# Here’s How Your Car Knows What Song Is Playing On The Radio – The Autopian
Decades ago, car radios only displayed basic information, such as the viewing area, stereo volume, equalizer, leveling, and fader settings. You listened to local DJs and relied on your music recognition skills to identify new music. However, around the turn of the new millennium, car radios started to display music titles. So how does your FM radio know what song is playing? This is mainly due to the technology called Radio Data System (RDS), or Radio Broadcast Data System (RBDS) in America. Let’s first learn about how FM radio works to broadcast stereo audio, and then we can learn how radio stations incorporate an additional data stream along with that.
### How FM Works
FM stands for Frequency Modulation, which means that FM radio broadcasts stereo audio by modifying a carrier signal with the audio signal you want to play. The audio signal modifies the carrier’s frequency, and the modified carrier signal is then sent to a receiver that decodes it to retrieve the audio signal back. FM radio stations usually broadcast in stereo with two separate audio channels. At the radio station, the Left audio channel and Right audio channel are added together to create a combined mono audio signal, with frequencies from 30 Hz to 15 kHz.
### The RDS That Lets Your Radio Know The Song
RDS data includes information on a station’s style of programming as well as the song titles and artists in one shot. If not, the string of text can be cycled out to display all the proper song information while providing a neat scrolling effect. Some small and cash-strapped independent broadcasters just didn’t buy into RDS technology, so the radio stations simply can’t be bothered to cycle out their RDS text, instead just displaying the name and the callsign of the radio station.
### Other Broadcasting Methods
These days, your car might know what song’s playing on the radio because the broadcast isn’t an analog FM signal at all. Welcome to HD Radio, which broadcasts digital and analog radio signals through the same bandwidth at the same time. With HD Radio, your receiver is capable of receiving a stream of digital audio signal flowing at up to 128 kBit/s in some FM implementations. This technology also allows for the transmission of tiny images on the airwaves through HD Radio’s “Artist Experience” function.
### Conclusion
Terrestrial radio has been going out of fashion with the rise of streaming and cheap data plans. If you’re sending Bluetooth streaming audio to a car’s head unit, it’ll still need a way to pull up track information. That’s when Gracenote technology comes in, built into various cars from Toyotas to BMWs and used for everything from radio to streaming.
