Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 223 - AVS Forum
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post #6661 of 12748 Old 11-11-2013, 12:58 PM
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Originally Posted by jim19611961 View Post

I measure in the 70-75db range with consistent and confident results. Two caveats though:

1) I use Omnimic, not REW for measuring.
2) I don't care that much what happens beyond -35db on waterfalls and decays.



The FFT shows what the noise floor is in the frequency domain. So I suggest this is more meaningful than using one average number to describe the noise floor as a whole.

While there is nothing intrinsically wrong with loud measurements (90+db), I do question their necessity.

 

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I agree with you here but it's probably also relative to the room in which Glenn took his measurements (i.e. relative noise floor).  It's conceivable to me that the noise floor in a studio room could be as low as 35dB in which case he has achieved the 40dB threshold we have been purporting in this thread.  HST, I'm curious what the consensus is on this issue (perhaps from those outside of the members contributing to this thread as Stuart points out we've gone round and round on this ad nauseam!)?

IMO, what needs attention is determining the noise floor to begin with. According to my FFT graph, no level exceeds 30db down to 20hz. I get about the same results from RTA. Yet, the db meter says 50db. So which is it?

 

Even more peculiar considering your graph doesn't go above 40dB all the way down to 10Hz! :confused:

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post #6662 of 12748 Old 11-11-2013, 01:00 PM
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Originally Posted by AustinJerry View Post

BTW, I know raising and lowering the bottom limit affects how the Waterfall looks, but I don't recall how the measurement SPL affects how it looks. I'll have to perform a test one of these days.

"raising and lowering the bottom limit" is like dragging an iceberg out of the water or pushing it in deeper. You simply see more or less of it.
SPL does NOT affect how the waterfall looks, you just see more or less noise at the bottom of the graph. Of course a low noise level is always a good thing but clipping is as bad as having too much noise.

 

Markus, I don't think the issue of SPL is wrt the limits displayed in the waterfall as much as it is wrt the SPL of the initial measurement BICBW.  I thought someone posted some waterfalls taken at different SPL's (not just changing the graph limits) and it showed appreciable differences in the rate of decay but again, ICBW.

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post #6663 of 12748 Old 11-11-2013, 01:03 PM
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?

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post #6664 of 12748 Old 11-11-2013, 01:23 PM
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^

Read this post

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post #6665 of 12748 Old 11-11-2013, 01:41 PM
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And then I'll find that there's absolutely no signficant difference other than the "iceberg" is shifted up or down:



Hope the animation is showing properly.

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post #6666 of 12748 Old 11-11-2013, 01:45 PM
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Quote:
Originally Posted by markus767 View Post

"raising and lowering the bottom limit" is like dragging an iceberg out of the water or pushing it in deeper. You simply see more or less of it.
SPL does NOT affect how the waterfall looks, you just see more or less noise at the bottom of the graph. Ringing is NOT affected by SPL of the test signal. Of course a low noise level is always a good thing but clipping is as bad as having too much noise.

I agree with you.

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post #6667 of 12748 Old 11-11-2013, 01:46 PM
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Quote:
Originally Posted by jkasanic View Post
 
Quote:
Originally Posted by kbarnes701 View Post
 

I agree. I wasn't suggesting otherwise. Just wondering if it actually matters. When I see GIK measuring at an average of well below 75dB it gives me pause for thought, that's all.

 

I agree with you here but it's probably also relative to the room in which Glenn took his measurements (i.e. relative noise floor).  It's conceivable to me that the noise floor in a studio room could be as low as 35dB in which case he has achieved the 40dB threshold we have been purporting in this thread.  HST, I'm curious what the consensus is on this issue (perhaps from those outside of the members contributing to this thread as Stuart points out we've gone round and round on this ad nauseam!)?

 

Good point wrt to their noise floor.

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post #6668 of 12748 Old 11-11-2013, 01:47 PM
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@Markus:  So what part of "I could be wrong" did you misunderstand?  That was the whole point of mentioning it again since you obviously didn't see it the first time or didn't feel the need to comment as you do now.

