Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 466 - AVS Forum | Home Theater Discussions And Reviews
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Old 03-16-2015, 12:59 PM
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^
If you send the REW test signal to channel 4 via HDMI it is handled as a LFE channel signal and is therefore boosted by 10dB in the AVR.

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Old 03-16-2015, 01:06 PM
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Originally Posted by markus767 View Post
^
If you send the REW test signal to channel 4 via HDMI it is handled as a LFE channel signal and is therefore boosted by 10dB in the AVR.
thanks, makes sense

So I'm reading the sub distance tweek article and this is what I did:
made sure the receiver has audyssey on and dyn eq and dyn volume off
Problem is , my receiver only will show multi in, and won't let me change to PLII. is this a problem?

blue line in attached graph is center only. green line is sub only. red is sub and center.
Since the combined sub and center response is greater than the sub or center by itself, does this mean I won't benefit from tweaking the distance? I tried changing the distance up and down and the spl in the70hz range didn't change much for the better either way. Audyssey originally set my sub at 13.5 ft (red line in second graph). the blue line in second graph is with sub at 15.5ft, and the purple is with sub dist at 11.5 feet. Thoughts? Thanks
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Old 03-16-2015, 01:41 PM
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Originally Posted by mattdub1 View Post
thanks, makes sense

So I'm reading the sub distance tweek article and this is what I did:
made sure the receiver has audyssey on and dyn eq and dyn volume off
Problem is , my receiver only will show multi in, and won't let me change to PLII. is this a problem?

blue line in attached graph is center only. green line is sub only. red is sub and center.
Since the combined sub and center response is greater than the sub or center by itself, does this mean I won't benefit from tweaking the distance? I tried changing the distance up and down and the spl in the70hz range didn't change much for the better either way. Audyssey originally set my sub at 13.5 ft (red line in second graph). the blue line in second graph is with sub at 15.5ft, and the purple is with sub dist at 11.5 feet. Thoughts? Thanks
Yup, looks like the distance tweak didn't help much. You could try going even further in each direction though just to see.

In the future, please post graphs with 5db steps on the left hand side. If you set the vertical limits to (the recommended) 55-105 that should do it.
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Old 03-16-2015, 01:51 PM
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Originally Posted by Alan P View Post
Yup, looks like the distance tweak didn't help much. You could try going even further in each direction though just to see.

In the future, please post graphs with 5db steps on the left hand side. If you set the vertical limits to (the recommended) 55-105 that should do it.
Oops sorry about that! Overall, do I have a decent curve here (the combined response) or are there some trouble spots I could try to clean up with maybe moving the sub position a bit? Thanks
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Old 03-16-2015, 02:10 PM
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TBH, you are showing quite a bit of bass resonance, a specially at 50Hz, which is a pretty important frequency. Depending on how satisfied you are with the bass response, you could consider adding bass traps.

You don't need to worry about setting to PLII Cinema--that is for HDMI setups that only support 2.0. Regardless of whether your HDMI is 7.1 or 2.0, the accepted method of measuring bass response is to output the signal to one of the front speakers (usually the center channel). The sub receives a signal by virtue of bass management. If you measure sub only using the LFE HDMI output, you will get a 10dB bass boost, as Markus has said. That isn't a problem, per se, as long as you understand what is happening.
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Old 03-16-2015, 02:57 PM
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Originally Posted by mattdub1 View Post
Oops sorry about that! Overall, do I have a decent curve here (the combined response) or are there some trouble spots I could try to clean up with maybe moving the sub position a bit? Thanks
I'll reserve final judgement until you re-post with the recommended limits, but....

It looks like you've got a lot of "wavering" in the FR between 40-150hz....not sure what's going on there. Also, it looks like you've still got good extension going below 15hz, can we see down to 10hz?

Did you do the sub crawl before placing your sub? Where's your crossover set? What are your L/C/R speakers? Do you use Audyssey? If so, where did it set your sub trim and where is it now?
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Old 03-16-2015, 04:21 PM
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Originally Posted by Alan P View Post
I'll reserve final judgement until you re-post with the recommended limits, but....

