Unfortunately, things are even worse than Nielsen admits.
As bad as PPM is in accurately measuring some formats on traditional (analog) AM and FM stations, HD (digital) stations have virtually no chance of getting their full credit from PPM regardless of format.
For reasons we’ll explain, an HD station playing identical content to a traditional analog station is unlikely to encode as well as the analog station.
Consequently, with identical audiences the HD station will have lower ratings.
PPM relies on the presence of masking content to insert inaudible identifying codes in a station’s programming. The greater the level of masking content, the “louder” the codes. The more often programming contains masking content, the more codes broadcast.
Some formats broadcast more masking content than others, so those formats broadcast codes more consistently than other formats. More consistent encoding means better ratings.
On the other hand, if a station broadcasts insufficient masking content, the encoder can’t insert codes and the station is essentially off the air as far as PPM is concerned.
Digital radio such as HD radio adds an additional wrinkle to this process.
To enable HD to deliver multiple digital streams within the bandwidth of an AM or FM channel, the digital channels are highly compressed using a proprietary algorithm that removes a great deal of content.
In this regard, HD radio is like a low quality MP3 copy of a song.
If you want to better understand what this means and you have access to a Voltair, replace the CD version of a song with a low quality MP3 version and watch your green encoding bars turn to red.
Were it not for PPM, the quality degradation that comes with the HD radio compression algorithm wouldn't be a ratings problem for HD Radio.
However, the process of compression eliminates large amounts of masking content, the very content PPM needs to consistently encode the broadcast.
HD radio turns highly encodable analog content into unencodable digital content.
Granted HD Radio has issues that go well beyond algorithms, but the medium shouldn't be further punished because of Nielsen's inability to accurately measure its audience.
Nielsen is currently testing enhancements to the PPM encoder to address encoding flaws that Voltair revealed.
Nielsen hasn’t announced any test details, but we’re skeptical that Nielsen will be testing the encoding reliability of HD-2 and HD-3 channels.
And we really doubt that results will be released publicly any way.
In a follow-up post we’ll get into the messy details of HD radio’s HDC compression algorithm (codec for shot) and explain the problem in greater detail.