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95-424: A PCM adaptor is a device that encodes digital audio as video for recording on a videocassette recorder . The adapter also has the ability to decode a video signal back to digital audio for playback. This digital audio system was used for mastering early compact discs . High-quality pulse-code modulation (PCM) audio requires a significantly larger bandwidth than a regular analog audio signal. For example,

190-422: A data compression algorithm. Adaptive DPCM (ADPCM) was introduced by P. Cummiskey, Nikil S. Jayant and James L. Flanagan at Bell Labs in 1973. Perceptual coding was first used for speech coding compression, with linear predictive coding (LPC). Initial concepts for LPC date back to the work of Fumitada Itakura ( Nagoya University ) and Shuzo Saito ( Nippon Telegraph and Telephone ) in 1966. During

285-462: A digital system do not result in error unless they are so large as to result in a symbol being misinterpreted as another symbol or disturbing the sequence of symbols. It is, therefore, generally possible to have an entirely error-free digital audio system in which no noise or distortion is introduced between conversion to digital format and conversion back to analog. A digital audio signal may be encoded for correction of any errors that might occur in

380-486: A digital-to-analog converter (DAC) performs the reverse process, converting a digital signal back into an analog signal, which is then sent through an audio power amplifier and ultimately to a loudspeaker . Digital audio systems may include compression , storage , processing , and transmission components. Conversion to a digital format allows convenient manipulation, storage, transmission, and retrieval of an audio signal. Unlike analog audio, in which making copies of

475-487: A frame rate of 30 frames per second (frame/s) or 25 frame/s – each field is half the lines of an interlaced image (alternating the odd lines and the even lines). Each of these fields is in turn composed of lines – a frame of 625 lines for PAL and 525 lines for NTSC, though some of the lines are actually for synchronizing the signal, and a field comprises half the visible lines in one vertical scan. Digital audio samples are then encoded along each line, thus allowing reuse of

570-411: A 16-bit PCM signal requires an analog bandwidth of about 1-1.5  MHz compared to about 15-20  kHz of analog bandwidth required for an analog audio signal. A standard analog audio recorder cannot meet this requirement. One solution arrived at in the early 1980s was to use a videotape recorder, which is capable of recording signals with higher bandwidths. A means of converting digital audio into

665-748: A 25 Hz power station exist in New Orleans for floodwater pumps. The 15 kV AC rail networks, used in Germany , Austria , Switzerland , Sweden , and Norway , still operate at 16 + 2 ⁄ 3  Hz or 16.7 Hz. In some cases, where most load was to be railway or motor loads, it was considered economic to generate power at 25 Hz and install rotary converters for 60 Hz distribution. Converters for production of DC from alternating current were available in larger sizes and were more efficient at 25 Hz compared with 60 Hz. Remnant fragments of older systems may be tied to

760-489: A DAC. According to the Nyquist–Shannon sampling theorem , with some practical and theoretical restrictions, a band-limited version of the original analog signal can be accurately reconstructed from the digital signal. During conversion, audio data can be embedded with a digital watermark to prevent piracy and unauthorized use. Watermarking is done using a direct-sequence spread-spectrum (DSSS) method. The audio information

855-420: A PCM adaptor and videocassette recorder combination. It is simplest if the same number of lines are used in each field, and, crucially, it was decided to adopt a sample rate that could be used on both PAL and monochrome NTSC equipment. Since monochrome NTSC has a field rate of 60 Hz, and PAL has a field rate of 50 Hz, their least common multiple is 300 Hz, and with 3 samples per line, this yields

950-432: A PCM adaptor-based system. Like a PCM adaptor, DAT could record only two tracks of audio at a time, but the smaller size of the equipment and media, as well as being able to accept multiple sampling rates and other flexibility, gave DAT many advantages over PCM adaptor-based systems. Digital recorders capable of multi-track recording such as Mitsubishi 's ProDigi format and Sony 's DASH format also became available on

