JPH03212863A - Digital audio device - Google Patents

Abstract

PURPOSE:To correct an adverse effect of a low pass filter in a recording system by providing a characteristic correcting circuit having a specific transfer function behind a reproducing system D-A converter. CONSTITUTION:When a transfer function of the recording side low pass filter 11 is denoted as G1, the characteristic correcting circuit 17 having a transfer function of 1/G1 or a transfer function of approximately 1/G1 is provided behind the reproducing system D-A converter 15. That is, a frequency characteristic of the characteristic correcting circuit 17 is axial symmetry to a characteristic of the recording side low pass filter 11 with a center of 0dB. Consequently, an audio output Sa' of the digital audio device is that an output of Sa.G1.G2 of a reproducing system low pass filter 16 is multiplied by 1/G1, and hence the frequency characteristic of the recording side low pass filter 11 can be corrected. By this method, an adverse effect of the low pass filter is eliminated, and a total transfer function of the system can be settled as 1.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a digital audio device, and more particularly to a digital audio device that corrects the adverse effects of a recording-side low-pass filter.

<Prior art> In a digital audio recording/playback system, a low-pass filter is inserted on the recording side to suppress aliasing distortion, and a low-pass filter is inserted on the playback side to remove unnecessary high-frequency components. There is.

FIG. 6 is a block diagram of a conventional digital audio recording/playback system, with the recording system on the left side of the dotted line and the playback system on the right side. 1 is a high-order low-pass filter that suppresses aliasing distortion by cutting high frequency components of fs72 or higher, where fs is the sampling frequency, and has frequency characteristics shown in FIG. 2 is an AD converter that samples the output signal of the low-pass filter 1 with a frequency zt number fs and outputs the obtained digital data; 3 records the input digital data on a storage medium 4, and also records the digital data on the storage medium. 5 is a DA converter that converts the digital data read from the storage medium into an analog signal; 6 is a DA converter that removes unnecessary high-frequency components from the DA converter output to smooth the signal waveform; It is a low-pass filter that

<Problems to be Solved by the Invention> In conventional recording/playback systems, there are low-pass filters in the recording system and the playback system, so the analog output Sa' output from the playback system is band-limited and ( (see FIG. 7), a phase shift occurs. As a result,
For analog output.

There was a problem that there was no high-frequency component necessary for music reproduction, and unnecessary vibration components that did not exist in the natural world were added, making it impossible to reproduce music at a high level.

By the way, the low-pass filter on the reproduction side can be removed using a high oversampling method, but the low-pass filter on the recording system cannot be removed.6 Based on the above, the purpose of the present invention is to correct the adverse effects of the low-pass filter on the recording system. The purpose of the present invention is to provide a digital audio device that can perform the following functions.

Means for Solving the Problem> In the present invention, when the transfer function of the recording side low-pass filter is G, the transfer function of 17G1 or approximately 17G0 is added after the reproduction system DA converter. This is achieved by providing a characteristic correction circuit having a transfer function.

<Function> If a characteristic correction circuit having a transfer function of 17G1 or approximately 1/G□ is provided after the reproduction system DA converter, the frequency characteristics of the low-pass filter in the recording system will be adjusted by the characteristic correction circuit. The negative effects of the recording-side low-pass filter are improved.

<Embodiment> FIG. 1 is a block diagram of a digital audio device according to the present invention, which can be applied to, for example, a DAT device.
The left side of the dotted line is the recording system, and the right side is the playback system.

11 is the audio signal S, where fs is the sampling frequency.
This is a high-order low-pass filter that suppresses aliasing distortion by cutting high frequency components of fs/2 or higher from a, and has a transfer function G□ and frequency characteristics shown by the solid line in FIG.

12 samples the low-pass filter output at frequency fs,
An AD converter 13 outputs the obtained digital data and records the input digital data on a storage medium such as a DAT tape 14.

A digital recording and reproducing device reads digital data from a DAT tape 14 and outputs it; 15 is a DA converter that converts the digital data read from the tape into an analog signal; 16 is an unnecessary high-frequency component (system This is a low-pass filter that smooths the signal waveform by removing carry frequency components) and has a transfer function 02.

