THE SOUND ENGINEERING MAGAZINE NOVEMBER 1972 S1.00 Built better. Performs longer. Casts less. Wire windings are OUT, conductive plastic is IN for Series 300 is offered in 6 different stroke lengths and high performance audio controls. With its new Series features longer life of 10 million traverses minimum, 300 SLIDELINETM, Duncan Electronics replaces noisy, infinite resolution and linear, audio and constant im- rough and "grainy" wire elements with smooth, noise- pedance outputs for every audio need! f ree RESOLON® conductive plastic which actually improves with use! Dual channels can be contained in a standard single housing only 1M6" wide the most compact dual at- RESOLON elements and precious metal wipers used - tenuator available to the industry. Two dual units can in all Series 300 controls bring consistent low -noise be coupled and driven by a common knob to create operation and superior performance to linear motion 4 channels for master controls or quadrasonics. faders for broadcast and recording. And, the cost is less than many high grade wirewound controls of For complete specifications, call or write for our FREE the past! Duncan Seriesbrochure. 300 A sound ide FG. gS 4d czttz. gS sign and rï cticiti'aie Rita S' few Vastly improved performance. F Resolon element as the '_ professional grade Series 300. This re- sults in far lower noise, longer life (5 million strokes minimum), in- finite resolution ti and smoother "feel." DUNCAN ELECTRONIC f DONNE 2865 Fairview Road Costa Mesa, California 92626 Phone: (714) 5458261 TWX 910-595-1128 Circle 10 on Reader Service Card COMING NEXT MONTH THE SOUND ENGINEERING MAGAZINE NOVEMBER 1972 VOLUME 6. NUMBER 10 David Robinson, the noted British engineer, appears in our pages for the first time with a construction article on A STEREO PHASE INDICATOR. He 22 INTERFACING A DOLBY SYSTEM describes the circuitry required to cre- John Woram ate the proper integration of signals and thus prevent random meter wav- ing. The unit is easy to build and a 26 ON THE BUSINESS OF HEARING very useful instrument. Marshall King Each summer, the Stratford Festival in Stratford, Ontario creates Shake- spearean productions in the classical 30 AUTOMATING THE AUDIO CONTROL manner. An intricate sound distribu- FUNCTION, part 4 tion system has been created for the Walter Jung theater by its Technical Director, Rob- ert Scales. In this article, he details the uses of multichannel techniques in the quest of the classical theater. Part 2 of Marshall King's provoca- tive essay on hearing and listening as practiced by the audio professional. A 2 THE AUDIO ENGINEER'S HANDBOOK stimulating discussion of the thing, George Alexandrovich we take for granted. db Visits-SCULLY. Our camera poked its lens into Scully's shiny, new 6 THEORY AND PRACTICE plant in Northern California and saw Norman H. Crowhurst their new faciilties for making multi- channel tape recorders. If you knew the old plant, you will note quite a 10 SOUND WITH IMAGES difference. Martin Dickstein 18 NEW PRODUCTS AND SERVICES 36 BOOKCASE advertisers 37 CLASSIFIED index 38 PEOPLE, PLACES, HAPPENINGS AKG 7 Altec 11 Auditronics 17 Custom Fidelity 15 db is listed in Current Contents: Engineering and Technology, DBX 14 Duncan Electronics . Cover 2 Robert Bach Larry Zide Electro -Voice Cover 4 PUBLISHER EDITOR Fairchild Sound 19, 20 Bob Laurie John Woram Gately Electronics 18, 28 ART DIRECTOR ASSOCIATE EDITOR Gotham Audio 4 A. F. Gordon Marilyn Gold Infonics 12 CIRCULATION MANAGER COPY EDITOR Miller- 17 Stephenson Eloise Beach Richard L. Lerner ReVox Facing Cover 2 ASST. CIRCULATION MGR. ASSISTANT EDITOR Shure 3 Sony Corporation 5 GRAPHICS Crescent Art Service Tascam 6, 13 db, the Sound Engineering Magazine is published monthly by Sagamore Publishing Company. Inc. Entire Telex 8 contents copyright © 1972 by Sagamore Publishing Co.. Inc.. 980 Old Country Road. Plainview, L.I., N.Y. 11803. Telephone (516) 433 6530. db is published for those individuals and firms in professional audio - Timekeeper Cover 3 recording. broadcast. audio -visual. sound reinforcement. consultants, video recording, film sound, etc. Appli- cation should be made on the subscription form in the rear of each issue. Subscriptions are 56.00 per year UREI 14 (57.00 per year outside U. S. Possessions. Canada. and Mexico) in U. S. funds. Single copies are 51.00 each. Controlled Circulation postage paid at Harrisburg, Pa. 17105. Editorial, Publishing. and Sales Offices: Windjammer 16 980 Old Country Road, Plainview, New York 11803. Postmaster: Form 3579 should be sent to above address. George Alexandrovich THE AUDIO ENGINEER'S HANDBOOK 0 THE SOUND ENGINEERING MAGAZINE SALES OFFICES New York 980 Old Country Road