Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 352 - AVS Forum
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post #10531 of 11671 Old 06-21-2014, 09:13 PM
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Thanks Jerry.

It was cheap....so I may just go with it. All I really use REW for is for measuring the subs anyway.
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post #10532 of 11671 Old 06-21-2014, 09:25 PM
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Yes, unplug left and right speakers, feed the AVR a mono signal to both channels, and you will be able to measure the subs by themselves. No problem.

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post #10533 of 11671 Old 06-21-2014, 10:46 PM
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Well, now the laptop won't output right over HDMI - audio is breaking up and the video signal is tinted pink....? Worked at first, but then went belly up for some reason.

Also, the battery won't charge! I knew I shouldn't have bought a refurb....this sucker is going back.
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post #10534 of 11671 Old 06-22-2014, 09:18 AM
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Quote:
Originally Posted by JohnPM View Post
%FS is percentage of full scale. It is a linear axis, so if the value it is showing is halved the trace would only go up half as far. A linear Y axis is common with time signals, unless there is a need to show a very large dynamic range, in which case a logarithmic axis makes it easier to get the range of interest onto the plot. The impulse response and its envelope are time signals.

"Full range" means without any filter applied to limit the range. The filtered IR graph allows various octave and one-third octave bandwidth filters to be applied to the impulse response. It then shows the impulse response after the filter has been applied. The envelope changes correspondingly. Applying a filter to a time signal changes its shape. In particular, applying low centre frequency bandpass filters to a signal will suppress all its rapid changes, since the filtered output will by definition not have high frequency content - just as a subwoofer cannot reproduce a finger snap, for example. Generally speaking, the lower the filter's centre frequency the more the amplitude of any sharp features passed through it will be reduced and the more they will be spread out in time. If the original signal did have a perfectly flat response it would itself be a perfect, single sample duration impulse. The outputs of the various filters would then be their own impulse responses, since the signal going into them would be an impulse.
Are you saying the absolute magnitudes of filtered ETC's are compromised after t=0? If so, then is it inaccurate to try and glean reflection frequency content at some given place in time over various center frequencies? Are time reversed filters better at this than the standard filters?

In a nutshell, can ETC slicing be used to accurately determine reflection frequency content by comparing the magnitude of slices in time?


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post #10535 of 11671 Old 06-22-2014, 09:43 AM
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Quote:
Originally Posted by Alan P View Post
Well, now the laptop won't output right over HDMI - audio is breaking up and the video signal is tinted pink....? Worked at first, but then went belly up for some reason.

Also, the battery won't charge! I knew I shouldn't have bought a refurb....this sucker is going back.
I don't know if this'll help, but you could try looking for a "low end" Acer Aspire. The model I'm thinking of is characterised by 15.6" display, 6-cell battery, 500GB HD, DVD writer drive, typically 4GB (8GB is usually $20 more, what I got), 3 x USB ports (just the right amount for display/REW cal + ext. mouse), 7.1 HDMI (192/24 audio), ext. speaker and mic jacks, web cam/mic, Gb ethernet, wifi, BT, etc. You can still find with Win7/64 (my pref.), works fine with ASIO or Java. These are quite highly rated online, and surprisingly the reviews are actually accurate! This is a great cheap laptop, way better than you'd expect, I was blown away because I didn't expect much...I specifically buy cheap laptops because I use them outside a lot and they tend not to last long, but this one's "like new" after almost 2 years. I'm going to guess the newer similar models are also good. I paid $300 2 years ago (with 8GB), but prices for laptops seem to have gone up recently, I guess back then was the tablet feeding frenzy so laptop sales/prices dropped. Just saying to not overlook the lower-end stuff, if REW is your main app, as some of it is very suitable. It's not slow either, kills my desktop with dbpoweramp etc., but it ain't no i7...

