JPS5832838B2 - signal conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has been made for the purpose of providing a signal conversion circuit with a simple configuration for converting a stereo signal for speaker reproduction into a stereo signal for headphone reproduction. be.

In general, stereo sources are provided to multiple speakers placed in a space so that the listener in the reproduction sound field can hear the sound as having the stereophonic sensation and sound quality intended by the producer. Since it is created as a stereo signal for speaker playback, if a listener listens to this speaker playback stereo signal as it is using headphones, it will be Normally, one can only hear sound with a three-dimensional sound sensation and sound quality that is completely different from that of the original.

This point will be specifically explained as follows.

Each channel signal SP of stereo signal for speaker playback
, SP Is 2 speakers SP, 5PlrS

r individually to form a three-dimensional reproduction sound field, and when listener M listens to a stereo signal within that reproduction sound field, listener M listens to the signal between the two speakers and both ears of listener M. You will hear different states of sound depending on the transmission characteristics.

By the way, the typical listening position of the listener in the sound field reproduced by the two speakers is a position equidistant from the two speakers SP r t SP 1, as shown in FIG. At the above-mentioned position, the listener faces the middle part of the two speakers SPr and SPl and listens to the sound radiated from the two speakers.

Taking this listening condition as an example, two speakers SP
r, the transmission characteristic between SP 1 and the front surface of the eardrum of both ears of listener M is that the transmission characteristic from the right speaker SPr to the right eardrum and the transmission characteristic from the left speaker SPl to the left eardrum are equal to each other. (Now, let this transfer characteristic be A), and the transfer characteristic from the right speaker force SPr to the left ear tympanic membrane,
The transmission characteristics from the left speaker SP1 to the right eardrum are mutually equal (this transmission characteristic is now referred to as B).

Now, the right speaker signal supplied to the right speaker SPr is
Pr8, the left speaker signal supplied to the left speaker SP1 is 5P18, the sound pressure in front of the eardrum of the right ear (signal of sound pressure change) is Er, the sound pressure in front of the eardrum of the left ear (signal of sound pressure change) ) is El, the left and right speaker signals S P 1 s tSPr8 emitted from the left and right speakers, and the sound pressure E1 . The relationship between Er and Er is expressed as the following equation (1).

In the stereo signal for speaker reproduction, each channel signal corresponding to the sound image to be localized in front of the listener M is generally a signal of the same phase and level, so the left and right speaker signals in this case are C1, that is, It is determined as in the above equation (2), and the above (2) is added to the equation (1).
By substituting the formula to find the sound pressures Er and El in front of the eardrums of listener M's left and right ears when listener M is listening with a sound image in front of him, the following (3 ) is shown by the formula.

In this way, the signals C of the same phase and the same level are given to the two speakers SPr and SPl, and the listener M in the reproduction sound field
When the listener M is listening as if a sound image exists in front of him, the listener M is not listening to the sound C radiated from the speaker SP tSPl, but to the transfer characteristic A between the speaker and the listener's both ears in the reproduction sound field. .

We are listening to a sound in the form of the product of the sum of B and C, that is, the sound of (A+B)C as shown in equation (3) above.

FIG. 2 is a characteristic curve diagram showing an example of the above-mentioned (A+B) characteristic.

Therefore, when a listener uses headphones to listen to a stereo signal for speaker reproduction that has signal content such that a sound image is localized in front of the listener when played back by the speaker, the stereo signal for speaker reproduction is In order to be able to hear high-quality sound under the same conditions as when played through speakers, the headphones used must have (A+B) characteristics of the input and the transmission characteristics to the front of the listener's eardrum. It is sufficient to use headphones that exhibit such characteristics, and headphones that are actually used are generally manufactured with such characteristics.

In other words, as mentioned above, a stereo source is generally produced as a signal for speaker reproduction so that the listener in the reproduction sound field using speakers can hear the sound with the 3D distortion and sound quality intended by the producer. On the other hand, the speaker playback signal created as described above may be listened to through headphones, but the listener may also listen to the above speaker playback signal through headphones without using the speaker. Since it is customary to evaluate headphones with good characteristics as headphones that can provide the same three-dimensional sound sensation and sound quality as when listening in a reproduced sound field, headphone manufacturers also evaluate the characteristics (transfer characteristics) as described above. The company has been manufacturing and selling headphones that have (A+B) characteristics), and the fact that commercially available headphones generally exhibit the above-mentioned (A+B) characteristics is based on the results of commercially available headphones conducted by the applicant's company. This is also supported by measurement results for many headphones.

As mentioned above, an example of the (A+B) characteristic is shown by the characteristic curve diagram in Figure 2, but (A+B)
Although there are differences in small irregularities depending on the shape of each person's head and ears, the characteristics generally have a positive trend of 4KHz to 5IG (with a peak of about 10 dB near z). It is something.