1045-537: A different sampling rate to a common sampling rate prior to processing. Audio data compression techniques, such as MP3 , Advanced Audio Coding (AAC), Opus , Ogg Vorbis , or FLAC , are commonly 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

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1140-523: A good compromise between lighting, motor, and transmission needs, given the materials and equipment available in the first quarter of the 20th century. Several 40 Hz systems were built. The Lauffen-Frankfurt demonstration used 40 Hz to transmit power 175 km in 1891. A large interconnected 40 Hz network existed in north-east England (the Newcastle-upon-Tyne Electric Supply Company , NESCO) until

1235-495: A higher frequency. Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency. Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in a grid , providing reliability and cost savings. Many different power frequencies were used in

1330-666: A mechanical generator varies with the input force and output load experienced. Excess load withdraws rotational energy from the generator shaft, reducing the frequency of the generated current; excess force deposits rotational energy, increasing frequency. Automatic generation control (AGC) maintains scheduled frequency and interchange power flows by adjusting the generator governor to counteract frequency changes, typically within several decaseconds . Flywheel physics does not apply to inverter -connected solar farms or other DC -linked power supplies. However, such power plants or storage systems can be programmed to follow

1425-454: A multiple of 900 Hz (to allow encoding in both NTSC and PAL), are thus 40.5, 41.4, 42.3, 43.2, 44.1, 45, 45.9, and 46.8 kHz. The lower ones are eliminated due to low-pass filters requiring a transition band, while the higher ones are eliminated due to some lines being required for vertical blanking interval; 44.1 kHz was the higher usable rate, and was eventually chosen. The sampling frequencies of 44.1 and 44.056 kHz were thus

1520-407: A proposed experiment that would relax frequency regulation requirements for electrical grids which would reduce the long-term accuracy of clocks and other devices that use the 60 Hz grid frequency as a time base. Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network. The practice arose because the frequency of

1615-522: A range of digital transmission applications such as the integrated services digital network (ISDN), cordless telephones and cell phones . Digital audio is used in broadcasting of audio. Standard technologies include Digital audio broadcasting (DAB), Digital Radio Mondiale (DRM), HD Radio and In-band on-channel (IBOC). Digital audio in recording applications is stored on audio-specific technologies including CD, DAT, Digital Compact Cassette (DCC) and MiniDisc . Digital audio may be stored in

1710-580: 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, manipulation, mass-production, and distribution of sound, including recordings of songs , instrumental pieces, podcasts , sound effects, and 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 significantly reduced

1805-596: A sample rate that is a multiple of 900 Hz. For monochrome NTSC the sample rate is 5 m × 60 × 3, where 5 m is the number of active lines per field, which must be a multiple of 5 (the rest used for synchronization), and for PAL the sample rate is 6 n × 50 × 3, where 6 n is the number of active lines per field, which must be a multiple of 6. The sampling rates that satisfy these requirements – at least 40 kHz (to encode up to 20 kHz sounds), no more than 46.875 kHz (requiring no more than 3 samples per line in PAL), and

1900-521: A similar function with Hi8 tapes. Formats like ProDigi and DASH were referred to as SDAT (stationary-head digital audio tape) formats, as opposed to formats like the PCM adaptor-based systems and Digital Audio Tape (DAT), which were referred to as RDAT (rotating-head digital audio tape) formats, due to their helical-scan process of recording. Like the DAT cassette, ProDigi and DASH machines also accommodated

1995-427: A small cassette unique to the format. DAT used tape 4 millimetres (0.16 in) in width loaded into a cassette 73 mm × 54 mm × 10.5 mm (2.87 in. x 2.12 in. x 0.41 in.) in size. The audio data was recorded to the tape by using helical scan recording, the same fashion that a VCR connected to a PCM adaptor would record to a videotape. In essence, DAT was a modernized, integrated, and miniaturized version of

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2090-442: A specified sampling rate and converts at a known bit resolution. CD audio , for example, has a sampling rate of 44.1  kHz (44,100 samples per second), and has 16-bit resolution for each stereo channel. Analog signals that have not already been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the aliasing distortion that is caused by audio signals with frequencies higher than

