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With the development of 4-channel stereo we are able to reproduce a full musical and acoustic experience in a living room for the first time. Effective 4-channel also allows production of acoustic experiences that are not possible with a live concert.

Sansui QS is a practical 4-channel matrix (4-2-4) system. It requires no special transmission, but utilizes current techniques of 2-channel stereo broadcast and is compatible with conventional stereo equipment.

Today, QS with the vario-matrix circuit in the decoder section has reached a new plateau of performance as the many recording engineers who are using it agree. It is one of the most effective 4-channel systems available today.

Sansui's professional encoder/decoder combination, the QSE4/QSD4 is quickly finding its way into recording studios and is part of a continuing cycle of increased sales for both professional and home 4-channel hardware and QS matrix-encoded records.

As more records are produced, more home equipment to play them is bought and more companies want to produce QS discs for the growing market. As you probably know, the cycle continues and accelerates as more FM broadcasters employ QS systems.

This, too, produces an increase in home demand and home units.
This guide has been prepared with you, the recording engineer, in mind to help you utilize the new techniques and freedom that the QS system offers. We trust it will be useful and informative.
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The rich emotional involvement we experience at live musical performances is a result of the sum of many factors. But strictly musically speaking, it is obvious that the melody is not the only important ingredient. The infinite combinations of direct and indirect sounds, creating innumerable harmonics, are also vital.

Four-channel has made it possible to recreate the beautiful effect of these direct and indirect sounds from appropriate speakers. In short, it brings reproduced sound one giant step closer to the original, live music. But that is not all, for it also opens up a whole new dimension in music listening enjoyment.

Now, let us probe into the pleasures, theories and principles of 4-channel sound.
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4-Channel Reproduces Concert Rail Sounds More Realistically

A large part of classical music, jazz and popular music is played by orchestras and bands in large concert halls. When we listen to recordings of such, music through stereo systems, we should feel as if we are seated right in the concert hall.

With a 4-channel system in the concert hall mode, the indirect sounds and reverberation filling the hall are picked up by specially-located microphones and reproduced out of the rear loudspeakers.

These microphones collect the sounds of the stirring of the audience and their applause as well. So when they are reproduced in your room, you get a very intense, true feeling of being at the concert, seated front and center in the hall.

Recording techniques for the front channels remain much the same as for conventional stereo recordings.
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"4-Channel Allows Creative "Use of the Musical Space around Us."

Music isn't always something to appreciate quietly and objectively, gazing at an imaginary stage reproduced by the loudspeakers in front of you.

When we listen to popular music such as jazz, rock, R and B, and so on, we often wish we could be with the musicians, playing with them and sharing their emotions.

The surround effect made possible by 4-channel is a new art of sound reproduction that puts you on the stage among the performing musicians by arranging them all around you. It has been said many times that once you hear rock music in surround stereo, you can't go back to 2-channel stereo.

Aside from popular music, the creative surround-effect of 4-channel has infinite possibilities for church music, operas, modern electronic music and so forth. It is something entirely beyond the conventionalism of ordinary stereo, and is certain to find different applications in various fields of music.
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When played in a church or cathedral, pipe organs produce solemn, majestic tones as they reverberate for prolonged periods of time (4- to 8 seconds) through the high-ceilinged spaces. In 4-channel, such reverberation can be made to flow from front to back in the listener's room, creating a spacious acoustic environment.

A small room can instantly be turned into a historic cathedral or a huge temple, filled with the music and majestic atmosphere typical of such a structure. Experience a new world of musical enjoyment via 4-channel.
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Composers and recording engineers have cooperated in the past to create new music in stereo and mono. These media have limitations, however, resulting from their artificiality. But now, 4-channel makes true dimensional sound reproduction possible.

It allows the recording engineer, for example, to locate a sound in the front, back, on the left, or right, or anywhere in the middle.

Suddenly, there is an almost limitless dimensional area for musical creativity which musicians are exploring eagerly.
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4-channel not only makes the directionality of each sound source more distinct, it also improves the quality of reproduced sound - even when the sound source is a single instrument, such as a piano.

This is largely because 4-channel makes fully-dimensional playback possible. All the traditional improvements in the electrical and physical properties of reproduced sound are retained, but now, the merging of direct and indirect sounds in the air measurably enhances sound quality.

For example, if a single pulse-like note were reproduced out of multiple speakers with certain time lags, it would hit the listener's ears with a greater dynamic range than if it were radiated from a single speaker.
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The QS system was conceived in 1969 at Sansui's Tokyo development laboratories. It was originally thought to be a system for stereo enhancement, which took advantage of what had hitherto been regarded as the main problem of stereo disc recording -- out-of-phase.

