Digital audio in the context of Sound wave

Radio broadcasting is the transmission of electromagnetic radiation (radio waves) to receivers over a wide area. Most broadcasts are audio (sound), sometimes with embedded metadata. Listeners require a broadcast radio receiver to receive these signals. "Terrestrial" broadcasts, including AM, FM, and DAB stations, originate from land-based transmitters, whereas "satellite radio" signals originate from a satellite in Earth orbit.

Stations may produce their own programming or be affiliated with a radio network that provides content either through broadcast syndication or by simulcasting, or both. The most common transmission technologies are analog and digital. Analog radio uses one of two modulation methods: amplitude modulation (AM) or frequency modulation (FM). Digital radio stations transmit using one of several digital audio standards, such as DAB (Digital Audio Broadcasting), HD Radio, or DRM (Digital Radio Mondiale).

An audio file format is a file format for storing digital audio data on a computer system. The bit layout of the audio data (excluding metadata) is called the audio coding format and can be uncompressed, or compressed to reduce the file size, often using lossy compression. The data can be a raw bitstream in an audio coding format, but it is usually embedded in a container format or an audio data format with a defined storage layer.

A podcast is a program made available in digital format for download over the Internet. Typically, a podcast is an episodic series of digital audio files that users can download to a personal device or stream to listen to at a time of their choosing. Podcasts are primarily an audio medium, but some distribute in video, either as primary content included in the feed, or as an external supplement to audio; popularised in recent years by video platform YouTube. In 2025, Bloomberg reported that a billion people are watching podcasts on YouTube every month.

A podcast series usually features one or more recurring hosts engaged in a discussion about a particular topic or current event. Discussion and content within a podcast can range from carefully scripted to completely improvised. Podcasts combine elaborate and artistic sound production with thematic concerns ranging from scientific research to slice-of-life journalism. Many podcast series provide an associated website or page with links and show notes, guest biographies, transcripts, additional resources, commentary, and occasionally a community forum dedicated to discussing the show's content.

An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of roughly 20 to 20,000 Hz, which corresponds to the lower and upper limits of human hearing. Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical audio signal back into sound.

Digital audio systems represent audio signals in a variety of digital formats.

Generative artificial intelligence (Generative AI, or GenAI) is a subfield of artificial intelligence that uses generative models to produce text, images, videos, audio, software code or other forms of data. These models learn the underlying patterns and structures of their training data and use them to produce new data based on the input, which often comes in the form of natural language prompts.

Generative AI tools have become more common since the AI boom in the 2020s. This boom was made possible by improvements in transformer-based deep neural networks, particularly large language models (LLMs). Major tools include chatbots such as ChatGPT, Copilot, Gemini, Claude, Grok, and DeepSeek; text-to-image models such as Stable Diffusion, Midjourney, and DALL-E; and text-to-video models such as Veo and Sora. Technology companies developing generative AI include OpenAI, xAI, Anthropic, Meta AI, Microsoft, Google, Mistral AI, DeepSeek, Baidu and Yandex.

The compact disc (CD) is a digital optical disc data storage format co-developed by Philips and Sony to store and play digital audio recordings. It employs the Compact Disc Digital Audio (CD-DA) standard and is capable of holding uncompressed stereo audio. First released in Japan in October 1982, the CD was the second optical disc format to reach the market, following the larger LaserDisc (LD). In later years, the technology was adapted for computer data storage as CD-ROM and subsequently expanded into various writable and multimedia formats. As of 2007, over 200 billion CDs (including audio CDs, CD-ROMs, and CD-Rs) had been sold worldwide.

Standard CDs have a diameter of 120 millimetres (4.7 inches) and typically hold up to 74 minutes of audio or approximately 650 MiB (681,574,400 bytes) of data. This was later regularly extended to 80 minutes or 700 MiB (734,003,200 bytes) by reducing the spacing between data tracks, with some discs unofficially reaching up to 99 minutes or 870 MiB (912,261,120 bytes) which falls outside established specifications. Smaller variants, such as the Mini CD, range from 60 to 80 millimetres (2.4 to 3.1 in) in diameter and have been used for CD singles or distributing device drivers and software.

Internet radio, also known as online radio, web radio, net radio, streaming radio, e-radio and IP radio, is a digital audio service transmitted via the Internet. Broadcasting on the Internet is usually referred to as webcasting since it is not transmitted broadly through wireless means. It can either be used as a stand-alone device running through the Internet, or as a software running through a single computer.

Internet radio is generally used to communicate and easily spread messages through the form of talk. It is distributed through a wireless communication network connected to a switch packet network (the internet) via a disclosed source.

An audio coding format (or sometimes audio compression format) is a encoded format of digital audio, such as in digital television, digital radio and in audio and video files. Examples of audio coding formats include MP3, AAC, Vorbis, FLAC, and Opus. A specific software or hardware implementation capable of audio compression and decompression to/from a specific audio coding format is called an audio codec; an example of an audio codec is LAME, which is one of several different codecs which implements encoding and decoding audio in the MP3 audio coding format in software.

Some audio coding formats are documented by a detailed technical specification document known as an audio coding specification. Some such specifications are written and approved by standardization organizations as technical standards, and are thus known as an audio coding standard. The term "standard" is also sometimes used for de facto standards as well as formal standards.