17 is a characteristic correction circuit, which includes a recording side low-pass filter 1;
If the transfer function of 1 is 01, it has a transfer function of 1/G1 or approximately 1/G, and the frequency characteristics are as shown by the dotted line in FIG.

That is, the frequency characteristics of the characteristic correction circuit 17 are line symmetrical with respect to the characteristics of the recording side low-pass filter 11 with respect to O dB.

From the above, the audio output S of the digital audio device
a' is the output 5a-G of the low-pass filter 16 of the reproduction system
1.G2 multiplied by 1/G1 (Sa-G), the frequency characteristics of the recording-side low-pass filter 11 can be corrected, and the band can be limited only to the reproduction-side low-pass filter 16. Note that high oversampling allows the reproduction-side low-pass filter to be omitted, thereby eliminating the adverse effects of the low-pass filter and making the overall transfer function of the system 1.

FIG. 3 shows one embodiment of the characteristic correction circuit 17, in which the characteristic correction circuit 17 is configured by a feedback configuration using a differential amplifier 17a and a circuit 17b having a transfer function 01, and the gain of the amplifier 17a is set to A. Then, the overall transfer function G can be expressed by the following formula (%)), and if A is very large, it becomes G41/Gi.

FIG. 4 shows another embodiment of the characteristic correction circuit 17, and is an example of a configuration that provides a characteristic of 1/G in a simplified manner.

In the figure, 17c is a bypass filter, 17d is an amplifier with a gain of B, and 17e is an adder. The bypass filter 17c converts the transfer function 61 of the recording side low-pass filter 11 in a frequency band higher than the frequency f,' to g1c second.
), then at high frequency *(f,'~f,,'), the transfer function G is expressed by the following equation.

G3·B=(1-g□)7g1 (see Figure 5). That is, Sa' = G
,・Sa, and G□ at f 0/ ≦f≦fo′ is g□
Then, Sa'=Sa-g-k+Sa-g-g・G,・B. Here, to set Sa'=Sa, G, ・B= (1-g
Requires the following conditions:

Note that the frequency f. ', the value of gi at -adB(41/
10000), the transfer function G of the bypass filter 17c is.

G, = (1/10@) (1-gi) 7g (however, m = a / 20).

From the above, the overall transfer function G in Fig. 4 is G'' (1+
G3・B),=1+(1-g□)/gwork=1/gt==L/G.

Therefore, the sound quality can be controlled by adjusting the gain B of the amplifier.

Above, the case where the present invention is applied to a digital audio device (DAT device) that can record and play back has been explained, but a digital audio device that is only a playback device (for example, a C
D player, etc.).

<Effects of the Invention> According to the present invention, when the transfer function of the recording side low-pass filter is 01, the 17G
Since a characteristic correction circuit having a transfer function of 1 or approximately 1/G is provided, the frequency characteristics of the low-pass filter in the recording system can be corrected by the characteristic correction circuit, and the adverse effects of the low-pass filter can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the digital audio device of the present invention, FIG. 2 is a frequency characteristic diagram of the low-pass filter and characteristic correction circuit, FIGS. 3 and 4 are examples of the characteristic correction circuit, and FIG. The characteristics diagram of the bypass filter shown in the figure, and FIGS. 6 and 7 are explanatory diagrams of a conventional audio device. 11... Recording side low-pass filter 13... Recording and reproducing device 15... DA converter 17... Characteristic correction circuit

Claims (1)

[Scope of Claims] A digital audio device that samples an audio signal input through a recording-side low-pass filter that cuts high-frequency components of 1/2 or more of the sampling frequency at the sampling frequency and reproduces the sampled signal from a recorded medium. When the transfer function of the recording side low-pass filter is G_1, a transfer function of 1/G_1 or approximately 1/G_1 is installed after the DA converter that converts digital data read from the recording medium into an analog signal. A digital audio device comprising a characteristic correction circuit having a transfer function.