By means of phase detector circuits, signals may be positioned at any point of the compass at will. Although the famous master patent of A.D. Blumlein *1) which was issued in 1931, spelled out the fundamentals upon which the QS system is based, Sansui was the first to investigate these phenomena and apply them in this new form.

Bearing in mind that QS was intended to enhance stereophonic recordings, we should perhaps review some basic criteria. In a standard stereo record we find that those signals intended to appear directly between the loundspeakers are recorded laterally; those on the left are on the inside side-wall, and those on the right on the outside side-wall. (Figure 1).

Looking at it another way, we could say that taking the lateral signal to have an angle of 0° , the left channel is at +45° and the right channel is at -45° (all angles measured counterclockwise from the record surface).

In other words, going from one side to the other we traverse an angle of 90°.

A. D. Blumlein described fully the technique of matrixing in what has become known as the MS system. (Mehr darüber steht auf Jörg Wuttkes Mikrofonseiten.) Much work was also done on this system in the middle 1950s, particularly in Europe.

Two important contributors were G. Lauridsen *2) and K. Bertram *3). A.K.G., Neumann, Schoeps and others have built coincident microphones to work with this system.

It is the writer's view that there will be a revival of interest in the MS system, since it lends itself very well to multiple channel recording. In one of its forms, a pair of crossed figure-eight microphones is used. (Figure 2).
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Without dwelling upon the details of the MS system, it must be realized that due to the phase relationship between the capsules, an instrument placed behind the microphone would give an electrical input in reverse phase to a signal originating at the front. To return to Figure 1, this would become a vertical excursion in the record.

D. Hafler *4) proposed a simple loudspeaker resistor matrix, which put these signals in the back of the room. (Figure 3). D. Cooper *5) et. al., proposed similar, if somewhat more sophisticated, systems.

In May, 1970, Sansui placed its Model QS-1 on the market. This model fulfilled the original design concepts of enhancing stereo recording by spreading the sounds around the room as a function of phase.

It was not surprising that having taken this forward step away from the 2-channel concept, interest quickly arose to produce a deliberate form of 4-channel recording.

In March, 1970, P. Scheiber *6) demonstrated his 4-channel recording system to the A.E.S. in New York at the studios of RCA.

This demonstration clearly showed the possibilities that lay ahead in working with this medium. But it also showed up its weak points.

There was insufficient separation between channels, and one really could not differentiate front and back sounds.

The original systems of Cooper and Sansui suffered from similar defects. However, it was Sansui who solved both these problems.

They introduced the phase shift network at the N.A.F.M.B. in Chicago in April, 1971. This gave clear distinction between front and back. In March, 1972, at the European A.E.S. in Munich, they introduced the variable matrix system.

This was further elaborated upon and was demonstrated in its present form at the A.E. S. in New York in September, 1972. The variable matrix was really the most important development in the field, since it gave sufficient separation (20 dB between all channels) to make the system usable as a practical tool, without reservations, for all recordings.

Equally important are the compatibility with stereo (i.e. 4-channel recordings give, in many cases, superior stereo reproduction) and the ease of production on existing equipment. Indeed, the only special equipment that has to be purchased by the recordist is the QS encoder.

The presently-available carrier disc system is capable, theoretically, of giving infinite separation between channels, and in this respect can claim an advantage over the matrix systems.

It does add the channels together well for stereo and mono playback, but this too is not without its problems, since direct summing can create a very unmusical result.

• Anmerkung : Das sogenannte "direct summing" bezeichnen wir als Auslöschungen.

In practice at the present time the separation across the left and the right is generally considered to be only marginally better than the QS system, and the separation between the front and the back is not quite as good.

Furthermore, the level, frequency response, dynamic range, and signal-to-noise ratio are somewhat below the standards attainable with present-day stereophonic systems.

• Anmerkung : Die SANSUI Ingenieure hatten bei CD-4 sofort die Schwächen mit den flachen 13kHz Tiefpassfiltern in den Frontkanälen gesehen

Also, much of the playback equipment in the field will not cope adequately with this system. It is possible that it could find an important position at some time in the future.
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(Das sind SANSUI's eigene Lobeshymnen, die eigenen Schwächen vergessend !!)

The exciting development of the Sansui QS vario-matrix circuitry, which has not yet been fully exploited, may well render these more sophisticated techniques unnecessary.

