JPS5857960B2 - sound reproduction device - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a stereo cassette with built-in two speakers, or a stereo cassette with built-in two speakers.
The present invention relates to an audio reproduction device that reproduces stereo and monaural signals with narrow speaker spacing, such as an audio multiplex receiver with built-in speakers.

Due to constraints such as external dimensions, the sound reproduction device with narrow speaker spacing cannot provide a good stereo effect and a sense of realism using normal reproduction methods.

The present invention provides a sense of realism in the reproduced sound of the monaural signal, a clearer sound image localization in the sound field expansion effect when reproducing the stereo signal, in a device that reproduces stereo signals and monaural signals, such as audio multiplexed television audio. In addition to providing a sense of realism, most of the signal control circuits for both monaural and stereo signals can be made compatible, and the sound image expansion of monaural and stereo audio can be rationally realized.

First, a conventional device of this type will be explained.

FIGS. 1, 2, and 3 show conventional sound image enlarging circuits dedicated to stereo signals.

Figure 1 shows the simplest sound image expansion circuit, with both left and right channels L.

From each of R, the main channel signal level ratio α(
An attempt is made to create a phase-inverted signal of α<1) and add it to the other channel to cancel or reduce the crosstalk sound component that occurs in both ears of the listener when playing back from two speakers, thereby obtaining a sound image enlargement effect. This is Surumome.

The circuit consists of amplifiers 1 and 2 of phase inversion type amplifier α and adders 3 and 4, but in this system, the low frequency components of the stereo signal are mainly in phase and divided into two channels. Since the signals are input, the low-frequency components are reduced at the time of mixing in the adders 3 and 4, and the ratio increases as the amount of expansion increases (α=1).

The sound image enlarging circuit shown in FIG. 2 was devised to eliminate the drawbacks of the circuit shown in FIG. 1.

The circuit shown in Fig. 2 has bypass filters 5 and 6 inserted before or after the amplifiers 1 and 2 shown in Fig. 1.The circuit shown in Fig. 2 has bypass filters 5 and 6 inserted before or after the amplifiers 1 and 2 shown in Fig. 1. The frequency balance of the reproduced sound is better compared to the method shown in Fig. 1, but it is not perfect and may cause the low frequency components of the sound image to be canceled. The resolution of this method is not as good as that of the method shown in FIG.

Figure 3 shows a further improvement on the method shown in Figure 2. In Figure 3,
Reference numeral 11.12 is a bypass filter for preventing low frequency signal cancellation, reference numerals 13 and 14 are inverting amplifiers for the amplification dust α, and after the inverting amplifiers 13 and 14, a low-pass filter 15.
16 is inserted.

17 and 18 are adders.

The above-mentioned low-pass filters 15 and 16 bring the frequency characteristics of the crosstalk sound between the listening ears closer to the mid-high frequency signal range,
This enhances the cancellation effect and at the same time improves the frequency characteristic balance of the reproduced sound to some extent.

Therefore, the resolution of sound image localization is also improved compared to the method shown in Figure 2, making it highly practical as a method for enlarging the sound image of stereo signals. The resolution of sound image localization is improved and becomes more complete.

Generally, in order to obtain sound image expansion for a monaural signal, it is necessary to perform amplitude and phase (or time) correlation operations for both ears of the listener. Figure 4 shows a basic example of a sound field expansion circuit for a monaural signal. shows.

In FIG. 4, numeral 19 is an input signal terminal to which a monaural signal is input, and 20 is a delay circuit which usually has an initial delay time of several ms to tens of ms.

The delayed signal outputs are mixed with the original input signals at adders 21 and 22 in mutually opposite phases (they may have phase characteristics), and are output to output terminals 0UT0 and 0UT2, respectively.
The frequency characteristics of this mixed two signals are as shown in Figure 5, for example, and the output amplitude alternates between peaks and dips with respect to the frequency as shown in the figure, and the relationship between the amplitude characteristics of 0UT1 and 0UT2 is completely symmetrical. Therefore, when these two signals are reproduced by two speakers, this characteristic relationship is maintained at both ears when listening at the center of the speakers.

This means that the sound pressure relationship between the ears changes constantly in response to changes in the frequency of the monaural input signal, and as a result, the listener perceives the direction of the sound to be toward the side with higher sound pressure intensity, resulting in a phenomenon in which the sound image expands. arise.

