JP2643349B2 - Audio signal playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [Field of Industrial Application] The present invention relates to a reproducing apparatus for digital audio signals, and relates to a reproducing apparatus which clarifies and incorporates the essence of good sound of a conventional analog LP record.

[Summary of the Invention] It was discovered that the essence of the goodness of the analog LP record reproduction sound compared to the reproduction sound of the digital audio reproduction device is in the presence of a sound of about 20 KHz or more and applied to a digital audio signal reproduction device, A digital audio signal reproducing apparatus, wherein a high-frequency sound signal having a frequency component exceeding a cutoff frequency of a D / A converted analog audio signal is generated and superimposed on the analog audio signal.

[Conventional technology]

The upper limit of human audible frequency is said to be about 20KHz even for people who have good ears, and about 20KHz (in some cases, about 15KHz) digital audio signals can be converted to digital signals and analog decoded without aliasing. Made like For example, in a digital audio disc, about 20 kHz or more is removed by a low-pass filter (low-pass filter), sampled at a sampling frequency of 44.1 kHz, and then converted to analog / digital (A / D). After analog (D / A) conversion, about 20KHz or more is removed to prevent the sound below about 20KHz from being blurred due to cross modulation, and an analog audio signal is taken out.
Digital audio tape recorder (DAT)
48KHz is used as the sampling frequency in the B-mode stereo of NHK satellite broadcasting television. Specifically, FIG. 6 shows a block diagram of a conventional recording system, FIG. 7 shows a block diagram of a conventional reproducing system, and FIG. 8 shows a spectrum distribution in the block diagram of the conventional technology.

With these digital audio technologies, a high signal-to-noise ratio (S / N ratio) and a wide dynamic range, which could not be obtained with conventional analog LP recording technology, can be obtained. Popularized.

However, some audio enthusiasts and music professionals who are obsessed with sound (the enthusiasts) will find that traditional analog
LP records have received a good reputation for better sound. What is the cause of the fact that LP records with poor S / N and a narrow dynamic range (poor physical characteristics) feel better (comfortable), and what are the countermeasures? ing. The following three are known as typical findings.

The first finding is that the accuracy at the time of A / D and D / A conversion is not perfect, so that particularly small sounds will be distorted at the time of A / D and D / A conversion. Even if the accuracy of the A / D and D / A converters is sufficiently high, quantization noise is generated, and the quantization noise causes distortion having a strong correlation with the input signal level, especially for a signal having a low input level. This is the idea.

However, although the first and second findings are proposals for improvement of digital audio technology, it is far from an explanation that analog is still good even if the S / N and dynamic range are as poor as 40 to 50 dB.

The third finding is that humans can actually sense high-frequency sounds of about 20 KHz or more, and analog LP records include them but digital audio does not.

Regarding the third finding, today, when the signal format of digital audio is variously defined and spread,
It seems that no proactive measures have been taken beyond trying to play LP records beautifully.

Here, in order to deeply pursue the third finding, more detailed conventional research results are cited. All are studies by Tsukuba University Riki Ohashi et al. According to the first cited document (Acoustic Society of Japan, H-84-42, October 22, 1984), the state of detection of a change in sound quality due to high-frequency limitation was examined. Certainly, it is reasonable to set the upper limit of detection to 20 KHz.
It has been reported that sounds above KHz can be detected, and the sound quality is beautiful and comfortable. (Subjects with no music history have not detected any sound above 26KHz.) Second cited reference (Acoustic Society of Japan, H-85-22, 19
According to the statement on June 25, 1985), high-frequency sounds not produced by single singing in statements and chorus were generated by repetition (even in singing), and their frequency spectrum was shown to the full scale of 50 KHz full scale. I have. 100K for Gamelan music
The spectrum above Hz is shown. It has been concluded that it is difficult to deny the possibility that such high-frequency components have been pursued empirically and fairly intentionally with respect to their use and their utilization.

