Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 304 - AVS Forum
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Audio Theory, Setup, and Chat > Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
spotts29's Avatar spotts29 12:34 PM 03-17-2014
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Originally Posted by spotts29 View Post

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Originally Posted by toofast68 View Post

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Originally Posted by Alan P View Post

You can still use the distance tweak when you have multiple subs being treated as one sub like in your case toofast. Whatever distance setting you have now, take measurements a few feet below that and a few feet above it. When you see the crossover start to smooth out (say between 10-11 feet), then change the unit of adjustment to really zero in on the best distance setting. What your looking for is the smoothest transition over the area of your crossover.
Yeah, that is what I am learning...now I just gotta find the time to figure it all out!

toofast68

I had a similar situation to the one you're describing with your MiniDSP. I used one of these to split the single subwoofer signal after a long run around the room, plugged it into both Input jacks of the MiniDSP, then plugged my subwoofer cables into the Output jacks. You have to be careful you keep which sub is which straight when you're configuring things in the MiniDSP plug-in, but if you do that, it all works OK in my experience.

Darn it, forgot to link neutro's tutorial (here), which I found really helpful when I was setting mine up.

artur9's Avatar artur9 03:40 PM 03-17-2014
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Originally Posted by toofast68 View Post

Long term I think I gotta rip into the front wall.

Outlaw Audio, for one, sells wireless sub connections. You might want to explore that before starting a demolition.
artur9's Avatar artur9 03:47 PM 03-17-2014
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Originally Posted by markus767 View Post

Not sure what you're asking about subs and DSP.

I have two questions if you don't mind.

(1) Is the sub distance tweak (in the AVR, correct?) just for addressing crossover integration?
(2) Ignoring other features of the DSP, is the idea to use its delay/distance features to avoid moving subs physically or is the goal something else?
markus767's Avatar markus767 03:56 PM 03-17-2014
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Originally Posted by AustinJerry View Post

I tend to agree with your assessment, Markus.  However, in case anyone is interested, I'll post the seat-to-seat variance measurements here so we can compare them to a single-spot measurement.  Can't hurt.

Sure, it's always interesting to see how rooms and specific setups behave.
AustinJerry's Avatar AustinJerry 03:59 PM 03-17-2014
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Originally Posted by artur9 View Post

Outlaw Audio, for one, sells wireless sub connections. You might want to explore that before starting a demolition.

I agree that these are an option to consider, but make sure the return policy is clear. I have Hsu ULS-15 subs, which have in-built wireless capabilities. However, due to the complexity of my home wireless network, I have never been able to get the wireless feature working without static interference.
3ll3d00d's Avatar 3ll3d00d 04:00 PM 03-17-2014

IME taking multiple measurements around a small area is done to establish the modal variations you can reasonably treat with EQ, in my case this means I drop a filter on the height and length axial modes as those 2 are the strongest and most consistent across the listening area. 

 

AIUI for higher frequencies, you're really aiming to correct the speaker not the room and so I'm not sure multiple measurements are even necessary to do that.


markus767's Avatar markus767 04:03 PM 03-17-2014
Quote:
Originally Posted by artur9 View Post

(1) Is the sub distance tweak (in the AVR, correct?) just for addressing crossover integration?

(Yes) and yes.
Quote:
Originally Posted by artur9 View Post

(2) Ignoring other features of the DSP, is the idea to use its delay/distance features to avoid moving subs physically or is the goal something else?

Delaying a source to another will change the response within the region where the sources overlap. It won't change the response of a single source at the listening position though.
Changing the location of a single source within the room will change its response at the listening position.
markus767's Avatar markus767 04:14 PM 03-17-2014
Quote:
Originally Posted by 3ll3d00d View Post

AIUI for higher frequencies, you're really aiming to correct the speaker not the room and so I'm not sure multiple measurements are even necessary to do that.

We don't have conclusive data what should be corrected at higher frequencies but I'd agree that the direct response seems to be more important than the steady-state response. Frequency dependent windowing might help to equalize speakers in a meaningful way. The better the tracking between speakers the better the imaging.
Other than that very early reflections near the source or near the listener migth affect the perceived direct response at the listening position. Looking at multiple measurements will reveal such issues.
jim19611961's Avatar jim19611961 06:03 PM 03-17-2014
Quote:
Originally Posted by markus767 View Post

We don't have conclusive data what should be corrected at higher frequencies but I'd agree that the direct response seems to be more important than the steady-state response. Frequency dependent windowing might help to equalize speakers in a meaningful way. The better the tracking between speakers the better the imaging.
Other than that very early reflections near the source or near the listener migth affect the perceived direct response at the listening position. Looking at multiple measurements will reveal such issues.