 

FWIW, the animation is not working in IE 10 but I'll take your word for it that there's no appreciable difference.  There seemed to be a consensus from other members in the thread that it did make a difference (note the posts subsequent to Keith's post that I linked to) so I trust everyone will benefit from your input.  Thanks.

 

EDIT:  The animation is working now and apparently my understanding of how to interpret waterfalls needs clarification.  The ringing appears to be much worse in the higher SPL measurement and noticeably different than just lowering the noise floor thereby exposing more of the iceberg.  According to your analogy, the iceberg appears to have grown at a specific depth above the water level (i.e. its amplitude at a given frequency at a given time) compared to the previous iceberg (at the lower SPL).

 

EDIT 2:  I think you've successfully educated me wrt waterfalls thanks to your animation.  Upon further inspection, I noticed that you offset the level of the measurement to coincide with the first measurement and now I can see the raising and lowering of the iceberg as you described it.  At first glance, by adding the offset to show the same relative SPL level the ringing appeared to be worse but when you consider the higher SPL it makes sense (at least to me).  When viewed as two separate graphs it wasn't nearly as clear.  Thanks.

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post #6669 of 12748 Old 11-11-2013, 01:48 PM
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Originally Posted by kbarnes701 View Post

Good point wrt to their noise floor.

I think its fair to say that rooms with LOTS of absorbent will typically have lower noise floors.

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post #6670 of 12748 Old 11-11-2013, 01:48 PM
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Quote:
Originally Posted by jkasanic View Post
 
Quote:
Originally Posted by markus767 View Post
 
Quote:
Originally Posted by AustinJerry View Post

BTW, I know raising and lowering the bottom limit affects how the Waterfall looks, but I don't recall how the measurement SPL affects how it looks. I'll have to perform a test one of these days.

"raising and lowering the bottom limit" is like dragging an iceberg out of the water or pushing it in deeper. You simply see more or less of it.
SPL does NOT affect how the waterfall looks, you just see more or less noise at the bottom of the graph. Of course a low noise level is always a good thing but clipping is as bad as having too much noise.

 

Markus, I don't think the issue of SPL is wrt the limits displayed in the waterfall as much as it is wrt the SPL of the initial measurement BICBW.  I thought someone posted some waterfalls taken at different SPL's (not just changing the graph limits) and it showed appreciable differences in the rate of decay but again, ICBW.

 

Yes, I did. And yes, it did.  It seems pretty obvious to me that a 115dB bass note will ring more than a 30dB bass note... BICBW.

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post #6671 of 12748 Old 11-11-2013, 01:54 PM
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Yes, I did. And yes, it did.  It seems pretty obvious to me that a 115dB bass note will ring more than a 30dB bass note... BICBW.

It depends what you mean. It will ring louder, proportional to the direct signal being louder, yes. But its shape on the graph and relativity to the direct remains the same.

The only instance that I can think of when this would be different is when lets say you have a picture hanging on a wall that wont start vibrating until the bass vibration is sufficient to dislodge it into movement. Same goes for any other semi-loose item that remains still at low spl, but will resonate at higher ones.

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post #6672 of 12748 Old 11-11-2013, 01:56 PM
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Originally Posted by jkasanic View Post

@Markus:  So what part of "I could be wrong" did you misunderstand?  That was the whole point of mentioning it again since you obviously didn't see it the first time or didn't feel the need to comment as you do now.

FWIW, the animation is not working in IE 10 but I'll take your word for it that there's no appreciable difference.  There seemed to be a consensus from other members in the thread that it did make a difference (note the posts subsequent to Keith's post that I linked to) so I trust everyone will benefit from your input.  Thanks.

I did comment on SPL, maybe you missed it. Please make the animation work or you won't understand.

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post #6673 of 12748 Old 11-11-2013, 01:58 PM
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FWIW, the animation is not working in IE 10 but I'll take your word for it that there's no appreciable difference. 

