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
@cto517 On a thread like this I am looking to learn. FWIW - I find the available online documentation for RIAA inconsistent, confusing, misleading, incorrect data .. no wonder, imo, it is difficult to grasp when we have experts like yourself contradicting words and terms we have read online..... trying to fill in the blanks.  A definition of terms for important Words would help to fill in some blanks.  Like for example - Constant Velocity, Constant Amplitude

Thanks for your suggestion. You are correct there are many terms being used incorrectly, Here is a list of proper terms. It is most important to use the correct terms and language.


Constant Amplitude is what a wave generator puts out, ususlly as a sine wave. The part that is constant and most important is that it does this at  constant voltage (+/-  by 0.5 db, or better). In Physics it means to move the same distance over all frequencies. If we recorded a record with constant amplitude the wiggle width of the grove would be constant. 

Constant velocity is a bit more difficult. We tend to drive at constant velocity (speed) on the freeway. However there are few things in audio that are constant velocity.

Velocity cartridge produces a voltage proportional to its cantilever speed (velocity). Therefore to produce the the same voltage it has to go much farther in the same time. Therefore the bass grove space get wider.

Amplitude cartridge produces voltage proportional to its cantilever offset or distance without regard to velocity.

Thats a start. Can you name a few more you would like to have defined?


@rauliruegas  @ramtubes : What is the purpose or your target on both OP's threads?

I'm asking because today 99.90% of all cartridges we audiophiles own are magnetic ones and the 99.95% of all the phono stages we own or are manufactured comes with the inverse RIAA eq. curve for magnetic/velocity cartridges.

I don't get yet in which way your threads can help any one of us to listen LPs. ! ! ? ? ? ? ? ? ?

What's all about?


This is about understanding. I find understanding something increases my enjoyment of it . Why not be educated? DId I say I was going to help anyone listen to LPs?

Yes we live in a velocity cartridge world except for the few who are still tackling the ampitude world. Neither is better than the other technically however it would be nice to see some amplitude contenders come along. 
Your last post makes no sense and is useless and does not makes any real contribution to this thread.

Perhaps not from your point of view, but you did ask what the purpose of the OP’s thread was (both of them) and I posted what I recall to be one of the purposes of the now deleted thread.

Sorry it all got lost on you and your feathers were ruffled.

BTW - care to translate this:

I don’t get yet in which way your threads can help any one of us to listen LPs. ! ! ? ? ? ? ? ? ?

I may have misinterpreted what the purpose or the target was when I previously responded, and yes I read your entire post. You are one of the few people on here whose posts I always read.
@rauliruegas  Please also refer to the graph near the top of Mr. Galo’s excellent article called Figure 1;

http://www.smartdev.com/RIAA.html

It refers to this graph as the “typical” RIAA response; in reality, it is far from the “ideal” response that one gets from the theoretical filters due to interaction of those filters. This, not the “ideal”, is what we have all been listening to for years with magnetic cartridges! Superimpose a 6dB/octave curve (Strain Gauge) and you will find that it deviates less than plus or minus one dB.


Unfortunately this link took me somewhere else. Can you check it please?

I thought this part of your quote best and shows that he knows there is a region that needs to fall at 6 dB/octave to get RIAA response. The problem remains on how to get it back to flat from 2200 Hz up. 

Peter Knows.
@johnss  with all the discussion on the RIAA curve, would suggest real vinyl philes consider the following; test your LP playback set up and see if the playback response is flat according to the RIAA spec

theres more to this 
.

Thanks for the write up. Its nice to see this level of interest.

Most digital multimeters fall off starting at a few KHZ and at 20 KHz are down as much s 40dB. Get an old HP AC Voltmeter and check it against an oscillator. The meter should not deviate over the audio range.

Used HP, Tektronix, Heathkit. eico and other test equipment are less than 10 cents on the dollar. An oscillator and meters come first Then you can just watch the music and see how much power you are using, your headroom, noise, lots of things.