This is a very important point (bolded). To your knowledge, is there established criteria for channel deviation (at some given frequency) as far as whats acceptable, good, great, bad, or otherwise? I would think more latitude would given below the transition frequency than above it.
3ll3d00d's Avatar 3ll3d00d 01:10 AM 03-18-2014
Personal experience says that a correction that uses frequency dependent windowing (and that corrects excess phase) produces a marked improvement in the stereo image (uncorrected it is clearly pulled to one side).

I don't know of a standard target though, just offering an anecdote on the efficacy of that approach. If there is one then it would have to specify the windowing/smoothing algorithm to apply wouldn't it as otherwise the responses are not going to be comparible in a meaningful way. The software I use calculates the IACC over various time periods to give a summary view on the similarity of the signals which seems an alternative approach to the same problem.
markus767's Avatar markus767 01:13 AM 03-18-2014
Quote:
Originally Posted by jim19611961 View Post

This is a very important point (bolded). To your knowledge, is there established criteria for channel deviation (at some given frequency) as far as whats acceptable, good, great, bad, or otherwise? I would think more latitude would given below the transition frequency than above it.

I don't know of any established criteria regarding speaker response deviation. An interchannel level different of 0.5dB can shift a phantom image by about 5%, so speakers should match better than that.

I'm not sure if lower frequencies are less important. In stereo level differences at lower frequencies translate to interaural phase differences. This would explain why reducing frequency response deviations between the speakers at lower frequencies improves imaging.
DonH50's Avatar DonH50 09:12 AM 03-18-2014
Comment on wireless links: Some of them have long delays that may make it harder to integrate. I checked out one a year or two ago, but the buffering to control drop-outs added ~100 ms latency, quite a bit for an AVR to compensate. I just ran the wires so didn't do any more research. There are probably other better (and worse) options.
RUR's Avatar RUR 09:36 AM 03-18-2014
Quote:
Originally Posted by DonH50 View Post

Comment on wireless links: Some of them have long delays that may make it harder to integrate. I checked out one a year or two ago, but the buffering to control drop-outs added ~100 ms latency, quite a bit for an AVR to compensate. I just ran the wires so didn't do any more research. There are probably other better (and worse) options.
Don, I used an Audioengine WiFi to sub in my family room setup with no problems. Did have to adjust the Audyssey-determined sub distance by six ms to get smooth xover response, but that's it. Everyone's MMV, I suppose.
jim19611961's Avatar jim19611961 09:43 AM 03-18-2014
Quote:
Originally Posted by markus767 View Post

I don't know of any established criteria regarding speaker response deviation. An interchannel level different of 0.5dB can shift a phantom image by about 5%, so speakers should match better than that.

I'm not sure if lower frequencies are less important. In stereo level differences at lower frequencies translate to interaural phase differences. This would explain why reducing frequency response deviations between the speakers at lower frequencies improves imaging.

I was thinking more in terms of when one is measuring at the LP and comparing the the left and right channel traces.





I made this last night and was wondering what if any of the deviations should be a concern. Obviously, their are places that deviate more than 0.5db. In my graph, and in others I see, 3-4db deviations are not uncommon.
markus767's Avatar markus767 10:48 AM 03-18-2014
^
I don't think steady-state measurements are a good indicator of how speakers perceptually track. They include all sorts of reflections that may or may not be relevant to imaging.
AustinJerry's Avatar AustinJerry 11:01 AM 03-18-2014

Is the smoothed L/R ETC a better way to measure it?  If yes, what does the following measurement say about left/right deviation?

 


markus767's Avatar markus767 11:07 AM 03-18-2014
^
Yes, a (band-limited) ETC provides a better look into it.
DonH50's Avatar DonH50 12:16 PM 03-18-2014
Quote:
Originally Posted by RUR View Post

Quote:
Originally Posted by DonH50 View Post

Comment on wireless links: Some of them have long delays that may make it harder to integrate. I checked out one a year or two ago, but the buffering to control drop-outs added ~100 ms latency, quite a bit for an AVR to compensate. I just ran the wires so didn't do any more research. There are probably other better (and worse) options.
Don, I used an Audioengine WiFi to sub in my family room setup with no problems. Did have to adjust the Audyssey-determined sub distance by six ms to get smooth xover response, but that's it. Everyone's MMV, I suppose.