Third citation (Nihon Keizai Shimbun, March 23, 1988, evening edition,
In the Urban Now section), along with an introduction of a group of audio critics who are particular about playing good sound from analog LP records, Riki Ohashi and his colleagues compared the differences in sound quality with and without high frequency components above 26KHz, High-frequency components directly stimulate the brain to stimulate the secretion of comforting substances such as dopamine. "

Referring to these cited references, raising the sampling frequency of digital audio signals to expand the frequency band that can be recorded and played back to frequencies that are conventionally considered inaudible to humans is economically burdensome and has gained public support. I don't think you can.

[Problems to be solved by the invention]

Based on the third knowledge described in the prior art, a digital audio signal reproducing device capable of reproducing with a sound quality more comfortable than an analog LP record including a high frequency sound of about 20 KHz or more without changing the conventional digital audio signal format. The challenge is to obtain.

[Means for solving the problem]

According to the present invention, in the audio signal reproducing apparatus provided with a D / A conversion means for converting a digital audio signal into a corresponding analog audio signal, the D / A
High-frequency sound signal generating means for generating a high-frequency sound signal having a frequency component exceeding the cutoff frequency of the analog audio signal output from the converting means, and an analog audio signal output from the D / A converting means. An audio signal reproducing device comprising: a signal superimposing unit for superimposing a high-frequency sound signal output from the high-frequency sound signal generating unit.

Further, the D / A conversion means may be supplied with an oversampled digital audio signal,
In addition, a configuration may be adopted in which filter means for preventing aliasing noise from being output from the signal superimposing means is provided. In any case, for a high frequency sound exceeding the cutoff frequency of the analog audio signal, the frequency band, level, waveform, vibrato, etc. of the high frequency sound and / or the fluctuation amount thereof can be adjusted and / or controlled. If this is the case, an even more suitable reproducing apparatus can be obtained.

[Action]

In the present invention, the inventor has made one discovery. In other words, the reason that high-frequency sounds, especially sounds with a frequency of 26 KHz or more, can be heard comfortably is due to the fact that the sound of the frequency band exists together with the music even if it is not a musical sound (that is, even if it is noise). is there.

This finding proves to be a natural rule with the following circumstantial evidence.

A sound with a poor S / N and a narrow dynamic range like an analog LP record is generally unnatural and hard to hear,
Even if a weak high-frequency component is included, it is often masked by noise and cannot be heard. Nevertheless, it is presumed that comfortable hearing is caused by the presence of noise itself.

According to the second cited document, it is understood that the musical tone exceeding about 26 KHz exists in a spectrum close to white noise with a fluctuation corresponding to music or the like.

According to the first to third references,
It is presumed that humans can actually sense high-frequency sounds of about 20 KHz or more by a mechanism that is not necessarily the same as the sound that can be heard from the ears. Therefore, first, the existence of the high-frequency sound together with the music is considered to be a necessary condition for feeling comfort.

In the present invention, the above means is used as an application of such discovery. Therefore, despite the fact that high-frequency sounds of about 20 KHz or higher were originally removed from digital audio signals,
By adding a high-frequency sound of about 20 KHz or more in the playback device, it is possible to reproduce comfortable music as if the signal of about 20 KHz or more had not been removed from the beginning.

〔Example〕

First, a digital audio signal reproducing apparatus according to a first embodiment of the present invention will be described with reference to the block diagram shown in FIG. Compared with the conventional reproduction system block diagram of FIG.
The difference is that the high-frequency sound signal generating circuit 18 is inserted between the preamplifier 17A and the power amplifier 17B of the line amplifier 17 via the signal superimposing means 3 as the high-frequency sound signal generating means 2 .

The high-frequency sound signal generation circuit 18 includes a high-frequency sound signal oscillator (oscillator) 18A which must be provided, and various circuits for adding a listener's preference and obtaining a more comfortable reproduced sound. The oscillator 18A may be configured to include one or a plurality of oscillation circuits that oscillate a sound signal of about 20 KHz or more, or may be configured to divide and synthesize the output of the clock generator 18, A function generator for making white noise may also be provided. When an oscillation frequency / oscillation waveform adjustment circuit (OSC adjustment circuit) 18B is connected to the oscillator 18A so that the oscillation frequency and oscillation waveform of the oscillator 18A can be adjusted from the outside, the selection range according to the listener's preference is expanded. For example, the oscillator 18A is connected to a VCA (Voltage Controled
Amplifier), and the OSC adjustment circuit 18B can be configured to include a control voltage generator.