In this circuit, when a stereo signal is input, the monaural component among the signal components exhibits an enlargement effect, but the left and right separated localization components do not have any enlargement effect.

Therefore, in a device that is intended to reproduce two types of signals, stereo and monaural, such as an audio multiplex television, in order to achieve each expansion, a stereo expansion circuit as shown in Figures 1 to 3 must be installed separately. Two signal control circuits such as a monaural expansion circuit as shown in FIG. 4 are required, which complicates the circuit configuration and is very disadvantageous in terms of cost.

In view of the above points, the present invention constitutes a stereo signal expansion circuit to which a monaural signal expansion circuit can be easily added. By making full use of the measured data, we will realize a practical monaural/stereo convertible sound image expansion circuit with high sound image localization accuracy.

The present invention is applied to stereo and monaural reproduction bags with narrow speaker intervals, such as audio multiplex televisions, and an example of an audio multiplex television will be described below.

There is an appropriate viewing distance for televisions, and the ratio of the reproduction sound listening distance to the stereo speaker spacing is large, so the listening angle with respect to the sound source speaker is from several degrees to over 10 degrees, which is the standard stereo listening angle. This is much smaller than the supposed 130 degrees.

For this reason, when performing stereo reproduction under normal conditions, a sufficient stereo effect cannot be obtained.

For this reason, a stereo sound image enlarging circuit is required.

FIG. 6 shows a schematic diagram of a stereo listening state.

In this case, speaker SP1. The speaker SP2 is a stereo speaker built into the audio multiplex television.

As mentioned above, in the case of audio multiplex television, the listening angle θ is small;
In this case, it is assumed that θ=15°.

A and B are transfer functions between the speaker 5P1 (speaker 5P2) and the listener's ears 23 and 24, respectively.

Speaker SP3 is connected to speaker SP1 due to the sound image magnification effect.
This is assumed to be the position of sound source enlargement localization, and the listening angle is assumed to be φ.

C and D are speaker SP3 and listener's both ears 23.2
It is a transfer function between 4 and 4.

The transfer function is unique to the sound source position, and in order to realize the sound source position at the listening angle φ, the speaker SP1. speaker SP
Transfer functions C and D must be realized in each of the listener's ears 23 and 24 using the transfer functions A and B of 2 and the signal control circuit in the second stereo channel system.

Figures 8 and 9 show measurement examples using an artificial type for the case of φ = 15° and φ-90°, which show how the responses of the transfer functions of A, B, C, and D will look. .

(Amplitude characteristics only) This measurement data was obtained by inputting an impulse to the sound source speaker and Fourier transforming the output of the artificial microphone after compensating for the unique transfer characteristics of the sound source speaker and artificial microphone. The spatial amplitude characteristics from the sound source speaker to the artificial ear canal are shown, and the main system amplitude characteristics are shown for a listening angle of θ-15° and a measurement distance of 90° of 1.5 m.

Next, as shown in FIGS. 7a and 7b, the transfer characteristic E1 of the signal control circuit that obtains the localization of A at the listening angle φ in the stereo listening system B at the listening angle θ. Let's try to find E2.

In FIG. 7A, the listener's binaural pressures due to the sound source of speaker SP3 are as follows.

Next, in Figure 7B, the listener's binaural sound pressure is the right ear sound pressure; (
Po') - E・*6+0・*B) (2) Left ear sound pressure: [P
Ll]=E1*B+E2*A Therefore, the above formula (1), (
From 2), in order to equalize the listener's binaural sound pressure, (Pu''I3CPR/) t (PL)3 (PL/) Therefore, the control circuits E1 and E2 to be obtained from equation (3) are as follows. becomes.

Furthermore, the signal control block based on the electric circuit shown in Figure 7 can be converted to the block shown in Figure 10, and furthermore, in a stereo system, the signal control block using the electric circuit
This is the control system shown in the figure.

10th... E2 is (4) (5) , the control block in FIG. 11.

From equation (6), we obtain equation (6).

From the above, the sound image enlargement reproduction system using the stereo signal system is the 11th
Although it can be realized as shown in the figure, in the present invention, the compatibility of the monaural signal sound image enlargement control system and the control circuit.
The control block shown in FIG. 12 is proposed as a monaural and stereo signal sound image enlargement control system.

