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Audio Glossary

HD Radio

HD radio stations transmit a digital signal, rather than an analog AM or FM signal as traditional radio has used for decades.  Digital has some benefits over analog.  Stations can transmit their signals farther (that is not often true) and the signal will be clearer (“CD-quality sound”) to those equipped with an HD receiver.  Stations can “multicast” their programs.  This means that they can transmit more than one channel at a time and thus tailor content more specifically for each channel.
HD Radio is a proprietary technology developed by iBiquity.  The “HD” does not stand for “high definition” as it is merely a brand name.


A podcast is an audio program that listeners can download to portable devices or their computers.   Internet makes tracking podcasts very difficult. Several companies try, and we rely on, the largest of them, for our data. The figures cited may not be comprehensive but still offer a glimpse of trends.

Satellite Radio

This system transmits audio with orbiting communication satellites rather than ground-based transmission, which provides some benefits.  While broadcast radio has a limited range, satellite signals can be received anywhere in the country and the signals are less prone to static. A downside is that satellite radio reception is affected by weather or physical obstacles more than terrestrial broadcast radio. Listeners of satellite radio must, like cable TV viewers, pay a monthly fee.

Internet Radio

This is a term used to describe two types of audio accessed over the Internet.  One is broadcast (or satellite) radio stations streaming their broadcasts online. The other is “pure play” Internet, such as Pandora. These services are available only over the Internet. Internet radio has also become a part of mobile radio.  However, PEJ makes a distinction between “cellphone radio” and internet radio picked up by mobile devices.  Because so many mobile phones now have ready access to the Internet, internet audio services have become a major problem for proponents of cellphone radio (below).

Cellphone Radio

These are cellphones that pick up AM/FM and HD radio stations.  As of 2009, most cellphones did not yet have this capability.

Portable People Meter

This is a portable,audience research device launched in 2008 by Arbitron. It is  worn by survey participants and it t tracks all radio signals that they have  contact with.  If they are near a radio, the device will pick up the station’s identity, the time and date.  The people meter does not distinguish between active listening and background signals the may come close to the wearer, such as at a supermarket.

Controversy over Arbitron’s people meter methodology generated  a number of lawsuits, most of them claiming  the system under represented ethnic minority audiences. All of the suits were settled or dismissed in early 2009. (for more on the controversy, see the 2009 report).


Arbitron is a radio ratings company founded in 1949, which  in recent decades has been the dominant radio ratings provider. Until 2008, Arbitron’s ratings were compiled using a written diary system in which participants wrote down what station they listened to and for how long.  In 2008, Arbitron began the transition to a digital collection system, the portable people meter above.


Nielsen is a media ratings company that has long been the major provider of television network and station ratings.  Nielsen stopped measuring radio in 1964, but in 2009 began measuring small- and medium-sized radio markets.