It looks like you've got a lot of "wavering" in the FR between 40-150hz....not sure what's going on there. Also, it looks like you've still got good extension going below 15hz, can we see down to 10hz?

Did you do the sub crawl before placing your sub? Where's your crossover set? What are your L/C/R speakers? Do you use Audyssey? If so, where did it set your sub trim and where is it now?
ok attached are the adjusted graphs with 5 db increments. The first graph is where blue is center only, green is sub only, and red is center channel with sub on crossed over at 80hz.
second graph is where audyssey set the distance (13.5 ft) in red. Blue line is 15.5 and purple line is 11.5 ft.

I did the sub crawl with my last down-firing sub and the left front corner seemed to be the best place, which is to the left of my left tower. That's where the new sub is as well. My options are now very limited given the size of this subwoofer (an absolute monster) so I will try rotating it into the room and play with the few feet of room around it I have. Right now, its about two feet in from the left wall firing directly at the side of my left tower. It is about 3 inches away from the front wall. My speakers are energy veritas v6.3 towers with v5.2c center channel. I do use audyssey as I have an older denon 590. When I ran audyssey, I turned the sub gain to -6 and audyssey set it at -7.5db. I bumped it up to -4.5 so running it 3db hot. I will add graphs of the 10hz extension later.
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Old 03-16-2015, 06:08 PM
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Originally Posted by mattdub1 View Post
My options are now very limited given the size of this subwoofer
Did you post the size of your room (WxHxL)? I wonder if that dip at 70Hz, which affects both speakers, is room mode related.
That could also be helped by bass trapping.
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Old 03-16-2015, 08:13 PM
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Did you post the size of your room (WxHxL)? I wonder if that dip at 70Hz, which affects both speakers, is room mode related.
That could also be helped by bass trapping.
Size of my room is roughly 15 feet wide, about 35 feet long, and 8 foot ceilings. It's shaped like a long hallway and my system is on the 15 foot wide wall. Couch is about 13 feet back from the front wall in middle of room, with about 22 feet behind it to the back wall. I have a bar that juts out into the room and the left front side of the room has a bathroom next to it with a sliding door that's open. it's all tile and I think the bathroom is definitely coming into play here. I shut the door and get a different curve.

I was able to slightly raise the dip around the crossover by moving my sub only about 6 inches back into the front left corner more. I tried shifting around inch by inch and I'm not sure if the result is better or worse. It raised the 70 hz dip I had but took a little spl in the 20-30hz range. Which one would you guys keep?? the attached graph has the old position with 70hz dip in green. the red is the new position. The purple is one of my positions with the bathroom door shut. these are unsmoothed graphs as well. I also attached a waterfall in pink of the current position, and one in purple of another position with the bathroom door shut. thanks
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Old 03-16-2015, 08:57 PM
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Thanks to Jerry's guide and the help I've received here, I think it's fair to say I've made some significant progress using REW: Looking at the ETC, the reflections have been reduced using panels to close to -20 dB. Also, the FR of my dual subs is relatively flat, though perhaps some more tweaking may be in order (or perhaps an eventual upgrade to XT32). I'm also pleasantly surprised to see that from what I understand my waterfall graph looks OK too. I seem to remember 50 dB reduction by 300 ms being a goal, and if so, I'm doing well at least after about 45 Hz. So from what I'm understanding I seem to have gotten lucky there.

What doesn't look great to me are the frequency response graphs I've taken (at least compared to what I've seen on this forum). Here is my FR graph of my mains:



I'm operating in a small (1200 cubic feet), mixed use room, so there really might not be too much I can do to flatten this. But I'm just curious, how bad does this look to people? The biggest issue to me seems to be the hump at 120 Hz and then the dip after. Is this the kind of thing that could reasonably be expected to be improved upon with bass traps? (I should add that I'm crossing over at 110 Hz. Going lower begins to open up a large dip just below the crossover, and I even though I've currently got one sub behind the couch, it still sounds good to me crossing over this high.)

One other weird thing I've noticed on my frequency response graphs is the measurement of the mains in direct (so no sub or Audyssey). Does it seem weird that there's such content at 40 Hz with just my Ascend CBM-170s?