In conclusion, it will be realized that there is no "perfect" system, but that the Sansui QS system does offer the greatest number of practical and economical advantages with the least number of disadvantages.

It should be noted that the term QS is being taken to mean the "regular matrix" system employing the Sansui "variable matrix" (QS vario-matrix).

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• 1. A.D. Blumlein, E.M.I. Ltd., British Patent 394-,325, et. al.
• 2. G. Lauridsen, The Danish State Radio.
• 3. K. Bertram, German Patent No. 1077710.
• 4. D. Hafler, formerly with Dynaco, U . S . A.
• 5. Dr. D. H. Cooper, University of Illinois. U.S.A.
• 6. P. Scheiber, U.S. Patent No. 3,632,88b.

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** Chapter II, III, IV and V have been written by Mr. John Mosely, Ferber Studios, Paris, France.
*"* In December, 1973, the Record Industry Association of America (RIAA) approved QS as "Type 2 Matrix Encoded 2 Signal Disc Record" standard.
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• 1. Stores Information in 2-Channel Media.
  QS permits use of conventional 2-channel media to store and transmit all information necessary for 4-channel playback. Current stereo transmitters /receivers, cutting equipment and other related hardware can continue to be used. FM stations in any country can broadcast QS-encoded 4-channel material without infringing in any way upon the present FCC or other government-pre scribed radio regulations.
• 2. Inter-Channel Separation of 20dB or More.
  QS employs a circumferentially uniform construction, and its encoding and decoding matrices are both rotationally symmetrical. Because of this and the new QS vario-matrix in the QS Decoder, it offers inter-channel separation of 20dB or more, without using the gain control method. If desired, greater separation can be obtained by altering the matrix coefficient.
• 3. Outstanding "Surround"1 Effects.
  The QS system's circumferentially uniform construction treats equally all signals originated anywhere in the 360 degrees of the original sound field. This enables the recording engineer to locate a sound source at any desired position.
• 4. Does Not Deteriorate Current High Fidelity Standards.
  Since QS does not alter current stereo recording and playback systems themselves, it does not degrade current standards of high fidelity sound reproduction, including the dynamic range, frequency response, signal level and distortion.
• 5. No Loss or Mislocation of Input Information through Encode/ Decode Process.
  Utilizing a unique phase-shift technique, the QS preserves the quality as well as the quantity of the input information throughout its entire encode-decode process.
• 6. QS-Encoded Sources Provide Better Stereo Perspective in z-Channel Playback than Conventional 2-Channel Sources, "
  In 2-channel playback, all signals to the front of LC and RC are located between the two speakers, while those to their back are reproduced outside of the two speakers serving to enhance the sense of stereo perspective. Moreover, such back information is distributed completely symmetrically to the left and right.
• 7. No Special Conditions Required for Recording or Playback.
  Thanks to the !Blend Out1 circuit, the QS Encoder does not place any limitation on the kind of program source to be encoded or the mixing technique to be utilized.
  QS-encoded sources are compatible with popular matrix decoders now on the market.
  Of course the conventional stereo phono cartridge, turntable, tape machines, etc. can remain unchanged.

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Since it is still considered more difficult to make a stereophonic recording than a monophonic recording, it seems a little surprising that many people appear to anticipate no problems whatsoever in working with four channels. In the writer's experience, it seems imperative to decide upon the specifications that the recording must meet, and then consider the problems most carefully, and finally work out the best solution.

For example, does one wish to attain compatibility between the 4-channel product and, say, a conventional stereo record ? Does one wish to be able to reproduce such a record monophonically ? Is the product to be directed at a few choice people (as was the case in some early stereo recordings) ? What are the requirements of frequency response, dynamic range, playing time, and noise ? What is meant by 4-channel recording ? Does it mean that one simply adds ambience to a conventional stereophonic presentation, or does it imply full use of the entire sound field created within and around the channels ?

Clearly these questions and a host of others have to be answered before one is able to set about making satisfactory recordings. The following information should be useful to musicians, producers and engineers, and give an insight into the general 4-channel position to people who work on the periphery of the subject.
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Perhaps compatibility is the most serious question that has to be faced. At the time of writing, it can be clearly stated that 4-channel recordings are here to stay, whatever form they may take.

Therefore, we believe that it is reasonable to suppose that 4-channel records and tapes will ease out (verdrängen) 2-channel records and tapes in much the same way that the 2-channel products eased out (verdrängt hatten) mono some years ago.

If you accept this corollary, then it follows that it is essential that the product must be compatible with existing stereophonic reproducing and recording equipment.