I understand what Jerry said re the surrounds/backs, but there's something to be said for easy access to the subs and center too, besides the fronts, with no cable fiddling. I do a quick "scan" of all my 7.1 (.2?) speakers whenever I start an REW session, just for the record, and it barely takes a minute. I use the ext. speaker out to do my (analog input only) stereo system. [Give me convenience or give me death! - DKs]

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post #10536 of 11671 Old 06-23-2014, 07:59 AM
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Thanks cfraser!

How about this one?
http://www.amazon.com/Acer-Aspire-ES...productDetails

Seems like a great deal, although I've never used Windows 8....haven't heard good things.
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post #10537 of 11671 Old 06-23-2014, 09:19 AM
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^ This is just/mainly for REW? Might be fine, but since the 7/5.1 HDMI seems to be a primary requirement, there's no way to verify this laptop does it until it's released. But I think it will based on the little info that's there, the "technical" description is similar to what mine was, perhaps better. That's my main thought. Second is the battery seems a bit small. Don't believe their run times, they're usually very "liberal", but for indoor/AC use it doesn't matter. Probably they reduced power consumption in the last couple years too.

I actually had other considerations when I selected my laptop, didn't even remember about REW until well after and luckily it was fine. DVD writer, decent battery size, and expandable RAM (for loading large google maps to have when out of cell/wifi range) were important for me, and many cheaper laptops don't have any of these. 4GB RAM, if it's the max allowed, is plenty fine for REW. They don't mention if it's expandable, and usually they do if it is, but in this laptop's case they might just not know yet. More RAM, up to a point, is more easily noticeable with laptops than it typically is with desktops, which tend to have much faster (and more power hungry) I/O and CPU interfaces.

I was just mentioning the features of a cheap laptop that works well for REW the other day. As a guide for you to find something inexpensive, if that mattered, within the same brand i.e. the identifying features, not a definitive list of desirable or even relevant features.

I would definitely take a chance on the one you linked, especially since it's from amazon with easy return option. Just consider if you might want to use it for other things.
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post #10538 of 11671 Old 06-23-2014, 10:13 AM
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Thanks again! I'm gonna pre-order it, and since I got Prime I won't be out anything if it doesn't work out.

And yes, this will be primarily for REW and some light web surfing in my recliner...that's probably about it. But it never fails, when I get a new piece of tech I always find more uses for it than originally planned and end up upgrading in the end....for example, I started with 2 PSA subs and now have 4.
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post #10539 of 11671 Old 06-23-2014, 12:16 PM
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^ One other thing you might want to check, perhaps at HTS, is to see if anybody using a similar Acer laptop with Win8 has had any ASIO issues. I have no experience with the combo, and Jerry's guide was with Win7. I set the laptop up pretty much exactly as in Jerry's guide, the number of HDMI channels not really mattering for that. Presume the latest "beta" of ASIO would work better with Win8 than the previous one (which I required for Win7 here); you want to run ASIO to make this laptop change worthwhile.

I played a bit with Win8 on another desktop and decided not to "upgrade" the laptop even though "free". Win8 has changed somewhat since then, with some more "familiar" Windows access/features added. I think that was the main Win8 complaint, it was originally more touch-screen/tablet/mobile-computing oriented.
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post #10540 of 11671 Old 06-23-2014, 12:21 PM
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Quote:
Originally Posted by jim19611961 View Post
Are you saying the absolute magnitudes of filtered ETC's are compromised after t=0?
No, there is nothing 'compromised' about them, they accurately reflect the effect of the filter.

Quote:
Originally Posted by jim19611961 View Post
If so, then is it inaccurate to try and glean reflection frequency content at some given place in time over various center frequencies?
Not if you turn off normalisation, it would not be meaningful to compare traces that have different normalisations due to their different peak values.

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Are time reversed filters better at this than the standard filters?
Not really. I have added a zero phase filter option for the next beta release though, to eliminate any time shift from the filter.

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Originally Posted by jim19611961 View Post
In a nutshell, can ETC slicing be used to accurately determine reflection frequency content by comparing the magnitude of slices in time?
Perhaps, as long as normalisation is turned off, though I'm not sure what the purpose would be. The spectral content of reflections is determined mainly by the area and absorption characteristics of the surfaces they reflect off.