Also, I figure it couldn't hurt to post the waterfall in case I'm mistaken in my favorable interpretation of what it show:





Thank you all who have helped me so much!
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Old 03-16-2015, 09:19 PM
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^ Bass response looks pretty flat. Waterfall looks decent. The frequency response graphs have some pretty severe dips, which you should probably try to identify. Look at room dimensions and modes. You might be able to smooth the FR out by moving the mains either closer together or further apart.
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Old 03-17-2015, 12:12 AM
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Originally Posted by Greenwood Ave View Post
...
I'm operating in a small (1200 cubic feet), mixed use room, so there really might not be too much I can do to flatten this. But I'm just curious, how bad does this look to people? The biggest issue to me seems to be the hump at 120 Hz and then the dip after. Is this the kind of thing that could reasonably be expected to be improved upon with bass traps? (I should add that I'm crossing over at 110 Hz. Going lower begins to open up a large dip just below the crossover, and I even though I've currently got one sub behind the couch, it still sounds good to me crossing over this high.)

..

Thank you all who have helped me so much!
Peter,

I had a similar issue in the 100Hz to 300Hz frequency response using Audyssey MultiEQ. When up-grading to Audyssey XT32, the correction filters did a much better job. See the frequency response graphs for the center channel + sub below. Speaker make and model is KEF E301c. The sub is Rythmik F12G. The Main Listening Position (MLP) hasn't changed. The only change was the receiver that went from Audyssey MultiEQ to XT32.

Audyssey MultiEQ:


Audyssey XT32:

Maranatz SR-7009, Oppo BPD-93, MTV 7000D, aTV, WDTV Live, Harmony 650 remote, KEF E301+T101, MiniDSP(2x4) & 10x10HD, Emotiva 2xXPA-5 (Gen2), Rythmik 2xF12G+2xF8, HiMedia Q16, LG 55EC9300 (on order).

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Old 03-17-2015, 01:17 AM
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The upper and lower "no EQ" curves don't match? The upper graph looks more like Dynamic EQ on vs. off?

Markus

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Old 03-17-2015, 02:33 AM
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^ Markus,

Went back to the mdat to dig up the sweep for Audyssey MultiEQ (using the Marantz NR-1504) and Audyssey XT32 (using the Marantz SR7009). I've combined both results into one graph shown below.

Center channel + sub: Audyssey MultiEQ vs. XT32 (1/12th smoothing)


The only difference between the two graphs is that the level when playing the sweep is -12dBFS for XT32 while it was -10dBFS for MultiEQ. So there is a 2dB differential level between the two graphs. Both Dynamic EQ and Dynamic Volume were OFF.

Edit: I've included additional graph showing the no smoothing low frequency from 15Hz to 300Hz
Center channel + sub: Audyssey MultiEQ vs. XT32 (no smoothing)

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Old 03-17-2015, 05:59 AM
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Quote:
Originally Posted by Greenwood Ave View Post
One other weird thing I've noticed on my frequency response graphs is the measurement of the mains in direct (so no sub or Audyssey). Does it seem weird that there's such content at 40 Hz with just my Ascend CBM-170s?
One thing I recently noticed with my monitors is that, although they do measure lower than expected, the distortion rises quickly to an unacceptable level.

In my case, the distortion goes from less than 1% up to and including 100% way down low. I think I'm saved from hearing it because I don't play that loudly.

