CA2067620A1 - Surround-tec j-50 surround sound adapter - Google Patents

Abstract

Abstract SURROUND-TEC Version 92-01 Model J-50 will decode any standard surround sound audio on most any amplifier/receiver without noticeable compromise of sound quality. It uses a complex phase decoding network to extract the phase encoded audio signal. It is clone right at the output of the amplifier that it is connected to.
This unit will extract the surround sound at a low cost and still give many hours of listening pleasure. When properly set up, it will greatly enhance the realism of the sound from Videos, CD's, TV, and Radio programs. This unit is a Dolby(TM) compatible system. It uses a completely different approach to do the job.
This unit uses the principle of passive circuitry to decode surround sound material. And, it does it with good quality results.
The separation quality and distortion of this unit is comparable to most any of the more expensive units. It uses a new approach to obtain the surround channels.
To get the full surround benefit, please take care that the music or material selected is in surround sound.
When used with standard stereo material, this surround adaptor will give the background ambience picked up by the recording studio's microphones during recording.
This adaptor uses a new system of decoding that is much simpler than the standard commercial units sold on the market. The output quality is high in relation to the cost.

Description

Patent Application o~ Inventor: Gerald L. Greenberg for Passive Matrix Surround Sound Decoder Background-Field of Inven-tion This invention relates to the directional informa-tion system, specifically to a system in which a number o~ input signals are encoded for recording or transmission on a medium into two or more channel signals, and where the channel signals are decoded into a number o-f output signals corresponding to the directional information input signals.
The decoder of this invention decodes the channel signals so that the directional e~fects are enhanced, Background-Description of Prior Art The quadraphony system is one which creates an impression of the original program in -full horizontal surround sound. This is e~ected with loudspeakers spaced horizontally around listeners in four locations. Howe~er, in some quadraphonic systems loudspeakers are placed at the four corners o~ the room. In other quadraphonic sys-tems, u~ed by motion picture theaters, loudspeakers are not all placed at the corners.
Instead they may be installed at the le-ft and righ-t front corners o-f the theater9 at -the center of the front stage and dispersed around the back wall of the theater.

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Loudspeakers placed a-t the front le-ft and right corners are still known as the left and right speakers. The ones placed a-t the back are known as the back~round or surround speakers.
In order for the recording played back through the loudspeakers to recreate a realistic impression o~ -the original program, the recordin~ must con-tain the direc-tional information. In some quaclrophonic systems, called the 4-4-4 format, four discrete input channels are actually recorded.
Another approach, the ~ 4 format, uses a matrix encloding of four audio imput channels into two channels, such as -two conventional stereo-recorded channels, which are decoded back to four audio outpu-t audio channels during playback.

The 4-2-4 sound system has limitations. ~,anadian Paten-t 1,~8~,112 -to Dolby Labora-tories Licensing Corporation, U.S.A., discloses that when the four directional audio input signals are transformed into two channel signals by the encoder, some directional information is los-t and it becomes impossible for -the decoder to reproduce signals perfectly identical to the original directional audio input signals.
Then -the cross-talk between adjacent channels and the reproduced sound signal may greatly reduce the directional effect of the quadraphonic system.
There have been other systems i.n the past usin~ quadraphonic systems. One well known one was the true four channel system with no encoding. This system was complex to set up, and cos-tly for most consumers. Encoding the information was also costly and not practical.
There are other decoding systems in the market place Most of them use an active circuitry technology. Since they use active circuits they require a power sllpply, and various powered networking, and amplifier stages. The active units a.l.l add some noise and distortion to the signal, and are extremely costly i~ very good spec.ifications are desired. A
lot of active units in the market place give the consumer a lot of unnecessary options. These extra options generally make the unit more complex -to use, thus confusing the end user.

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Objects and Advantages Accordingly, besides the objects and advantages o-~ the passive decoder described in my patentJ several objec-ts and ad~antages o~ -the present invention are:
The passive decoding technology means o~ this invention does not have pumping, breathing or noise generation, ~hich most active ones have.
~ecause it is passi~e, -the decoder will reproduce -the surround information -to the same quali-ty level by means o~`
the ampli~ier driving it.
True sound listeners do not want to hear the characteristics o~ sounds that are not there. These sound characteristics are genera-ted by some active units, with added Eea-tures, among them church or hall, which do not reproduce the -true information.
The passive decoder will give a very high per~ormance ~or a low cost when compared to active units, which are extremely costly i-E good performance is desired.
My passive decocler does not employ any unnecessary options and still gives the required performance without increased cost.
The passive decoder o-~ this in~ention is simple to connect.
It is connected directly to the left and righ-t ou-tput o~ a standarcl stereo amplifier or receiver. The main stereo speakers remain connected to -their normal position. The input of the passive decoder connects in parallel to the stereo speakers.
The output means oE the clecoder drives the background (rear) xpeakers. Since the frequency response oE the surround information is limited, small efficient good quality speakers are only required. They need not be full si~e speakers like the ones used in -the front main skereo channels. The signal means leaving the decoder will contain the surround content means extrac-tecl ~rom the main output means signal.

