Is smoothing a graph really a misrepresentation? - AVS Forum
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post #1 of 23 Old 04-06-2013, 02:25 AM - Thread Starter
 
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When smoothing is used, in my opinion, it's a misrepresentation of what's been recorded. In my opinion, smoothing makes a graph look better then it really is.

(I'm not a purist)

My question, is smoothing a legitimate evaluative tool or is smoothing just a way to make a bad looking graph look good or a decent graph look that much better?

Is smoothing a legitimate tool or a bogus deceiver?

And if a legitimate tool, how much smoothing is beneficial in regards to removing small aberrations that are meaningless to our ears?

I see smoothing of 1/6th octave as some sort of accepted norm and to me, that amount of smoothing seems to remove everything but the kitchen sink.

,,,confused.gif

The first graph has no smoothing applied and the second graph is the same graph, one sixth octave applied.

...

In my view, each is an obvious misrepresentation of the other.

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post #2 of 23 Old 04-06-2013, 07:01 PM
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I think it depends on what kind of information you are looking for, Bman. Many people like the EXACT numbers and obviously it is the "most correct" transmission of information.

OTOH as I look at both your graphs, they both show peaks, and they both show valleys, so I see the same "trends" in both graphs.

If you want the smoothing feature, which obviously works better when the numbers are closer to each other, then rounding is the method the software will use. Rounding is not a good method when the numbers are not numerically close to one another.

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post #3 of 23 Old 04-06-2013, 07:16 PM - Thread Starter
 
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Originally Posted by wvu80 View Post

I think it depends on what kind of information you are looking for, Bman. Many people like the EXACT numbers and obviously it is the "most correct" transmission of information.

Personally, I'm not looking for anything other than understanding. In the case of my use of graphs, I don't see legitimacy in smoothing out graphs as to do so, my opinion, hides the warts and to me, graphs are intended to expose the warts. My question is to see if there's something I'm missing.

Smoothed vs no smoothing applied as I see posted graphs, representing room measurements, smoothing applied. To me, presenting a smoothed graph, especially at 1/6 octave, intends to remove warts and make someone's efforts look more successful then they are.

The point of the question is to find out what it is I'm missing. Myself? Unless compelling reason to change, I'll continue with no smoothing applied. The question is nothing more than a generalized, curiosity question with hopes that responses will help me better understand, what's what with what.

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post #4 of 23 Old 04-07-2013, 02:01 AM
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The argument for smoothing, AFAIK, goes as follows:
1. The human ear has limited spectral resolution.
2. Music and real life sounds is usually broadband phenomenon in the sense that the amplitude of frequencies close to each other at the same moment in time tend to be highly correlated.
3. Therefore, one can correct a system by correcting smoothed response. Take for example your system with a ~40dB dip at ~83Hz. It would be insane to try to boost 83Hz by 40dB to cancel out the null. But the 1/6 octave smoothed plot shows only a ~10dB dip. It would make more sense to make a ~10dB boost with a filter with 1/6 octave bandwidth. The unsmoothed plot would then show elevated response around say 75Hz and 90 Hz while the 40dB 83Hz null remains. But the 1/6 octave smoothed response would show close to flat. The psychoacoustical argument is that the system modified in such a way would sound close to an actual ruler flat system.

But I suspect that for optimizing subwoofer placement the unsmoothed graph would be a lot more informative while for EQing the final system the smoothed graph would be more useful.
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post #5 of 23 Old 04-07-2013, 04:22 AM - Thread Starter
 
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Thanks!

(personally, I'm hung up on the +/-3dB, anechoic standard we're all held to)

Looking at smoothed vs no smoothing applied, in the way you described above, lends validity to both application; I understand. In our case, if sound mixers stay out of our null, we're golden. tongue.gif

My take on your above: optimize graphed subwoofers for placement (harsh application, no smoothing applied, +/-3dB graphed efforts), while graphing EQ'd efforts for the way we hear what's left behind; 1/6th octave smoothing; transitory reception, real world application.