I intend to reduce the distortion by crossing over higher and doing more aggressive bass management. Just need some measuring time.
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Old 03-17-2015, 06:03 AM
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Greenwood Ave, I noticed you are using audyssey flat. Is that what everyone should be using when taking measurements? or did you try any placement optimization prior to running audyssey and then this graph is a result after pre-audyssey optimizations?
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Old 03-17-2015, 06:05 AM
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^ Bass response looks pretty flat. Waterfall looks decent. The frequency response graphs have some pretty severe dips, which you should probably try to identify. Look at room dimensions and modes. You might be able to smooth the FR out by moving the mains either closer together or further apart.
Jerry, doesn't he have alot of ringing? that's what it looks like to me, but I could be wrong as I'm new to reading these graphs
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Old 03-17-2015, 06:27 AM
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Jerry, doesn't he have alot of ringing? that's what it looks like to me, but I could be wrong as I'm new to reading these graphs
I have seen worse, Matt. On his waterfall, the resonance is worse below 50Hz. When you get that low, correction becomes increasingly difficult.
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Old 03-17-2015, 06:29 AM
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Greenwood Ave, I noticed you are using audyssey flat. Is that what everyone should be using when taking measurements? or did you try any placement optimization prior to running audyssey and then this graph is a result after pre-audyssey optimizations?
As long as you identify whether you are using Audyssey or Audyssey Flat, it doesn't matter. The only difference is in the high frequencies. Feel free to use either, depending on what you are looking for.
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Old 03-17-2015, 06:34 AM
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Originally Posted by mattdub1 View Post
ok attached are the adjusted graphs with 5 db increments. The first graph is where blue is center only, green is sub only, and red is center channel with sub on crossed over at 80hz.
second graph is where audyssey set the distance (13.5 ft) in red. Blue line is 15.5 and purple line is 11.5 ft.

I did the sub crawl with my last down-firing sub and the left front corner seemed to be the best place, which is to the left of my left tower. That's where the new sub is as well. My options are now very limited given the size of this subwoofer (an absolute monster) so I will try rotating it into the room and play with the few feet of room around it I have. Right now, its about two feet in from the left wall firing directly at the side of my left tower. It is about 3 inches away from the front wall. My speakers are energy veritas v6.3 towers with v5.2c center channel. I do use audyssey as I have an older denon 590. When I ran audyssey, I turned the sub gain to -6 and audyssey set it at -7.5db. I bumped it up to -4.5 so running it 3db hot. I will add graphs of the 10hz extension later.
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Size of my room is roughly 15 feet wide, about 35 feet long, and 8 foot ceilings. It's shaped like a long hallway and my system is on the 15 foot wide wall. Couch is about 13 feet back from the front wall in middle of room, with about 22 feet behind it to the back wall. I have a bar that juts out into the room and the left front side of the room has a bathroom next to it with a sliding door that's open. it's all tile and I think the bathroom is definitely coming into play here. I shut the door and get a different curve.

I was able to slightly raise the dip around the crossover by moving my sub only about 6 inches back into the front left corner more. I tried shifting around inch by inch and I'm not sure if the result is better or worse. It raised the 70 hz dip I had but took a little spl in the 20-30hz range. Which one would you guys keep?? the attached graph has the old position with 70hz dip in green. the red is the new position. The purple is one of my positions with the bathroom door shut. these are unsmoothed graphs as well. I also attached a waterfall in pink of the current position, and one in purple of another position with the bathroom door shut. thanks
anyone have any thoughts on these graphs I posted? thanks
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Old 03-17-2015, 06:37 AM
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Jerry, doesn't he have alot of ringing? that's what it looks like to me, but I could be wrong as I'm new to reading these graphs
Probably not a lot of ringing. You always have to look at the data with different window settings to get a better understanding because there's always a trade-off between frequency and time resolution.

What we see below 50Hz might just be noise. Take another measurement exactly at the same position. If the shape of the ridges changes then it's noise.

The peak at 120Hz is modal and should be addressed.
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Old 03-17-2015, 08:13 AM
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Looking at the ETC, the reflections have been reduced using panels to close to -20 dB.
The idea is to get reflections at all frequencies down to the transition area below -20db. A full range ETC wont show you that. Banded ETC or a spectrogram will.

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Old 03-17-2015, 08:22 AM
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Quote:
Originally Posted by AustinJerry View Post
^ Bass response looks pretty flat. Waterfall looks decent. The frequency response graphs have some pretty severe dips, which you should probably try to identify. Look at room dimensions and modes. You might be able to smooth the FR out by moving the mains either closer together or further apart.
Great suggestion, Jerry. I did experiment with moving the speakers closer together once, and it didn't seem to make much difference. But I will double check. I was just thinking that my couch could come up another foot or so as well. The room dimensions are a little hard to analyze, I think, Since the room is basically a square but with a small bathroom size chunk taken out of the corner and then the ceiling is slanted at a fairly steep angle.


