Digital audio is sound, recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is encoded as numerical samples in continuous sequence. For example, in CD audio, samples are taken 44100 times per second each with 16 bit sample depth. Digital audio is the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s. In a digital audio system, an analog electrical signal representing the sound is converted with an analog-to-digital converter into a digital signal using pulse-code modulation; this digital signal can be recorded, edited and copied using computers, audio playback machines, other digital tools. When the sound engineer wishes to listen to the recording on headphones or loudspeakers, a digital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, sent through an audio power amplifier and to a loudspeaker.
Digital audio systems may include compression, storage and transmission components. Conversion to a digital format allows convenient manipulation, storage and retrieval of an audio signal. Unlike analog audio, in which making copies of a recording results in generation loss and degradation of signal quality, digital audio allows an infinite number of copies to be made without any degradation of signal quality. Digital audio technologies are used in the recording, mass-production, distribution of sound, including recordings of songs, instrumental pieces, sound effects, other sounds. Modern online music distribution depends on digital recording and data compression; the availability of music as data files, rather than as physical objects, has reduced the costs of distribution. Before digital audio, the music industry distributed and sold music by selling physical copies in the form of records and cassette tapes. With digital-audio and online distribution systems such as iTunes, companies sell digital sound files to consumers, which the consumer receives over the Internet.
An analog audio system converts physical waveforms of sound into electrical representations of those waveforms by use of a transducer, such as a microphone. The sounds are stored on an analog medium such as magnetic tape, or transmitted through an analog medium such as a telephone line or radio; the process is reversed for reproduction: the electrical audio signal is amplified and converted back into physical waveforms via a loudspeaker. Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation and amplification. Analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in a digital system do not result in error unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols, it is therefore possible to have an error-free digital audio system in which no noise or distortion is introduced between conversion to digital format, conversion back to analog.
A digital audio signal may optionally be encoded for correction of any errors that might occur in the storage or transmission of the signal. This technique, known as channel coding, is essential for broadcast or recorded digital systems to maintain bit accuracy. Eight-to-fourteen modulation is a channel code used in the audio compact disc. A digital audio system starts with an ADC; the ADC converts at a known bit resolution. CD audio, for example, has a sampling rate of 44.1 kHz, has 16-bit resolution for each stereo channel. Analog signals that have not been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the aliasing distortion, caused by audio signals with frequencies higher than the Nyquist frequency. A digital audio signal may be transmitted. Digital audio can be stored on a CD, a digital audio player, a hard drive, a USB flash drive, or any other digital data storage device; the digital signal may be altered through digital signal processing, where it may be filtered or have effects applied.
Sample-rate conversion including upsampling and downsampling may be used to conform signals that have been encoded with a different sampling rate to a common sampling rate prior to processing. Audio data compression techniques, such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are employed to reduce the file size. Digital audio can be carried over digital audio interfaces such as AES3 or MADI. Digital audio can be carried over a network using audio over Ethernet, audio over IP or other streaming media standards and systems. For playback, digital audio must be converted back to an analog signal with a DAC which may use oversampling. Pulse-code modulation was invented by British scientist Alec Reeves in 1937 and was used in telecommunications applications long before its first use in commercial broadcast and recording. Commercial digital recording was pioneered in Japan by NHK and Nippon Columbia and their Denon brand, in the 1960s; the first commercial digital recordings were released in 1971.
The BBC began to experiment with digital audio in the 1960s. By the early 1970s, it had developed a 2-channel recorder
IPod Hi-Fi is a speaker system, developed and manufactured by Apple Inc. and was released on February 28, 2006, for use with any iPod digital music player. The iPod Hi-Fi retailed at the Apple Store for US$349 until its discontinuation on September 5, 2007; the iPod Hi-Fi was announced by Steve Jobs on February 28, 2006, alongside the first Intel-based Mac mini. High price, more expensive than other similar products such as the iBoom and Bose's SoundDock. Lack of an AM/FM radio. Placement of the iPod itself in a vulnerable location compared to other similar devices such as the Bose SoundDock; this is due to the iPod device sitting atop the unit, with no other method of securing the player to the dock besides the 30-pin dock connector. The supplied remote control has limited functionality; the remote can only skip between tracks within the selected playlist. The menu button switches between the audio-in port. IPod compatibility: Only some iPod models can use the iPod Hi-Fi dock; the stereo comes with adapters for third generation, fourth generation and fifth generation iPods, the first and second generations of the iPod nano.
