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Blesser: Can PPM Really Detect All Audio?

Engineering observer poses questions about Arbitron’s technology

Dr. Barry Blesser, director of engineering for equipment maker 25-Seven Systems, has raised a few questions about the Arbitron Portable People Meter and its inner workings in a white paper, “Technical Properties of Arbitron’s PPM System.”

Proceeding on the assumption that stations using the system should know more about it, Blesser (a columnist for Radio World Engineering Extra, which is not involved in the research) said he studied publicly available documents and wonders if Arbitron at some point lowered the energy of the so-called “watermarking” system in response to complaints from broadcasters that the encoding was audible in certain circumstances.

The former MIT engineer also questions how real-world situations affect the meter’s ability to detect audio in cases of “environmental obstacles” that might muffle the sounds. “High-frequency content may also be blocked and absorbed if the listener has attached the portable PPM monitor to his or her clothing in a way that it faces the upholstery of a plush chair or if the listener has placed the device in a purse or backpack.”

We’ve reported that Arbitron says the meter can detect audio while in a purse or a pocket. The company did not immediately respond to a request for comment from RW.

25-Seven Systems makes profanity delay and audio time management systems. It had received questions from stations regarding whether its products could interfere with the PPM encoding process. The company is certain they do not, according to a spokesman; but to be sure, Blesser dug into the PPM system. The manufacturer has no desire to make PPM encoders/decoders itself, said the spokesman.

Blesser also wrote in the paper that his “examination of the PPM system is purely speculative, based on patent disclosures and anecdotal reports distributed in radio industry publications.” He encouraged Arbitron to release more technical information about PPM.

Related story:
Forr Helps PPM Encode Each Signal,” March 2009