In Figure 12, RIN and LIN represent the R channel and L channel.
Channel signal input terminals Fl shown at 25 and 26 and G at 30 are signal control circuits.

27 and 28 are phase inverters, and 29 and 31.32 are adders, respectively.

Comparing the output signals of the control system shown in FIG. 11 and the control system shown in FIG.

H output. UT therefore has (7), (9), (8)
The condition for making F and G in FIG. 12 equivalent from (11) and (1 cm) is as follows.

(13), and by substituting (4) and (5) for αa, we get.

From the above, in order to obtain the same stereo sound image enlargement effect with the signal control system of FIG. 12 as the signal control system of FIG.
), it can be seen that it is sufficient to give the transfer characteristic shown by the equation.

Note that the circuit F is mainly an element for determining the directionality of a sound image, and the circuit G is an element mainly for creating an amplitude difference and a phase difference (time difference) of sound to both ears.

That is, it can be realized by the signal control system shown in FIG.

Therefore, the transfer function data measured earlier, A, B, C, D
Therefore, θ-15°.

The calculation results when φ=90° are shown in FIGS. 14 to 17.

Figure 14 shows the amplitude characteristics of F, Figure 15 shows the phase characteristics of F,
FIG. 16 shows the amplitude characteristics of G, and FIG. 17 shows the phase characteristics of G.

As a result of differentiating the phase characteristic shown in FIG. 17G with respect to frequency, a delay time τs of 170 (μS) was obtained in this calculation example.

As mentioned above, in the control block shown in FIG. 13, if the transfer characteristics shown in FIGS. 14 to 17 are realized by the electric circuit,
An ideal stereo sound image enlarging circuit can be realized.

Next, a circuit to which a monaural signal sound image enlarging circuit is added will be explained.

FIG. 18 shows a monaural and stereo compatible sound image enlarging circuit according to the present invention, and the signal path of the monaural signal sound image enlarging circuit will be explained.

33 is an adder, and the input signal from ROM2 LOH is
The signals are added by an adder 33 via a directionality judgment circuit -4%, given an initial delay of several ms to more than ten ms by an analog signal delay element (BBD) 34, and input to a low-pass filter 35. Adder 3 in mode a
7.39 with an inverted phase, where it is combined with the direct signal from the directionality determination circuit.

38.42 is a phase inverter.

The output signals of the adders 37 and 39 have amplitude characteristics as shown in FIG. 5, and a sound image enlarging effect can be obtained on the same principle as the conventional monaural signal sound image enlarging circuit shown in FIG.

In the monaural sound image enlarging circuit of the present invention, the BBD input signal is taken from the output side of the ROM and LOH directionality determination circuits, so if a low-pass filter with characteristics opposite to those shown in FIG. 14 is constructed, the BBD clock pulse This makes it possible to achieve elimination and flatness of the output signal, and also to improve the flatness of the frequency characteristics of the combined output signals of the adders 37 and 39.

Further, according to the present invention shown in FIG. 18, a binaural difference generating circuit 41
By adding the output signal of the output signal and the output signal of the low-pass filter 35 by the adder 40, a sound image enlargement effect is produced for both monaural and stereo signal components at the contact point of the switch 36.

This is effective when left and right independent localization signals and center localization in-phase signals coexist, such as in a normal stereo source, and a sense of distance is added to the center localization sound image, further enhancing the sound image expansion effect.

As described above, according to the present invention, a monaural delay circuit is separately provided, and by using a switch circuit, monaural and stereo sound image enlargement effects can be easily obtained.

Next, the direction judgment circuit, that is, tool A + B Shows the physical circuit.

The circuit shown in FIG. 19 is the simplest, consisting of a capacitor C with a low resistance R, and is sufficient for practical use.

43 is a signal input terminal, 44 is an output terminal, and a frequency characteristic that increases by 6 dB10Ct from the frequency determined by T1=CR1 is obtained, and FIG. 20 shows a circuit showing the frequency characteristic.

Figure 21 shows an example of a structure consisting of two transistors and a CR, where 45 is an input terminal, R1°R2 is a bias resistor, and Ql
A phase inversion circuit is constructed by inserting a low resistor R3°R4 into the emitter and NILFT of the transistor Q1.

Also C1. Transistor Q2, which constitutes a phase shifter with R5, is an emitter follower, and the shifter output signal is frequency-corrected with C2, R7, and C3.

