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RIAA, Questions only please

I have closed the previous thread on RIAA and concluded that very few indeed understand the curves or the purpose. Here is my closing statement from that thread. For those who want to understand and have valid well stated questions I am happy to answer. 

Not wanting to leave the party without a clear and accurate statement I will say the following:

The answer to the question concerning noise reduction is that the simple filter that RIAA decided upon was to raise the high frequencies gradually by about 12 dB starting below 500 Hz, being up 3 dB at the 500 Hz pole. The circuit then cancells the pole with a zero at 2,200 Hz and there is then 3 dB of boosting left as one goes to 20 Khz. It is all done very gently with just two resistors and two capacitors.

By reversing this process on playback we get to enjoy 12 dB less noise above 500 Hz.

The RIAA part of things is the same for all cartridges. However we are accustomed to seeing RIAA combined with the 6 dB/octave compensation for a velocity cartridge. That takes off 12 dB, and along with two things that happen at the very ends of the response, brings the total EQ for a velocity cartridge to 40 dB. Next time you look at an RIAA curve ask yourself why there is that flat bench between 500 and 2,200 Hz.

An amplitude cartridge needs only the RIAA EQ of 12 dB. Which also speaks to the fact that the majority of the spectrum of a record is cut at constant amplitude. When you put a sewing needle in a paper cup and play the record you are getting amplitude playback not velocity.

I study these things because they interest me. Anyone can look up the parts values to make an RIAA filter or inverse RIAA. What interests me is that some manufacturers still get it wrong.

128x128ramtubes
uberwaltz's avatar
uberwaltz
13,381 posts
 
Raul,Roger ,Ralph, Al and all the other fine contributors to this thread and it's previous incarnation.

My compliments to imhififans post and link was not meant to slight any of your fine contributions and I hope that was not your takeaway from it.
I have been intrigued, enthralled and immersed in both threads since inception.
However even if you overlook the differences of opinions and the contradictions of some posts I still found myself struggling to grasp some of the technicalities of said posts at times.

What I meant in my earlier post here was that linked article was just a lot easier to comprehend and digest as a near one stop shop take on the subject.

Nothing more and hope that is understood.
imhififan's avatar
imhififan
2,109 posts
 
Wow! thank you guys, I was just simply provide a link that Roger ( ramtubes) looking for.We should thanks Roger for spending his precious time to open this discussion to unlock the mystery of vinyl disc recording-equalization, answering questions, sharing his expertise and knowledge to us.BTW, Raul (rauliruegas) is the first poster mention the article by Gary A. Galo.
atmasphere's avatar
atmasphere
11,577 posts
 
What the article leaves me uncertain about, however, given that in modern times a cutting head is to at least a loose approximation a velocity-based transducer (meaning that it converts signal amplitude to groove velocity), is **how** the cutter is caused to cut at constant amplitude at those frequencies.
I think I can answer that. Since the cutter isn't by any means a true constant velocity device, it gets equalized so it is. The CV equalizer is a pretty complex set of time constants; I'd hate to have to work them all out, since the actual cutter response is more like a loudspeaker with some odd peaks in it (complete with a 'nose' in the high frequencies, just like any raw driver response) than anything else. 

Now the slick way to set up the whole thing would be to combine the qualities of both the RIAA curve into the CV equalizer curve so that the output was both at the same time but I suspect in order to preserve hair follicles this wasn't done and probably won't ever :)



johnss
564 posts
 
@Ramtubes,
Thanks Roger for the tip, ;yes I usually watch ebay for used test gear from those mfgrs.

best regrds.

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