Thanks good to know. I know folk use them without such issues, chances are the one I tried was a poor choice. Good buffering/error correction, but high latency. Always trades...
toofast68's Avatar toofast68 12:24 PM 03-18-2014
Quote:
Originally Posted by DonH50 View Post


Thanks good to know. I know folk use them without such issues, chances are the one I tried was a poor choice. Good buffering/error correction, but high latency. Always trades...

Is this what we are talking about ?  Or am I lost in threads and being a dumb head :D

 

http://www.rocketfishproducts.com/products/home-theater/RF-WSW312.html

 

I've never used, but something I might need to in the future  :-)


DonH50's Avatar DonH50 12:27 PM 03-18-2014
On the ETCs and FR plots relative to imaging, I think time and FR both impact imaging. This is a very simplistic view, probably wrong or at least full of holes, but I suspect time of arrival (TOA); and,
frequency response (and volume) play a part.

Looking at the ETCs, assuming there is an absolute time reference, you'd want the initial (direct) sound to arrive at the same instant. A couple of years ago I discovered that we (humans) can actually distinguish much finer time differences than I expected, into the microsecond region. Probably not something you'd notice with music and movies, but localization studies were eye-opening (to me). After the initial step, ETC's are complicated by all sorts of reflections close and far so other than a general feeling they should be as well-matched as possible I would not worry too much.

If the frequency response is much different, and I am not sure what "much" is for this relative measure, then instruments will tend to move around as they go up and down the scale, and images can be "blurred" due to different overtones being emphasized in one or the other speaker.

For me, and perhaps nobody else, this supposition implies both time and frequency response is key to accurate, precise, stable imaging. That may be one reason I have always favored a more dead (less reverberant/reflective) room than others who prefer a lot of "ambiance". In my room, the ambiance must come from the recording, and is not (or minimally) altered by what my room does to it.

IMO - Don
kbarnes701's Avatar kbarnes701 12:39 PM 03-18-2014
Quote:
Originally Posted by DonH50 View Post


For me, and perhaps nobody else, this supposition implies both time and frequency response is key to accurate, precise, stable imaging. That may be one reason I have always favored a more dead (less reverberant/reflective) room than others who prefer a lot of "ambiance". In my room, the ambiance must come from the recording, and is not (or minimally) altered by what my room does to it.

IMO - Don

 

100% agree and it's good to come across someone with the same goal. I too believe there is all the ambiance I need already baked into the recording. But I only listen to movies in the HT, so obviously multichannel. Different strokes etc...


DonH50's Avatar DonH50 12:54 PM 03-18-2014
Quote:
Originally Posted by toofast68 View Post

Quote:
Originally Posted by DonH50 View Post

Thanks good to know. I know folk use them without such issues, chances are the one I tried was a poor choice. Good buffering/error correction, but high latency. Always trades...
Is this what we are talking about ?  Or am I lost in threads and being a dumb head biggrin.gif

http://www.rocketfishproducts.com/products/home-theater/RF-WSW312.html

I've never used, but something I might need to in the future  :-)

That type of product, yes, though I have not used that particular one, and have done almost zero research on others. The parameter of interest is latency (delay), and that is not spec'd for a lot of these things. It is not a problem if you are using them in another room, but if you are using them in the same room to complete speaker system hook-up you need one with low enough latency that the AVR can compensate "distance" (which now appears longer due to the added time delay through the wireless link).
toofast68's Avatar toofast68 12:55 PM 03-18-2014
Quote:
Originally Posted by DonH50 View Post


That type of product, yes, though I have not used that particular one, and have done almost zero research on others. The parameter of interest is latency (delay), and that is not spec'd for a lot of these things. It is not a problem if you are using them in another room, but if you are using them in the same room to complete speaker system hook-up you need one with low enough latency that the AVR can compensate "distance" (which now appears longer due to the added time delay through the wireless link).

 

Gotcha...but if my learning is doing me any good...looks like the miniDSP should be able to compensate for that distance.


DonH50's Avatar DonH50 12:56 PM 03-18-2014
I don't know. A miniDSP is on my wish list, but I just don't have the play time. Maybe when I retire, or at least get the last kid out of the house. smile.gif
jim19611961's Avatar jim19611961 01:03 PM 03-18-2014
Quote:
Originally Posted by DonH50 View Post

On the ETCs and FR plots relative to imaging, I think time and FR both impact imaging. This is a very simplistic view, probably wrong or at least full of holes, but I suspect time of arrival (TOA); and,
frequency response (and volume) play a part.