The high-frequency sound signal generation circuit 18 of this embodiment further has a
It is configured such that it can pass or not pass through a band frequency filter group that can adjust a pass frequency band of an arbitrary band of z or more and a pass level of each band. Further, the level of the high-frequency sound signal is adjusted by the level adjusting circuit 18D and connected to the power amplifier 17B via the switch a (signal superimposing means).
3 ) Yes.

Furthermore, a fluctuation function generation circuit 18E is provided, and the output of the circuit 18E controls the amplification factor of the level adjustment circuit 18D so that amplitude fluctuation can be added to the high-frequency sound signal.
The configuration is such that the band fluctuation can be added to the high-frequency sound signal by controlling the band frequency band of 18C, and the frequency fluctuation (vibrato) can be added by controlling the oscillation circuit of the oscillator 18A. The switches a to h can be arbitrarily intermittently connected, and the circuits 18B to 18E other than the oscillator 18A and the switch a do not necessarily have the essential functions. Providing everything provides a playback device that can be adjusted / controlled more comfortably for the listener.

Here, the fluctuation function generating circuit 18E may generate a 1 / f fluctuation (f is a frequency) known as a natural sound or an intrauterine sound, or may receive a signal of 20KHz or less from the preamplifier 17A and generate a 20KH
By generating a fluctuation function according to the signal level of a certain band (for example, 3 KHz to 20 KHz) of the signal of z or less, the fluctuation may be controlled in accordance with the music. In the latter case, a music signal of about 20 KHz or more that is not included and cut by the recording system can be restored in a pseudo manner by the reproducing apparatus of the present embodiment.

In the first embodiment, the high-frequency sound signal generation circuit 18
The high-frequency sound signal is superimposed on the analog audio signal by inputting the output of
3 ) However, in order to reduce the chance of occurrence of intermodulation with an analog audio signal of 20 KHz or less, it is desirable to input the signal to an amplification stage such as a speaker that is as close as possible to an electroacoustic transducer.

Next, a second embodiment of the present invention will be described based on FIG. 2 a) a block diagram and b) an example of a spectrum.

 In the second embodiment, compared to the first embodiment,
Basampling means4To D / A conversion means1In front of
Convert the oversampled digital signal to D / A
Exchange means1What you are typing is different. And
No signal superposition means 3. Filter means5(Low pass
Filter 16) can also be provided before the first implementation
It is different from the example.

The oversampling means 4 has a sampling frequency f _s
Twice or more frequency (e.g. 2f _s) consist oversampling circuit 14A for changing the sampling frequency. For example, when a digital audio signal sampled at f _s = 44.1 KHz is oversampled at 2f _s = 88.2 KHz, the frequency band of the harmonic component added by sampling becomes 2f as shown in the spectrum example of FIG. Move to a higher frequency band around _s .

Thereby, even if the cutoff frequency of the low-pass filter 16 is increased, aliasing distortion can be prevented, and
Upper limit of analog audio signal and low pass filter 16
A vacant band is generated between the band and the upper limit of the pass frequency. By inserting the high-frequency sound signal into this band, there is no fear of causing cross-modulation with the harmonic components, and if necessary, an empty frequency band is provided between the analog audio signal and the analog audio signal and the high-frequency sound signal. A sound signal can be superimposed. Therefore, the signal superimposing means 3 is a power amplifier.
It is not necessary to be in the vicinity of 17B, and can be configured as in the second embodiment.

FIG. 2 (b) shows the original signal and its harmonic components schematically represented by an ideal filter instead of the actual analog audio signal and its harmonic components for convenience of explanation.