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post #10541 of 11671 Old 06-23-2014, 08:21 PM
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Jerry,

I came across the following post regarding some background on why band limited (500 Hz to 2 kHz) pink noise is the preferred source to set acoustic levels. This is in reference to page 46 of the guide, when one is carrying out the mic calibration.

"With low-frequency components present, there’s lots of level bouncing around, and when played back in a room, the effects of standing waves are to add a frequency-by-frequency ±15 dB variation to the level typically. One way to solve this problem is to band limit the noise to above the Schroeder frequency; that room-volume dependent frequency where not much else above it in the soundfield can be called diffuse. For small rooms, 500 Hz will do.

At the high-frequency end of the range, there’s lots of trouble, too. Half-inch measurement microphones exhibit an 8 dB difference between direct sound and diffuse field sound at 20 kHz, and 6 dB at 10 kHz. These are big differences that will show up in an overall measurement, depending on whether you are direct- or diffuse-field dominated, and which way you aim the mic. Also, for interchangeability with the largest range of differing systems where “house curves” or the X curve of motion picture sound is in effect starting their rolloff at 2 kHz, rejecting frequencies above 2 kHz leads to maximum utility.

So pink noise, band limited to 500 Hz to 2 kHz is the preferred source to set acoustic levels.
It is broad enough so that single-frequency standing waves don’t make the measurement inaccurate,
and narrow enough that low- and high-frequency acoustical and sound system effects are minimized.


Using this two-octave band noise also solves another problem. The standard of the motion-picture industry for level setting is the ubiquitous Radio Shack sound level meter. Everybody should have one.

Get the cheaper analog meter that has better resolution than the more expensive digital one. I have calibrated more than 100 of these meters over a period of years, and find them out of the factory to mostly be within 1 dB, pretty good for such a cheap device. However, they do vary one to the next in their C weighting filter, so that broadband noise may show a different level meter-to-meter when they are calibrated on a mid-range tone (or noise)."

I believe the above is written by Tomlinson Holman, co-founder and Chief Scientist of Audyssey and the TH in THX. Is it worthwhile to consider this?

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post #10542 of 11671 Old 06-23-2014, 09:02 PM
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Hi Steve, thanks for sharing this. JohnPM, REW Author, must agree, because if you use REW's "Speaker Cal Signal", as shown in the screen shot below, it is indeed Pink Noise 500-2000Hz. Of course, the "Sub Cal Signal" is different, but the Guide suggests that either is appropriate for calibrating the mic. I have tried both, and the results are close enough to being the same that I cannot tell the difference. At least close enough for government work.


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post #10543 of 11671 Old 06-23-2014, 11:11 PM
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So pink noise, band limited to 500 Hz to 2 kHz is the preferred source to set acoustic levels.
It is broad enough so that single-frequency standing waves don’t make the measurement inaccurate,
and narrow enough that low- and high-frequency acoustical and sound system effects are minimized.
Yes, that's how it's done. The question remains if such band-limited steady-state measurements really correlate well with how humans perceive loudness of speakers in rooms.

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post #10544 of 11671 Old 06-24-2014, 05:20 AM
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Anything bigger then a suggested minimum. Ideally, one that covers all 3 speaker reflection points. A dirty great big rectangle thing, with lighting, if you like lighting.
For me personally, as a minimum, I would use double width of your current panels over each speaker reflection point.
My first ceiling panel is done. Taking the advice here, I went 2x the size I was planning. When it was done, I realized that the layout of the lights in the room allows me to put 4 of these up, instead of the two or three smaller ones that I was planning. Might as well use as much as possible of that pink fluffy that came in the bundle... This is 6" + 2" air gap, and 48" by 45" (the insulation is 15" wide, so 45" was the right measurement for three pieces side-by-side)



I only built one to see what I could learn. I'll be using that information for the next 3. I did solve the "how do I hang these two inches from the ceiling" rather elegantly, I think. But, the truth is that I just used the idea of the GIK brackets, and made my own.