The iPod shuffle does not have a dock connector, so can only connect to the audio-in port and cannot be recharged by the stereo. So, with the exception of the iPod shuffle, the iPod Hi-Fi can be used with all iPods with a dock connector, however will only charge iPods that support Firewire charging. An adapter must be used to charge newer iPod models and the iPhone 3G, 3GS, 4 and 4S because they require a lower voltage: the iPod Hi-Fi supplies 12VDC while the newer devices accept 5VDC. On September 5, 2007, the iPod Hi-Fi was discontinued by Apple, disappeared from Apple's online store. Engadget received an official statement from Apple: HomePod CNET Review PC Magazine Review Stereophile Review Independent User Review
Euroblock, short for "European-style terminal block", is a low-voltage disconnectable connector and terminal block combination used for microphone- and line level-audio signals, for control signals such as RS-232 or RS-485. It is known as the Phoenix connector from one of the manufacturers, Phoenix Contact, a German company whose US operations were established in 1981 in Harrisburg, Pennsylvania, it is known as "Combicon", which might be a Phoenix brand name. The Euroblock is a solderless connector. Once the wires are installed, the entire assembly is plugged into a matching socket in the electronic device. Euroblocks are more convenient than the terminal strips they replace as the signal cables can be disconnected from or connected to the electronic device, rather than unscrewing and re-screwing each wire individually
A binding post is a connector used on electronic test equipment to terminate a single wire or test lead. They are found on loudspeakers and audio amplifiers as well as other electrical equipment. A binding post contains a cap that screws down on that rod. Binding posts evolved from 19th century general purpose fasteners into 20th century electrical binding posts. Examples of binding posts used during 19th century are telegraph blasting machine devices. Caps are insulated with plastic and color-coded: red means an active or positive terminal. Caps during the 19th century were bare metal until synthetic plastic, such as Bakelite, became available in early 20th century. During the late 1940s, General Radio created a new binding post. Today it is known as a "five-way" or "universal" binding post, which allows many types of connection methods: Banana plugs, inserted into the top open end of the binding post. Bare wire clamped. Bare wire clamped. Pin connector, inserted into a hole drilled through the metal post and clamped by the screw-down portion of the binding post.
Lug terminal, with a 1/4-inch inner diameter, clamped. Alligator clip. So-called isolated binding posts are not sufficiently isolated to protect users from coming into contact with their metal parts carrying voltage; as such they are not suitable to be used for carrying dangerous voltages. On several types of equipment it has been becoming common to no longer use the traditional binding posts, but safety banana jacks; the universal property of binding posts is lost here, since safety banana jacks can only be used with traditional and safety banana plugs. In the past, it was common for multiple five-way binding posts to have their drilled holes lined up, but this impaired safety as two wires or pin connectors could be inserted from opposite sides of two binding posts and the tips of the wires or probes might inadvertently short together. Holes are now aligned in such a fashion that such shorts cannot occur. In order to permit the use of double banana plugs, the most common distance between the centers of the plugs should be 3⁄4 inch, which originated on General Radio test equipment during the 1920s, however 3⁄4 inch is not the only spacing.
Fahnestock clip — an earlier device, now supplanted by binding posts Banana connector About.com glossary definition Binding Posts - Pomona Electronics
The AirPort Express was a Wi-Fi base station product from Apple Inc. part of the AirPort product line. While more compact and in some ways simpler than another Apple Wi-Fi base station, the AirPort Extreme, the Express offered audio output capability the Extreme lacks; the AirPort Express was the first AirPlay device to receive streamed audio from a computer running iTunes on the local network. AirPort Express outperformed the stringent requirements of the ENERGY STAR Program Requirements for Small Network Equipment Version 1.0. According to a Bloomberg report on November 21, 2016, "Apple Inc. has disbanded its division that develops wireless routers, another move to try to sharpen the company’s focus on consumer products that generate the bulk of its revenue, according to people familiar with the matter."In an April 2018 statement to 9to5Mac, Apple announced the discontinuation of its AirPort line leaving the consumer router market. Apple will continue supporting the AirPort Express, however the company now provides a list of recommended features when consumers are searching for a new wireless router.
When connected to an Ethernet network, the Express could function as a wireless access point. The last model allowed up to 50 networked users, it could be used as an Ethernet-to-wireless bridge under certain wireless configurations. It could be used to extend the range of a network, as well as audio server; the model introduced in June 2012 included two Ethernet ports: one WAN and one LAN. The first version was introduced by Apple on 7 July 2004, included an analog–optical audio mini-jack output, a USB port for remote printing or charging the iPod, one Ethernet port; the main processor of the 802.11g AirPort Express was a Broadcom BCM4712KFB wireless networking chipset, which had a 200 MHz MIPS processor built in. The audio was handled by a Texas Instruments Burr-Brown PCM2705 16-bit digital-to-analog converter. An updated version supporting the faster 802.11 Draft-N draft specification and operation in either of the 2.4 GHz and 5 GHz bands, with all other features identical, was introduced by Apple in March 2008.
The revised unit included an 802.11a/n mode, which allows adding Draft-N to an existing 802.11b/g network without disrupting existing connections, while preserving the increased throughput that Draft-N can provide. Up to 10 wireless units can connect to this AirPort Express; the AirPort Express uses an audio connector that combines a 3.5 mm minijack socket and a mini-TOSLINK optical digital transmitter, allowing connection to an external digital-to-analog converter or amplifier with internal DAC. Standard audio CDs ripped in iTunes into Apple Lossless format streamed to the AirPort Express will output a bit-for-bit identical bitstream when compared to the original CD. DTS-encoded CDs ripped to Apple Lossless audio files - which decode as digital white noise in iTunes - will play back when the AirPort Express is connected via TOSLINK to a DTS-compatible amplifier–decoder; this is limited to 44.1 kHz when streaming from iTunes. Any higher quality content, such as high fidelity audio that uses up to 24-bit and/or 192 kHz will be truncated down to 16-bit and 44.1 kHz.
