Radio and Streaming Glossary: 40 Terms Explained
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Radio has its own vocabulary, and internet streaming adds more. This glossary explains the terms you are most likely to meet on this site and in discussions about radio, in plain language and in alphabetical order.
- AAC
- Advanced Audio Coding, an audio codec that generally sounds better than MP3 at the same bitrate. It is widely used for streaming, and DAB+ digital radio uses a version of it.
- AM
- Amplitude modulation, an analogue broadcasting method in which the strength of the radio wave carries the sound. AM signals can travel long distances but are prone to noise and interference. See also medium wave.
- Bandwidth
- In streaming, the amount of data your connection can carry per second. A stream needs at least as much bandwidth as its bitrate, or it will stutter.
- Bitrate
- The amount of data used for each second of audio, usually measured in kilobits per second (kbps). Higher bitrates generally mean better sound and more data used. See the data usage guide.
- Buffer
- A short store of audio that a player downloads ahead of what you are hearing, so that a brief network interruption does not cut the sound. A bigger buffer is more reliable but adds latency.
- Call sign
- A unique set of letters that identifies a broadcast station and is assigned by a regulator in some countries, for example KEXP in the United States. Many stations also use a brand name instead.
- Codec
- Short for coder-decoder: the method used to compress audio for sending and decompress it for playback. Common streaming codecs are MP3, AAC, Ogg Vorbis and Opus.
- Commercial radio
- Stations funded mainly by advertising and sponsorship rather than by public money or listener fees.
- Community radio
- Locally run, usually non-profit stations that serve a neighbourhood, town or community of interest, often with volunteer presenters and programmes in local or minority languages.
- DAB and DAB+
- Digital Audio Broadcasting, a digital radio system that carries several stations together in one multiplex. DAB+ is a newer version that uses the more efficient AAC codec. See FM, AM, DAB and internet radio compared.
- Dead air
- Unintended silence in a broadcast or stream.
- Digital radio
- A general term for radio that is transmitted as digital data, such as DAB and HD Radio. It is sometimes also used loosely for internet radio.
- Encoder
- Software or hardware that converts a station's audio into a compressed stream, using a codec and a chosen bitrate, and sends it to a streaming server.
- FM
- Frequency modulation, an analogue broadcasting method in which changes in the frequency of the wave carry the sound. FM gives good stereo sound but a shorter range than AM.
- Frequency
- How many times a radio wave oscillates per second, measured in hertz. Analogue stations are identified by their frequency, such as 98.5 MHz on FM or 1,000 kHz on AM.
- Geo-blocking
- Restricting a stream so that it only works for listeners in certain countries, usually because of licensing. See why some radio stations are blocked abroad.
- HD Radio
- A digital radio system used mainly in the United States, in which a digital signal is broadcast alongside, or in the same channel as, an analogue AM or FM signal.
- HLS
- HTTP Live Streaming, a method that splits audio into short segments listed in a playlist file (ending in
.m3u8) which the player fetches over ordinary web connections. It scales well, but not every browser plays it natively. - HTTPS
- The secure form of the web protocol, which encrypts data between your browser and a server. Browsers may block audio from non-secure (
http) addresses on secure pages, which is why this site lists only stations with HTTPS streams. - Icecast
- Free, widely used streaming-server software that sends a station's audio to many listeners as a continuous stream. Many independent stations use it. See also SHOUTcast.
- ICY metadata
- Small pieces of text, such as the current song title, that Icecast and SHOUTcast streams can send alongside the audio.
- Internet radio
- Radio delivered over the internet instead of through the air. Stations can be internet-only or can stream the same programme they broadcast on AM, FM or DAB. See what internet radio is.
- Latency
- The delay between something happening in the studio and you hearing it. Internet streams usually run several seconds behind broadcast radio because of encoding, transmission and buffering.
- Live stream
- Audio sent continuously as it is produced, as opposed to a file you can start and stop at will. You cannot skip ahead in a live stream.
- Medium wave
- The main AM broadcasting band, at roughly 530–1700 kHz depending on the region. Its signals can travel far, especially after dark.
- MP3
- A long-established audio codec that plays almost everywhere. Many streams still use it, commonly at 64–192 kbps.
- Multiplex
- A single digital broadcast channel that carries several radio (or television) services together. In DAB radio it is also called an ensemble.
- Ogg Vorbis
- A free and open audio codec, used by some independent and community stations.
- Opus
- A free and open audio codec that performs well for both speech and music, even at low bitrates.
- Podcast
- An audio programme published as files that you can download or stream on demand, as opposed to a live stream. Many radio stations also release their shows as podcasts.
- Public service broadcaster
- A broadcaster funded wholly or partly by public money or a licence fee, with a duty to inform, educate and entertain, such as the BBC in the United Kingdom, ABC in Australia or CBC in Canada.
- SHOUTcast
- Streaming-server software, like Icecast, that sends audio to listeners as a continuous stream.
- Shortwave
- Radio waves at roughly 3–30 MHz that can travel very long distances by bouncing off the upper atmosphere. Shortwave has long been used for international broadcasting.
- Simulcast
- Broadcasting the same programme at the same time on more than one platform, such as FM and the internet.
- Stream URL
- The web address from which a station's audio stream can be played. It points to the audio itself rather than to a web page.
- Streaming server
- The computer or service that receives a station's encoded audio and delivers it to listeners. Pressing Play connects your browser to this server.
- Talk radio
- A format built around spoken-word content such as discussion, interviews, news and phone-ins rather than music.
- Top 40
- A format centred on the most popular current songs, traditionally based on weekly sales or airplay charts.
- Transmitter
- The equipment that sends a broadcast signal through an antenna. Its power and the height of its antenna determine how far the signal reaches.
- Web radio
- Another name for internet radio.