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Adaptive Biasing
In magnetic tape recording, adaptive biasing is the technique of continuously varying the bias current to a recording head in accordance with the level of high-frequency audio signals. With adaptive biasing, high levels of high-frequency audio signals cause a proportionate decrease in bias current using either feedforward or preferably a negative feedback control system. Compared with the use of fixed bias current, adaptive biasing provides a higher maximum output level and higher dynamic range at the upper end of the audible spectrum and to a lesser extent, mid-range frequencies. The effect of adaptive biasing is most pronounced in compact cassette and low-speed reel-to-reel media. The first commercial implementation, the feedforward system Dolby HX was developed by Dolby Laboratories by 1979 and was rejected by the industry. The subsequent negative-feedback system Dolby HX Pro was developed by Bang & Olufsen and marketed by Dolby, and became the ''de facto'' standard of the consu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tape Recorder
An audio tape recorder, also known as a tape deck, tape player or tape machine or simply a tape recorder, is a sound recording and reproduction device that records and plays back sounds usually using magnetic tape for storage. In its present-day form, it records a fluctuating signal by moving the tape across a tape head that polarizes the magnetic domains in the tape in proportion to the audio signal. Tape-recording devices include the reel-to-reel tape deck and the cassette deck, which uses a cassette tape (format), cassette for storage. The use of magnetic tape for sound recording originated around 1930 in Germany as paper tape with oxide lacquered to it. Prior to the development of magnetic tape, magnetic wire recording, wire recorders had successfully demonstrated the concept of magnetic recording, but they never offered audio quality comparable to the other recording and broadcast standards of the time. This German invention was the start of a long string of innovations ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Hysteresis
Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become ''magnetized''. Once magnetized, the magnet will stay magnetized indefinitely. To demagnetize it requires heat or a magnetic field in the opposite direction. This is the effect that provides the element of memory in a hard disk drive. The relationship between field strength and magnetization is not linear in such materials. If a magnet is demagnetized () and the relationship between and is plotted for increasing levels of field strength, follows the ''initial magnetization curve''. This curve increases rapidly at first and then approaches an asymptote called magnetic saturation. If the magnetic field is now reduced monotonically, follows a different curve. At zero field strength, the magnetization is offset from the origin by an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FM Radio
FM broadcasting is a method of radio broadcasting that uses frequency modulation (FM) of the radio broadcast carrier wave. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to transmit high fidelity, high-fidelity sound over broadcast radio. FM broadcasting offers higher fidelity—more accurate reproduction of the original program sound—than other broadcasting techniques, such as AM broadcasting. It is also less susceptible to Electromagnetic interference, common forms of interference, having less static and popping sounds than are often heard on AM. Therefore, FM is used for most broadcasts of music and general audio (in the audio spectrum). FM radio stations use the very high frequency range of radio frequency, radio frequencies. Broadcast bands Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. Usually 87.5 to 108.0 MHz is used, or some portion of it, with few exceptions: * In the Commo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gramophone Record
A phonograph record (also known as a gramophone record, especially in British English) or a vinyl record (for later varieties only) is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near the outside edge and ends near the center of the disc. The stored sound information is made audible by playing the record on a phonograph (or "gramophone", "turntable", or "record player"). Records have been produced in different formats with playing times ranging from a few minutes to around 30 minutes per side. For about half a century, the discs were commonly made from shellac and these records typically ran at a rotational speed of 78 rpm, giving it the nickname "78s" ("seventy-eights"). After the 1940s, "vinyl" records made from polyvinyl chloride (PVC) became standard replacing the old 78s and remain so to this day; they have since been produced in various sizes and speeds, most commonly 7-inch discs pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Range Compression
Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or ''compressing'' an audio signal's dynamic range. Compression is commonly used in sound recording and reproduction, broadcasting, sound reinforcement system, live sound reinforcement and some instrument amplifiers. A dedicated electronic hardware unit or audio software that applies compression is called a compressor. In the 2000s, compressors became available as software plugins that run in digital audio workstation software. In recorded and live music, compression parameters may be adjusted to change the way they affect sounds. Compression and limiting are identical in process but different in degree and perceived effect. A limiter is a compressor with a high #Ratio, ratio and, generally, a short #Attack and release, attack time. Compression is used to improve performance and clarity in public address ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Audio Tape Specifications
