Radio and Streaming Glossary
Radio and streaming come with a lot of jargon. This glossary explains the terms you will meet on station pages, in apps and in our guides, in plain English and in alphabetical order.
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- AAC (Advanced Audio Coding)
- A widely used audio codec that generally sounds better than MP3 at the same bitrate. Its low-bitrate variant, HE-AAC, is used by many internet streams and by DAB+ digital radio.
- AM (amplitude modulation)
- The oldest broadcast radio technology, used on medium, long and short wave. AM signals can travel very long distances, especially at night, but have limited, mono sound quality. See internet radio vs FM, AM and DAB+.
- AutoDJ
- A feature of radio hosting and playout software that plays music automatically from a playlist when no presenter is live.
- Bitrate
- The amount of data used per second of audio, measured in kilobits per second (kbps). Higher bitrates usually mean better sound and more data use; a 128 kbps stream uses about 57.6 MB per hour.
- Buffer / buffering
- A few seconds of audio your player downloads in advance so that short network hiccups do not interrupt playback. “Buffering” on screen means the buffer has run out and the player is waiting for more data.
- Call sign
- An official identifier assigned to a broadcast station, such as the four-letter names beginning with K or W used by stations in the United States.
- Codec
- Short for coder-decoder: the method used to compress audio for transmission and decompress it for playback. Common radio codecs are MP3, AAC, Ogg Vorbis and Opus.
- Community radio
- Non-profit stations run by and for a local community or interest group, often with volunteer presenters and locally made programmes.
- Container / format
- The file or stream format that wraps the encoded audio, for example an MP3 stream, an AAC stream in ADTS, or an Ogg stream carrying Vorbis or Opus.
- DAB / DAB+ (Digital Audio Broadcasting)
- Digital radio transmitted over the air. Several stations share one multiplex. DAB+ is the newer, more efficient version using HE-AAC and is the standard in most countries that use DAB.
- Directory (radio directory)
- A searchable list of stations and their stream addresses. AllRadioList is a directory built on the open Radio-Browser database; it links to streams rather than hosting audio.
- Drive time
- The morning and late-afternoon hours when many people listen while commuting. These are usually a station’s most popular and most valuable time slots.
- Encoder
- Software or hardware that compresses live audio with a codec and sends it to a streaming server.
- FM (frequency modulation)
- Analogue broadcast radio, usually between 87.5 and 108 MHz. FM offers good stereo sound within the range of a transmitter, typically a city or region.
- Format (station format)
- The overall style of a station’s programming, such as news/talk, adult contemporary, classic rock or classical.
- Frequency
- The position on the dial where a broadcast station transmits, given in MHz for FM and kHz for AM.
- Geo-blocking
- Restricting a stream to listeners in certain countries, usually because of music or sports rights. A geo-blocked station may play at home but not abroad.
- Genre tag
- A label such as “jazz” or “news” attached to a station to describe its content. On AllRadioList, tags come from the community directory and power the genre filter.
- HD Radio
- A digital broadcasting system used mainly in the United States, which adds digital signals and extra channels alongside existing FM and AM stations.
- HE-AAC
- High-Efficiency AAC, a version of AAC designed to sound good at low bitrates such as 32–64 kbps.
- HLS (HTTP Live Streaming)
- A streaming method that splits audio into short segments listed in a playlist file ending in
.m3u8. It is used by many large broadcasters. Not every browser plays HLS natively. - HTTPS stream
- A stream delivered over a secure, encrypted connection. Browsers block insecure (http://) audio on secure websites, so AllRadioList only lists HTTPS streams.
- Icecast
- Free, open-source streaming server software used by a large number of independent internet radio stations. It sends audio as a continuous stream and can include the current song title.
- Internet-only station
- A station that broadcasts only online, with no FM, AM or DAB transmitter.
- Latency (stream delay)
- The time between something happening in the studio and you hearing it. Internet streams are typically several seconds to about a minute behind live, because of encoding and buffering.
- Metadata
- Text sent alongside the audio, most often the current artist and song title, shown in your player.
- Mono / stereo
- Mono is a single audio channel; stereo uses separate left and right channels. Speech stations sometimes stream in mono to save data.
- MP3
- The long-established audio codec, supported by practically every device and browser.
- Multiplex
- A single digital broadcast signal that carries several stations at once, used by DAB and DAB+.
- Ogg Vorbis
- An open, royalty-free audio codec popular with independent stations. Most modern browsers support it, though older Apple devices may not.
- Opus
- A modern open codec that is very efficient at low bitrates and especially good for speech.
- Playlist file (.m3u, .pls)
- A small text file that points to a stream’s address. Clicking one often opens a separate media player rather than playing in the browser.
- Playout software
- The program a station uses to schedule and play music, adverts, jingles and recorded shows.
- Public broadcaster
- A broadcaster funded wholly or partly by the public, through a licence fee or government grant, with a public-service remit. Examples include the BBC, NHK and ABC (Australia).
- Radio-Browser
- A free, open, community-maintained database of internet radio stations and their stream addresses, used by AllRadioList and many radio apps. Read how we list stations.
- RDS (Radio Data System)
- A system that sends small amounts of text with an FM signal, such as the station name, song title and traffic alerts.
- Sample rate
- How many times per second audio is measured, usually 44.1 or 48 kHz for streams. It matters less to listeners than bitrate.
- SHOUTcast
- Long-established streaming server software and directory, similar to Icecast.
- Simulcast
- Broadcasting the same programme on more than one platform at once, for example on FM and as an internet stream.
- Stream URL
- The web address of a station’s audio stream. Your browser connects to it directly when you press Play.
- Streaming server
- A server that receives a station’s single encoded stream and sends a copy to every listener.
- Talk radio
- A format built on speech: discussion, interviews, phone-ins and commentary rather than music.
- Transmitter
- The equipment and antenna that send a broadcast signal over the air for FM, AM or DAB.
- Variable bitrate (VBR)
- Encoding that changes the bitrate moment to moment depending on how complex the audio is. Most live radio streams use a constant bitrate (CBR) instead, which is more predictable.
- Votes (station votes)
- Community ratings in the Radio-Browser directory. On AllRadioList, “Top Rated” sorts stations by votes, while “Most Popular” sorts by how often they are played.