2185-437: A standard audio file formats and stored on a Hard disk recorder , Blu-ray or DVD-Audio . Files may be played back on smartphones, computers or MP3 player . Digital audio resolution is measured in audio bit depth . Most digital audio formats use either 16-bit, 24-bit, and 32-bit resolution. Line frequency The utility frequency , (power) line frequency ( American English ) or mains frequency ( British English )

2280-504: A standard PCM adaptor, the Model 700 also utilized a VCR for a transport. In 1987, a few years after the PCM adaptor's introduction, Sony introduced a new cassette-based format for digital audio recording called Digital Audio Tape (DAT). Since DAT did not rely on a separate video cassette recorder, it was a much more portable and less-cumbersome format to use than a PCM adaptor-based system. DAT recorders had their own built-in transport using

2375-456: A transport medium for video-based encoding of digital audio streams. Digital audio In a digital audio system, an analog electrical signal representing the sound is converted with an analog-to-digital converter (ADC) into a digital signal, typically using pulse-code modulation (PCM). This digital signal can then be recorded, edited, modified, and copied using computers , audio playback machines, and other digital tools. For playback,

2470-418: A video format was necessary. Such an audio recording system includes two devices: the PCM adaptor, which converts audio into pseudo-video, and the videocassette recorder. A PCM adaptor performs an analog-to-digital conversion producing series of binary digits, which, in turn, is coded and modulated into a black and white video signal, appearing as a vibrating checkerboard pattern, which can then be recorded as

2565-502: A video signal. Most video-based PCM adaptors record audio at 14 or 16 bits per sample, with a sampling frequency of 44.1 kHz for PAL or monochrome NTSC , or 44.056 kHz for color NTSC. Some of the earlier models, such as the Sony PCM-100, recorded 16 bits per sample, but used only 14 of the bits for the audio, with the remaining 2 bits used for error correction for the case of dropouts or other anomalies being present on

2660-457: A way to increase speed of slow engines, in very large ratings (thousands of kilowatts) these were expensive, inefficient, and unreliable. After about 1906, generators driven directly by steam turbines favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of commutators in rotary converters. The synchronous speed N in RPM is calculated using

2755-556: Is calculated at 08:00 each day in a control center in Switzerland . The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60  s / min × 60 min/ h × 24 h/ d = 4 320 000 cycles per day. In North America , whenever the error exceeds 10 seconds for the Eastern Interconnection , 3 seconds for

2850-407: Is effectively a voltage conversion device with no moving parts and requiring little maintenance. The use of AC eliminated the need for spinning DC voltage conversion motor-generators that require regular maintenance and monitoring. Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at

2945-454: Is little certitude in the details of the history of 60 Hz vs. 50 Hz. The German company AEG (descended from a company founded by Edison in Germany) built the first German generating facility to run at 50 Hz. At the time, AEG had a virtual monopoly and their standard spread to the rest of Europe. After observing flicker of lamps operated by the 40 Hz power transmitted by

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3040-410: Is operated on a low-frequency current, the filament cools on each half-cycle of the alternating current, leading to perceptible change in brightness and flicker of the lamps; the effect is more pronounced with arc lamps , and the later mercury-vapor lamps and fluorescent lamps . Open arc lamps made an audible buzz on alternating current, leading to experiments with high-frequency alternators to raise

3135-439: Is reversed for reproduction: the electrical audio signal is amplified and then converted back into physical waveforms via a loudspeaker . Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation, duplication, and amplification. Analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in

3230-500: Is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user . In large parts of the world this is 50  Hz , although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country . During the development of commercial electric power systems in

3325-481: Is the only utility frequency shown for that region. Other power frequencies are still used. Germany, Austria, Switzerland, Sweden, and Norway use traction power networks for railways, distributing single-phase AC at 16 + 2 ⁄ 3  Hz or 16.7 Hz. A frequency of 25 Hz is used for the Austrian Mariazell Railway , as well as Amtrak and SEPTA 's traction power systems in

