Audio Engineering & Production
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Audio Engineering & Production FMX Broadcasting without overmodulation," Orban explains. The Optimod FMX generator is a standalonestereo generator with an FMX compressor that is designed to plug directly into Orban's FM processing and is opti- mized for the Optimod-FM 8100 and older 8000 models. But Orban says it can also be interfaced to other manufacturers' processing as long as there's an effective low- pass filter and peak limiting. Orban is continuing to test the system to see how it works in the presence of processing and to de- termine any multipath problems that might exist. A product will be available late this year or early Figure 4: "A" is the normal stereo subcarrier, "B" is the same L- R information next year, with pricing in the with the 20 dB FMX gain and flattop compression characteristic. Subtracting "A" $3000 range. from "B" results in "C," which modulates the FMX subcarrier in the CBS design. Aphex is also interested in mar- Inovonics' feedforward pulse -width modulation results in "D," a softer com- keting an FMX product. The com- pression curve. pany was contemplating entering pressed FMX signal is 20 dB, but itable FMX thatwillhave the FM stereo generator field and will be up to individual manufac-selectable preemphasis and 15 decided after researching the mar- turers to determine the time con- kHz low-pass filters to be compati- ket that any new offering should stants of the compression and theble with other manufacturers' pro- be prepared for the future by final shape of the re-entrant char-cessing. CRL anticipates that an incorporating the FMX system. acteristic curve. It will also be upFMX product could be introduced "We felt that in order to be high to them to determine how theat next year's NAB. performance we had to offer FMX. FMX system will be integrated One of the things CRL will be It will be an option to our FM with processing that they mightlooking at is the problem of stereo generator," says Marvin include in their FM generator. overmodulation caused by peaks. Ceasar, president. He says there One other issue that has arisenChanging the compression thresh- will be a product available later is how to deal with actual programold is a solution. this year that will be priced about material that has peaks causing Orban's Optimod FMX model $2000 without FMX, $3000 with overmodulation when the S and S' 8150A is still in the development it. amplitude levels together exceedstage, and Bob Orban stresses that Ceasar says that the develop- 100 percent. Possible solutions in-more field tests are needed to see ment of two previous Aphex prod- clude baseband clipping, or peakhow the system reacts to the use ofucts,the Compellor and limiting, or altering the compres- processing. Dominator, helped pave the way sion characteristic in some way. One of Orban's concerns was for the type of companding noise Circuit Research Labs helped inthat the addition of the FMX sig- reduction system used in FMX. CBS's development of the FMXnal in the original CBS prototype Aphex will not incorporate any ad- prototype by providing a digitallyresults in overmodulation, as high ditional processing other than the synthesized S' channel. The com- as 126 percent with some program companding intoits FMX pany is currently analyzing testmaterial. That would mean that generator. data collected from a PCM record-overall modulation would need to The problem of potential ing on a Delco 2000 in the field un- be reduced to avoid such problems overmodulation resulting from der medium multipath conditions. where they exist. But Orban ad- program material will be solved It will be these test results that de- dresses the problem by makingthrough peak limiting, not the termine if CRL does go forth onthe knee threshold (start of re- baseband clipping the CBS FMX product development. entrant curve) and the compres- prototype uses. Aphex is planning "We announced that we would sion -ratio -re-entrant part of thea product with low distortion and go into FMX if there were no com- curve program -dependent. high separation, and it will be patibility problems and if it would "It looks at the relationship be- watching the receiver market to benefit broadcasters," says Ron tween sum and difference signals, see whether FMX will catch on. Jones, chairman of the board. both their phase and amplitude, A slightly different approach to If CRL does go forth with FMX, and decides how large the Q chan- FMX is represented in a design by Jones says, the product will be an nel (FMX signal) can be to achieve Inovonics, Inc. President Jim FM stereo generator with switch -the maximum noise reduction Wood says the company became 52 BM/E SEPTEMBER 1986.