Let us look at the Sansui QS system, which is being used by many companies and labels world-wide. With the exception of back center, where the signal is totally out of phase and produces a split image, as depicted by the dotted lines in the figure below, it will be seen that the sound field is totally symmetrical. Therefore, the subtleties of placement are maintained.

Furthermore, since an equal signal to all four channels is in quadrature (i.e. the channels are at 90 degrees to one another when played in stereo), the cutting level of the center channel on a disc is restricted to +6dB as opposed to 12dB obtained by the discrete system. Therefore, if compatibility is of major importance, the QS system offers the greatest number of advantages.
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It "must" be very clearly understood that all 4-channel systems, and particularly the matrix variety, require far greater linearity and stability phase-wise than do stereophonic recordings.

The reasons for this are clear when one appreciates that the location of a sound is dependent upon its phase angle. Therefore, if one uses a system that does not have phase coherence (Übereinstimmung) with frequency response, one will find that a musical instrument will shift its location, depending upon the particular note that is being played.

Because of this, it is essential before starting to work, to ensure that the entire recording system is checked thoroughly for phase coherence throughout the entire audio spectrum.

The best means of doing this is to use an oscilloscope checking two channels at a time, whereby the one is connected to the X axis and the other to the Y axis. Then an oscillator should be employed and be fed into the channels under test simultaneously.

If the system is linear, a diagonal straight line will appear on the oscilloscope. If there are phase discrepancies, then the straight line will turn into a sausage-shape (or more precisely, form a lissajous pattern).

The most likely place to encounter trouble will be with tape recorders. It has been our experience that only a few types of recorders of the most modern design are sufficiently stable, so as not to give phase shift, and therefore to be usable for 4-channel recording. The performance of the tape machines can be varified in the same way as the remainder of the equipment, i.e. with an oscillator and an oscilloscope.

Needless to say, the monitoring system must also be most carefully checked, to ensure that not only is it in phase, but that it is giving a center signal for an appropriately seated operator. At least in the early days of working with 4-channel systems, it is advisable for the operator to sit in the center of the sound field or, to compensate for the weakness of the human ear, somewhat to the back of the center. Further, it is desirable to use four identical loudspeakers.
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It may be argued that the critics of the QS system complain about the diminishing front image when the 4-channel format is played back in stereo. Let us now consider this matter most carefully.

Those people who have worked with this system (as opposed to those who merely talk about it) have come to the unanimous conclusion that the correct way to work with the QS is detailed below:
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• 1. Starting with a multi-track original, one roughly positions the instruments with any desired treatment - i.e. equalization, limiting, echo, etc. - in their required location in or around the sound field. (At this point, one would be listening to the four main busses).
• 2. Next, listen to the output of the encoder. It may be found that some of the instruments have lost their presence, and others appear at different levels or in unexpected places. There may also be an unpleasant swishing sound. All these effects are due to problems of phase correlation and crosstalk between channels. Let us examine this matter more closely, since with full understanding of the problems, it will be possible to make the very best recordings, and also avoid encountering similar difficulties in the future.

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Ergänzung : Über die Probleme beim Multitracking

(**** Despite the fact that with modern multi-track recording techniques, one tends to give each instrument its own track, one often finds a considerable amount of acoustical crosstalk spilling over from one microphone into another, and hence from one track into another. Therefore, when one goes to make an accurate placement through an encoder, one is liable to find the problems stated above.

Here again the "phase bogey" raises its ugly head. It is necessary, therefore, to cancel out these undesirable effects which may often be done by a slight alteration in level or panning, or in more extreme cases, by altering the frequency response.

Perhaps the best method of correction can be found in the bridge type panning mechanism that was proposed by K. Bertram, which was designed in the 1950s in order to obtain the best possible result with the MS recording technique.

Surprisingly enough, this system too depended very much on accurate inter-channel phase relationships in order to give its best results. In any event, by careful experimentation and gentle manipulation of the controls, one will very rapidly achieve a satisfactory result.

Assuming that one is employing the entire sound field, it will soon be appreciated that, contrary to the criticism of diminishing the sound field, one will find that it has been considerably enhanced, and indeed the back channels appear outside the loudspeakers.

Therefore, one is obtaining a broader spread of sound than one has been accustomed to in conventional stereo recording. It is, of course, normal for the front channels to appear somewhat inside the loudspeakers (unless widening compensation has been applied). Nevertheless, an excellently defined linear presentation of all instruments will be achieved with relative ease. ****)
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• 3. Now go back to the 4-channel input and make certain that one has the desired quadraphonic presentation.