~' :: :. : -Summary Of The Invention The decoder o~ this invention decodes at least two channel signals in a directional inforMation system means where a-t least four inpu-t systems means containing directional information have been encoded into the two or more channel signals.
The decoder includes a first means for generating a-t least a firs-t dominance signal means indicative of the logari-thm of the ratio of the amplitudes of -the sum of and the difference between left and ri~ht channel signals, whether the ampli-tude of one signal dominates the other.
The second generation means detects, as between two signals, one being equal to khe sum O-r the pair of channel signals, and the other being equal to the difference between them, whether the amplitude of one signal dominates the other.
In the passi~e surround sound decoder of this invention, a low pass ~ilter means is required -to -fil-ter ou-t high frequency summed signals. The rolloff rate means required is 5 Db per octive at 7 kHz. This filter means fil-ters out high frequency noise and dis-tortion.
By means of extracting the sunl of -the difference between -the left and right channels con-tai.ning the information, you are le-f-t with the background channels.
The total background information means is obtained according to the following equation:
Bkg - ((R-L)-~(L-R)) An internal phase delay means is required to give the spatial effect. This passive decoder accomplishes the effec-t by using the inductive reactance means of the speakers connected to the outpu-t means of this device.
Since -there are two speakers connec-ted to the output of this device ~rear left and right) each one containing a coil, the reactance means of the coils may be used as a delay line means to produce a phase delay.
The average speaker coil has the e~uivalent of approximately 1.3 mH (.0013 Henery). When used with the proper R C
(resistor capacitor~ network means, a phase delay means may be accomplished.

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Drawing Figures In the drawings, the embodiments of the invention have block numbers, and different alphabetic letters.
Fig. 1 is a block diagram of the embodiment of the decoder.
Fig. 2 is a circuit diagram of the embodiment of the decoder.

Reference Block numerals in Figure 1 Dr~wings:

Functions Of Surround Adaptor Block 10 and 11 is the spirious harmonic filter circui-t.
Block 12 and 14 is the rolloff filter circuit (-5Db @ 7Khz).
Block 13 is the speaker load coupler, and forms part of -the phase shift network for the output.
Block 15 and 16 are the speakers required and supplied by the end user.

Reference Letters in Figure 2 Drawings:

C1, C4 shows 4.7 uF / 50 Volts (non polarized~.
C2, C3 shows .0039 uF / 250 Volts (non polarized).
R1 shows 1.1 ohm / 5 Watts.

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. , Description-Figs 1 to 2 The circuit consists of 2 identical sides. ~ach side -takes its signal from the left and righ-t output of the amplifier.
One side processes from the left while the other from the right.
There is a (+) and (-) re-ference input on each side of the circuit. The (+) and ~-~ refers to the polarity of the re~uired input signal. The polarity of the incoming signal is important Eor the operation of the circuit to extract the phase di-fference between the two signals.
In re-ference to the input of the said device (passive surround sound decoder~ the (~) side o~ both the right and left inp~t is connected directly to the cutput of the said device. The (-) side is connected to the output of the said decoder through a small capacitor C2 and C3 on each side respectivly. This capacitor is to attinuate ~cancel) high frequency oscillations, and degenerate high frequency harmonics.
The two rear speakers connected to the said decoder, are connected in series through R1. The (+) phase of each speaker is connected to the (~) output o-f the said decoder.
The resistor Rl serves as a load coupler to limit the current flow from the unit.
Across each speaker, is a capacitor C1 and C4. These capacitors in series with R1 act as a low-pass fil-ter for the speakers. The average rolloff given from this fil-ter is about -5 Db at 7000 Hz.
The combination of the inductance of the speaker coils in series with R1, and the capacitors C1 and C4 in paralle]~
also give the required phase delay to give some spacial effect in the sound. The inductive reactance of each speaker coil acts as a simple delay line for the opposite speaker in series with it. The resul-tan-t accustical delay is about 7 to 10 msec even -though electrically it is very small. This has to do with the ballistics of the speaker cone when driven wi-th -the circuit in the said surround sound decoder.

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,: : ~ : . , - , The combination of Cl, R1, C4, and the speakers act as the required rolloff fil-ter and phase shift delay circuit. The phase shif-t delay assists in creating the diamen-tional effect to enhance -the surround sound.
Mos-t speakers are rated ~ and 8 ohms. There are some at 6 ohms. Therefore, to compromise differences the circuit here has been optimized for 6 ohms. There is barely any audible difference when 4, ~, or ~ ohm speakers are used.

In re~erence to Cl, Rl, C4, and the speakers:
Rl is in series with Cl and C4. ~he speakers are in parallel to C1 and C4. This eorms an R, L, and C net~ork.
A-t 7000 Hz the impedance of Cl and C4 is 4.8 ohms~
Ef~ectively, C1 and C4, being in parallel to the speaker, act as a rollof-f ~ilter, and as the input -frequency increases so does the reactance of C1 and C4.
The reac-tance of the capacitor may be expressed as;
Xc = 1/(6.28 * F * C) Where Xc is the reactance (Z), 6.28 is Pie constant, and C
is the capacance in micro-Farids.
Therefore, the combination o~ Cl and C4 in parallel to each speaker acts as a rolloff filter. Rl is of a high enough resistance to not allow the rol:Loff effect to go back to the amplifier, and ~1 also acts as part of the phase shift delay circuit with -these components. The main output Or -the amplifier is also not effected due to its internal source resistance ~ein~ extremely low (usually less than 0.2 ohms).
The total reactance of each network, consisting ot` C1, or C4, and its associated speaker, is about 5.3 ohms at 700 Hz.
At 700 Hz the phase delay is about 78 Degrees in reference to the input signal.
The phase delay is expressed as;
ATN (y/x) ATN is the ArcTangent, y is the reac-tance (Z), and x is the fixed resistance.
The phase delay of each side is calculated b~ taking the ArcTangent of -the total reactance of C1, or C4, and its associated speaker, divided by the the value of Rl.

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Claims

SUBSTITUTE
REMPLACEMENT
SECTION is not Present Cette Section est Absente