Unfortunately, the hardest part of all of this is finding MATCHING fabric.

Standing under that panel and talking sounds, and FEELS strange.

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post #10545 of 11671 Old 06-24-2014, 05:50 AM
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I did solve the "how do I hang these two inches from the ceiling" rather elegantly, I think. But, the truth is that I just used the idea of the GIK brackets, and made my own.
First off, nice work! Hard to tell from the pic but if a c-channel bracket makes the bracket visible from the seated position then maybe try an s instead so the mounting to the ceiling is inside the perimeter of the treatment. Might not make that much difference with a 2" air gap though.

Also, at 6" depth + 2" air gap I would've thought OC703 or Rockwool would have more effect but I think you could be right on the border between those and pink fluffy.
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post #10546 of 11671 Old 06-24-2014, 06:05 AM
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Thanks! It's actually just an L bracket screwed to a purpose built "stub" that comes out of the frame. It came silver, I just hit it with the same black spray paint that I am using on the wooden frames. I changed the furthest out hole into a slot with a jig saw for easy mounting (see the GIK bracket). The flange is outside the frame of the treatment so that it can be easily tightened up (the screw is accessible). It turns out to be nearly invisible unless you are looking for it...The flash photography here is somewhat misleading. If you ask just about anyone who has been in the room, they would be hard-pressed to guess that the ceiling is dark green and not black. But, you are right...with the 2" gap, you'd see the mounting bracket either way. I'm quite happy with it.

I have plenty of 2' wide SafeNSound (rockwool) on hand to make more wall treatments. But advice here was to use pink fluffy at 6" of depth (with a graph to show the slight improvement in the bass region). Either way, the pink stuff was really inexpensive compared to the rockwool, so if the performance is going to be close, I'd rather use the pink stuff for the ceiling. And here's another SIGNIFICANT advantage of the pink stuff... It's MUCH lighter weight, so less likely to sag the fabric over time. [ I hope. :-) ]

This is constructed of 1x2s, (which are really 0.75 x 1.75) which means that there is a 2.5" air gap along all four edges as well. I plan to take pictures of the construction on the next one.

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post #10547 of 11671 Old 06-24-2014, 06:18 AM
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This is constructed of 1x2s, (which are really 0.75 x 1.75) which means that there is a 2.5" air gap along all four edges as well. I plan to take pictures of the construction on the next one.
I saw this idea as well in a DIY acoustic panel thread and thought it was a pretty cool way to limit reflections from the treatment itself.
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post #10548 of 11671 Old 06-24-2014, 06:28 AM
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I saw this idea as well in a DIY acoustic panel thread and thought it was a pretty cool way to limit reflections from the treatment itself.
Yes, I've seen that. It is interesting.

However, there's also this:

http://www.gikacoustics.com/diy-acoustic-panel-frames/

which seems to indicate that the difference is very minor. In my case, I could have used 6" wood for the sides and made the build about 60% less work. But leaving the sides open has at least some benefit, and the wood was cheaper. :-) The amount of time these take to put together (at the wood level) is so trivial that it just doesn't matter.
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post #10549 of 11671 Old 06-24-2014, 07:41 AM
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Yes, I've seen that. It is interesting.

However, there's also this:

http://www.gikacoustics.com/diy-acoustic-panel-frames/

which seems to indicate that the difference is very minor. In my case, I could have used 6" wood for the sides and made the build about 60% less work. But leaving the sides open has at least some benefit, and the wood was cheaper. :-) The amount of time these take to put together (at the wood level) is so trivial that it just doesn't matter.
Thanks...interesting article.
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post #10550 of 11671 Old 06-24-2014, 07:53 AM
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Quote:
Originally Posted by steveting99 View Post
Jerry,

I came across the following post regarding some background on why band limited (500 Hz to 2 kHz) pink noise is the preferred source to set acoustic levels. This is in reference to page 46 of the guide, when one is carrying out the mic calibration.

