 4x oversampling digital filter, Figure 4 is a timing waveform diagram to explain the circuit operation of Figure 3, and Figure 5 is a block diagram showing the basic circuit configuration of the 4x oversampling digital filter. FIG. 6 is a block diagram showing a conventional example. Explanation of symbols of main parts 1... PCM decoder 2L, 2R... D/A converter 3L, 3R Old... Low pass filter 6... Data separation circuit 7. ...Data selector 9...4x oversampling digital filter

Claims (2)

[Claims] (1) Data separation means for separating two-channel audio serial data into data for each channel, and outputting each data output from the data separation means as two-channel data in a combination specified by a predetermined control signal. A digital audio signal processing circuit comprising: a data selector; and means for converting each channel data output from the data selector into analog audio signals. (2) The digital audio signal processing circuit according to claim 1, wherein the data separation means is an oversampling digital filter.