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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.

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almarg's avatar
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almarg
9,670 posts
 
Atmasphere 2-28-2019

At one point you were insisting that the cutter’s constant velocity characteristic was compensated by that of the cartridge....

Hi Ralph,

Actually it wasn’t Roger who asserted that. I stated that based on what was said in the following writeup:

http://pspatialaudio.com/displacement.htm

What Roger said is that the velocity characteristic of the cutter is compensated for by a 60 db EQ applied in the cutting process. And that the 40 db playback EQ compensates for the velocity characteristic of the phono cartridge, as well as for a pre-emphasis of approximately 12 db.

Based on comments you subsequently provided in the now deleted thread, though, backed up by the extensive first-hand experience with cutting equipment that you have, both statements are incorrect. And of course you and I both disagree with Roger’s statements to the effect that pre-emphasis covers a range of approximately 12 db, rather than approximately 40 db, over the 20 Hz to 20 kHz frequency range.

Roger, FWIW, while many of us here generally try to adhere to ground rules that may be stated by the originator of a thread, as you can infer from most of the responses that have already been posted a ground rule which excludes the possibility of dissent or disagreement, assuming it is presented in a civil manner, is not normal practice here.

Best regards,
-- Al

atmasphere's avatar
atmasphere
11,794 posts
 
A question: are you going to apologize for mis-characterizing our preamps in public?
The statement below does not make sense. Could you clarify?

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.
At one point you were insisting that the cutter's constant velocity characteristic was compensated by that of the cartridge, since this isn't the case, how does that all work out?

quincy
352 posts
 
"Roger, I think you would make more headway with those of us who are not engineers by dumbing down your statements so as to make your point more clear to those of us who are not steeped in the jargon. We are not stupid, just ignorant."

I second that comment....I was disappointed you removed the original thread.  I don't recall anyone getting nasty or rude?  I'm not an EE but do have a reasonable amount of intelligence to grasp concepts, and really enjoy threads that discuss the science of high end audio.
lewm
13,030 posts
 
We have an equation with 3 variables: the filter built into the cutter head, the filter built into the phono stage, and the degree to which any magnetic cartridge is actually “perfect” as a velocity dependent transducer of kinetic energy into signal voltage. We were just getting into that last subject on the other thread. No cartridge is perfect in this regard. But this is one reason why phono stages can sound so different from one another. 

Roger, I think you would make more headway with those of us who are not engineers by dumbing down your statements so as to make your point more clear to those of us who are not steeped in the jargon. We are not stupid, just ignorant.
gbanderhoos
20 posts
 
Agreed.  However, Roger seems more interested in conducting semantic arguments than in educating anyone.  I was reading a thread in the tech forum about RMS power and it was fairly civil until Roger jumped in and it became almost comical in how pedantic his argument was.
Regarding the previous thread, there was some good information presented, but honestly, I don't know why it couldn't have all been said in 10-15 posts;  the rest was just senseless arguing.
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cleeds
5,947 posts
 
testpilot
It's too bad that the previous thread is now locked as it contained a lot of insightful and useful information ...
I agree. I followed the thread closely, even though I never commented in it. It's unfortunate that now no one can follow that discussion.
testpilot
930 posts
 
It's too bad that the previous thread is now locked as it contained a lot of insightful and useful information.  I personally get more from a discussion than I do from a lecture.
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bdp24
9,788 posts
 
Roger, as the filter that goes out to 20Khz takes only two resistors and two capacitors to create, and the value of those parts in well known, why do we see variations from perfect RIAA eq on the order of anywhere from 0.1 to 1.0 dB or more amongst various phono amps? Can the same value resistors and caps be used in two different RIAA filters, yet the results will be different as a consequence of other factors in the phono amps design?
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