RIAA equalization From Wikipedia, the free encyclopedia Jump to:
navigation,
search 
The RIAA equalization curve for playback of vinyl records.
RIAA equalization is a specification for the correct playback of
gramophone records, established by the
Recording Industry Association of America (RIAA). The purpose of the
equalization is to permit greater playback times, improve sound quality, and to limit the vinyl damages that would otherwise arise from recording analog records without such equalization.
The
RIAA equalization curve has operated as a
de facto global
industry standard for the recording and playback of vinyl records since 1954. 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 RIAA curve
RIAA equalization is a form of
preemphasis on recording, and
deemphasis on playback. A record is cut with the low
frequencies reduced and the high frequencies boosted, and on playback the opposite occurs. The result is a flat frequency response, but with noise such as hiss and clicks arising from the surface of the medium itself much
attenuated. The other main benefit of the system is that low frequencies, which would otherwise cause the cutter to make large excursions when cutting a groove, are much reduced, so grooves are smaller and more can be fitted in a given surface area, yielding longer playback times. This also has the benefit of eliminating physical stresses on the playback
stylus which might otherwise be hard to cope with, or cause unpleasant
distortion.
A potential drawback of the system is that
rumble from the playback
turntable's drive mechanism is greatly amplified, which means that players have to be carefully designed to avoid this.
RIAA equalization is not a simple low-pass filter. It carefully defines transition points in three places - 75 µs, 318 µs and 3180 µs, which correspond to 2122 Hz, 500 Hz and 50 Hz. Implementing this characteristic is not especially difficult, but more involved than a simple
amplifier. Most
hi-fi amplifiers have a built-in phono preamplifier with the RIAA characteristic, though it is often omitted in modern designs, due to the gradual obsolescence of vinyl records. A solution in this case is to purchase an outboard preamplifier with the RIAA equalization curve, which adapts a
magnetic cartridge to a standard
line-level 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 issues of the
sound card being used to capture the signal.