Technical Properties of the Arbitron PPM System

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I believe that the following general principle is valid: The PPM system is designed to handle specific difficult cases, but a combination of difficult cases is likely to produce failure. A radio station must therefore determine if such combinations exist for any of its programming.

While acknowledging Arbitron's assertions about reliability and respecting its proprietary intellectual property, any radio station can run experiments to measure performance and robustness. The results of such experiments will show whether certain programs in certain listening environments break the technical assumptions upon which the system operates.

Looking Forward

This article was written to frame questions and to explore what is not currently known. When there is more data, the implications will become clearer. At this point, my examination of the PPM system is purely speculative, based on patent disclosures and anecdotal reports distributed in radio industry trade publications. That the various sources of information are consistent does not prove that the picture is accurate or complete.

My best guesses at the scenarios most likely to fail are:

  • Audio program material with low-level high-frequency content, implying low-level watermarking tones. •
  • Listening in a noisy environment or with the monitor positioned to receive only a muffled signal, increasing the likelihood that the PPM monitor will not correctly detect the stations' IDs.

    When combined, these individual weaknesses might create a "perfect storm."

    Making the audience measuring process more transparent and reliable, as well as providing an unbiased playing field for all participants, will benefit all the stakeholders in our industry. Adopters of any innovation owe it to themselves to understand how the technology works. Technology is science, not magic, and providers of technological solutions are best served by an informed and enfranchised user base.

    Former MIT professor Dr. Barry Blesser is a recognized authority on audio technology, both as an inventor and an expert witness in several high-profile technology cases. Blesser has designed radio broadcast and professional audio products for a wide range of companies, including EMT, Orban and Lexicon, and served as chief technology officer for Studer. Blesser is a past president of the Audio Engineering Society, a consulting technical editor of its journal, and a recipient of its Silver and Governors medals. MIT Press recently published his book Spaces Speak, Are You Listening? Experiencing Aural Architecture.

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