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Genius!2: Bob Orban and improving radio #8

Sarah Sharples 24 October 2016
Genius!2: Bob Orban and improving radio #8

Bob Orban: I believe that I invented two technologies that were equally important to the industry. The first was overshoot-compensated low-pass filters that greatly reduced the peak-to-average ratio of the waveform that was applied to an AM or FM transmitter’s modulator; the second was distortion-canceled clipping.

When I made a prototype of my first FM broadcast audio processor around 1973, I observed that certain audio material (like muted trumpets) caused severe peak over-modulation when applied to what was then a start-of-the-art FM stereo encoder. I brought this up with Belar founder Arno Meyer, who blamed overshooting and ringing in the encoder’s 15kHz low-pass filter. It occurred to me that if I integrated the audio processor and low-pass filter, and if I was able to develop a non-linear low-pass filter that didn’t overshoot while still constraining the spectrum applied to the stereo coder to less than around 17kHz, this would solve the problem and would also significantly increase in on-air loudness without additional compression or peak limiting. I showed a prototype of the combined compressor/limiter/filter to Eric Small, a broadcast consultant for whom I was doing some consulting, and he was impressed by its potential.

Bob O 2Because of stringent (regulatory body) FCC rules regarding type acceptance of transmission equipment, I proposed integrating the stereo encoder with the processor/filter so that existing coders would not have to be modified to bypass their filters. Eric agreed that this was a good idea, and proposed taking over the marketing and promotion of what was to become the Optimod 8000. Because it increased on-air loudness by about 3dB compared to existing air chains, the product was extremely successful, selling over 3,000 units and increasing Orban’s annual sales by an order of magnitude.

The distortion-cancelling clipper can be blamed on the Jefferson Airplane, specifically the song White Rabbit, which had some intense “ess” sounds (“One pill makes you ssssmall…”) In 1977 I was developing my first AM processor (Optimod 9000A), which used a lot of high frequency boost ahead of a clipper that was the main peak controlling element. Because of clipper-induced difference-frequency IM distortion, every “ess” was distorted, sounding more like an “f.” It occurred to me that I could remove the difference frequency IM distortion in the frequency range where typical AM radios are flat (about 0 to 2kHz) by lowpass-filtering just the clipper distortion (derived by subtracting the clipper’s output from its input) and then adding it out-of-phase to the clipper’s output. Before the subtraction, the output had to be delayed to match the delay of the distortion filter. I implemented this idea, fired up Alice, and was immediately blown away by esses that were now very clean-sounding.

Bob O 3Optimod 9000A used a bucket brigade delay line for the delay compensation. The BBD’s noise and distortion characteristics weren’t good enough for FM, so I developed a major refinement to distortion-canceled clipping: using the FM 15kHz low-pass filter (with group delay equalisation) as the delay element in the distortion cancelation. This invention was the heart of Optimod-FM 8100, which was in production for over 10 years, with over 10,000 units sold. The 8100 and its companion “XT2” six-band compressor accessory took Orban FM processing to the beginning of the DSP-based processor era, when our Optimod 8200 became the first commercially successful DSP-based FM transmission processor. We are now up to 8700, and still going strong!

Earlier this year, Orban was acquired by DaySequerra. I continue to head the Orban engineering team within the combined company, and to actively invent and innovate with the goal of continuing our 40+ years of technological leadership in the broadcast industry.

www.orban.com

Pictures: Top: Bob Orban at the whiteboard in 1982. Second: Orban (left) and John Delatoni demo Optimod-AM 9000 Engineering prototype at NAB 1977. Last: Orban in the lab in 2015.

 

Published earlier this year and sponsored by QSC Audio, Genius!2 is the second edition celebrating those clever people whose inventions have transformed the world of professional audio. The 30-page supplement is also available to read in a handy digital-edition form

 

 

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