Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 485 - AVS | Home Theater Discussions And Reviews
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post #14521 of 14534 Old Yesterday, 06:27 PM
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Originally Posted by AustinJerry View Post
Bass resonance, which is what we are trying to measure, is caused by the low frequency contribution of subs + main speakers. If you want to impress us with your performance, measure center + subs, or left + right + subs.

Center plus subs plus LOUDER - is this decent ?
I know have some super low freq ringing....but that is way down low I think.


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post #14522 of 14534 Old Yesterday, 06:39 PM
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^ IMO, looks pretty decent.

BTW, you really should present your graphs with a log scale. Maybe you could correct and re-post?
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post #14523 of 14534 Old Yesterday, 08:59 PM
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Can do I just have to figure out exactly what you mean....
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post #14524 of 14534 Old Today, 06:13 AM
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Originally Posted by toofast68 View Post
Can do I just have to figure out exactly what you mean....
Sure. Here is a graph with a linear scale:



And here is a graph (same measurement) with a log scale (the difference is in the spacing on the horizontal scale):



You can toggle between the two modes by clicking the "Freq Axis" button in the top right corner.

Notice that the two graphs look quite different, and the graph in log format actually makes it much easier to identify issues in the lower frequencies. Going forward, you should always post using a log scale--for our purposes, the linear scale is of no value.
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post #14525 of 14534 Old Today, 06:43 AM
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Originally Posted by AustinJerry View Post
Notice that the two graphs look quite different, and the graph in log format actually makes it much easier to identify issues in the lower frequencies. Going forward, you should always post using a log scale--for our purposes, the linear scale is of no value.
Ok, here is the log version..to my untrained eyes (but learning) it does not look quite as good. But I guess not much I can do about the super low stuff anyways....


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post #14526 of 14534 Old Today, 08:09 AM
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Originally Posted by toofast68 View Post
Ok, here is the log version..to my untrained eyes (but learning) it does not look quite as good. But I guess not much I can do about the super low stuff anyways....


First of all, the bass resonance looks to be well under control. Addressing anything under 20Hz is very difficult. Besides, what lives down there? Nothing in music content, which is where resonance is really audible. Probably only LFE effects on movies, and I don't think you will be able to hear much of a difference. Time to move on to the Impulse Response (ETC) graph and look at specular reflections...

BTW, notice how much more revealing the log graph is. In linear mode, you may not have seen that there are slightly different issues at 30Hz vs. 20Hz.
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post #14527 of 14534 Old Today, 08:29 AM
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Originally Posted by toofast68 View Post
Ok, here is the log version..to my untrained eyes (but learning) it does not look quite as good.
Isn't there a bit of rising resonance as the graph approaches 300Hz? What would cause that?
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post #14528 of 14534 Old Today, 09:54 AM
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Click image for larger version

Name:	distortion 128k.jpg
Views:	19
Size:	298.0 KB
ID:	672649

Click image for larger version

Name:	distortion 1M.jpg
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Size:	282.7 KB
ID:	672657

These two measurements are EXACTLY the same (one taken right after the other), except one is a 128k sweep (top graph), and the other a 1M sweep (bottom graph). At 21.5hz, the 128k shows 7.6% distortion, the 1M shows 3.13%.

I have observed other differences in data vs sweep length in the low end, notably in waterfalls . Therefore, it may be recommended to do 1M sweeps when finalizing a change.

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post #14529 of 14534 Old Today, 10:59 AM
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Originally Posted by jim19611961 View Post
Attachment 672649

Attachment 672657

These two measurements are EXACTLY the same (one taken right after the other), except one is a 128k sweep (top graph), and the other a 1M sweep (bottom graph). At 21.5hz, the 128k shows 7.6% distortion, the 1M shows 3.13%.

I have observed other differences in data vs sweep length in the low end, notably in waterfalls . Therefore, it may be recommended to do 1M sweeps when finalizing a change.
Yes, but which one is correct, the one which shows the better result? Wishful thinking?
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post #14530 of 14534 Old Today, 11:12 AM
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Yes, but which one is correct, the one which shows the better result? Wishful thinking?
No, not wishful thinking. For each doubling of the sweep length, you gain 3db in S/N. JohnPM has said this. So 1M has a better S/N over a 128k by 9db. Its possible that neither is absolutely correct. But my bet is that the 1M is more correct.

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post #14531 of 14534 Old Today, 11:35 AM
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Originally Posted by jim19611961 View Post
No, not wishful thinking. For each doubling of the sweep length, you gain 3db in S/N. JohnPM has said this. So 1M has a better S/N over a 128k by 9db. Its possible that neither is absolutely correct. But my bet is that the 1M is more correct.
Yes, now that you mention it, I do recall that comment by John.

Perhaps we should compare the shorter and longer sweep results. If not much difference, shorter is quicker.
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post #14532 of 14534 Old Today, 11:48 AM
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Quote:
Originally Posted by jim19611961 View Post
No, not wishful thinking. For each doubling of the sweep length, you gain 3db in S/N. JohnPM has said this. So 1M has a better S/N over a 128k by 9db. Its possible that neither is absolutely correct. But my bet is that the 1M is more correct.
in room THD measurements, IME, are pretty sensitive to low level environmental noise hence I suspect you're likely to get more robust results from using multiple sweeps.

Is that possible with a USB mic? ISTR multiple sweeps being problematic when multiple clocks are in the picture.
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post #14533 of 14534 Old Today, 09:50 PM
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Quote:
Originally Posted by jim19611961 View Post
No, not wishful thinking. For each doubling of the sweep length, you gain 3db in S/N. JohnPM has said this. So 1M has a better S/N over a 128k by 9db. Its possible that neither is absolutely correct. But my bet is that the 1M is more correct.
I assumed it was in the REW User guide, so never asked. But since I see it being talked about here, I wonder... What is the recommended setting then as far as the sweep parameteres/options that can be used?
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post #14534 of 14534 Old Today, 09:52 PM
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Ok, here is the log version..to my untrained eyes (but learning) it does not look quite as good. But I guess not much I can do about the super low stuff anyways....


This looks excellent! Congratrs. Can you tell us a little about your room setup, where the MLP is, where the sub is placed etc? How about room treatments? I assume you must have some treatments going to have this great of a result (either that or you are sitting on top of your sub ).
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