3420-469: Is then modulated by a pseudo-noise (PN) sequence, then shaped within the frequency domain and put back in the original signal. The strength of the embedding determines the strength of the watermark on the audio data. Pulse-code modulation (PCM) was invented by British scientist Alec Reeves in 1937. In 1950, C. Chapin Cutler of Bell Labs filed the patent on differential pulse-code modulation (DPCM),

3515-790: The Higashi-Shimizu Frequency Converter . Utility frequencies in North America in 1897 Utility frequencies in Europe to 1900 Even by the middle of the 20th century, utility frequencies were still not entirely standardized at the now-common 50 Hz or 60 Hz. In 1946, a reference manual for designers of radio equipment listed the following now obsolete frequencies as in use. Many of these regions also had 50-cycle, 60-cycle, or direct current supplies. Frequencies in use in 1946 (as well as 50 Hz and 60 Hz) Where regions are marked (*), this

3610-507: The Lauffen-Frankfurt link in 1891, AEG raised their standard frequency to 50 Hz in 1891. Westinghouse Electric decided to standardize on a higher frequency to permit operation of both electric lighting and induction motors on the same generating system. Although 50 Hz was suitable for both, in 1890 Westinghouse considered that existing arc-lighting equipment operated slightly better on 60 Hz, and so that frequency

3705-552: The Nyquist frequency (half the sampling rate). A digital audio signal may be stored or 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 change signals that have been encoded with

3800-696: The Texas Interconnection , or 2 seconds for the Western Interconnection , a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half-hour. Real-time frequency meters for power generation in the United Kingdom are available online – an official one for the National Grid, and an unofficial one maintained by Dynamic Demand. Real-time frequency data of

3895-720: The United States was made by Thomas Stockham at the Santa Fe Opera in 1976, on a Soundstream recorder. An improved version of the Soundstream system was used to produce several classical recordings by Telarc in 1978. The 3M digital multitrack recorder in development at the time was based on BBC technology. The first all-digital album recorded on this machine was Ry Cooder 's Bop till You Drop in 1979. British record label Decca began development of its own 2-track digital audio recorders in 1978 and released

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3990-498: The Warren Power Station Master Clock and self-starting synchronous motor. Nikola Tesla demonstrated the concept of clocks synchronized by line frequency at the 1893 Chicago Worlds fair . The Hammond Organ also depends on a synchronous AC clock motor to maintain the correct speed of its internal "tone wheel" generator, thus keeping all notes pitch-perfect. Today, AC power network operators regulate

4085-576: The 1600-series adaptors by way of disabling the chroma and dropout compensator circuits of the VCRs, which would hinder the proper recording of the monochrome-video-based digital audio data from the 1600-series adaptors if enabled. The BVU-200B packaged with the PCM-1600 also was modified to have its video head switching point moved to the vertical blanking interval of the digital-audio-bearing video signal being recorded to prevent errors or interference with

4180-524: The 1914 edition of the standard. Remnant installations at other frequencies persisted until well after the Second World War. Because of the cost of conversion, some parts of the distribution system may continue to operate on original frequencies even after a new frequency is chosen. 25 Hz power was used in Ontario , Quebec , the northern United States, and for railway electrification . In

4275-581: The 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Until 2006, some 25 Hz generators were still in existence at the Sir Adam Beck 1 (these were retrofitted to 60 Hz) and the Rankine generating stations (until its 2006 closure) near Niagara Falls to provide power for large industrial customers who did not want to replace existing equipment; and some 25 Hz motors and

4370-434: The 1970s, Bishnu S. Atal and Manfred R. Schroeder at Bell Labs developed a form of LPC called adaptive predictive coding (APC), a perceptual coding algorithm that exploited the masking properties of the human ear, followed in the early 1980s with the code-excited linear prediction (CELP) algorithm. Discrete cosine transform (DCT) coding, a lossy compression method first proposed by Nasir Ahmed in 1972, provided