The audio output feature of the AirPort Express on a system running Mac OS X Lion or earlier can only be used to wirelessly stream audio files from within iTunes to an attached stereo system. It cannot be used to output the soundtrack of iTunes video content to an attached stereo. OS X Mountain Lion introduced a feature to output system-wide audio directly to AirPort Express; this allows output of the audio of protected video content within iTunes, correctly maintains the audio sync with the image displayed on-screen. Video is synced with output audio when playing the video through an AirPort Express if the video is in a format supported by QuickTime Player. For Windows and Mac operating systems there are a few software options available for streaming system-wide audio to the AirPort Express, such as Airfoil, TuneBlade and Porthole. On August 28, 2018 Apple added AirPlay 2 support to the 2012 AirPort Express, giving it access to HomePod like features July 2004: AirPort Express released March 2008: AirPort Express 802.11n released June 2012: AirPort Express 802.11n released AirPort Extreme AirPort Time Capsule
S/PDIF is a type of digital audio interconnect used in consumer audio equipment to output audio over reasonably short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fibre optic cable with TOSLINK connectors. S/PDIF interconnects components in other digital high-fidelity systems. S/PDIF is based on the AES3 interconnect standard. S/PDIF can carry compressed 5.1 / 7.1 surround sound. S/PDIF is a data link layer protocol as well as a set of physical layer specifications for carrying digital audio signals between devices and components over either optical or electrical cable; the name stands for Sony/Philips Digital Interconnect Format but is known as Sony/Philips Digital Interface. Sony and Philips were the primary designers of S/PDIF. S/PDIF is standardized in IEC 60958 as IEC 60958 type II. A common use for the S/PDIF interface is to carry compressed digital audio for surround sound as defined by the standard IEC 61937; this mode is used to connect the output of a DVD player or computer, via optical or coax, to a home theatre amplifying receiver that supports Dolby Digital or DTS.
Another common use is to carry two channels of uncompressed digital audio from a CD player to an amplifying receiver. S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in the professional audio field; this resulted from the desire of the various standards committees to have at least sufficient similarities between the two interfaces to allow the use of the same, or similar, designs for interfacing ICs. S/PDIF remained nearly identical at the protocol level, but changed the physical connectors from XLR to either electrical coaxial cable or optical fibre, both of which cost less than the XLR connection; the RCA connectors are colour-coded orange to differentiate from other RCA connector uses such as composite video. The cable was changed from 110 Ω balanced twisted pair to 75 Ω coaxial cable, using RCA jacks. Signals transmitted over consumer-grade TOSLINK connections are identical in content to those transmitted over coaxial connectors, though TOSLINK S/PDIF exhibits higher jitter.
S/PDIF is used to transmit digital signals of a number of formats, the most common being the 48 kHz sample rate format and the 44.1 kHz format, used in CD audio. In order to support both systems, as well as others that might be needed, the format has no defined data rate. Instead, the data is sent using biphase mark code, which has either one or two transitions for every bit, allowing the original word clock to be extracted from the signal itself. S/PDIF is meant to be used for transmitting 20-bit audio data streams plus other related information. To transmit sources with less than 20 bits of sample accuracy, the superfluous bits will be set to zero. S/PDIF can transport 24-bit samples by way of four extra bits. S/PDIF protocol is identical to AES3 with one exception: the channel status bit differs in S/PDIF. Both protocols group 192 samples into an audio block, transmit one channel status bit per sample, providing one 192-bit channel status word per channel per audio block; the meaning of the channel status word is different between AES3 and S/PDIF.
For S/PDIF, the 192-bit status word is identical between the two channels and is divided into 12 words of 16 bits each, with the first 16 bits being a control code. Bits 8–14 of the control code are a 7-bit category code indicating the type of source equipment, bit 15 is the "L-bit", which indicates whether copy-restricted audio is original or a copy; the L-bit is only used. The L-bit polarity depends on the category, with recording allowed if it is 1 for DVD-R and DVR-RW, but 0 for CD-R, CD-RW, DVD. For plain CD-DA, the L-bit is not defined, recording is prevented by alternating bit 2 at a rate of 4–10 Hz; the receiver does not control the data rate, so it must avoid bit slip by synchronizing its reception with the source clock. Many S/PDIF implementations cannot decouple the final signal from influence of the source or the interconnect; the process of clock recovery used to synchronize reception may produce jitter. If the DAC does not have a stable clock reference noise will be introduced into the resulting analog signal.
However, receivers can implement various strategies. TOSLINK optical fiber, unlike coaxial cables, are immune to RF interference; the fiber core of TOSLINK, may suffer permanent damage if bent. ADAT Lightpipe Dolby Digital Plus I²S McASP Manchester code S/PDIF at Epanorama.net More about channel data bits Interfacing AES3 and S/PDIF