Since the widespread adoption of reel-to-reel audio tape recording in the 1950s, audio tapes and tape cassettes have been available in many formats. This article describes the length, tape thickness and playing times of some of the most common ones. All tape thicknesses here refer to the total tape thickness unless otherwise specified, including the base, the oxide coating and any back coating. In the United States, tape thickness is often expressed as the thickness of the base alone. However, this varies from manufacturer to manufacturer and also between tape formulations from the same manufacturer. Outside of the US, the overall thickness is more often quoted, and is the more relevant measurement when relating the thickness to the length that can be fit onto a reel or into a cassette. Reel-to-reel quarter-inch The tape decks of the 1950s were mainly designed to use tape wide and to accept one of two reel formats: * reels, almost always with metal flanges, which fit ove ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emphasis (telecommunications)
In signal processing, pre-emphasis is a technique to protect against anticipated noise and loss. The idea is to boost (and hence distort) the frequency range that is most susceptible to noise and loss beforehand, so that after a noisy and lossy process (transmission over cable, tape recording...) more information can be recovered from that frequency range. Removal of the distortion caused by pre-emphasis is called de-emphasis, making the output accurately reproduce the original input. Emphasis is commonly used in many places ranging from FM broadcasting ( preemphasis improvement) and vinyl (e.g. LP) records to PCI Express. For example, high-frequency signal components may be emphasized to produce a more equal modulation index for a transmitted frequency spectrum, and therefore a better signal-to-noise ratio for the entire frequency range. In audio signals In processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within a frequency ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whose level (logarithmic quantity), levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ). The strict original usage above only expresses a relative change. However, the word decibel has since also been used for expressing an Absolute scale, absolute value that is relative to some fixed reference value, in which case the dB symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is "#Voltage, V" (e.g., "20 dBV"). As it originated from a need to express power ratios, two principal types of scaling of the decibel are used to provide consistency depending on whether the scaling refer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulation Noise
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message signal onto a carrier signal to be transmitted. For example, the message signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. This carrier wave usually has a much higher frequency than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, receiving a radio wave requires a radio antenna with a length that is one-fourth of the wavelength of the transmitted wave. For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. Another purpose of modulation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal representing sound or a video signal representing images, in an electronic device or communication channel. Distortion is usually unwanted, and so engineers strive to eliminate or minimize it. In some situations, however, distortion may be desirable. For example, in noise reduction systems like the Dolby noise-reduction system, Dolby system, an audio signal is deliberately distorted in ways that emphasize aspects of the signal that are subject to electrical noise, then it is symmetrically "undistorted" after passing through a noisy communication channel, reducing the noise in the received signal. Distortion is also used as a Distortion (music), musical effect, particularly with electric guitars. The addition of Electronic noise, noise o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal-to-noise Ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. SNR is an important parameter that affects the performance and quality of systems that process or transmit signals, such as communication systems, audio systems, radar systems, imaging systems, and data acquisition systems. A high SNR means that the signal is clear and easy to detect or interpret, while a low SNR means that the signal is corrupted or obscured by noise and may be difficult to distinguish or recover. SNR can be improved by various methods, such as increasing the signal strength, reducing the noise level, filtering out unwanted noise, or using error correction techniques. SNR also determines the maximum possible amount of data that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Direct Current
Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow through semiconductors, electrical insulation, insulators, or even through a vacuum as in electron beam, electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A archaism, term formerly used for this type of current was galvanic current. The abbreviations ''AC'' and ''DC'' are often used to mean simply ''alternating'' and ''direct'', as when they modify ''Electric current, current'' or ''voltage''. Direct current may be converted from an alternating current supply by use of a rectifier, which contains Electronics, electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