4465-415: The 19th century. Very early isolated AC generating schemes used arbitrary frequencies based on convenience for steam engine , water turbine , and electrical generator design. Frequencies between 16 + 2 ⁄ 3  Hz and 133 + 1 ⁄ 3  Hz were used on different systems. For example, the city of Coventry, England, in 1895 had a unique 87 Hz single-phase distribution system that

4560-576: The Au Sable Electric Company used 30 Hz at transmission voltages up to 110,000 volts in 1914. Initially in Brazil, electric machinery were imported from Europe and United States, implying the country had both 50 Hz and 60 Hz standards according to each region. In 1938, the federal government made a law, Decreto-Lei 852 , intended to bring the whole country under 50 Hz within eight years. The law did not work, and in

4655-507: The United States. Other AC railway systems are energized at the local commercial power frequency, 50 Hz or 60 Hz. Traction power may be derived from commercial power supplies by frequency converters, or in some cases may be produced by dedicated traction powerstations . In the 19th century, frequencies as low as 8 Hz were contemplated for operation of electric railways with commutator motors. Some outlets in trains carry

4750-619: The Westinghouse company objected that this would be undesirable for lighting and suggested 33 + 1 ⁄ 3  Hz. Eventually a compromise of 25 Hz, with 12-pole 250 RPM generators, was chosen. Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC. A General Electric study concluded that 40 Hz would have been

4845-609: The Westinghouse standard. The first generators at the Niagara Falls project , built by Westinghouse in 1895, were 25 Hz, because the turbine speed had already been set before alternating current power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. The machines could have been made to deliver 16 + 2 ⁄ 3  Hz power suitable for heavy commutator-type motors, but

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4940-1072: The advent of the National Grid (UK) in the late 1920s, and projects in Italy used 42 Hz. The oldest continuously operating commercial hydroelectric power station in the United States, Mechanicville Hydroelectric Plant , still produces electric power at 40 Hz and supplies power to the local 60 Hz transmission system through frequency changers . Industrial plants and mines in North America and Australia sometimes were built with 40 Hz electrical systems which were maintained until too uneconomic to continue. Although frequencies near 40 Hz found much commercial use, these were bypassed by standardized frequencies of 25, 50 and 60 Hz preferred by higher volume equipment manufacturers. The Ganz Company of Hungary had standardized on 5000 alternations per minute (41 2 ⁄ 3  Hz) for their products, so Ganz clients had 41 2 ⁄ 3  Hz systems that in some cases ran for many years. In

5035-490: The audio data being recorded to the tape using a multi-track stationary tape head. PCM adaptors allowed for stereo digital audio recording on a conventional NTSC or PAL video tape recorder . The 1982 introduction of the CD by Philips and Sony popularized digital audio with consumers. ADAT became available in the early 1990s, which allowed eight-track 44.1 or 48 kHz recording on S-VHS cassettes, and DTRS performed

5130-466: The basis for the modified discrete cosine transform (MDCT), which was developed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987. The MDCT is the basis for most audio coding standards , such as Dolby Digital (AC-3), MP3 ( MPEG Layer III), AAC, Windows Media Audio (WMA), Opus and Vorbis ( Ogg ). PCM was used in telecommunications applications long before its first use in commercial broadcast and recording. Commercial digital recording

5225-554: The choice of frequency in an AC system. Lighting, motors, transformers, generators, and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise among competing requirements. In the late 19th century, designers would pick a relatively high frequency for systems featuring transformers and arc lights , so as to economize on transformer materials and to reduce visible flickering of

5320-482: The computer can effectively run at a single time. Avid Audio and Steinberg released the first digital audio workstation software programs in 1989. Digital audio workstations make multitrack recording and mixing much easier for large projects which would otherwise be difficult with analog equipment. The rapid development and wide adoption of PCM digital telephony was enabled by metal–oxide–semiconductor (MOS) switched capacitor (SC) circuit technology, developed in