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post #6 of 23 Old 04-08-2013, 02:03 PM
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What I do, and what I believe is the accepted norm in the REW threads, is to use no smoothing on sub frequency graphs and anywhere from 1/24 to 1/6 smoothing on full range graphs. Personally, I like 1/6th on full range because it looks sooooo purty. wink.gifbiggrin.gif

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post #7 of 23 Old 04-08-2013, 02:06 PM - Thread Starter
 
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Originally Posted by Alan P View Post

Personally, I like 1/6th on full range because it looks sooooo purty. wink.gifbiggrin.gif

And.....one can't knock "purty." biggrin.gif
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post #8 of 23 Old 04-08-2013, 02:26 PM
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As stated above I have read that we hear up to 1/6 th octave smoothing. Meaning in your graph above we would hear the unsmoothed graph the same as your 1/6th smoothed graph. I don't smooth below 100hz but use 1/6th above. Try running an unsmoothed response to 20khz, it has lines everywhere, we don't not hear this.
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post #9 of 23 Old 04-08-2013, 05:12 PM - Thread Starter
 
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Then I'm pretty much good as the graph below, represents today's EQ effort, represented as one sixth smoothing applied.

10dB graph, 1/6 smoothing applied.



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post #10 of 23 Old 04-08-2013, 05:35 PM
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Quote:
Originally Posted by BeeMan458 View Post

Then I'm pretty much good as the graph below, represents today's EQ effort, represented as one sixth smoothing applied.

10dB graph, 1/6 smoothing applied.


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Whether smoothed or not, you have a significant, (at least 10 dB), problem in the 80 - 100 Hz range. This will be easily audible and will suck the life out of your bass. Your graph before you added the 3rd sub is not significantly different in that range than your current graph.



The reason for this is as follows:

If you are still using the same crossovers, (40 Hz L/R's and 60 Hz CC and surrounds), that stuff going on at 80 Hz is caused by... your speakers... not your subs. There is virtually nothing you can do with your subs that will impact the 80 to 100 Hz range, with 40/60 Hz crossovers.

If you want to prove this to yourself, take measurements of your mains with the subs off, and your subs with the mains off. You'll immediately see that the 80 - 100 Hz range, and all the problems in this range, are being produced by the speakers.

You have 2 choices:

1. Raise your crossovers to 80 Hz. This will put the range you want to impact into the range of your subs.
or
2. Adjust your speaker positions as they are currently the drivers that are generating the 80-100 Hz range.

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post #11 of 23 Old 04-08-2013, 06:27 PM - Thread Starter
 
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Per Chirs' recommendation at Audyssey, all speakers are set to small, crossovers are set to 80Hz and the sub is set to LFE.

The short wall behind my sitting position seems to be the problem as this isn't a problem to the left or right of where I sit as the walls are open in those locations and as you know, the rule is, no sound treatments allowed.

I understand how speakers affect the graph as I took measurements with the speakers disconnected so they wouldn't influence the readings and saw first hand what you're referring to. I'll play with the speaker positioning tomorrow and see what changes take place.

Thanks for the speaker tip.

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post #12 of 23 Old 04-08-2013, 06:55 PM
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Quote:
Originally Posted by BeeMan458 View Post

Per Chirs' recommendation at Audyssey, all speakers are set to small, crossovers are set to 80Hz and the sub is set to LFE.

The short wall behind my sitting position seems to be the problem as this isn't a problem to the left or right of where I sit as the walls are open in those locations and as you know, the rule is, no sound treatments allowed.

I understand how speakers affect the graph as I took measurements with the speakers disconnected so they wouldn't influence the readings and saw first hand what you're referring to. I'll play with the speaker positioning tomorrow and see what changes take place.

Thanks for the speaker tip.

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If you're using 80 Hz crossovers, the problem may be the subwoofer Distance setting. Getting the subs time aligned with the speakers, (which is what the subwoofer Distance setting does), is critical. Try playing around with adjustments to the subwoofer Distance setting. I would start with adding 3 or 4 feet. Once you find the better "macro" setting, then play around with "micro", 0.2' increments to really dial it in.

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post #13 of 23 Old 04-08-2013, 08:37 PM
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Smoothing is a display tool. Like most tools it can be used to both good or bad effect. Ideally it serves to better communicate what matters or what you are looking to show/see. At worst it can obscure relevant information and misrepresent what's going on.

If you've spent most of your time measuring and looking at subwoofer measurements, your conclusion is not so surprising. If you dig further into how measurements work and the realities of achieving different degrees of resolution over different frequency ranges, especially in wide bandwidth measurements, you'll see how useful smoothing can be.

