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◎ 6 Channel sphere surround

Recent times, multi channel (surround) sound recording is not unusual. It is said that reproducibility of the sound field is satisfactory.

Really I try hearing, but I feel there are no ceiling and no floor. (I cannot understand, whether living in the room or outdoors). I think it is the unnatural playback sound. Depending on the channel of the top and bottom added (6 channel sphere surround), the solution was tried.　

Here, problem is the expedient. Regarding to the multi channel systems generally,
 a) The equipment and material which can handle the multi channels.
 b) The compatibility which utilizes sound source property.
 c) Arrangement, and interference of speaker.

And so on it is the case that it is problem, but this time, the result which was examined, until recently the equipment and material and being diversion possible, it made the matrix system sound source property it is many, a) b) probably can supply fault sufficiently. 

If it is matrix system, reappearance and to be cheapness and easy, until now, objective appraisal to be little, it is the reason which also value of experiment being large selects. 

As for encoding system of the matrix, CBS SONY SQ4ch system with the Sansui QS4ch system , in addition, the rear exists monaural (3 ch) Dolby system, and so on various systems.

The among these, normal position possibility, not be located on 4 speaker centers, by the fact that it expands, the QS4ch which has the possibility where it can handle the only top and bottom sound field information was designated as transmission system of 6 channel system. 

I produced a decoder with the QS4ch/SQ4ch/QS6ch logic this time and evaluated those methods and a difference of having logic or not.

◎ The commentary of the decoder with the QS4ch/SQ4ch/QS6ch logic

Each encode / decode expression are as follows.

・ The encode calculating formula of the QS4ch method

L = 0.92 * LF ＋ 0.38 * RF ＋ 0.92 * LR * i ＋ 0.38 * RR * i

R = 0.38 * LF ＋ 0.92 * RF − 0.38 * LR * i − 0.92 * RR * i

・ The decode calculating formula of the QS4ch method

LF = 　L ＋ 0.414 * R

RF = 　R ＋ 0.414 * L

LR = −L * i ＋ 0.414 * R * i

RR = R * i − 0.414 * L * i

・ The encode calculating formula of the SQ4ch method

L = LF − 0.707 * LR * i ＋ 0.707 * RR

R = RF − 0.707 * LR ＋ 0.707 * RR * i

・ The decode calculating formula of the SQ4ch method

LF = L

RF = R

LR = 0.707 * L * i − 0.707 * R

RR = 0.707 * L − 0.707 * R * i

The method that I adopted

LF = 　L

RF = 　R

LR = −0.5 * L * ( 1−i ) − 0.5 * R * ( 1＋i )

RR = 　0.5 * L * ( 1＋i ) ＋ 0.5 * R * ( 1−i )

・ The encode calculating formula of QS6ch methods

L = 0.92 * LF ＋ 0.38 * RF ＋ 0.92 * LR * i ＋ 0.38 * RR * i ＋ 0.65 * ( 1＋i ) * UP ＋ 0.65 * ( 1−i ) * DN

R = 0.38 * LF ＋ 0.92 * RF − 0.38 * LR * i − 0.92 * RR * i ＋ 0.65 * ( 1−i ) * UP ＋ 0.65 * ( 1＋i ) * DN

・ The decode calculating formula of QS6ch methods

LF = 　L ＋ 0.414 * R

RF = 　R ＋ 0.414 * L

LR = −L * i ＋ 0.414 * R * i

RR = 　R * i − 0.414 * L * i

UP = −0.707 * L * i ＋ 0.707 * R

DN = 0.707 * L − 0.707 * R * i

The method that I adopted

LF = 　L ＋ 0.414 * R

RF = 　R ＋ 0.414 * L

LR = −L * i ＋ 0.414 * R * i

RR = 　R * i − 0.414 * L * i

UP = 0.5 * L * ( 1−i ) ＋ 0.5 * R * ( 1＋i )

DN = 0.5 * L * ( 1＋i ) ＋ 0.5 * R * ( 1−i )

　　　　　The following, block .

　　

・Equalizer circuit

The RIAA equalizer circuit is a Kaneda-style initial version (simple). 　The sorting of first grade FET is required.

・Matrix decode circuit

・QS4ch method　： 　

Add with　a factor of 1 / √ 2 (0.414) between the forward channel. Subtract with　 a factor of 1 / √ 2 (0.414) between the rear channel. And, each +90 degrees,-90 degrees phase-shifted rear channel. In addition, localization of both lateral side will be improved by the phase-shifting each +60 degrees, -60 degrees.

・SQ4ch method　：

If operate at between 0 and 90 degrees as the standard, to decode the backward channel, phase will be asymmetric. In order to prevent this, calculate with each -45 degrees and +45 degrees.

・QS6ch method　：

Left and right channels of the front and rear is QS4ch system. Up and down channel is rear channel of SQ4ch system.　

・Sound source direction distinction circuit

・QS4ch method　：

It is direction distinction from the front left and the backward right volume ratio, the front right and the backward left volume ratio.