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For certain types of recording, especially symphony orchestras recorded conventionally, (i.e. a stereo presentation in the front channels, with ambience added at the back), it is clearly both undesirable and unacceptable under these conditions to allow the 4-channel frontal presentation to shrink when these reocrds are played back stereophonically.

By reference to the diagram showing the stereo foldover from four channels to two, it will be seen that the center side channels transfer directly into the loud speakers for stereo playback.

It will be found in practice, therefore, that by blending or pan-potting a small amount of the left front or right front signals towards the back, that this image shift can be reduced to insignificant proportion. For this purpose, the QSE-4- encoder has been fitted with left center and right center inputs, so that blending can take place more easily.

Simple experimentation will prove this point, and the engineer will be surprised to find how little blending is necessary, in order to give the widened frontal image. Dependent upon the amount of blend used, the front channels will appear to come slightly forward in 4-channel playback, but this effect has been regarded as a plus factor by people who have used it.

Similarly, if it is desired to alter the back channel perspective, this too can be done by blending or panpotting between the back and center channels. Once again, after making any alteration of this nature, A/B between the 4- and 2- channel modes.
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One of the greatest advantages of the QS system is its symmetry in both 4-channel and 2-channel modes. With the single exception of back center (if a signal placed there is important for mono reproduction), there are no places in or around the sound field that should be avoided or require special attention.

It is highly desirable that all people using the system familiarize themselves with these advantages at the very outset. By simply feeding one audio track to a 4-channel panpot, and listening in the 4-channel, 2-channel and mono modes, one soon learns how the system performs and how easy it is to work with.

Bild vom Multi-Panpot hier .................
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It is anticipated that just as the independent producer of recordings now gives the record company a 2-track master tape, he will probably in the future be presenting a 4-track master tape.

This will, in any event, be necessary for those companies who are duplicating 4-track discrete tapes for sale to the public. Under these circumstances, one may find that the tapes do not encode too well on the basis of a straight transfer. Should this occur, it should only be necessary to make small alterations to levels, frequency response, or panning, as has been suggested previously, in order to produce a satisfactory end product, without any of the undesirable effects discussed herein.

The writer has found that the best method of operation is to prepare a 4-track discrete master at the same time as the 2-track encoded master. In this case, the 4-track recorder is paralleled to the encoder input. By this means, one will then achieve a perfect A/B between the decode of the encoded tape and the 4-track master, thereby making an automatic safety copy.
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It is now necessary to verify that the encoder/decoder and tape machine are working correctly. To this end it is essential to be able to perform a number of A/B functions.

• 1. Performance of the encoder and decoder is verified by A/B-ing between discrete (i.e. the input) and the output of the decoder when coupled to the encoder. One expects, therefore, to hear no change when A/B-ing between "discrete" and "decode/encode".
  If any shifting takes place, again it will almost certainly be due to phasing problems, and the offending track should be isolated and corrected. If any alterations are made, one should re-listen to the encoder output, i.e. 2-channel position, to make certain that nothing has changed.
• 2. With the tape machine running, check first that there is no change of sound between encoder output (i.e. tape machine input) and tape out. Remembering that this is likely to be the weakest link in the chain, you must pay great attention to this point.
• 3. Next, A/B between decode program, i.e. feeding the recorded tape into the decoder, and decode of encoder. Here again there should be no image shift or sound change. If any is found, it will probably be most satisfactory to rewind the 2-track tape and play it in synchronization with the original tape. This way, there will be no time lag, and any differences will be heard more easily.

