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Entries found for search: distortion

crossover distortion : A type of distortion present in some amplifiers which increases for low-level signals. In many amplifiers, the output devices are connected so that one of them is active during the positive half of the waveform, an the other one is active for the negative half. There is a region near zero current where the signal is transferred from one to the other. If this is not done smoothly, there will result a small discontinuity in the output waveform. This discontinuity causes higher-order harmonic distortion, and being constant in value, is more noticeable with low-level signals than with stronger ones. See crossover frequency.

saturation distortion : The distortion that results on magnetic recording tape when the applied audio signal is greater than its retentivity.

phase distortion : An effect caused when phase-shift in an audio device is not a linear function of frequency. In other words, different frequencies experience different time delays. This changes the waveform of the signal and is especially injurious to transients. Most transducers produce significant phase distortion. As low frequencies travel slightly faster than high frequencies and as air absorbs high frequencies more readily than low ones, the more delay there is between low frequencies and the higher harmonics of a sound, the sound becomes progressively more smeared and is perceived as more distant.

frequency distortion : Frequency distortion results when the amplitude of the output of a system or a device varies as the frequency of the input varies, while the amplitude of the input is held constant.

harmonic distortion : The onset of harmonic distortion is the displacement of energy from a single frequency to its harmonics. The presence of harmonic frequencies added to an output signal by an electrical circuit or speaker, generally undesirable, caused by the system not being perfectly linear, such as when an amplifier is operated in a nonlinear portion of its transfer curve. It is expressed as a percentage of the original signal:

(Total Signal - Fundamental Signal) THD = Total Signal In a perfect audio device, such as an amplifier or tape recorder, the output signal would be a replica of the input signal with no changes except possibly the amplitude of the signalmaybe power level. See also doubling.

intermodulation distortion : While harmonic distortion adds frequencies that are harmonically related, intermodulation distortion adds nonharmonic partials to the original signal. IM is a measure of how two frequencies that are present at the same time affect each other. Amplitude intermodulation distortion is caused when combinations of two or more frequencies generate new frequencies which are sums and differences of the original signal, i.e., the amplitude modulation of one signal by another. If an amplifier is used to amplify each tone equally, but if the gain of the amplifier varies with signal level (i.e., it is nonlinear), high-frequency sounds will be amplified by different amounts depending on whether a nearby low-frequency sound is near zero or near its peak. Therefore, the high-frequency signal will undergo changes in amplitude at the rate of the low-frequency signal, modulating the high-frequency sound which will be heard to flutter in the presence of the low-frequency sound. PIM is another component of intermodulation distortion, but to a lesser degree.

linear distortion : Any type of distortion that a linear system is capable of producing, as opposed to nonlinear distortion. Some types of linear distortion are frequency response errors and time-delay errors such as phase-shift.

magnetic distortion : A type of distortion in dynamic loudspeakers caused by nonlinearities in the interaction between the magnetic field in the gap and the voice coil.

multipath distortion : Multipath distortion is a type of distortion afflicting FM and television broadcasting. It is the receipt of the transmitted signal over more than one path due to reflections of the audio/video waves off of hills, buildings, etc. Because the path lengths are different, there is a delay between the various signal arrival times. In TV, this causes the familiar "ghosts," or multiple images, on the screen. In radio, this is the "caught between stations" effect.

scale distortion : Because the human ear has a sensitivity which varies with frequency and with loudness level, a musical ensemble must be reproduced at the same loudness as the listener would experience at the actual event if frequency distortion is not to occur. This happens because of the apparent amplitudes of the different frequencies will differ, with accentuation of the extreme high and low frequencies. Also called volume distortion. See equal loudness curves.

quantization distortion : See granulation.

phase distortion synthesis : A form of modulation synthesis in which the spectrum of a DCOís output signal is altered by modulating the DCOís clock frequency within each cycle, while the over-all frequency is kept constant. The oscillatorís clock frequency speeds up and slows down, producing rapid phase changes as the waveshape is alternately compressed and expanded (distorted) to fit within the regulated period. Popularized by the Casio CZ-series synthesizers.

nonlinear distortion Linearity would predict an invariant ratio of gain to input voltage in an audio device such as an amplifier. Manifested as harmonic distortion and intermodulation distortion, there is a point at which the amplifier gain is reduced as the input gain is increased. This is the nonlinear region of the amplifier. All audio devices have local peculiarities or deviations from linearity at specific signal levels. See also distortion, linear distortion.

third harmonic distortion : That part of harmonic distortion which represents only the third harmonic (three times the fundamental frequency) of a sine wavepure tone input to an electronic device. The third harmonic of any tone is musically an octave and a fifth above the original tone, and is easily noticeable in the output. For this reason, the MOL of analog tape recorders, for example, is often specified as that level at which third harmonic distortion reaches 3%..

transient distortion : This includes transient intermodulation distortion (TIM). The beginning and ending transients of musical sounds are largely what determine their timbre, rather than their harmonic content. An audio device which passes steady-state signals perfectly well may distort the loud, high-frequency transients, causing audible coloration of the music. Low transient distortion means a device must have a wide, linear frequency response, no phase distortion, and no hangover. TIM is caused by amplifier slew-limiting and is principally a problem in solid-state amplifiers that use large amounts of negative feedback.

distortion : Also called correlated noise. Any (usually) unwanted sound which varies with the input signal. (1) Any undesirable change in the characteristics of an audio signal of six types: The two types of (i) nonlinear distortion are intermodulation distortion and harmonic distortion. Other types of distortion are (ii) frequency distortion (pitch-shift), (iii) phase distortion (time shift), (iv) transient distortion, (v) scale (volume) distortion, and (vi) frequency modulation distortion. There are other factors which cause music reproduction to be untrue to the original but which are not considered distortion, such as background noise, and a lack of directional realism and proper ambience due to the use of too few channels of reproduction. See noise. (2) A sound modulation technique whereby the original waveform is distorted intentionally.



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