Works in Firefox

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post #6674 of 12748 Old 11-11-2013, 02:00 PM
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@Markus:  So what part of "I could be wrong" did you misunderstand?  That was the whole point of mentioning it again since you obviously didn't see it the first time or didn't feel the need to comment as you do now.

FWIW, the animation is not working in IE 10 but I'll take your word for it that there's no appreciable difference.  There seemed to be a consensus from other members in the thread that it did make a difference (note the posts subsequent to Keith's post that I linked to) so I trust everyone will benefit from your input.  Thanks.

I did comment on SPL, maybe you missed it. Please make the animation work or you won't understand.

 

See my edits above.  Thanks for the clarification.

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post #6675 of 12748 Old 11-11-2013, 02:08 PM
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You're welcome. Please also see http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/6630#post_23935432

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post #6676 of 12748 Old 11-11-2013, 02:18 PM
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Absolute measurement SPL is meaningless for interpreting waterfalls and the like, as long as the noise floor is low enough. The ONLY thing of interest in a waterfall graph is where the ringing starts relative to the first slice and how fast it decays. Everything else is irrelevant. Stop looking at the bottom of the graphs, the relevant data is at the top!

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post #6677 of 12748 Old 11-11-2013, 03:29 PM
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Quote:
Originally Posted by kbarnes701 View Post

Yes, I did. And yes, it did.  It seems pretty obvious to me that a 115dB bass note will ring more than a 30dB bass note... BICBW.

It depends what you mean. It will ring louder, proportional to the direct signal being louder, yes. But its shape on the graph and relativity to the direct remains the same.
 

 

The former..

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post #6678 of 12748 Old 11-11-2013, 04:43 PM
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Originally Posted by markus767 View Post

"raising and lowering the bottom limit" is like dragging an iceberg out of the water or pushing it in deeper. You simply see more or less of it.
SPL does NOT affect how the waterfall looks, you just see more or less noise at the bottom of the graph. Ringing is NOT affected by SPL of the test signal. Of course a low noise level is always a good thing but clipping is as bad as having too much noise.
Best explanation I've seen put forward...close to theory of relativity smile.gif
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post #6679 of 12748 Old 11-11-2013, 04:50 PM
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So I am thinking about toying with 100-120 crossover to attack that issue I have. If I raise sub x over I can use mini dsp there. Any thoughts?


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post #6680 of 12748 Old 11-11-2013, 04:59 PM
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So I am thinking about toying with 100-120 crossover to attack that issue I have. If I raise sub x over I can use mini dsp there. Any thoughts?


Id give it a try, sure.

Might turn down the sub a bit (+9db) over rest.

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post #6681 of 12748 Old 11-11-2013, 05:42 PM
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Warning:  REW Help Files induce confusion and panic!  did you read the Guide that we collectively put together for newcomers like yourself?

Ok....ok.....not so intimidating now that I've read through the step by step guide. Who ever wrote that up (Austin ?) really took there time and knows what they are doing, and for that I (we) thank you!

Just a clarification....step 5 goes over how to calibrate the mic using a SPL meter. It then says that you do not need to do this with the UMIK-1, I just want to make sure I don't need a SPL meter.

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post #6682 of 12748 Old 11-11-2013, 05:50 PM
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An SPL meter is something you should have regardless of mic but the point in the guide is that the UMIK-1 is already calibrated in REW so a separate calibration (using an SPL meter) is not required.

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post #6683 of 12748 Old 11-11-2013, 05:52 PM
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Id give it a try, sure.

Might turn down the sub a bit (+9db) over rest.

I have it that way on purpose. I haven't nailed down a preference yet as I have only had the Submersives a short while. I may disengage the low shelf filter and just use dynamic EQ and PGM 2 on the Submersives which gives a 3db bump below about 40-45hz down. I was going for what I read about in developing a house curve. Basically play a 30hz and 100hz sine wave and they should sound the same perceived loudness. It made sense trying to make the lowest all the way to the highest notes on a bass guitar to sound the same perceived loudness. Obviously we know the spl meter would read higher. I know we all have our tastes but there is no way I could do flat bass. I like the curve. When I listen to music I like the kick drum to have a punch to it, not anemic sounding making me wonder if the sub is actually on. That doesn't make sense to me. Why even buy a sub if you can't hear it? I am not meaning to be condescending at all. It just made a lot of sense to me that I want all sounds to be the same perceived loudness in the end.