5415-433: The correct voltage, but using the original train network frequency like 16 + 2 ⁄ 3  Hz or 16.7 Hz. Power frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for computer power , military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances; the increased frequency greatly increases series impedance due to

5510-535: The costs of distribution as well as making it easier to share copies. 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. Popular streaming services such as Apple Music , Spotify , or YouTube , offer temporary access to

5605-464: The customer's equipment. Generators operated by slow-speed reciprocating engines will produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam turbine . For very slow prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. While belt drives were common as

5700-459: The daily average frequency so that clocks stay within a few seconds of the correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at a nominal value within a few hundred parts per million. In the synchronous grid of Continental Europe , the deviation between network phase time and UTC (based on International Atomic Time )

5795-429: The digital audio data. Editing was accomplished by using a 1600-series adaptor and two or more of these VCRs with a DAE-1100 or DAE-3000 editing controller. The 1600-series were the first systems used for mastering audio compact discs in the early 1980s by many major record labels, with the final U-matic 1600-format digital audio tapes being sent to CD pressing plants to be recorded to a glass master disc used for making

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5890-399: The digital file, and are now the most common form of music consumption. 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 then stored on an analog medium such as magnetic tape , or transmitted through an analog medium such as a telephone line or radio . The process

5985-429: The early 1960s it was decided that Brazil would be unified under 60 Hz standard, because most developed and industrialized areas used 60 Hz; and a new law Lei 4.454 was declared in 1964. Brazil underwent a frequency conversion program to 60 Hz that was not completed until 1978. In Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting the country under 60 Hz. In Japan,

6080-570: The early 1970s. This led to the development of PCM codec-filter chips in the late 1970s. The silicon-gate CMOS (complementary MOS) PCM codec-filter chip, developed by David A. Hodges and W.C. Black in 1980, has since been the industry standard for digital telephony. By the 1990s, telecommunication networks such as the public switched telephone network (PSTN) had been largely digitized with VLSI (very large-scale integration ) CMOS PCM codec-filters, widely used in electronic switching systems for telephone exchanges , user-end modems and

6175-427: The early days of electrification, so many frequencies were used that no single value prevailed (London in 1918 had ten different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). Standardization allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids. It

6270-402: The economics of electricity production, since system load was more uniform during the course of a day. The first applications of commercial electric power were incandescent lighting and commutator -type electric motors . Both devices operate well on DC, but DC could not be easily changed in voltage, and was generally only produced at the required utilization voltage. If an incandescent lamp

6365-409: The existing synchronization circuitry – as video, the resulting images look like lines of binary black and white (rather, gray) dots along each scan line. The line frequency (lines per second) was 15,625 Hz for PAL (625 × 50/2), 15,750 Hz for 60 Hz (monochrome) NTSC (525 × 60/2), and 15,750/1.001 Hz (approximately 15,734.26 Hz) for 59.94 (color) NTSC, and thus to record audio at

6460-399: The first European digital recording in 1979. Popular professional digital multitrack recorders produced by Sony/Studer ( DASH ) and Mitsubishi ( ProDigi ) in the early 1980s helped to bring about digital recording's acceptance by the major record companies. Machines for these formats had their own transports built-in as well, using reel-to-reel tape in either 1/4", 1/2", or 1" widths, with

6555-543: The formula, where f is the frequency in hertz and P is the number of poles. Direct-current power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of mercury arc valve rectifiers , rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies. With AC, transformers can be used to step down high transmission voltages to lower customer utilization voltage. The transformer

6650-414: The inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle. Transformers , for example, can be made smaller because the magnetic core can be much smaller for the same power level. Induction motors turn at a speed proportional to frequency, so a high-frequency power supply allows more power to be obtained for

6745-445: The lamps, but would pick a lower frequency for systems with long transmission lines or feeding primarily motor loads or rotary converters for producing direct current . When large central generating stations became practical, the choice of frequency was made based on the nature of the intended load. Eventually improvements in machine design allowed a single frequency to be used both for lighting and motor loads. A unified system improved

