You should have been in Las Vegas to hear Dr. Berry Blesser, Director of Research for The Telos Alliance, describe the science and technology behind watermarking like PPM, the process of embedding and then retrieving information concealed within audio.
It was the second NAB engineering talk on PPM at this year’s convention, this one delivered by the technical expert the US government called on when the Feds decided to look into complaints about PPM.
The issues and challenges Dr. Blesser discussed impact every radio station in PPM markets.
He delivered the sort of information Arbitron should have delivered in 2007 instead of the happy talk that filled NAB convention PPM sessions back then.
We’ve asked Dr. Blesser for permission to reproduce his PowerPoint presentation, and we intend to publish the presentation at Radio Insights. In the meantime here are some key issues to ponder.
The ability of PPM to determine which station a person is listening to depends primarily on the content the station is broadcasting. The greater the proportion of content between 1 kHz and 3 kHz, the “louder” the embedded information, and the more likely you’ll get credit for the listening.
That’s because PPM codes ride beneath the content in this range, so if there is no content, there is no code. You might as well be off the air.
The amount of information in this range varies by format, but even within formats, the density of 1-3 kHz information can vary, so the belief that some formats do better than others in PPM is only partially correct.
Our take: Start monitoring the spectral content of your programming. At least download a Spectrum Analyzer iPad app and pay close attention to how much content falls between 1 and 3 kHz.
Talk stations and music stations with morning shows that talk a lot may be surprised how seldom they broadcast 1-3 kHz content.
A second issue is ambient noise in the listening environment.
Ambient noise can compound the problem of getting credit. The PPM encoder adjusts the level of the codes based on the level of the content, maintaining a level that is a fraction of the content.
The problem is that the encoder has no idea what environment a listener is in, or what the ambient noise level is.
If your 1-3 kHz content is low, the code level is low too. But what if it’s drive-time and a large proportion of your panelists are listening while driving? There’s a good chance you’re not going to get credit for a portion of that listening.
Ironically, this point was driven home during a separate presentation by John Kean, Senior Technologist at NPR. He presented results of an NPR study showing how people listen to the radio in noisy environments.
Worse yet, a great deal of ambient noise like road noise falls into the 1-3 kHz range, further burying the PPM codes.
Combine a low level code with a noisy environment, and you are probably going to lose credit for some quarter-hours.
We recently wrote that PPM can kill formats, but it turns out that the problems are much broader than we thought. Every format has some content that encodes poorly.
Radio stations using Voltair are finding that some songs don’t encode well. They are either pulling the songs or giving them sound codes so they don’t play around each other. They also may only play them late in the quarter-hour.
It turns out that compressed audio like MP3s don’t encode well. MP3s tend to lack a dense mid-range so there’s less energy for the PPM codes to hide behind.
After the presentation we tuned around the Las Vegas radio dial with a Spectrum Analyzer. The first graph at the left is a well known talk show host speaking. The energy (think volume) of the content is the vertical axis. The frequency is the horizontal axis. (Click on them to enlarge.)
Notice the absence of content in the 1-3 kHz range. This is an extreme example where the host was speaking quietly for effect. At other times there were opportunities for the encoder to inject information, but for much of the time the encoder was probably silent.
The second example is a music station close by on the dial.
The song shown here is a pop alt hit, and while it looks much different it too shows low content in the critical range relative to the rest of the spectrum. There’s more content for the PPM codes to hide behind, but not as much as other songs the station played.
Listening to Dr. Blesser speak we were reminded of the many panels at NAB Radio Shows where program directors talked about PPM and how they were shutting up their jocks.
The conventional wisdom was that PPM panelists don’t like talk. They just want lots of music. Little did we know that it was the meter not the panelist that didn’t like talk.
Much of what we’ve “learned” about PPM is just plan wrong.