However, as is well known, headphones are used while being attached to each listener's ears individually, and when they are used, the sound produced by the two speakers shown in Figure 1 is generated within the sound field reproduced by the two speakers. Since there is no loss talk, when listening to a stereo signal for speaker reproduction using headphones, it is possible to obtain a sound image that shows a completely different localization state from the sound image localization state for speaker reproduction. it is obvious.

For this reason, conventionally, stereo signals for speaker playback were
It has been proposed to create a signal that includes the amount of crosstalk that would occur in the sound field reproduced by two speakers, and to use this signal as a stereo signal for headphone reproduction.

FIG. 3 is a block diagram showing a typical configuration example of the previously proposed signal conversion circuit. In FIG. 3, 1 indicates the right channel signal ■r (hereinafter input signal 2 is the input terminal for the left channel signal II of the stereo signal for speaker reproduction (hereinafter sometimes referred to as input signal ■l), 3 is for headphone reproduction. The right channel signal Or of the stereo signal (hereinafter referred to as the output signal Or
4 is an output terminal for the left channel signal o1 (hereinafter sometimes referred to as output signal 01) of the stereo signal for headphone playback,
D is a delay circuit (or phase shift circuit), F is a filter that attenuates high frequencies, and ADDl.

ADD2 is an adder, and the above-mentioned delay circuit and filter F are connected in cascade, and the crosstalk characteristic B/A in the reproduced sound field shown in FIG.
When the transmission characteristic from the right (or left) speaker to the right (or left) ear tympanic membrane is A, and the transmission characteristic from the right (or left) speaker to the left (or right) ear tympanic membrane is B,
A characteristic similar to the crosstalk characteristic B/A in the reproduced sound field as shown by B/A is obtained.

Since the signal conversion circuit shown in the third diagram described above is designed to exhibit a transfer characteristic as shown in the following equation (4), the output signal Or > 01 of this signal conversion circuit is converted so that the characteristic is A. If it is supplied to a pair of headphones, equation (4) becomes (1)
Therefore, if a signal converted from a stereo signal for speakers to a stereo signal for headphone playback by the signal conversion circuit shown in FIG. can hear sounds showing the same sound image localization as listener M in FIG.

However, as mentioned above, general headphones (A+
B) Since it is made with the characteristics shown in Figure 3, the signal obtained by converting the signal using the signal conversion circuit shown in Figure 3 can be applied to ordinary headphones as a stereo signal for headphone playback. Even if the sound image is localized correctly, the listener will only be able to hear poor quality sound with emphasis on the low frequency range.

In this way, in the signal conversion circuit configured as shown in Figure 3, although it is possible to listen to a sound image with the same localization using headphones as when playing back through speakers, the sound quality is not satisfactory. Couldn't get playback sound.

The problem of unsatisfactory poor sound quality of the reproduced sound in the signal conversion circuit having the configuration shown in Figure 3 above can be solved by using a signal conversion circuit as shown in Figure 4 proposed in, for example, Japanese Patent Laid-Open No. 51-29101. This problem can be solved by using a conversion circuit, but the signal conversion circuit shown in the fourth diagram uses the sound quality adjustment circuit EQ to perform sound quality adjustment on the input signal of each channel signal to the signal conversion circuit shown in the third diagram already mentioned. Because it was made in
Although it is necessary to add a sound quality adjustment circuit EQ, as mentioned above, the sound quality adjustment circuit EQ to be added has an extremely complicated configuration, so there is a drawback that it is not easy to realize.

In other words, the characteristic EQ required by the sound quality adjustment circuit EQ to be used in the signal conversion circuit shown in FIG. This is because the circuit having the above structure has a complicated structure.

Note that the characteristic EQ shown by equation (5) that the above-mentioned sound quality adjustment circuit EQ should have is derived as follows.

As mentioned above, since general headphones have the (A+B) characteristic, there is The characteristic of is shown by the following equation (a).

Furthermore, the transfer characteristic of the signal conversion circuit shown in Figure 4 is as shown in (b) below.
It is shown by the formula.

Therefore, the transfer characteristic from the input side of the signal conversion circuit to the listener's eardrum is determined by the following equation (a) and (b):
c) It will be as shown in the formula.

Since the EQ in the correct case is the characteristic EQ required by the sound quality adjustment circuit in the signal conversion circuit shown in Figure 4, the following equation (d) can be obtained by substituting equation (1) - equation (C). , Next, rearranging equation (d) results in equation (e).

It is clear that equation (e) becomes equation (5) described above.

The present invention is a signal conversion circuit used to convert a stereo signal for speaker reproduction into a stereo signal for headphone reproduction. The present invention provides a signal conversion circuit with a simple configuration that also has a correction function, and satisfactorily solves the various problems of the conventional art described above.
Hereinafter, the specific contents will be explained in detail with reference to the accompanying drawings.

FIG. 5 is a block diagram of an embodiment of the signal conversion circuit of the present invention, and in this FIG. Terminals 3 and 4 are right and left channel signals Or, 0 in the stereo signal for headphone playback.
Output terminals 1, 5r, 51°, 7r, and 71 are sign adders, respectively, and 6rt61 has characteristics approximately equal to the crosstalk characteristics B/A of the reproduced sound field, that is, approximately B/A.
The circuits 6r and 61 are constructed by a combination of a delay circuit (or phase shift circuit) and a filter.