Plainview, N.Y. 11803 516- 433 -6530 Dallas Roy McDonald Associates, Inc. Semmons Tower West Suite 714 Dallas, Texas 75207 More on the Subject of Pads 214- 637 -2444 A couple of months ago you may tween the two is only in splitting the have read my column about resistive R1 resistor into two legs of the bal- pads. When you read it it was al- anced H pad. In calculating a bal- ready a couple of months old be- anced pad one should first find the Denver cause publishers need time to put an value for RI an Roy McDonald Associates, Inc. for unbalanced pad 846 Lincoln Street issue together and print it. Reaction and then divide it into two. One Denver, Colorado 80203 from readers usually comes month or important condition for using this 303 -825 -3325 so after the issue appears. If I wish method is to have Rs equal Rt. to reply or print your ideas another Next we have a graph which was two months go by before you can calculated for a 600 -ohm circuit, but read it. With these delays understood, using arithmetic you can convert it I'd like to share with you the efforts to any other impedance. FIGURE 2 of audio engineer John W. Wood shows the graph. One coordinate (Y) Houston from Valdosta, Georgia who sent me is calibrated in decibels of loss or at- Roy McDonald Associates, Inc. an interesting letter about how he fig- tenuation. The other (X) is repre- 3130 Southwest Freeway Houston, Texas 77006 ures pads. In his letter he expressed senting the values of common -point 713 -529-6711 the hope that other readers may bene- impedance. Common -point impedance fit from considering his method. I is a resistance measured in the pad thought that it was a fine idea since shown in FIGURE 1 (A) across the a reason for having a magazine is to resistor R2. This reading of common - share with others your experiences point resistance combines not only and your knowledge, as well as learn- the resistance of R2 but also the ef- Los Angeles ing from the others. fects of all other impedances such as Roy McDonald Associates, Inc. John's method consists of using a 1313 West 8th Street graph which he precalculated and COMMON POINT (CP) Los Angeles, California 90018 483 plotted for symmetrical T or H pads. IMPEDANCE (OR RESISTANCE) 213- -1304 Symmetrical means that source and load impedances are equal. This hap- pens most of the times in balanced I R vR Rs RL lines where transformers are used. 1 SOURCE R2 And the place where transformers are LOAD S< Portland found is on the inputs and outputs of i ( I Roy McDonald Associates, Inc. systems as well as in the patch bays. 2305 S. W. 58th Avenue Since all inputs and outputs often ap- (A) Portland, Oregon 97221 pear on the jack bay we can relate this 503 -292 -8521 method to equalizing levels in the Rin Rii2 patch system so that all points of the system selected for easy access have Rs RL the same levels. Let's look at the method of using RI/2 RI/2 the graph. Look at FIGURE 1 which San Francisco shows the pads (A) and (B). (A) is (B) Roy McDonald Associates, Inc an unbalanced pad and (B) is bal- 625 Market Street Figure 1. At (A) an unbalanced pad; San Francisco, California 94105 w anced. Note that the difference be- at (B) balanced. 415- 397 -5377 it 7, on record... Now it's official! An association equipment survey quoted in BM /E magazine produced some very revealing information on FM broadcast industry pre- ferences - particularly in the category of phono cartridge usage, where a whopping 57% of the respondents expressed their preference for Shure cartridges ... more than all other brands combined. It didn't particularly surprise us because we know our M44 series with its uncommon combination of clear sound, low cost, exceptional ruggedness and excellent back -cuing characteristics, has been the broadcast standard for years. And our peerless V -15 Type lI Improved? There simply isn't a better cartridge for "high fidelity" FM operations. Write for the free Shure "Guide to the Conversion of Mono- phonic Broadcast Facilities for Stereo Records," as well as the complete Shure Phono Cartridge Catalog. Shure Brothers Inc. r 1--1 1=t 222 Hartrey Ave., Evanston, III. 60204 S V Circle 11 on Reader Service Card 25 Since to begin with you knew what age across the output terminals goes the attenuation will be and you have up. This is accomplished simply by calculated the values of Rl and R2, the p.c. layout or otherwords how a pad can now be built. If the pad and where you connect the feedback has to be an H pad divide the value conductor. But this is a subject for 5 of R1 by two and you have all the another time. In the mean time you resistor values you ought to know for have to use other methods to calcu- o 600 500 400 30C 200 100 a balanced pad.