6840-461: The late-19th and early-20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240  V , and those that now use 60 Hz tend to use 100–127 V. Both frequencies coexist today (Japan uses both) with no great technical reason to prefer one over

6935-804: The market were the Nakamichi DMP-100, the JVC VP-100, the Sharp RX-3, the Sansui PC-X1 and the Hitachi PCM-V300. dbx, Inc. also manufactured a pseudo-video adaptor, the Model 700 . It differed from the above-listed models in the fact that it did not use PCM, but rather delta-sigma modulation . This resulted in a higher quality digital recording with more dynamic range than what standard PCM modulation could offer. Like

7030-439: The materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). Once AC electric motors became common, it was important to standardize frequency for compatibility with

7125-578: The obligatory 44.1 kHz sampling rate, but also 48 kHz on all machines, and eventually a 96 kHz sampling rate. They overcame the problems that made typical analog recorders unable to meet the bandwidth (frequency range) demands of digital recording by a combination of higher tape speeds, narrower head gaps used in combination with metal-formulation tapes, and the spreading of data across multiple parallel tracks. Unlike analog systems, modern digital audio workstations and audio interfaces allow as many channels in as many different sampling rates as

7220-461: The other and no apparent desire for complete worldwide standardization. In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust generation onto the grid over the course of the day to ensure a constant number of cycles occur. This is used by some clocks to accurately maintain their time. Several factors influence

7315-529: The professional audio market about the same time as the introduction of PCM adaptors. Other tape-based digital audio recording systems overcame problems that made typical analog recorders unable to meet the bandwidth (frequency range) demands of digital recording by a combination of higher tape speeds, narrower head gaps used in combination with metal-formulation tapes, and the spreading of data across multiple parallel tracks. Despite obsolescence, hobbyists are still capable of using modern-day DVDs or Blu-ray discs as

7410-688: The replicated CDs. Several semi-professional/consumer models of PCM adaptors were also released by Sony: Technics also made a battery-powered portable PCM adaptor, the SV-100, a hi-fi component adapter, the SV-110, and a version with a built-in VHS videocassette transport, the SV-P100. All the Technics (Panasonic) PCM adapters are limited to 14-bit resolution. Other makes and models of PCM adaptors offered on

7505-446: The required over 40 kHz required encoding multiple samples per line, with 3 samples per line being sufficient, yielding up to 15,625 × 3 = 46,875 for PAL and 15,750 × 3 = 47,250 for NTSC. It is desirable to minimize the number of samples per line, so that each sample can have more space devoted to it, thus making it easier to have a higher bit depth (16 bits, rather than 14 or 12 bits, say) and better error tolerance, and in practice,

7600-467: The result of a need for compatibility with the 25-frame (PAL countries) and 30-frame black and white (NTSC countries) video formats used for audio storage at the time. Audio samples are recorded as if they were on the lines of a raster scan of video, as follows: analog video standards represent video at a field rate of 60 Hz ( NTSC , North America – or 60/1.001 Hz ≈ 59.94 Hz for color NTSC) or 50 Hz ( PAL , Europe), which corresponds to

7695-404: The same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships. A United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power. Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1916 with Henry Warren 's invention of

7790-510: The same speed as a 25 Hz machine with 10 poles, making the machines large, slow-speed, and expensive. A ratio of 60/30 would have simplified these designs, but the installed base at 25 Hz was too large to be economically opposed. In the United States, Southern California Edison had standardized on 50 Hz. Much of Southern California operated on 50 Hz and did not completely change frequency of their generators and customer equipment to 60 Hz until around 1948. Some projects by

7885-517: The signal was stereo, requiring 3 × 2 = 6 samples per line. However, some of these lines are devoted to (vertical) synchronization: specifically, the lines during the vertical blanking interval (VBI) could not be used, so a maximum of 490 lines per frame (245 lines per field) could be used in NTSC, and about 588 lines per frame (294 lines per field) on PAL (Note that, in video, PAL has (up to) 575 visible lines while NTSC has up to 485). The Sony PCM-1600

