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RIAA equalization is a specification for the recording and playback of phonograph records, established by the Recording Industry Association of America (RIAA). The purposes of the equalization are to permit greater recording times (by decreasing the mean width of each groove), to improve sound quality, and to reduce the groove damage that would otherwise arise during playback. The RIAA equalization curve was intended to operate as a de facto global industry standard for records since 1954. However, it is almost impossible to say when the change actually took place. Before then, especially from 1940, each record company applied its own equalization; there were over 100 combinations of turnover and rolloff frequencies in use, the main ones being Columbia-78, Decca-U.S., European (various), Victor-78 (various), Associated, BBC, NAB, Orthacoustic, World, Columbia LP, FFRR-78 and microgroove, and AES. The obvious consequence was that different reproduction results were obtained if the recording and playback filtering were not matched. ==The RIAA curve== RIAA equalization is a form of pre-emphasis on recording and de-emphasis on playback. A recording is made with the low frequencies reduced and the high frequencies boosted, and on playback the opposite occurs. The net result is a flat frequency response, but with attenuation of high frequency noise such as hiss and clicks that arise from the recording medium. Reducing the low frequencies also limits the excursions the cutter needs to make when cutting a groove. Groove width is thus reduced, allowing more grooves to fit into a given surface area, permitting longer recording times. This also reduces physical stresses on the stylus which might otherwise cause distortion or groove damage during playback. A potential drawback of the system is that rumble from the playback turntable's drive mechanism is amplified by the low frequency boost that occurs on playback. Players must therefore be designed to limit rumble, more so than if RIAA equalization did not occur. RIAA equalization is not a simple low-pass filter. It defines transition points in three places: 75 µs, 318 µs and 3180 µs, which correspond to 2122 Hz, 500 Hz and 50 Hz (rounded values).〔'Cut and Thrust: RIAA LP Equalization' by Keith Howard, Stereophile, Vol. 32, No. 3, March 2009, pp. 53–62 http://www.stereophile.com/features/cut_and_thrust_riaa_lp_equalization/index.html〕 Implementing this characteristic is not especially difficult, but is more involved than a simple amplifier.〔'On RIAA Equalization Networks' by Stanley P. Lipshitz, Journal of the AES, Vol. 27, No. 6, June 1979, pp. 458–481.〕 In the past, almost all hi-fi preamplifiers, integrated amplifiers, and receivers had a built-in phono preamplifier with the RIAA characteristic, but it is often omitted in modern designs, due to the gradual obsolescence of vinyl records. Add-on phono preamplifiers with the RIAA equalization curve are available; these adapt a magnetic phono cartridge to an unbalanced −10 dB consumer line-level RCA input. Some modern turntables feature built-in preamplification to the RIAA standard. Special preamplifiers are also available for the various equalization curves used on pre-1954 records. Digital audio editors often feature the ability to equalize audio samples using standard and custom equalization curves, removing the need for a dedicated hardware preamplifier when capturing audio with a computer. However, this can add an extra step in processing a sample, and may amplify audio quality deficiencies of the sound card being used to capture the signal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RIAA equalization」の詳細全文を読む スポンサード リンク
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