I actually have it +6-9db for music and +3db for movies.

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Using a house curve...how much boost should the low shelf filter have?

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post #6685 of 12748 Old 11-11-2013, 06:42 PM
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The only instance that I can think of when this would be different is when lets say you have a picture hanging on a wall that wont start vibrating until the bass vibration is sufficient to dislodge it into movement. Same goes for any other semi-loose item that remains still at low spl, but will resonate at higher ones.

This is my concern also, and probably makes more sense to movie listeners who can have peaks > 105dB @ reference level. Almost everything in my rattly old wooden house is not completely rigid,
It just makes to much sense to me to measure at this high level, but then, maybe common sense doesn't translate confused.gif

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Using a house curve...how much boost should the low shelf filter have?

AFAIK, this depends on the room and personal preference.
From what I have read and my own testing, the best way to determine the house curve is to play tones at various frequencies and adjust the level until they have the same apparent loudness.
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post #6686 of 12748 Old 11-11-2013, 06:48 PM
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Using a house curve...how much boost should the low shelf filter have?

I read...When I say read I mean Home Theater Shack articles that are offshoots of REW and that whole world over there. I read every room will be different. If I tried to make a 30hz and 100hz sine wave have the same perceived loudness I would need like a 14db low shelf filter. I have 8 currently and I feel it is a bit too much. That 30 and 100 is a very rough outline and they state all rooms and preferences will vary. I think maybe a 5db with PGM 2 on my subversives would do. So I would say try a 4db, 8db and 12db and see how you like it smile.gif

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Great thanks!!

Just didnt want to go too high and kill headroom

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I am getting a bit confused. I set up in anticipation of setting a higher crossover. Here is two sweeps both at 120hz crossover and the mic didn't move at all. Why are they not identical?


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post #6689 of 12748 Old 11-11-2013, 07:22 PM
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and more confusion. I certainly know a measurement will not look the same identically as another day because the mic position can't be duplicated exactly. But this seems drastic...



Perhaps it is not drastic and I am reading too much into that drop? I guess it is there on the first as well just not so sharp

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post #6690 of 12748 Old 11-11-2013, 07:22 PM
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Quote:
Originally Posted by markus767 View Post

Absolute measurement SPL is meaningless for interpreting waterfalls and the like, as long as the noise floor is low enough. The ONLY thing of interest in a waterfall graph is where the ringing starts relative to the first slice and how fast it decays. Everything else is irrelevant. Stop looking at the bottom of the graphs, the relevant data is at the top!
Markus, since you're one of the folks here who's most familiar with REW and its interpretation, maybe you could go into a little more detail in the interpretation of the graph you posted below.
Quote:
Originally Posted by markus767 View Post

^
And then I'll find that there's absolutely no signficant difference other than the "iceberg" is shifted up or down:



Hope the animation is showing properly.
The animation does a great job of illustrating the iceberg analogy. The small differences near the bottom of the graph (aside from just exposing more of the bottom of the iceberg appear to simply be the slight differences that occur between measurements, even with identical mic placements.

Now you mentioned 2 things:
A) Important = where the ringing starts relative to the first slice and how fast it decays
B) Not important, the bottom of the graph

For A) The ringing in the ~50-55Hz region begin fairly high up and continues all the way down and I assume that means that it's something that should be looked into. In comparison, the ~30Hz region starts extending out pretty low down on the graph. Does that mean it's nothing to be concerned about? Likewise with the ~100Hz region. The mountain begins to stick out pretty low (~25db) down from the top of the graph (the first slice?). Granted, in the 100Hz region the time to decay in the noise floor is already pretty short, but if, for example it still extended out to 450ms at the bottom of the graph, would it still be insignificant?


Max
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