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MiiB 12th May 2011 10:21 AM

RIAA Equalization Standard...
 
The Riaa Standard deviation curve has specific and well defined poles. the 50Hz the 500 Hz and the 2122Hz...poles.

But then theres is some companies that seem to have their own version or interpretation of the Riaa curve..and by reading Thorsten response there seems to quite a bit difference...between these different riaa-curves...

Is there a place or a good resource where i can gather more info on this..???

DF96 12th May 2011 11:23 AM

There is essentially only one RIAA curve. The classic paper is by Lipshitz.

There are two minor variations. One 'official' variation adds an LF rolloff from 20Hz, as a rumble/warp filter. An unofficial variation adds an HF boost (I forget the time constant: 7.5us?) to counteract HF cut in the cutting room - some prefer this, others don't.

Any other variation would be, in my opinion, an attempt to put 'musicality' above accuracy. Adjusting RIAA by ear, as some appear to do, is almost guaranteed to get it wrong although the result may sound pleasant. Others get it wrong because the interaction between components in a single network can be counter-intuitive, so a naive calculation leads people astray. I believe one of the motivations for Lipshitz writing his paper was the high proportion of published or commercial designs which were simply wrong, even when the designer wanted to get it right.

SY 12th May 2011 12:47 PM

One other source of confusion is the existence of multiple standards back in the day, with Columbia, Decca, Victor, NAB, FFRR, and a zoo of others all setting individual "standards." Non-standard standards became rare after 1954, but for those with collections of antediluvian disks, attention must be paid to the EQ beyond getting RIAA right.

Bonsai 12th May 2011 01:11 PM

There is only ONE RIAA curve and all LP's should confirm to this. I think Thorstens comments were really more around how individual (recording) engineers fiddle with the qualization in terms of boosting bass or treble for example.

The original curve was publisjed in 1964, and there was a second major amendment in 1976 which added the 20Hz breakpoint to counteract the arm resonances and disc warp.

davidsrsb 12th May 2011 02:30 PM

I have seen plenty of test results which show that the designer has messed about with the 75us pole to get 1~2dB of boost from 2kHz upwards, presumably to counter MM generator droop

stinius 12th May 2011 02:56 PM

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stinius 12th May 2011 02:57 PM

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stinius 12th May 2011 02:57 PM

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ThorstenL 12th May 2011 05:43 PM

Hi,

Quote:

Originally Posted by MiiB (Post 2569543)
The Riaa Standard deviation curve has specific and well defined poles. the 50Hz the 500 Hz and the 2122Hz...poles.

But then theres is some companies that seem to have their own version or interpretation of the Riaa curve..and by reading Thorsten response there seems to quite a bit difference...between these different riaa-curves...

Is there a place or a good resource where i can gather more info on this..???

First, I think it is important to be clear what RIAA means.

RIAA = Recording Industry Association of America (more precisely the USA).

Basically this means the guys whose main reason for being in this day and age is to sue it's customers for downloading music.

It was and is a Interest/lobbying group (who gave you the "home taping kills music" campaign and DMCA among others). It is not an organisation who'se decrees have any relevance in law or indeed can enforce adherence to any standards it issues. Even where it's members where concerned it had no way to force them to adhere to any of it's standards (you can be sure the RIAA would not censure or throw out Columbia Records for not using the RIAA EQ).

In the 1950's RCA managed to get the RIAA to adopt it's so-called "New Ortophonic" cutting EQ as standard recommendation to it's members. This meant that other major players at the time (including Columbia) where snubbed and pissed. You can "see" the outcome.

One of the reason for the choice of the RCA Ortophonic curve was that it sat neatly between several of the major competing EQ's (you can see that in measurements of the PH-77 in stereophile). The remaining differences between the different LP EQ's (let's ignore 78's) after RIAA could easily be compensated for in the major part using the even then standard Baxandall tone controls, well at least up to the point when people like John Curl and Mark Levinson hit on the not neccesarily bad idea to remove tone controls).

Now, outside the USA (e.g. most of the world) the RIAA was and still is not even relevant. Local standards existed Europe. Some of this story is well covered in the Sound Restoration e-book originating from the BBC Sound Archive's Peter Copeland.

The whole subject of EQ is really complex (I have in one case the same DG Stereo LP with CCIR EQ, RIAA EQ and Decca EQ - meaning each LP sounds substantially the same if matched with correct EQ but dramatically different if played with RIAA) and there is little material really widely available. You could try the PH-77 pages on AMR's website, I have summarised some of what I found, but it was simplified for release on the website.

Making the EQ of a Phonostage adjustable is quite trivial in principle, doing it for a large numbers of curves and accurately so can be a little challenging (which is probably why FM Acoustics simply used rotary pots with free adjustment). Due to the central location in Europe Germany/Austria/Switzerland had possibly the largest exposure to different EQ's, so adjustability of the EQ curve for LP is not exactly big news there (it is not that common, but definitely heard of).

In principle a simple Baxandall Tone control can also be used, if it is well calibrated, so you know exactly where the +/- 2dB HF boost/cut is and where the LF attenuation settings are.

Of course, in the High End Audio world such a suggestion would be tantamount to Heresy, Witchcraft and Manichaeism (burn the witch, burn...).

Ciao T

john curl 12th May 2011 07:14 PM

Who cares? It is the STANDARD that matters. To deviate from the 'standard' without a reset option, gives critics like SY further ammunition to criticize hi end audio design. Let's try to minimize the criticism of our efforts, if possible, don't you agree?


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