What Is HD Radio in a Car?

This technology expands terrestrial radio broadcasts into the digital age.

Benjamin Hunting | 

Apr 18, 2023 | 3 min read

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Most people hear the term HD Radio and assume that it provides high-definition audio just as HDTV focuses on high-definition video. While both HDTV and HD Radio both make use of digital technology, that’s where the similarities end. Rather than deliver “high definition” audio, HD Radio instead takes advantage of digits to expand the broadcast capabilities of radio stations on both the AM and FM dials.

Here’s a look at what HD Radio is and how it works in your car.

How Does HD Radio Work?

HD Radio is a technology that was commercialized in 2002 by a company called iBiquity. It takes advantage of the frequencies that are adjacent to where an analog station is already broadcasting by using them to deliver digital content. This is called multicasting, and it allows listeners to choose between either the standard analog signal or one of several digital signals. The digital content is often a simulcast of the analog, but additional channels can also be part of the same HD Radio signal.

Audio content that is broadcast via HD Radio can be encoded at bit rates of between 24 and 120 kilobits per second (Kbps), depending on how many channels are in use by a station at any given time. Lower bit rates are typically reserved for talk radio, while higher bit rates are used to broadcast music.

What Are the Advantages of HD Radio?

There are several reasons why radio stations adopted HD Radio as a complement to their analog broadcast. A 120 Kbps signal approaches CD levels of quality when it comes to audio and is just under the bit rate used by the free Spotify streaming web player. It is also static free. That quality difference is a big sell in particular for AM radio stations, which can push through a clearer signal on HD Radio (and in stereo), compared to what is available to them with analog.

Broadcasters can also present alternate programming by splitting the HD Radio signal, which offers the chance to provide more than one show at a time via the same broadcast. While this lowers broadcast quality, it does improve the variety of what a station has to offer without requiring an investment in an additional frequency or broadcast tower.

Some stations use HD Radio to transmit song, artist, and radio show information to a receiver, which makes it easier to identify what you are listening to, along with traffic information.

Can Any Car Listen to HD Radio?

HD Radio is not a subscription service. Like AM and FM radio, it’s available free over the air within its broadcast radius. In order to tune in, a vehicle must have a compatible head unit. Today, most if not all automobiles are compatible with HD Radio, but older vehicles can’t listen to these signals unless they upgrade using aftermarket components.

Benjamin Hunting

Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.