(**** Clearly, if the decode of the encoder against the original tape gave a satisfactory A/B, and decoding of the 2-track product does not, then the problem must lie in the tape machine. As was mentioned in the introductory remarks, it has been the writer's experience that only the most modern machines emanating from certain manufacturers have been found to be satisfactory. If it is not possible to correct these audible errors by changing from one tape machine that is readily available within the studio to another, it may be necessary to purchase new equipment. If one experiences these difficulties, it would be advisable to check the cutting channel that will be used to transfer the 2-track tapes to disc, to make certain that its tape machine is free from the aforementioned anomalies. ****)
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• 4. It will be realized that, where the entire sound field is employed, monophonic reproduction is likely to suffer in varying degrees, dependent upon the particular recording. Since record companies, at least in the United States, have made special monophonic disc jockey copies since the early days of stereo, it may not be considered necessary to try to produce the "ideal" sound for monophonic reproduction.
  There are two other solutions which will give satisfactory reproduction under most conditions. The QSD-4 in the MONO DOMESTIC position will bridge together the encoder or tape machine outputs, and present the sum of the two channels. It is only necessary to use this position, if it is desired to reproduce the recording in question on older types of monaural domestic replay equipment.
  By A/B-ing between encoder, or tape out, and mono domestic, one will be able to hear how the sound level alters, and decide what changes of balance, etc. need to be made, to be artistically satisfactory.
  This will normally be achieved by slight alterations of levels and panning, as in the case of making the stereo mix-A/B-ing process to ensure that both the resultant stereo and 4-channel mixes are still satisfactory.
• 5. The QSD-4 also contains a "mono broadcast" switch position.
  This places a 90 degree phase shift upon one of the stereo channels before adding it to the other. By this means one will achieve a satisfactory summing of all information contained on tape to within 3dB. It is anticipated that the broadcast stations will have this equipment available to be used on occasions where they consider the mono signal to be of paramount importance.

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Before proceeding with routine production, an encoded tape should be transferred to a lacquer record, fully processed and pressed. The test pressing should then be A/B-ed against the 2-track encoded tape. Similar precautions must be taken in setting up and checking out the record player, as has.been advocated several times previously.

Particular attention needs to be paid to the correctness of the angle of the pickup, (i.e. It must be absolutely perpendicular to the surface of the record.) It is advisable to check the reproducing system into a decoder, using the NAB standard test record. It should be confirmed that the cutting stylus, fed by encoded signals, would move in the manner as described below.
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• 1. The right-hand tone should give an equal signal to right front and right back channels.
• 2. The lateral tone should give an equal signal to left front and right front channels.
• 3. The vertical tone should give an equal signal to left back and right back channels.
• 4. The left channel tone should give an equal signal to left front and left channels.

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Assuming that the reproducing amplifiers have been correctly checked for phase and frequency response, it will probably be found that any discrepancies that are noted will be due to the performance of the particular cartridge. If it is not possible to obtain the correct readings by slight alteration to the angle of the cartridge, it would be advisable to exchange the cartridge for another one.

It should now be possible to perform an accurate A/B of disc to tape through the decoder. If this is satisfactory, then it can be assumed that all equipment is functioning correctly, and one can now proceed with production.

If there are any discrepancies, one should listen in the 2-channel mode to disclose where the differences occur. One may then find it necessary to check systematically through the lacquer channel by A/B-ing a lacquer against the tape.

If this produces a perfect A/B, it may then be assumed that the fault lies somewhere within the factory, probably in electroplating.

Provided one has passed all the checkpoints, one should now be in a position to make excellent compatible quadraphonic and stereophonic recordings employing the surround stereo techniques, via the QS system.
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This check list is intended to be used as a quick guide for people who are familiarizing themselves with the QS regular matrix system. However, before using it, please read the instruction book carefully and make certain that all the equipment is properly aligned.
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• 1. Listening to the discrete input, roughly position the instruments in and around the sound field as required, with such equalizations, etc., as is necessary.
• 2. Listen to the encoder output, making sure that all instruments appear in their required location for stereophonic reproduction, and that there are no signals being lost or producing undesirable effects upon each other.
• 3. Balance very carefully in the encoder out mode and then A/B back to discrete.
• 4. If mono compatibility is desired, then A/B between encoder out and mono (domestic or broadcast as appropriate). Here again make any balance alterations as are necessary, and check between mono encoder out and 4-channel.
• 5. A/B between discrete and decode encoder. This checks the performance of the encoder and decoder.
• 6. With the 2-channel tapemachine running in the record mode, A/B between encoder out and tape out, making certain that there are no audible changes.
• 7. A/B between decode of encoder and decode of program (i.e. the 2-track tape).

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As a matter of principle, you should do your main monitoring and mixing in the mode that is most important. As a practical matter, it will probably be found most satisfactory to work mainly in 2-channel stereo, since the greatest number of customers are liable to be listed in this mode. It seems to be axiomatic that a good compatible encoded stereophonic recording will render excellent 4-channel results.

We have produced a series of QS 4-channel handbooks to cover the whole area of the industry. There are such QS handbooks for:

• (1) general public
• (2) equipment dealers and distributors
• (3) record dealers and distributors
• (4) recording engineers
• (5) FM broadcasters
• (6) electronics engineers

We sincerely hope that reading the above series through will give you comprehensive understanding of the whole concept of what 4-channel is all about.
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