Using the Paragraphic EQ to set Turnover and Rolloff

[James]

Not clear exactly how to use the Paragraphic EQ to set the Turnover and Rolloff......simultaneously.

I have a recording that went into my computer as RIAA. I did reverse RIAA before I started my clean up. Once that was completed, I wanted to return it to its proper curve, which in this case is NAB. I understand NAB to be 500 and -16. I see both of those options in the presets, but I don't see them together. I do see 'NAB Tape Playback Curve', but visually, that seems different than either the 500 or the -16 settings. So, I am a bit lost.

Again, this was just my particular example in wanting to set it to NAB. What if I wanted it set to 300 and -14? Or whatever? If I run the one and then the other, my first setting will be cancelled out by the new setting, correct? I understand that I can set my EQ for 300 and then manually manipulate the graph to achieve the -14, but I have no idea how to do that. I know how to move the dots...but how to set it to get it where it is proper is unknown to me....

Thanks for any clarification!

[Craig Maier]

What version of the software are you running? DC8.5 has an additional shelf - a low frequency one in the paragraphic EQ. It always had a high frequency shelf (top band). With DC8.5, you just use two filters, the low frequency shelf and the high frequency shelf. Turn the rest off. If you do not have DC8.5 and have DC8, it is a free upgrade to 8.5 by downloading the demo version from www.diamondcut.com

So, that is where to start. If you do not have either version, look at the Virtual Phono Preamp - it may have some presets that do what you want without much manipulation of the graphs.

Craig

ps - the dual - shelf in the DC8.5 paragraphic EQ give you near infinite flexibility to create any combination of turnover/rolloff curves for phonographic recordings.

[James]

Craig,

Thank you for your response. I have version 8.5.

Still a bit confused. What I figured out, perhaps incorrectly, was as follows: To set up a NAB curve (500 and -16) I went to the drop down menu and looked for the Rolloff at 16db setting. I noted the Freq/Amp/Octave setting. Then, I went up to the 78 rpm 500Hz Turnover curve preset and selected it. Then I simply changed the Freq/Amp/Octave numbers to those I saw for the Rolloff at 16db drop down and the graph added that. I am guessing that I now am looking at the correct setting for NAB (500 and -16)? Is this correct?

I am not sure what the low freq shelf is all about....nor the number of filters. I see how to select the low shelf, but I am not sure what that means. I don't see how to select the high shelf....or how to 'turn the rest off'. I am looking in the manual but not seeing information on that....

Thank you for your help...

[Craig Maier]

Hi,

The top frequency band on the paragraphic EQ is always a shelf; it is never a resonant filter. The bottom filter in version 8.5 can be converted from a 2nd order resonant filter into a shelf filter by checking the box. So, to create phonographic curves in the most accurate way, set the paragraphic EQ for only 2 filters. The right-most one will be the Rolloff portion of the curve (shelf) and the left-most one will be the Turnover portion of the curve. Only two shelving filters are needed to create any phonographic curve with the new system. With the old system (before DC8.5), it took many filters to create the various phonographic curves because it did not have the low frequency shelf filter. Once you have it set for those two filters, you can manipulate the curves to create any curve shape that you desire. Let me know if this clarification has been helpful.

Craig

[Craig Maier]

Here is a screen shot of a generic phonographic EQ curve using the paragraphic EQ. Note that 2 filters (only) are selected and that the Low Freq Shelf is checkboxed.

[Craig Maier]

I just noticed that the DC8 version 8.5 has a Virtual Phono Preamp preset titled Approximate NAB LP Curve.

Craig

[James]

Craig,

As always, thank you for your patience. You all at DCart have been great since day 1 (I go back to the floppy disc days).

I understand that I can set the filter up to manipulate it an infinite number of ways, but what is the most simple way to simply set it to 375 and 8.5...or 500 and 16....or NAB? I know once I set something, I can save that setting, but how to get there, that is my question. I guess I look at equalization as a bit more of a exact thing than most of the filters. You play with the sliders to de-click a given record and the settings will vary for many reasons...but for equalization, there are lists of basic setting for a given label. So if I want to set one to 250 and 14 how can I quickly (and accurately) do that? Does the manner I described above work? I guess I am trying to recreate the various pre-amps that allow me to simply turn a knob and have the exact settings that are required.

[Craig Maier]

Hi,

The settings found in the Virtual Phono Preamplifier are in some cases "Exact" (as annotated) and some are "Approximate" (as annotated). Approximate means that they are within a db and Exact mean that they are immeasureably close to the theoretical curve. As for using the paragraphic EQ to create curves (which will be approximate, not exact unlike the Virtual Phono Preamplifier) both the lower frequency shelf (turnover) and the upper frequency shelf (rolloff) display their frequency values and amplitude values in the display windows in the lower left of the filter. You can also see the values on the graph that you create by moving the two inflection points. The value(s) of amplitude and frequency shown in the display windows correspont to the inflection point (larger squre box) that you have clicked on and are adjusting via the mouse.