・SQ4ch method　：

It is direction distinction from the volume ratio of front right and left, the volume ratio of the rear right and left and the volume ratio of center front and rear.

・QS6ch method　：

It is direction distinction from the front left and the backward right volume ratio, the front right and the backward left volume ratio, the volume ratio of the top and bottom.

As for the volume ratio, is Diode the band pass of two signals ; after logarithm conversion, both waves rectification for a difference of both. 　In addition, signal is summed before taking the ratio, but that the symmetry is lost, so the separation is worse. (Study is required because becomes asymmetrical when summing)　By the addition between two signals and the minute noise addition, I prevent false distinction in the minute signal beforehand.

・Directionality emphasis circuit

・QS4ch logic method　：

I add a crosstalk ingredient occurring to the channel of both sides of the sound source direction as a reverse correlative person in charge and cancel it.

・SQ4ch logic method　：

A sound source does 90 degrees phase shifting of the crosstalk ingredient of the backward right and left channel in the case of front right and left channel, the front in the case of the rear and I add it as a reverse correlative person in charge and cancel it.

・QS6ch logic method　：

I add the front left and the backward right, the front right and the backward left crosstalk ingredient as a reverse correlative person in charge, and a sound source cancels it in the case of the top and bottom. In addition, I add the crosstalk ingredient of the top and bottom as a reverse correlative person in charge, and a sound source cancels it in the case of circumference. （But, as for this QS6ch logic, a sound source does not cancel the crosstalk with a simple model at the time of truth right truth left）

◎ Comparison of each method

An audition room is Western-style room 10 tatamis. The speaker is FE87 of Shinano. The all around speaker is height of the room corner ear.

The sound source is a sound. The hearing of the sound image when I let circumference (zero degree, +-22.5 degrees, +-45 degrees, +-90 degrees, +-112.5 degrees, +-135 degrees, 180 degrees) do normal position with a bread pot. And it is the level of each method and crosstalk, a calculation value of the phase (counterclockwise direction gets worse).

◎ The audition comparison of four channel methods

・Discrete method

　I hear the rear approaches forward when turning to the front, and right and left do not do normal position at all. It is clogged up and understands that I cannot recognize a normal position position definitely (at a limit of the human ability) even if it is a discrete method pro-temporary law, ideal.

・QS4ch method

　Case without the logic, rear sound field approach forward, and the sound image of the just beside moves forward, and normal position (the rear in particular) becomes sweet. Even if I get narrow, the sound field becomes it and similar sound field / normal position in comparison with the discrete method. It is right and left asymmetry, but does not understand it only for the feeling that I heard closely.

　When there was a logic, the separation improvement of the corner was mainly seen. However, unlike the SQ method, which will be described later, because there is a practical separation performance even without logic in the QS system, there is no significant difference due to the presence or absence of logic.

・SQ4ch (symmetric improvement) method

　Without logic, in the standard system, therefore topologically asymmetrical, front center of the sound image will move to the right degree 10. Since have a scheme in consideration of symmetry time, improvement in left-right symmetry was seen. Hardly separating the front and rear, the rear of the sound image is also very unclear, the reproducibility of the sound field can say that very low. In addition, since there is very strong phase relationship between the channels, will not be able to recognize the placement of the instrument by moving slightly the position of the head.

　If the logic is there, dramatic separation improvement before and after the corner was seen. Either forward or backward, the only direction the sound is small is monaural. Compared with QS4ch logic system, sound image will hear it slightly stable. However, the sound source is not a single direction, if that can not be direction discrimination, separation is significantly worse. Placement of the instruments it will not be able to recognize most. Therefore, also be equipped with a logic in SQ method, it will not be able to play properly when it is recorded in the way.

　Symmetrical improvement method can improve localization of the forward and backward. However, it can be seen that the asymmetry between the front and rear of the left and right to increase, it was found that there is a problem. (Since the original asymmetry of the front can be relaxed by the logic) Future, symmetrical improvement scheme will consider in the direction to cancel.

・QS6ch method

　When there is no logic, crosstalk increases with increase of the sound source, the sound field will be narrowed considerably. But was able to get up and down the effect of sound field. (However, separation is better than SQ system) Front and back do not do a reverse aspect reason, normal position of the sound of the bottom.

When there was a logic, the separation improvement of the corner, improvement of the separation of the top and bottom were seen. The sound of the bottom does normal position, too. However, 6ch system discontinuity exists in the space sphere. Lower - +45 degree phase shifter and rear + -90 degree phase shifter is not connected. Therefore, there is a basic problem of noise can not be avoided by the sound that you want to move, and measures must be taken in the future, and challenge was remaining practical..

◎ Future problem, a summary

　By a natural audio and past recording material and compatibility were high, and it was inexpensive, and, by this experiment, a beginning of the many channels reproducing system realization that I could build was seen. I repeat experiments such as the improvement of the circuit, the straight record and want to perform further inspection in future.