We can always perform some degree of smoothing in our mind, but simple processing of the display can help give some perspective when looking at large amounts of data.

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post #14 of 23 Old 04-09-2013, 05:39 AM - Thread Starter
 
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Thanks for the response Mark. I can glean a boatload from raw data sets in the form of a graph but when graphs are cleaned up with smoothing, much of the important interpretive data points are swept away. In the case of the above graphs, in my opinion, smoothing steals the validity of the measuring process by shortchanging the depth of what graphed measurements reveal: for a given point and time; room ringing, depth of extension, cancellation and reinforcement.

In the same light, I find using a 5dB graph to overly exaggerate measured material. I find 10dB graphs to be representative of how we hear. Not as exacting to read but more representative of how we hear and therefor, representative of the recorded sonic information.

In my opinion, as a clinician, one tends to get caught up in nuances and fails to adjust the need for accuracy to real world listening conditions. In other words, a real world audience doesn't listen in the clinical sense we measure for when in the process of "enjoying" the transient information of an action based movie sound track.

For personal interpretive purposes, working with your comments, I look to 1/24th smoothing as opposed to 1/6th smoothing. Doing so seems to remove "some" room ringing, but not so much that one is still able to see at what frequency ringing is taking place. And at the same time, 1/24th smoothing removes graphed niggles which under normal listening conditions, considering the fast paced transient nature of action based movie sound tracks, tossed information is not going be noticed as missing to the normal listening audience. A noticed added benefit, using 1/24th smoothing doesn't misrepresent the much valued depth of extension I see 1/6th smoothing being guilty of misrepresenting; contracts the head of the graph.

Based on my above, using your comments as a guide, am I understanding the usefulness of the smoothing process correctly?

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post #15 of 23 Old 04-09-2013, 09:43 AM
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I think what people are saying that you may be missing is that for subwoofer measurements (like the examples you posted) smoothing isn't really necessary and likely only serves to make the graph look "nicer" but for full range speaker measurements smoothing is all but required.

For example see the unsmoothed and smoothed speaker measurements below:


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post #16 of 23 Old 04-09-2013, 11:37 AM - Thread Starter
 
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Thanks for the reply. In the case of my comments, all that I've been viewing are subwoofer based measurement graphs as I see many subwoofer measurement graphs represented in 1/6th octave smoothing. As you suggest, when applying 1/24th octave smoothing to today's EQ efforts, there's not much difference between no smoothing applied and 1/24th octave smoothing applied.

No smoothing applied.................................................One twenty-forth octave smoothing applied

...

What I'm trying to do is gain a better understanding of how anal one should be regarding the reading of subwoofer based measurement graphs and when is it better to clean a subwoofer measurement graph up a bit as opposed to needlessly leaving all it's niggles on the graph. As one can easily see, by the time 1/6th octave smoothing is applied to today's efforts, by comparison to other standards, the pesky null is pretty much gone:

One sixth octave smoothing applied



I feel using 1/6th octave is a clear misrepresentation of reality but that's the standard I see many using. confused.gif

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post #17 of 23 Old 04-09-2013, 01:45 PM
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Quote:
Originally Posted by BeeMan458 View Post

I feel using 1/6th octave is a clear misrepresentation of reality but that's the standard I see many using. confused.gif

Your original statement nor title of this thread qualified your smoothing comments to only relate to low frequencies. It is a less off the mark statement when only looking at measurements below 100Hz, but it still depends on what you are looking for.

I believe the 1/6th octave data-smoothing displays you've seen come from defaults in some programs rather than conscious efforts to deceive. The same can be said of your graphical smoothing using 10dB/div on a 100dB vertical scale! This is gross graphical smoothing and what we often see for some full range driver OEMs. Most anything looks smooth on a 100dB scale with limited vertical size.

As a long time calibrator and speaker/subwoofer designer, I can assure you that a 5-6dB/division scale on the graphs you posted with ~50dB on the vertical scale is much more useful in determining what you can hear. With a 5dB/division scale it's very easy to see that within one visual division plus a small bit fits a +/-3dB window. It also gives a quick visual correlation of 10, 15 and 20dB changes which make for notable and major loudness differences.

Smoothing of subwoofer responses can make perfect sense when trying to view the direct response of a subwoofer in a near field measurement or when looking at an outdoor measurement where we know the hair in the measurement is from environmental noise or reflections which can be very hard to 100% eliminate.

