Originally Posted by Pitou
I have to admit, I don't know what is the RIAA correction. Could you explain a bit?
RIAA correction is a very specific EQ applied to the signal BEFORE its put on the record. When you play it back the opposite EQ is used, and you get a flat response.
It is not an EQ like someone might use an EQ to fix the fact that their crappy speakers have no bass. It adds X at the beginning of the process, and subtracts x at the end. The end result is exactly the same as what went in.
Why we use RIAA:
Early in the development of the electronically-recorded record (and probably before), it was noted that the most annoying type of noise was pops and clicks. To solve this problem some smart dudes figured out that audibility of pops & clicks could be reduced if you EQ'ed the highs way high. It was also noted that if you had too much bass on the disc it caused weird problems - so these guys attenuated the bass before they cut the disc. When you play it back you attenuate the highs (which also attenuates the effect of dust - you like that?) and amplify the lows to get a flat result.
Pretty much everyone agreed that this was a good idea in general, but nobody could agree on exactly how to implement it so at first there was a lot of confusion and disagreement between MFR's. This was kind of sucky because an RCA record might not sound right on a doiche-gramaphone-player.... Eventually RIAA came around and set up their standard that everyone agreed (or was forced) to follow so all records made after a certain time would play properly on anyone's gear.
So the problems with digital RIAA is that the signal directly out of the cartridge is ~40db higher at 20khz than at 20hz. This requires a boatload of manipulation in the digital domain which comes after the noise is introduced by the ADC which of course treats noise as signal and amplifies it right along.
With an analog phono stage noise is still an issue (its always an issue - 95% of all problem solving in audio is simply moving the problem somewhere else) but the importance of the soundcard is reduced.