RIAA equalization

RIAA equalization is a specification for the correct playback of vinyl recordss. The purpose of the equalization is to permit greater playback times, improve sound quality, and to limit the physical extremes that would otherwise arise from recording analogue records without such equalization.

The RIAA equalization curve operates as a de facto global industry standard for the recording and playback of vinyl records.

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.

The only real 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 roll-off points in three places - 75µS, 318 µS and 3180µS, which correspond to 2122 Hz, 500 Hz and 50 Hz (the last being a high pass to combat rumble). Implementing this characteristic is not especially difficult, but more involved that a simple linear amplifier. The phono input of most hi-fi amplifiers have this characteristic built-in, though it is omitted in many modern designs due to the gradual obsolescence of vinyl records. A solution in this case is to buy a special preamplifier which will adapt a magnetic cartridge to a standard input, and implement the RIAA equalization curve separately.