Conventionally, it is generally difficult to obtain a filter having ideal characteristics.
_{There is} an example in which the oversampling of _s , for example, 8 _fs , avoids the drawbacks due to the gradual cut-off characteristics of the analog filter, and improves the filter characteristics by configuring a digital filter. The two embodiments have a good consistency with these techniques and can be a simple configuration.

Next, a third embodiment of the present invention will be described based on FIG. 3 a) a block diagram, b) an example of a spectrum (before superimposing a high frequency signal), and c) an example of a spectrum (after superimposing a high frequency signal).

The third embodiment is different from the second embodiment in that the position of the signal superimposing means 3 is provided after the filter means 5 (low-pass filter 16). In the third embodiment, the cutoff frequency of the low-pass filter 16 can be set to about 20 KHz as in the conventional example. However, as shown in FIG. Can be set as high as possible within a range in which no problem occurs.

Thus, the cutoff frequency of the low-pass filter 16 can be the same in both the second embodiment and the third embodiment, and the oversampling circuit 14A, the D / A conversion circuit 14B, the aperture circuit 15, The integrated circuit such as the low-pass filter 16 can be arbitrarily designed comprehensively and with consistency with the conventional technology.

Next, a fourth embodiment will be described with reference to the block diagram shown in FIG. In the fourth embodiment, as high range signal generator 2 A as compared to prior art FIG. 7, the high-pass filter 19, the sampling frequency rejection trap 2
0, tone control amplifier 21, a power amplifier 22, a linear adder 24 is added as a switch g, signal superimposing means 3 A.

In the fourth embodiment, the reproduced signal is reproduced without removing about 20 KHz or more, which has been conventionally removed by the low-pass filter, so that harmonic components distributed over the upper and lower sampling frequencies of about 20 KHz can be increased. Attempts are to be taken as acoustic vibration from an electroacoustic transducer such as a speaker as a range sound signal. Thus, the same purpose is intended to be achieved by using the harmonic component as a high-frequency sound signal without providing the high-frequency sound signal generation circuit 18 in the first embodiment. However, the low-pass filter 16
Output of the aperture circuit 15 directly to a line amplifier
When connected to 17, the sound will be blurred due to intermodulation with harmonic components of about 20 KHz or more in the band of about 20 KHz or less,
We take preventive measures. First of all, about 20KHz or more is reproduced by the amplifier of another route, and cross-modulation with about 20KHz or less is prevented. Furthermore, by removing the sampling frequency, which is the center of the power spectrum of the harmonic component, by the trap 20, the spectrum distribution of the harmonic component is substantially flattened,
A high-frequency sound signal close to the natural music spectrum is obtained, and the occurrence of cross-modulation in the linear adder 24 and the electroacoustic transducer is prevented. Further, the tone control amplifier 21 can adjust a signal level, a frequency characteristic, and the like according to a listener's preference.

Since the harmonic component is originally generated when sampling an audio signal of music or the like, the high-frequency sound signal extracted therefrom has a fluctuation corresponding to the music or the like.

In addition, it is possible to connect the output of the power amplifier 22 to a speaker dedicated to high-frequency sounds extracted from harmonic components,
In the fourth embodiment it is to be able to connect the output from the superimposed about 20KHz or less of the audio signal by a linear adder 24 (signal superimposing means 3 A) generally of the speaker system. The linear adder 24 is desired to have a configuration in which a nonlinear circuit is not passed as much as possible in order to prevent intermodulation between a signal of about 20 KHz or less and a high-frequency sound signal of about 20 KHz or more. For example, the output of the line amplifier 17 and the output of the power amplifier 22 can be simply connected in parallel or mixed by a resistor network. Alternatively, the output of the power amplifier 22 can be superimposed on the power supply line of the output transistor of the line amplifier 17.