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Originally Posted by steveting99 View Post
I had a similar issue in the 100Hz to 300Hz frequency response using Audyssey MultiEQ. When up-grading to Audyssey XT32, the correction filters did a much better job. See the frequency response graphs for the center channel + sub below. Speaker make and model is KEF E301c. The sub is Rythmik F12G. The Main Listening Position (MLP) hasn't changed. The only change was the receiver that went from Audyssey MultiEQ to XT32.
Good to hear! I've read that many informed people feel XT32 is a big upgrade over XT. I've definitely found myself occasionally glancing at refurbished receiver prices.

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I intend to reduce the distortion by crossing over higher and doing more aggressive bass management. Just need some measuring time.
I haven’t looked too much at distortion graphs yet. I wasn’t very clear, but I mostly just included that graph since I thought it was so strange how the bass goes down and then so far back up at 40 Hz. It seems so different than most of the FR graphs I’ve seen. I guess I was just worried that I had ANOTHER problem with my mic or something. Everything else seems pretty consistent and normal, so perhaps this is just how the it measures. Perhaps this explains why Audyssey keeps detecting my mains as “full range.”

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Originally Posted by markus767 View Post
Probably not a lot of ringing. You always have to look at the data with different window settings to get a better understanding because there's always a trade-off between frequency and time resolution.

What we see below 50Hz might just be noise. Take another measurement exactly at the same position. If the shape of the ridges changes then it's noise.

The peak at 120Hz is modal and should be addressed.
When you say noise do you mean background noise? Like a fridge in the next room or traffic or something?

About addressing the peak at 120 Hz, the first thing I will try is moving the mains and MLP around as much as I am able to. After that would you be optimistic that bass traps or a reasonable sort (say 4” OC) could make a difference there? I'm probably not ready to jump into MiniDSP right now, but I do know this is something else to consider.

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Old 03-17-2015, 08:31 AM
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Originally Posted by jim19611961 View Post
The idea is to get reflections at all frequencies down to the transition area below -20db. A full range ETC wont show you that. Banded ETC or a spectrogram will.

mdat's ?
OK. I've been looking at the ETC graphs as specified in Jerry's guide (at least as I am understanding it). My laptop is at home, but will post an mdat tonight and I will be curious what you say. Thank you.
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Old 03-17-2015, 10:02 AM
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When you noise do you mean background noise? Like a fridge in the next room or traffic or something?
Yes, all of that.

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About addressing, peek at 120 Hz, the first thing I will try is moving the mains and MLP around as much as I am able to.
Good idea. Just make sure you still maintain a symmetrical setup. You don't want to sacrifice imaging for that peak.

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After that would you be optimistic that bass traps or a reasonable sort (say 4” OC) could make a difference there? I'm probably not ready to jump into MiniDSP right now, but I do know this is something else to consider.
More like 8" with an 8" air gap behind the absorber. Even then you need to cover a large area to achieve a significant effect. Better use an EQ. First use measurements to find out if that peak is spatially isolated or if it affects a larger area. In the latter case EQ will most likely work just fine.

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Old 03-17-2015, 10:50 AM
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I made tremendous progress with my Alchemys and REW today. Unfortunately, the wireless keyboard slipped out of my hands and did this:



Needless to say, any money I might possibly have considered putting towards Dirac Live is no longer available.



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Old 03-17-2015, 10:59 AM
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Old 03-17-2015, 11:00 AM
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Wow, a plastic keyboard did that?!
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Old 03-17-2015, 11:07 AM
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Quote:
Originally Posted by jim19611961 View Post
The idea is to get reflections at all frequencies down to the transition area below -20db. A full range ETC wont show you that. Banded ETC or a spectrogram will.

mdat's ?
Jim, you keep advocating for banded ETC measurements, yet when I responded to your request here, you never helped me interpred what the banded ETC's are really revealing.
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Old 03-17-2015, 11:34 AM
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Jim, you keep advocating for banded ETC measurements, yet when I responded to your request here, you never helped me interpred what the banded ETC's are really revealing.
That link really didnt take me to a question on your part on the issue.

But what banded ETC's give us is a view to what reflections are at a given frequency band.

Here is an example. What questions do you have about it?

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