Music streaming services are a type of online streaming media service that focuses primarily on music, and sometimes other forms of digital audio content such as podcasts. These services are usually subscription-based services allowing users to stream digital copyright restricted songs on-demand from a centralized library provided by the service. Some services may offer free tiers with limitations, such as advertising and limits on use. They typically incorporate a recommendation system to help users discover other songs they may enjoy based on their listening history and other factors, as well as the ability to create and share public playlists with other users.

Streaming services saw a significant pace of growth during the 2010s, overtaking online music stores as the largest source of revenue to the United States music industry in 2015, and accounting for a majority since 2016. As a result of their ascendance, streaming services (as well as music-oriented content on video sharing platforms) were incorporated into the methodologies of major record charts; the "album-equivalent unit" was developed as an alternative metric for the consumption of albums, to account for digital music and streaming.

Livestreaming, live-streaming, or live streaming is the streaming of video or audio in real time or near real time. While often referred to simply as streaming, the real-time nature of livestreaming differentiates it from other non-live broadcast forms of streamed media such as video-on-demand, vlogs and video-sharing platforms such as YouTube and TikTok.

Livestreaming services encompass a wide variety of topics, including social media, video games, professional sports, and lifecasting. Platforms such as Facebook Live, Periscope, Kuaishou, Douyu, bilibili, YouTube, and 17 include the streaming of scheduled promotions and celebrity events as well as streaming between users, as in videotelephony. Livestreaming sites such as Twitch and Kick have become popular outlets for watching people play video games, such as in esports, Let's Play-style gaming, or speedrunning. Live coverage of sporting events is a common application.

DisplayPort (DP) is a digital interface used to connect a video source, such as a computer, to a display device like a monitor. Developed by the Video Electronics Standards Association (VESA), it can also carry digital audio, USB, and other types of data over a single cable.

Introduced in the 2000s, DisplayPort was designed to replace older standards like VGA, DVI, and FPD-Link. While not directly compatible with these formats, adapters are available for connecting to HDMI, DVI, VGA, and other interfaces.

HDMI (High-Definition Multimedia Interface) is a brand of proprietary digital interface used to transmit high-quality video and audio signals between devices. It is commonly used to connect devices such as televisions, computer monitors, projectors, gaming consoles, and personal computers. HDMI supports uncompressed video and either compressed or uncompressed digital audio, allowing a single cable to carry both signals.

Introduced in 2003, HDMI largely replaced older analog video standards such as composite video, S-Video, and VGA in consumer electronics. It was developed based on the CEA-861 standard, which was also used with the earlier Digital Visual Interface (DVI). HDMI is electrically compatible with DVI video signals, and adapters allow interoperability between the two without signal conversion or loss of quality. Adapters and active converters are also available for connecting HDMI to other video interfaces, including the older analog formats, as well as digital formats such as DisplayPort.

In digital audio using pulse-code modulation (PCM), bit depth is the number of bits of information in each sample, and it directly corresponds to the resolution of each sample. Examples of bit depth include Compact Disc Digital Audio, which uses 16 bits per sample, and DVD-Audio and Blu-ray Disc, which can support up to 24 bits per sample.

In basic implementations, variations in bit depth primarily affect the noise level from quantization error—thus the signal-to-noise ratio (SNR) and dynamic range. However, techniques such as dithering, noise shaping, and oversampling can mitigate these effects without changing the bit depth. Bit depth also affects bit rate and file size.

Comfort noise (or comfort tone) is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines.

Some modern telephone systems (such as wireless and VoIP) use voice activity detection (VAD), a form of squelching where low volume levels are ignored by the transmitting device. In digital audio transmissions, this saves bandwidth of the communications channel by transmitting nothing when the source volume is under a certain threshold, leaving only louder sounds (such as the speaker's voice) to be sent. However, improvements in background noise reduction technologies can occasionally result in the complete removal of all noise. Although maximizing call quality is of primary importance, exhaustive removal of noise may not properly simulate the typical behavior of terminals on the PSTN system.

A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies. The DCT, first proposed by Nasir Ahmed in 1972, is a widely used transformation technique in signal processing and data compression. It is used in most digital media, including digital images (such as JPEG and HEIF), digital video (such as MPEG and H.26x), digital audio (such as Dolby Digital, MP3 and AAC), digital television (such as SDTV, HDTV and VOD), digital radio (such as AAC+ and DAB+), and speech coding (such as AAC-LD, Siren and Opus). DCTs are also important to numerous other applications in science and engineering, such as digital signal processing, telecommunication devices, reducing network bandwidth usage, and spectral methods for the numerical solution of partial differential equations.

A DCT is a Fourier-related transform similar to the discrete Fourier transform (DFT), but using only real numbers. The DCTs are generally related to Fourier series coefficients of a periodically and symmetrically extended sequence whereas DFTs are related to Fourier series coefficients of only periodically extended sequences. DCTs are equivalent to DFTs of roughly twice the length, operating on real data with even symmetry (since the Fourier transform of a real and even function is real and even), whereas in some variants the input or output data are shifted by half a sample.

A hard disk recorder (HDR) is a system that uses a high-capacity hard disk to record digital audio or digital video. Hard disk recording systems represent an alternative to reel-to-reel audio tape recording and video tape recorders, and provide non-linear editing capabilities unavailable using tape recorders. Audio HDR systems, which can be standalone or computer-based, are typically combined with provisions for digital mixing and processing of the audio signal to produce a digital audio workstation (DAW).

Direct-to-disk recording (DDR) refers to methods which may also use optical disc recording technologies such as DVD, and Compact disc.