Does that help?

Craig

[Craig Maier]

Hi Again,

Another thing to note is that the high frequency shelf sets the asymptote of the pole-zero pair. As I recall, the various phonographic curves called out in the Diamond Cut helpfile/documentation are given as the dB attenuation at 10 kHz. So, there is not necessarily a correlation between the High Frequency rolloff shelf and a given Phono EQ attenuation at 10 kHz. Check the helpfile for the attenuation values for LP curves. I am pretty sure that they are in chart form there.

Craig

note: shelf type filters (pole - zero pairs) exhibit a first order response in their midband meaning that their major slope is 6 dB/Octave. Of course, if you move the high frequency and low frequency shelf filters too close together, their slopes will interact mathematically and can be different in that case.

[James]

No...I just don't understand. I follow everything you are saying about moving stuff around, except the part on how to set something to (either exact or approximately) 500 Turnover and 12 Rolloff....or 250 Turnover and 8.5 Rolloff...or whatever. I see in your example picture above the two points as 'number of filters' is set to 2. Good. Here are my steps to recreate that.

1) I open the Paragraphic EQ filter and choose the '78 RPM 500 Hz Turnover Curve' setting.

2) I change number of filters from 5 to 2 (5 seems to be the preset). Doing this, I notice that the curve as delivered in the preset is changed a bit, but not sure what to do about that. Seems to be what happens where you remove the points.

3) Low shelf is checked (as seems to be the default).

4) Now I move the filter (point below the line) over to the right so as to find my 12db Rolloff setting. Here is where it seems to get very complicated. Where do I move the point to? The preset says that the 12db Rolloff is at 10KHz. So, do I simply move it so that the the point is on the 10KHz line and be sure that the right part of the line goes off the grid at -12db?

I guess....for me (and perhaps me alone) it would seem much easier to have the option for two sliders. One for Turnover and one for Rolloff. Each is marked with the primary (what, 6-9 each?) settings that were used...everything from flat on. Then, one can simply play with the various settings just like one would have on a Scott preamp from the 1950's....to the Owl....to any of the preamps that are available now. That way, you have the feeling of spinning knobs. Just seems it would be so much easier and more intuitive. It is great to have the options that are available now. But sometimes you just want to quickly run though the options that are standard.

[Craig Maier]

First thing that is wrong - when using the new two-point shelfing functions, do not use the old resonant filter presets. They are of no meaning with the shelfing feature because they use the 2nd order resonant filters, so that is the first error. Just forget those presets when using the pole-zero filters and create the graph you need with two filters set for shelfing. Use the two graphical inflection points to create a graph that agrees with the frequency and amplitude response that you desire to realize the curve of your choice. It would probably be best to forget the frequency and amplitude digital readouts (unless you want to do a lot of math). The graphical display tells the whole story in terms of creating custom phono eq curves. The x-axis frequency on the graph is very accurate as well as the y-axis for amplitude.

Craig

[Craig Maier]

Hi,

I just looked at the original problem posted here on this thread involving creating the NAB Phono EQ curve. I looked at the response of the Virtual Phono Preamplifier Preset titled "Approximate NAB LP Curve" and used the spectrum analyzer to measure its accuracy. It is roughly 0.3 dB off at 10 kHz. That is well beyond the capability of human hearing in terms of error to be detectable and substantially beyond the accuracy of the encoding equipment that created that curve when they cut the record master with analog filters.

Craig

[Craig Maier]

Here is a rolloff curve using the double-shelf (2 inflection points) of the paragraphic EQ. This curve has the rolloff characteristic of the NAB curve and has an attenuation factor of -16 dB @ 10,000 Hz.

[James]

Thanks for the reply Craig!

As I mentioned, NAB was just an example. I am also curious about 250 and -8...or 400 and -16....or whatever.

Since you posted the image with the NAB curve, I will go with that. I see how the Rolloff is -16 dB @ 10,000 Hz. For NAB, the Turnover is 500Hz. What in the image above is showing me your Turnover is at 500Hz?

[Craig Maier]

I did not set it for a specific turnover - - - just took one of the factory defaults and modified it for a NAB Rolloff. However it does appear that it happens to be set for around around a 400 Hz turnover setting (which is not quite correct for NAB - needs to be moved up to 500 Hz). My focus was on the Rolloff portion of the curve since I thought that was the major issue.

Craig

ps - it looks at close inspection to be off by around 1 dB at 500 Hz, but correct for 400 Hz.