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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@imhififan
http://hifisonix.com/wordpress/wp-content/uploads/2018/01/Disc-Recording-Equalization-Demystified.pd... Thanks for sharing this. We need more of you finding articles of quality. As you can see the author found the subject difficult too but made some good points I had not known previously. |
Great article imhififan. Contains an excellent glossary, and what appears to be a complete definition of terms. For my own benefit as a form of reference, I challenge those in the know, to tell us of any inaccuracies, incorrect data, misleading information, in that article. ***************** For additional information. A web page that I was familiar with in the past, from the IASA, these definitions relate to earlier 78’s, and the link contains an interesting table at the bottom. The table shows how varied the EQ’s were between companies, and just how limited in frequency the 78’s were. A clear case of too many cooks in the kitchen ? 8^0 The control knobs on the preamps that allowed for setup of the different EQ’s must have been interesting. https://www.iasa-web.org/tc04/mechanical-carriers-replay-equalisation |
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