"With low-frequency components present, there’s lots of level bouncing around, and when played back in a room, the effects of standing waves are to add a frequency-by-frequency ±15 dB variation to the level typically. One way to solve this problem is to band limit the noise to above the Schroeder frequency; that room-volume dependent frequency where not much else above it in the soundfield can be called diffuse. For small rooms, 500 Hz will do.

At the high-frequency end of the range, there’s lots of trouble, too. Half-inch measurement microphones exhibit an 8 dB difference between direct sound and diffuse field sound at 20 kHz, and 6 dB at 10 kHz. These are big differences that will show up in an overall measurement, depending on whether you are direct- or diffuse-field dominated, and which way you aim the mic. Also, for interchangeability with the largest range of differing systems where “house curves” or the X curve of motion picture sound is in effect starting their rolloff at 2 kHz, rejecting frequencies above 2 kHz leads to maximum utility.

So pink noise, band limited to 500 Hz to 2 kHz is the preferred source to set acoustic levels.
It is broad enough so that single-frequency standing waves don’t make the measurement inaccurate,
and narrow enough that low- and high-frequency acoustical and sound system effects are minimized.


Using this two-octave band noise also solves another problem. The standard of the motion-picture industry for level setting is the ubiquitous Radio Shack sound level meter. Everybody should have one.

Get the cheaper analog meter that has better resolution than the more expensive digital one. I have calibrated more than 100 of these meters over a period of years, and find them out of the factory to mostly be within 1 dB, pretty good for such a cheap device. However, they do vary one to the next in their C weighting filter, so that broadband noise may show a different level meter-to-meter when they are calibrated on a mid-range tone (or noise)."

I believe the above is written by Tomlinson Holman, co-founder and Chief Scientist of Audyssey and the TH in THX. Is it worthwhile to consider this?
I wrote that 5 years ago but the original article which I quoted seems to have gone...
"Official" Audyssey thread (FAQ in post #51779)
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post #10551 of 11671 Old 06-24-2014, 08:04 AM
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Perhaps, as long as normalisation is turned off, though I'm not sure what the purpose would be. The spectral content of reflections is determined mainly by the area and absorption characteristics of the surfaces they reflect off.
Click image for larger version

Name:	06 24 14 normalized.jpg
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ID:	133570

Click image for larger version

Name:	06 24 14 slices no normalization.jpg
Views:	17
Size:	315.7 KB
ID:	133578

So which of these are you saying is more accurate for reflection frequency content?


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or.....

should I time align the first peak at time zero so they look like these?

Click image for larger version

Name:	06 24 14 normalized time aligned.jpg
Views:	14
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ID:	133586

Click image for larger version

Name:	06 24 14 unormalized time aligned.jpg
Views:	20
Size:	315.4 KB
ID:	133594


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^
Deselect "normalized".

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post #10554 of 11671 Old 06-24-2014, 09:02 AM
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Originally Posted by markus767 View Post
^
Deselect "normalized".
So, for clarity, you agree with the 2nd pic?

And you agree with JohnPM?


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Last edited by jim19611961; 06-24-2014 at 09:21 AM.
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post #10555 of 11671 Old 06-24-2014, 12:47 PM
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Originally Posted by jim19611961 View Post
So which of these are you saying is more accurate for reflection frequency content?
You can't compare signals which are individually normalised as each has been scaled up by a different amount according to the peak value in that signal. Viewing filtered time signals is not a good way to determine frequency content though, if that is your aim then alter the IR window settings so that it spans only the reflection of interest, but bear in mind the more you narrow the window to isolate a particular reflection the worse the frequency resolution of the resulting plot. I'm not clear how knowing the frequency content would help with anything, however.

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post #10556 of 11671 Old 06-24-2014, 01:05 PM
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It seems to me that what you need, if temporal alignment of the reflections arising from different portions of the spectrum is what you want, is to time align the measurements via loop back and use n band limited sweeps.