In small rooms (any home theater) we do want to generally be looking at 1/12th octave resolution or greater so we can see room modes and determine what we can or should do about them, if anything. Unless some specific sound effect lands directly on a narrow peak, it can be minimally noticeable, and with a null it is a matter of omission which will only be audible on comparison to a system or location which doesn't omit that range.

It's always important to understand the limitations of any measurement you're taking and understand what it can and cannot tell you. It is easy to also change a measurement's parameters to window out different data which would appear as smoothing without any being applied. There are also many different measurement types, not only the one you have played with in REW's default subwoofer setting. When looking at a graph it's important to know the measurement type and conditions before you can read too much into the displayed curve.

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post #18 of 23 Old 04-09-2013, 01:52 PM - Thread Starter
 
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Quote:
Originally Posted by Mark Seaton View Post

Your original statement nor title of this thread qualified your smoothing comments to only relate to low frequencies.

Sorry, wasn't trying to be misleading. I've only been looking at subwoofer graphs so by posting in a subwoofer forum, I made the wrong conclusion regarding my question being subwoofer centric.

Quote:
As a long time calibrator and speaker/subwoofer designer, I can assure you that a 5-6dB/division scale on the graphs you posted with ~50dB on the vertical scale is much more useful in determining what you can hear. With a 5dB/division scale it's very easy to see that within one visual division plus a small bit fits a +/-3dB window. It also gives a quick visual correlation of 10, 15 and 20dB changes which make for notable and major loudness differences.

So the graph below is more representative of what we're hearing?

5dB/division on a 50dB vertical scale, no smoothing applied:



Quote:
In small rooms (any home theater) we do want to generally be looking at 1/12th octave resolution or greater so we can see room modes and determine what we can or should do about them, if anything. Unless some specific sound effect lands directly on a narrow peak, it can be minimally noticeable, and with a null it is a matter of omission which will only be audible on comparison to a system or location which doesn't omit that range.

Which would be represented by the below graph?

5dB/division on a 50dB vertical scale, 1/12th octave smoothing applied:



Quote:
It's always important to understand the limitations of any measurement you're taking and understand what it can and cannot tell you. It is easy to also change a measurement's parameters to window out different data which would appear as smoothing without any being applied. There are also many different measurement types, not only the one you have played with in REW's default subwoofer setting. When looking at a graph it's important to know the measurement type and conditions before you can read too much into the displayed curve.

The main thing I wish to take away from the question, as a layperson, to make sure I have a better understanding of subwoofer graphs and what is considered a rationally displayed image and what's considered irrational smoothing when compared to what we actually hear while listening to a movie sound track.


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post #19 of 23 Old 04-11-2013, 04:25 PM
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Beeman,

Please take the following as informational in a spirit of trying to help you. smile.gif

In another thread, you recently posted the following:
Quote:
Originally Posted by BeeMan458 View Post

In our case, I spent a great deal of time setting the phase on the three subs and now, distance changes have pretty close to zero impact on subwoofer measurements. A distance change of fifteen feet will show up as nothing more than a background anomaly.

The subwoofer Distance setting in your receiver is not used to time the subs with each other. It is used to time the combined response of the subs with the speakers. If, as you stated in Post 11 above, you are using 80 Hz crossovers, you clearly have a problem with the interaction of your subs with your speakers around the crossover frequency:



The response in the red oval tells me that your subs are mis-timed with your speakers. They are cancelling each other out. To correct this, you need to adjust the subwoofer Distance setting in your receiver while measuring BOTH your speakers and subs, and with your crossovers on. Start with adding 4 ft. to the subwoofer Distance setting. If that improves things, add another foot. If that improves it even more, keep adding in 1 ft. increments until you see a degradation. Then back up and try the smallest increments available in your receiver. Superimpose one measurement on the next so you can see the effect. You're looking to go from the blue trace to the green trace:



When you get close, the subtle changes will take you from the green trace to the blue trace:



Good luck.

