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Old 22nd October 2011, 09:32 PM   #311
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by AndrewT View Post
I am asking: why adopt 7.82 or 7.83 or 7.5 or another other fixed "standard"?
If the replay curve exactly matches the record curve, then does it make a difference to the final sound whether the "standard" adopts one value over another?
If the replay system can be "focused" to the curve used during the vinyl pressing, I wonder what difference that could make. Your question opened my mind to another one... Why are there so many variants ? Maybe people where searching for the "perfect tuned" curve and adopted what should seem the best considering manufacturing costs/systems availability at the time, in several regions of earth. I understand now that there are four or five determinant curves coming from Japan, Germany, Russia and USA.... What should be picked as the "best one" ?

Anyway, admiting that the majority of the pressings I am working with are relatively new (30 years) and it´s origine is USA I can deduct these use Riaa standard. After building severall phono preamps using passive filters between amplifying stages, I know there are some time constants we must try to follow very close in order to have the correct "instrument timbre".

I do not know if this aplies to designs using active filters (feedback) but Rüdiger´s post seems to translate what I mean. It is much simpler to design a digital filter to follow whatever curve we want so these must be very acurate. Any difference in the time constants used (even small) makes a big and audible difference.
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Old 23rd October 2011, 06:17 PM   #312
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Originally Posted by Onvinyl View Post
Another way to decode the riaa-emphasis is to use software filters. I have such a system running since a few month, actually using the biquad coefficients provided by Scott. Yes, it is ADC -> software filter engine -> DAC during playback. The result is amazing.
It can't be that difficult to compute the coefficients for those mentioned other curves. Perhaps somone knows how to obtain these by the aid of TI's coefficient calculator?
I seem to miss some understandig how to adjust the parameters to get along...
Or is it possible to compute those coefficents out of a Laplace transform?

Rüdiger
The curves can be computed by useing Laplace...I do this in LT-spice to evaluate the filterings I design...Then I can get verification on how close they are to theoretical values and how tolerant they are to componentvalue tolerances..
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Old 23rd October 2011, 06:45 PM   #313
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The curves can be computed by useing Laplace...I do this in LT-spice to evaluate the filterings I design...Then I can get verification on how close they are to theoretical values and how tolerant they are to componentvalue tolerances..
Yes, me as well. But software de-empahsis using biquad coefficients (that form IIR-Filters with some soundmangling software) is something else. I'm almost sure it is not possible to compute coefficients with Laplace, but somehow it must be possible...

Rüdiger
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Old 9th December 2011, 09:09 AM   #314
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This is the results I have for deviation on other curves from the RIAA curve...

Or to be more precise the frequency responce you get when you play NON RIAA records through a RIAA Filter.
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File Type: jpg RIAA-deviation.JPG (125.0 KB, 164 views)
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Old 9th December 2011, 12:39 PM   #315
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Hi Miib

The differences are substantial.
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Old 9th December 2011, 01:17 PM   #316
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They are, see if most of the Deutche Gramophone really has the coumbia curve, then they are upvards shifted, and have a thin and not so bodied sound, and guess what.. That is exactly how most of them sound...
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Old 9th December 2011, 02:07 PM   #317
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I know.... I always prefered Spanish DECCA pressings when choosing classical music.
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Old 9th December 2011, 02:31 PM   #318
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Quote:
Originally Posted by Onvinyl View Post
Yes, me as well. But software de-empahsis using biquad coefficients (that form IIR-Filters with some soundmangling software) is something else. I'm almost sure it is not possible to compute coefficients with Laplace, but somehow it must be possible...

Rüdiger
Correct, IIR coefficient computation is not a closed form problem. If you search under Bob Orban's name and RIAA you will find the proceedure (though I can't seem to now). There are plenty of bad approximations out there Goldwave (when I compared it) was way off.
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Old 10th December 2011, 10:41 PM   #319
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It might be that

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Old 12th December 2011, 02:27 PM   #320
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Yes, the original seems to have been archived off. I used a thermal annealing algorithm (unfortunately in in-house software) that did the same thing after many iterations but I could just leave it in the backround. You make an initial guess using the ordinary bi-quad formulas, this works but is in reality far off what can be achieved with tweeking. I exchanged emails with Bob, his "error" was very trivial in that he used 50.5 Hz were it should have been 50.05Hz (or is that visa-versa?). In fiddling with that I derived the ones for the next sampling rate up.

EDIT - I might publish a MATLAB/OCTAVE script to do any RIAA type equalization in Linear Audio but it will have to wait a couple of issues.
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