7980-487: The sound above the range of human hearing. Commutator -type motors do not operate well on high-frequency AC, because the rapid changes of current are opposed by the inductance of the motor field. Though commutator-type universal motors are common in AC household appliances and power tools, they are small motors, less than 1 kW. The induction motor was found to work well on frequencies around 50 to 60 Hz, but with

8075-423: The standard frequency system via a rotary converter or static inverter frequency changer. These allow energy to be interchanged between two power networks at different frequencies, but the systems are large, costly, and waste some energy in operation. Rotating-machine frequency changers used to convert between 25 Hz and 60 Hz systems were awkward to design; a 60 Hz machine with 24 poles would turn at

8170-400: 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 the channel code used for the audio compact disc (CD). If an audio signal is analog, a digital audio system starts with an ADC that converts an analog signal to a digital signal. The ADC runs at

8265-767: The synchronous grid of Continental Europe is available on websites such as www .mainsfrequency .com . The Frequency Monitoring Network (FNET) at the University of Tennessee measures the frequency of the interconnections within the North American power grid, as well as in several other parts of the world. These measurements are displayed on the FNET website. In the United States, the Federal Energy Regulatory Commission made time error correction mandatory in 2009. In 2011, The North American Electric Reliability Corporation (NERC) discussed

8360-400: The videotape. The use of video for the PCM adapter helps to explain the choice of sampling frequency for the CD, because the number of video lines, frame rate and bits per line end up dictating the sampling frequency one can achieve. A sampling frequency of 44.1 kHz was thus adopted for the compact disc , as at the time, there was no other practical way of storing digital audio than by using

8455-545: The western part of the country (Nagoya and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano , Sakuma Dam , Minami-Fukumitsu , and

8550-491: Was chosen. The operation of Tesla's induction motor, licensed by Westinghouse in 1888, required a lower frequency than the 133 Hz common for lighting systems at that time. In 1893 General Electric Corporation, which was affiliated with AEG in Germany, built a generating project at Mill Creek to bring electricity to Redlands, California using 50 Hz, but changed to 60 Hz a year later to maintain market share with

8645-404: Was completely established only after World War II . By about 1900, European manufacturers had mostly standardized on 50 Hz for new installations. The German Verband der Elektrotechnik (VDE), in the first standard for electrical machines and transformers in 1902, recommended 25 Hz and 50 Hz as standard frequencies. VDE did not see much application of 25 Hz, and dropped it from

8740-405: Was in use until 1906. The proliferation of frequencies grew out of the rapid development of electrical machines in the period 1880 through 1900. In the early incandescent lighting period, single-phase AC was common and typical generators were 8-pole machines operated at 2,000 RPM, giving a frequency of 133 hertz. Though many theories exist, and quite a few entertaining urban legends , there

8835-474: Was not until after World War II – with the advent of affordable electrical consumer goods – that more uniform standards were enacted. In the United Kingdom, a standard frequency of 50 Hz was declared as early as 1904, but significant development continued at other frequencies. The implementation of the National Grid starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. The 50 Hz standard

8930-499: 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 also began to experiment with digital audio in the 1960s. By the early 1970s, it had developed a 2-channel recorder, and in 1972 it deployed a digital audio transmission system that linked their broadcast center to their remote transmitters. The first 16-bit PCM recording in

9025-603: Was the first commercial video-based 16-bit recorder. The 1600 (and its later versions, the 1610 and 1630) used special U-matic -format VCRs also furnished by Sony for transports , such as the BVU-200B (the first model of VCR optimized to work, and sold with, the PCM-1600 in 1979), BVU-800DA, VO-5630DA, and the later DMR-2000 and DMR-4000, which were based on the industrial VO-5850 and the broadcast BVU-800 video machines respectively. These were all in essence modified versions of existing Sony U-Matic video recorders adapted for use with

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