That is, the frequency characteristic is determined by the time constant determined by "2R7=Tl t R+RT1=T2° XR 4C2=T3.

The delay time for a stereo signal is created by a phase shift and a low-pass filter, and is determined by Ts→C1R5+T3.

Figure 22 shows its characteristics.

When we confirmed the expansion effect of the circuit shown in Figure 18, which is composed of these circuits, we found that the sound image localization in stereo is clearly superior to any conventional method in terms of clarity and sound quality. confirmed.

In addition, the sound image enlargement effect was sufficiently felt even in monaural mode, and was particularly effective in TV broadcasts of song programs and sports broadcasts.

The present invention has the above configuration, and according to the present invention, the following effects can be obtained.

(1) Sound image localization is clearer than in the conventional example, and a stereo sound image enlargement effect with less discomfort can be obtained.

(2) There is little deterioration in sound quality due to increasing the sound image expansion width.

(3) By simply adding a monaural-dedicated delay circuit, a monaural and stereo compatible expansion circuit can be constructed.

(4) By combining the two delayed output signals, the expansion effect of the normal stereo source can be further enhanced.

[Brief explanation of drawings]

Figures 1 to 3 are block diagrams of conventional stereo sound image enlargement circuits, Figure 4 is a block diagram of a conventional monaural sound image enlargement circuit, Figure 5 is a frequency characteristic diagram of the output signal of the circuit, and Figure 6 is a block diagram of a conventional stereo sound image expansion circuit. is a schematic diagram for stereo listening, Figure 7A is a schematic diagram showing the listening state at the listening angle φ, Figure 7B is a schematic diagram of a two-channel control system equivalent to Figure 7A, and Figure 8 is a diagram showing the listening angle. Fig. 9 is an amplitude characteristic diagram of transfer functions C and D at a listening angle of 90. Fig. 10 is a block diagram of a monaural control system equivalent to Fig. 7 B. , FIG. 11 is a block diagram of a stereo sound image enlargement control system equivalent to FIG. 7B, and FIG. 12 is a block diagram showing the basic configuration of the sound reproduction device of the present invention.
Figure 13 is a block diagram showing the same device in terms of transfer functions;
Figure 15 shows the calculation results of the amplitude characteristics of the directional judgment circuit of the same device, Figure 15 shows the calculation results of the phase characteristics of the circuit, and Figure 16 shows the amplitude of the binaural difference creation circuit of the same device. FIG. 17 is a diagram showing the calculation results of the width characteristic, FIG. 17 is a diagram showing the calculation result of the phase characteristic of the same circuit, FIG. 18 is a block diagram of another embodiment of the present invention, and FIG. 19 is a diagram showing the directionality determination of the same device. The electrical circuit diagram of the circuit, FIG. 20 is a frequency characteristic diagram thereof, FIG. 21 is an electrical circuit diagram of a binaural difference generating circuit of the same device, and FIG. 22 is a frequency characteristic diagram thereof. 25, 26... Directionality judgment circuit, 27, 28
... Phase inverter, 29 = ... Adder, 3
0...Binaural difference generation circuit, 31, 32...
・Adder, 33... Adder, 34...
Analog signal delay element, 35...Low pass filter, 36...Switch, 37...
Adder, 38... Phase inverter, 39, 40...
... Adder, 41 ... Binaural difference generation circuit, 4
2... Phase inverter.

Claims (1)

[Claims] The transmission characteristics between the 12 speakers and the listener's ears located on the center line between these two speakers are calculated using a sound source assumed to be located at an arbitrary position outside the two speakers and the listener's ears. It has a directionality judgment circuit and a binaural difference generation circuit for converting the transmission characteristics between the two ears, and the directionality judgment circuit is inserted into the thread path of each left and right channel of the stereo, and For one channel, the output of the gender determination circuit is added through a phase inverter, and the added output is input to the binaural difference generation circuit, and the output of the binaural difference generation circuit is added to the output side of each of the directionality determination circuits. For one channel, the sum is added through a phase inverter, and a delay element and a low-pass filter are provided to give an initial delay of several milliseconds to tens of milliseconds to the summed output obtained by adding the outputs of the respective directionality determination circuits. A sound reproduction device characterized in that the sound reproduction device is configured to add the signal to the output of the binaural difference generating circuit via the binaural difference generating circuit.