In the signal conversion circuit shown in FIG. 5, the right channel signal (■) in the stereo signal for speaker reproduction supplied to the terminal 1 is input to the inverting input terminal of the sign adder 5r and the non-inverting input terminal of the sign adder 7r. given and also terminal 2
The left channel signal {circle around (1)} in the stereo signal for speaker reproduction supplied to the left channel signal 1 is applied to the inverting input terminal of the sign adding adder 51 and the non-inverting input terminal of the sign adding adder 71.

Further, the output signal of the sign addition adder 71 is applied to the non-inverting input terminal of the sign addition adder 5r, and the output signal of the sign addition adder 7r is added to the non-inverting input terminal of the sign addition adder 51. Given.

The output signal of the sign addition adder 5r is supplied to the non-inverting input terminal of the sign addition adder 7r via a circuit 6r having -characteristics, and the output signal of the sign addition adder 51 is B - is supplied to the non-inverting input terminal of the sign adder 71 via the circuit 61 having the characteristic of -.

Therefore, the above-mentioned signal conversion circuit shown in FIG. This is expressed by equation (6).

Below, by sequentially transforming the above equation (6b), we finally get (
6g) formula is obtained.

The above equation (6g) is based on the output terminals 3 and 4 of the signal conversion circuit shown in FIG.
In other words, if headphones made to exhibit the (A+B) characteristic are connected as described above, the transmission characteristic from the input to the eardrums of both ears of the listener using the headphones will be as shown in Figure 1. This shows that the transfer characteristic is equal to the transfer characteristic of equation (1) shown for the listener in the sound field reproduced by two speakers, and therefore, if the signal conversion circuit of the present invention is used, the listener will be able to achieve (A+B ) It is possible to perform headphone playback with good sound quality using general headphones that are made to have these characteristics.

As described above, according to the signal conversion circuit shown in Figure 5, a stereo signal for speaker reproduction can be converted into a stereo signal for headphone reproduction in a good manner, including the problem of the frequency response characteristics of headphones used for listening. However, its configuration is significantly simpler than that of the conventional signal conversion circuit shown in FIG. 4, which has the above-mentioned sound quality correction function.

In other words, in the signal conversion circuit of the present invention, unlike the conventional example shown in FIG. As a result, a circuit that has the crosstalk characteristics of the reproduced sound field required for this purpose is also used as a circuit that has the crosstalk characteristics of the reproduced sound field that should be used in the sound quality adjustment (sound quality correction) circuit. In order to obtain a circuit in the state shown in FIG. It is composed of the whole.

Therefore, according to the signal conversion circuit of the present invention, all of the problems with the conventional signal conversion circuits described above, which convert a stereo signal for speaker reproduction into a stereo signal for headphone reproduction, are satisfactorily solved. can be,
According to the present invention, it is possible to provide at a low cost a signal conversion circuit with excellent characteristics that allows a listener to listen to a stereo signal for headphone reproduction with good sound quality.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the transfer characteristics between the speaker and the listener's eardrum in a reproduction sound field using two speakers, Figure 2 is a characteristic curve diagram of the (A + B) characteristic, Figures 3 and 4. The figure is an explanatory block diagram of a conventional example of a signal conversion circuit.
The figure is a block diagram of one embodiment of the signal conversion circuit of the present invention. 1.2... Input terminal for stereo signal for speaker reproduction, 3, 4... Output terminal for stereo signal for headphone reproduction, D... Delay circuit, F...・・・
・Filter, ADDl, ADD2...-Adder, 5
r, 51,7r. 71... Sign addition adder, 6r, 61...
-Circuit with characteristics.

Claims (1)

[Claims] 1. A stereo signal for headphone playback that provides a listener using headphones with a sound image localization similar to the sound image localization given to the listener when the left and right speakers perform playback using the stereo signal for speaker playback. ,
A signal conversion circuit that generates from the stereo signal for speaker reproduction described above, which supplies each channel signal of the stereo signal for speaker reproduction as an input signal, and also converts the stereo signal for headphone reproduction to be individually supplied to headphones. Each channel signal in the signal is expressed as the crosstalk characteristic B/A in the reproduction sound field, that is, the right (
When the transmission characteristic from the right (or left) speaker to the right (or left) ear tympanic membrane is A, and the transmission characteristic from the right (or left) speaker to the left (or right) ear tympanic membrane is B,
The crosstalk characteristics in the playback sound field as shown by B/A are mixed in the same phase into the input signals of the other channels through a circuit having characteristics approximately equal to B/A, and each of the channels described above is 5. A signal conversion circuit configured to mix an input signal of 1 to an input signal of the same channel in an opposite phase through a circuit having a characteristic substantially equal to the crosstalk characteristic B/A in the reproduction sound field described above.