Portable People Meter

The Portable People Meter (PPM) is a system developed by Arbitron (now Nielsen Audio) to measure how many people are exposed or listening to individual radio stations and television stations, including cable television. The PPM is worn like a pager, and detects hidden audio tones within a station or network's audio stream, logging each time it finds such a signal.

Although the makers of the PPM claim that it is more accurate than traditional alternatives like handwritten logs or wired meters, critics have raised issues about its accuracy. Another sales argument is that the device is immune to human forgetfulness, something that can be an issue in studies that rely on self-reporting by test subjects.

There are several parts to the PPM system:

The original PPM concept required the base station to be connected to a telephone line to transmit panelists' listening data from the PPM to the collection point. The PPM 360, introduced in 2010, uses cellular telephone technology to accomplish this without the need for a wired telephone service. They also have a motion sensor to detect when the PPM is being worn by an active person: After a period of 30 minutes of no activity, they go into a low-power "sleep" mode to conserve battery life.

The original concept for the PPM can be traced to a brainstorming session at Arbitron in November 1988. Concerns over the forthcoming move from analog video to high-definition digital television had engineers concerned that the technology then in use would become obsolete overnight. Drawing upon his experience in testing laboratories, Dr. Gerald Cohen proposed embedding an identifying signal in the audio and later decoding it. The rationale was simple. Dr. Cohen argued that audio was less likely to undergo as drastic a change in content and technology as would video, hence any technology developed would not likely to become obsolete in a few years.

The concept was presented to the company at that time and was also written up in a short concept document. A preliminary investigation was undertaken, but the technology was never given serious consideration. The concept was written off and forgotten as Arbitron had larger issues in its competition with the Nielsen Company for television ratings. Arbitron lost that battle and went back to its core business — radio ratings.

Dr. Cohen's idea lay dormant until 1992 when Drs. Richard Schlunt and Patrick Nunally approached Arbitron. Meeting with Ronald Kolessar, Director of Technology, Dr. Cohen and others, they presented a new variation of the idea — selectively embed a code into the frequency spectrum of the baseband audio stream and use digital signal processing in a small wearable device to recover the embedded code buried in what a person watches or hears.

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