Home　Japanese

◎ 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

　QS4ch method, an SQ4ch method, a QS6ch method, each encode / decode expression are as follows.

　・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 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 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　： 　In the front, in the addition, the rear, as for the subtraction and the backward channel, it is +90 degrees, -90 degrees phase shifting with 1/ √ 2 (0.414) according to the standard each.

・SQ4ch method　： 　The phase becomes the asymmetry when I decode it according to the standard. 　The backward channel operates it between -45 degrees and +45 degrees not 0 degrees and 90 degrees to prevent this.　

・QS6ch method　： 　The all around channel is a QS4ch method. 　A top and bottom channel is a backward channel of the SQ4ch method.

・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 LED the band pass of two signals (sorted it); after logarithm conversion, both waves rectification for a difference of both. （In addition, it is recommended a diode（several series）than LED with a little unevenness）　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）

In addition, the applied voltage of FET of the VCR element prevents distorted increase by less than 1Vp-p, the source voltage return to the gate voltage.

◎ 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 SQ4ch method to mention later, there is not the big difference by the logic presence so that originally there is some selectivity.

　・SQ4ch (symmetric improvement) method

　By a case without the logic, the standard method, right and left asymmetry reason, the sound image of the front center moved to the around 10 degrees right side topologically, but improvement of the symmetricalness of right and left was seen because I did it with the method that considered a symmetry this time.　 However, the front and back most do not divide it, and the backward sound image is very indistinct, too, and the plasticity of the sound field is bad at allIn addition, I become normal position lack of foresight when phase relations between the channel strongly move some positions of the head. When there was a logic, the dramatic separation improvement of the corner was thought to be front and back. 　Because small volume becomes monaural, in front and back, I hear the sound image is more stable than the QS4ch logic method that mentioned above. But the separation of the sound turns worse very much when there is a sound source in plural courses.

　・QS6ch method

　Crosstalk increases by a case without the logic, the increase of the sound source (but the separation is better than the SQ4ch method), and the sound field becomes considerably small. 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.

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.