RIAA equalization
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, but when the change actually took place is difficult to determine.[1]
Before then, especially from 1940, each record company applied its own equalization; over 100 combinations of turnover and rolloff frequencies were 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.
IEC RIAA curve[edit]
In 1976, an alternative version of the replay curve (but not the recording curve) was proposed by the International Electrotechnical Commission, differing from the RIAA replay curve only in the addition of a pole at 7950 μs (approximately 20 Hz).[12] The justification was to reduce the subsonic output of the phono amplifier caused by disk warp and turntable rumble.
This so-called IEC amendment to the RIAA curve is not universally seen as desirable, as it introduces considerable amplitude and—of more concern—phase errors into the low-frequency response during playback. The simple first-order roll-off also provides only very mild reduction of rumble,[11] and many manufacturers consider that turntables, arm, and cartridge combinations should be of sufficient quality for problems not to arise.
Some manufacturers follow the IEC standard, others do not, while the remainder make this IEC-RIAA option user selectable. It remains subject to debate some 35 years later.[2] This IEC Amendment was withdrawn in June 2009, though.
TELDEC/DIN Curve[edit]
Telefunken and Decca founded a record company (Teldec) that used a characteristic which was also proposed for German DIN standards in July 1957 (Entwurf DIN 45533, DIN 45536, and DIN 45537). Incidentally, this proposed standard defined exactly the same characteristic as the intermediate CCIR Recommendation No. 208 of 1956, which was valid until about mid-1959. Nevertheless, the proposed DIN standards were was adopted in April 1959 (DIN 45533:1959, DIN 45536:1959, and DIN 45537:1959): that is, at a time when the RIAA characteristic was already well-established; and it was in effect until November 1962, when the German DIN finally adopted the RIAA characteristic (DIN 45536:1962 and DIN 45537:1962). The extent of usage of the Teldec characteristic is unclear, though.
The time constants of the Teldec characteristic are 3180 μs (approximately 50 Hz), 318 μs (approximately 500 Hz), and 50 μs (approximately 3183 Hz), thus differing only in the third value from the corresponding RIAA values.[13] Although the Teldec characteristic is close to the RIAA characteristic, it is different enough for recordings recorded with the former and played back with the latter to sound a little dull.[14]