More surprises about the curves
I discovered these interesting facts in the website of AMR Audio which also makes a phono preamp equaliser with 23 equalisation curves. To read more, click http://www.amr-audio.co.uk/html/faq_ph.html#ref
FAQ: If the RIAA equalisation curve was standardised in the 1950s, why are different equalisation curves required?
The simple answer is that as not all LPs have been equalised using the same RIAA equalisation, additional equalisation curves are needed.
At the introduction of the Long Play record (LP) in 1948, most record companies implemented their own particular equalisation curve and continued to experiment with equalisation in order to extract the best performance from the new medium. This led to a baffling array of different and incompatible equalisation curves being applied worldwide.
In the mid-1950s, most of the record companies agreed to adopt the RCA Orthophonic equalisation curve, the Recording Industry Association of America (RIAA) promulgated this curve as a common standard which became known as the “RIAA equalisation”.
However, as this was essentially an American standard, it had little impact outside of the USA. The RIAA equalisation only became a truly international standard by the mid-to-late 1970s when European recording labels slowly and finally began to adopt the RIAA equalisation. It was even later when some Asian recording labels joined the bandwagon and adopted the RIAA standard. Right up to the fall of the Berlin Wall in 1989, many Eastern European recording labels (including Russian recording labels) were still, using their own CCIR equalisation.
To further complicate matters, even after officially agreeing to implement the RIAA equalisation curve, many recording labels still continued to use their own, proprietary equalisation, even well into the 1970s. Columbia is one such prominent example in the USA, Decca/Telefunken/Teldec in Europe is another.
According to Peter Copeland in his excellent “Manual of Analogue Sound Restoration Techniques”:
“I consider the whole subject should be a warning to today’s audio industry; practically everything which could go wrong did go wrong, and it isn’t anybody’s fault. But much worse is everyone’s apparent attempts to hide what happened.”
Related posts: http://hi-fi-avenue.blogspot.com/2011/09/what-is-right-tonal-balance.html