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post #10557 of 11671 Old 06-24-2014, 01:10 PM
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Originally Posted by JohnPM View Post
You can't compare signals which are individually normalised as each has been scaled up by a different amount according to the peak value in that signal. Viewing filtered time signals is not a good way to determine frequency content though, if that is your aim then alter the IR window settings so that it spans only the reflection of interest, but bear in mind the more you narrow the window to isolate a particular reflection the worse the frequency resolution of the resulting plot. I'm not clear how knowing the frequency content would help with anything, however.
The idea here is to be able to compare how single frequency bands behave over time. It's interesting to know if and how reflections get spectrally distorted over time.

Markus

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post #10558 of 11671 Old 06-24-2014, 02:13 PM
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Originally Posted by JohnPM View Post
You can't compare signals which are individually normalised as each has been scaled up by a different amount according to the peak value in that signal. Viewing filtered time signals is not a good way to determine frequency content though, if that is your aim then alter the IR window settings so that it spans only the reflection of interest, but bear in mind the more you narrow the window to isolate a particular reflection the worse the frequency resolution of the resulting plot. I'm not clear how knowing the frequency content would help with anything, however.
Somewhat for the same reason you want the frequency response to be generally flat, in optimizing a listening room, you want even distribution of frequency content in your reflections as well. This is especially true if you employ a Haas Kicker which may have a peak response of -6db at 25ms for instance. The value of measuring the frequency content of such a purposeful intended reflection should be obvious.

Add to this Marcus's comment as well.

In addition, I still do not understand why the peak values are so different from band to band when the frequency response has little deviation from frequency to frequency. If the direct signal, or t=0 is equivalent to the frequency response (direct response), it doesn't make sense to me that my measured 500hz 1/1 band compared to my 4K 1/1 band deviates by 15db in favor of the 4K slice when the FR deviates only by 3db, 500hz being the louder. Thats a 18db differential.

Click image for larger version

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As you can see from my FR (1/24th oct smoothing), the variance at 500hz to 4K is subtle.

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But in this un-normalized filtered graph, there is 15db difference. Why?


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post #10559 of 11671 Old 06-24-2014, 03:07 PM
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Originally Posted by markus767 View Post
The idea here is to be able to compare how single frequency bands behave over time. It's interesting to know if and how reflections get spectrally distorted over time.
Spectrogram or waterfall with suitably configured windows are better tools for that.

John

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post #10560 of 11671 Old 06-24-2014, 03:36 PM
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Originally Posted by jim19611961 View Post
If the direct signal, or t=0 is equivalent to the frequency response (direct response), ...
You seem to be getting time and frequency signals a bit confused here, perhaps as a result of plots like the waterfall that combine the two. Apologies if what follows is teaching grandma to suck eggs, but just to be clear on terminology...

A waterfall shows the evolution of the frequency content of a signal over time. It is not a time signal, but a plot of frequency content with a second time axis.

The impulse response is a time signal, it has different values at different times, just as a sine wave is a time signal. The impulse response itself is a plot of the time history of what would be recorded at the measurement position if the speaker were capable of emitting an impulse. It is no more meaningful to talk about the t=0 value of an impulse response telling you something about its frequency content than it would be to say the same about the t=0 value of a sine wave (which would always be zero!). They are both simply the value of a time signal at a single moment in time. If the sine wave happened to be at 1 kHz and you passed it through an octave band filter centred at 1 kHz it would emerge pretty much unaltered. If you passed it through an octave band filter centred at 500 Hz its amplitude would be reduced by about 20 dB, which is the approximate attenuation of the 500 Hz octave band filter at 1 kHz. It would still pass through zero every 0.5 ms (at the zero crossing of each half cycle) but the peak positive and negative amplitudes it reached at 0.25 ms, 0.75 ms, 1.25 ms, 1.75 ms etc would be one-tenth as large as those of the original signal. The filtered IR plots are, just as the name says, the result of passing the impulse response through a filter. It remains a time signal, and looking at the effect the filter had on the sample value at a particular time just isn't meaningful.

John

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