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post #20 of 23 Old 04-11-2013, 04:39 PM
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Quote:
Originally Posted by Mark Seaton View Post

I believe the 1/6th octave data-smoothing displays you've seen come from defaults in some programs rather than conscious efforts to deceive.
That, and the fact that you can't hear finer than 1/6 octave resolution, so there's no point worrying about it. In terms of what you can correct using a fully parametric EQ 1/6 octave is all you need. For that matter if all you have is a 31 band 1/3 octave EQ then 1/3 octave resolution is all you can make use of. There's no sense in knowing about, and losing sleep over, that which you cannot fix. Sometimes the bliss of ignorance is the road best taken.

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post #21 of 23 Old 04-11-2013, 05:13 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by Mark Seaton View Post

I believe the 1/6th octave data-smoothing displays you've seen come from defaults in some programs rather than conscious efforts to deceive.
That, and the fact that you can't hear finer than 1/6 octave resolution, so there's no point worrying about it. In terms of what you can correct using a fully parametric EQ 1/6 octave is all you need. For that matter if all you have is a 31 band 1/3 octave EQ then 1/3 octave resolution is all you can make use of. There's no sense in knowing about, and losing sleep over, that which you cannot fix. Sometimes the bliss of ignorance is the road best taken.

For in-room analysis and efforts to optimize low frequency response via placement and EQ/processing, greater than 1/6th octave, preferably 1/24th or comparable, is beneficial. Too coarse a view can easily lead to corrections which might boost or cut adjacent frequency ranges. The complex modal issues in a room results in much higher Q problems. While smoothing is a very useful tool in full range applications to confirm trends, over simplification of such EQ efforts when not in a wide open space are the exact sort of efforts which have given EQ a bad name in the past.

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post #22 of 23 Old 04-11-2013, 05:29 PM
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Quote:
Originally Posted by BeeMan458 View Post

Quote:
Originally Posted by Mark Seaton View Post

Your original statement nor title of this thread qualified your smoothing comments to only relate to low frequencies.

Sorry, wasn't trying to be misleading. I've only been looking at subwoofer graphs so by posting in a subwoofer forum, I made the wrong conclusion regarding my question being subwoofer centric.

Quote:
As a long time calibrator and speaker/subwoofer designer, I can assure you that a 5-6dB/division scale on the graphs you posted with ~50dB on the vertical scale is much more useful in determining what you can hear. With a 5dB/division scale it's very easy to see that within one visual division plus a small bit fits a +/-3dB window. It also gives a quick visual correlation of 10, 15 and 20dB changes which make for notable and major loudness differences.

So the graph below is more representative of what we're hearing?

5dB/division on a 50dB vertical scale, no smoothing applied:



Quote:
In small rooms (any home theater) we do want to generally be looking at 1/12th octave resolution or greater so we can see room modes and determine what we can or should do about them, if anything. Unless some specific sound effect lands directly on a narrow peak, it can be minimally noticeable, and with a null it is a matter of omission which will only be audible on comparison to a system or location which doesn't omit that range.

Which would be represented by the below graph?

5dB/division on a 50dB vertical scale, 1/12th octave smoothing applied:


Do note I said 1/12th octave resolution or better, not that 1/12th octave is necessarily preferred. In some cases the measurement itself might only have ~1/12th octave resolution. As you can see, nothing important is really obscured or overly minimized.
Quote:
Quote:
It's always important to understand the limitations of any measurement you're taking and understand what it can and cannot tell you. It is easy to also change a measurement's parameters to window out different data which would appear as smoothing without any being applied. There are also many different measurement types, not only the one you have played with in REW's default subwoofer setting. When looking at a graph it's important to know the measurement type and conditions before you can read too much into the displayed curve.

The main thing I wish to take away from the question, as a layperson, to make sure I have a better understanding of subwoofer graphs and what is considered a rationally displayed image and what's considered irrational smoothing when compared to what we actually hear while listening to a movie sound track.

As Bill already posted about, audibility is a little tricky and more coarse, but my earlier post about certain movie soundtracks highlighting problems which might be in many cases inaudible is still a reality.

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Just trying to get some sort of graphed standard that I can hang a hat on. My takeaway of your above, 1/12th smoothing is not a standard but simply a realistic smoothing, for generalized use that balances micro measurements with graphed macro reading of measurements. I'm not trying to understand the complexities of graphing at yours or Bill's level of understanding. Your above suggestions have given me guidelines to set up the graph so as to smooth and get rid of niggles as well as set graphed parameters that's all around useful to others and myself.

Thanks for the recommendations.
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