I think they both count also. But the kind of room interaction you have dictates the weighting I think. In a dead room, the FR is almost entirely representing the direct response (above the transition frequency) given reflections are minimal. In a highly reflection full room, the FR can be noticeably augmented by those reflections making the FR in this case less the case of seeing the direct only or mostly.
Quote:
Originally Posted by DonH50 View Post

Looking at the ETCs, assuming there is an absolute time reference, you'd want the initial (direct) sound to arrive at the same instant. A couple of years ago I discovered that we (humans) can actually distinguish much finer time differences than I expected, into the microsecond region. Probably not something you'd notice with music and movies, but localization studies were eye-opening (to me). After the initial step, ETC's are complicated by all sorts of reflections close and far so other than a general feeling they should be as well-matched as possible I would not worry too much.

Making sure the direct "wave" from each speaker hits your ears at the same time is imaging 101 IMO, which is why in the past I have emphasized finding the exact timing center at the listening position to make sure it corresponds with the center of your listening chair. How to do this has already been covered.
Quote:
Originally Posted by DonH50 View Post

If the frequency response is much different, and I am not sure what "much" is for this relative measure, then instruments will tend to move around as they go up and down the scale, and images can be "blurred" due to different overtones being emphasized in one or the other speaker.

Again, how much this factor is pertinent depends on your room reflection characteristics. In a dead room, The FR is more telling I think.
Quote:
Originally Posted by DonH50 View Post

For me, and perhaps nobody else, this supposition implies both time and frequency response is key to accurate, precise, stable imaging. That may be one reason I have always favored a more dead (less reverberant/reflective) room than others who prefer a lot of "ambiance". In my room, the ambiance must come from the recording, and is not (or minimally) altered by what my room does to it.

IMO - Don

One thing you might want to look at Don is band limited ETC's. Many who claim a dead room as a desirable goal really mean its dead from 1K and up. Band limited ETC's probably/may reveal significant reflections below that frequency. This I have emphasized much in the past also.

Quote:
Originally Posted by markus767 View Post

^
Yes, a (band-limited) ETC provides a better look into it.

Agree this is another angle to look at. A full range ETC that shows everything below -20db misleads one to assume all your early high gain reflection are under control at all frequencies when in fact they probably are not. And I think you are suggesting this avenue of exploration in that reflections at any frequency which are audible and uneven from channel to channel compromise imaging.
DonH50's Avatar DonH50 01:06 PM 03-18-2014
^^^ Good comments, thank you. I have done very little with ETC's, something I need to do more. Just need more time for toys!

The interactions get complicated, natch, with FR "weighting" impacted through interactions among direct and reflected sounds (interference patterns), and time cues provided by direct sound and early and late reflections. I don't claim to be an acoustics expert; been decades since those grad classes, and I did not stay at a Holiday Inn last night. smile.gif
jim19611961's Avatar jim19611961 02:01 PM 03-18-2014
This is the kind of analysis/data that Markus (and I too) thinks bring more clarity to the issue.



Left (black) and Right (Red) ETC at 250hz, 1 octave slice, 200us smoothing.





500hz







1K







2K








4K





(the 37ms broad spike isnt really there when your sitting at the LP. Your head blocks that reflection)
jim19611961's Avatar jim19611961 02:10 PM 03-18-2014


This shows a fullrange (200us smoothed) ETC (red) compared to a band limited 250hz (black) (200us smoothed 1 octave). Just illustrating that a full band ETC doesn't give you a clue to whats happening at specific frequencies.
AustinJerry's Avatar AustinJerry 02:11 PM 03-18-2014
Clearly there is a difference between the right and left reflections. Question is, is the difference terrible, or really good? IOW, what is the guideline?
jim19611961's Avatar jim19611961 02:15 PM 03-18-2014
Quote:
Originally Posted by AustinJerry View Post

Clearly there is a difference between the right and left reflections. Question is, is the difference terrible, or really good? IOW, what is the guideline?

Since there seems little already researched data on the subject, we are going to have to figure this out ourselves I am afraid. The beginning of this understanding would be for several to post the same data and look at what kind of variances we see from room to room.

If we can agree to 1 octave windows. 200us smoothing. And 250, 500, 1K, 2k and 4k slices/bands. Then we can all be on the same page.
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