Next, a fifth embodiment will be described with reference to the block diagram of FIG. The fifth embodiment is based on the same concept as the fourth embodiment. However, for the sake of simplicity, the harmonic components of about 20 KHz or more used as high-frequency sound signals have the same line amplifier as the signals of about 20 KHz or less. In order to allow the signal to pass through 17, a cross-modulation prevention measure has been taken. The first trap 24 is a sampling frequency trap provided for the same purpose as the trap 20 of the fourth embodiment, and may have the same configuration as the trap 20. Second
The trap 25 has a configuration that eliminates the frequency overlap due to aliasing in the reproduction system by just providing a clear blank range between the signal of about 20 KHz or less and the high frequency sound signal of about 20 KHz or more, and the line amplifier. It is intended to prevent the occurrence of cross modulation of a signal of about 20 KHz or less at 17 mag and a high-frequency sound signal of about 20 KHz or more.

As a result, for example, 21 KHz to 25 KHz are not included, for example, 4 KHz
An audio signal including a harmonic component from which the sampling frequency of 4.1 KHz has been removed as a high-frequency sound signal is output from the line amplifier 17.

Although these embodiments have been described focusing on the reproduction of digitally converted audio signals, it is needless to say that the present invention can be applied to the reception of PCM audio broadcasting of television signals, and the audio band limit is not about 20 KHz. It is also effective for broadcasting and recording playback limited to about 15KHz.

〔The invention's effect〕

According to the present invention, a digital audio signal reproduction that can reproduce an audio signal on which a high-frequency sound signal exceeding a cutoff frequency of an analog audio signal output from a D / A conversion means is superimposed as an application of a newly discovered law of nature. A device is obtained. The device is approximately
The device can adjust the characteristics of the high-frequency sound signal of 20KHz or higher, and can make the high-frequency sound fluctuate according to the music.

As a result, the digital audio signal is originally about 20KH
About 20KHz despite removing high frequencies above z
A digital audio signal reproducing apparatus that can reproduce comfortable music and the like as if the above-mentioned signals have not been removed and that satisfies the sensibility of a person (mania layer) beyond the conventional analog LP record can be obtained. .

Moreover, the present invention can be implemented by adding the means of the present invention only to a reproducing apparatus without changing the signal format of digital audio which has already become widespread.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is an a) block diagram and b) an example of a spectrum showing a second embodiment of the present invention. FIG. 3 shows a) block diagram, b) an example of a spectrum, and c) an example of a spectrum showing a third embodiment of the present invention. FIG. 4 is a block diagram of a fourth embodiment of the present invention, and FIG. 5 is a block diagram of a fifth embodiment of the present invention. FIG. 6 is a block diagram of a conventional recording system, FIG. 7 is a block diagram of a reproducing system of the prior art, and FIG. 8 shows a spectrum distribution in the block diagram of the prior art. 1 ...... D / A converter 2, 2 A, 2 B ...... high range sound signal generation means 3, 3 A, 3 B ...... signal superimposing means 4 ...... oversampling means 5 ...... filtering means 14A ...... over Sampling circuits 14, 14B D / A converter 16 Low-pass filter 17 Line amplifier 17A Preamplifier 17B Power amplifier 18 High-frequency sound signal generation circuit 18A High-frequency sound signal oscillator

Claims (4)

(57) [Claims] 1. An audio signal reproducing apparatus comprising a D / A converter for converting a digital audio signal into a corresponding analog audio signal, wherein a cutoff frequency of the analog audio signal output from the D / A converter is High-frequency sound signal generation means for generating a high-frequency sound signal having a frequency component exceeding the high-frequency sound signal output from the high-frequency sound signal generation means to an analog audio signal output from the D / A conversion means An audio signal reproducing device, comprising: signal superimposing means for superimposing a signal. 2. The audio signal reproducing apparatus according to claim 1, wherein an oversampling digital audio signal is supplied to said D / A conversion means. 3. The D / A conversion means is supplied with an oversampled digital audio signal, and is provided with a filter means for preventing aliasing of a signal output from the signal superposition means. The audio signal reproducing device according to claim 1, wherein the audio signal is reproduced. 4. The apparatus according to claim 1, wherein a level and / or a frequency component of said high frequency sound signal and / or a fluctuation amount thereof can be adjusted and / or controlled. Audio signal playback device.