AVS Forum banner

Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs

2M views 38K replies 1K participants last post by  LastButNotLeast 
#1 · (Edited)
The purpose of this thread is to explain how to both physically hook up the connections between your computer and AVR/Pre-Pro to get started with REW (Room EQ Wizard) and to share information on the proper use of REW including proper techniques for both measuring and interpreting graphs, what you should be looking for in each graph, how to fix problems using room treatment, speaker placement, listener placement, and other tweaks, both before and after EQ, and delve more into topics not often talked about which when dealt with properly can drastically change (for the better) your listening experience to become true audio nirvana.

I highly recommended reviewing the very thorough guide created by AustinJerry (My heartfelt thanks to you, Jerry, for taking the time and effort to put this together and keep it updated) which contains information contributed by myself and many other AVS'ers on both how to connect your equipment and how to use REW in (post 275).
 
#6,981 ·

Quote:
Originally Posted by sdrucker  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952290

 
Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952234


IDK. All my speakers are from the same manufacturer so timbre-matching isn't too much an issue. And I always choose identical L, C and R speakers - I can't stand it when a different centre speaker is used and you can hear the timbre change when something pans left to right or v-v. I realise that not everyone can accommodate identical LCR speakers but I highly recommend it where possible. I find it difficult enough to optimise all this without having to also cope with speakers from different manufacturers!

Yeah, i can just see having a Mythos ST as a powered center behind the TV....
 

LOL. Well, yeah... it's why I wouldn’t choose speakers like that for a movies-system. One of the influential factors in choosing my M&K S150s is that they are an identical set across the front. As were my last speakers and the speakers before them and the speakers before them.... centre channel is so important for movies of course. Perhaps THE most important channel of them all.
 
#6,982 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/6950_50#post_23952419


Jim - thanks for this. I can see exactly what you mean. This is the sort of analysis that I find very helpful. I have to say I haven't been aware of any wandering of the image, but do remember that I only use the system for movies, and voices are rarely just dead centre as one might expect from a vocalist on a music track. In fact, I have always thought (post treatments) that my imaging was really very, very good. That is not to say, of course, that it could not be better. But for a movies-only system, do you think I would benefit from the no doubt considerable time expenditure required to improve things?  If I used the system for music I would definitely adopt a different approach as any 'wandering' then would drive me nuts. But with movies, the actor is for ever (usually) moving about the screen, and visual dominance of our senses being what it is, the voice appears to follow the actor, even though we know it is actually (usually) rooted to the centre channel. So there is an element of wandering built in. I do think is perhaps easier to work with a room used exclusively for movies than it is for one used with music, or hardest of all, a room used for both.


Do you see any other problems in the 15 graphs I uploaded?

The first thing id do is make sure your data is good, That is, make sure the mic is EXACTLY the same distance from the L and R channels. Using OM, run track #2 (both channels, short sine sweep) and find the place where the 5-20K part of the graph is flat and maxed out in terms of splDB level. This is also a good way to determine if your listening chair is in the right spot.


Rerun the measurements.


If after this, there are still problems, they may be easy to fix. Lets see what the new data looks like first.


I agree that for movies, pinpoint exacting image locations is not as important (for reasons you pointed out). But getting this more right can only make things better.


It didnt see anything else at a glance with your other graphs that stuck out as bad to me
 
#6,983 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6930#post_23951098


Nyal - does this summarise as 1/6 smoothing >300Hz and unsmoothed
 
#6,984 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6930#post_23951100


I thought I had a handle on this but the more I read the more uncertain I become .... so playing a mono source on a two channel system is a problem then due to this comb filtering?  I ask because I do this frequently on my separate stereo system and I don't hear anything odd even if I don't sit exactly equidistant from the speakers. 

Tis true, if you read a bit about what some of the detractors of stereo say about mono signals played back in both channels.
 
#6,985 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952432


LOL. Well, yeah... it's why I wouldn’t choose speakers like that for a movies-system. One of the influential factors in choosing my M&K S150s is that they are an identical set across the front. As were my last speakers and the speakers before them and the speakers before them.... centre channel is so important for movies of course. Perhaps THE most important channel of them all.

Agreed. Of course, when I bought them I was thinking of music first, and tested the powered Mythos supertower speakers on music rather than movies.


In fact, timbre matching of the DefTech line aside, that's why I picked up a powered center channel ultimately, with the idea of having better blending across the three in-front speakers due to the extra amplification for mid-bass. I'd tried the non-powered Mythos Nine and Ten (the latter uses the same midrange/tweeters as the Mythos ST) and didn't like it as much because I felt that the mid-bass and upper midrange was lacking, and the center stood out. It certainly sounds better for music with the CS-8080 as the center. At one point, my bass feel was so good that listening to concert BluRays had an almost "live" feel to how the bass strings were plucked. I lost some of that while getting the center image down better, and with REW, as you know we're never happy with what we have...



OTOH, if I knew what we knew now, I might have played more with positioning and/or treatments before switching the Mythos Nine/Ten out. But I should mention that a fair number of DT users like the powered centers, even if they have real subs.
 
#6,986 ·
BTW with reference to the spectrogram / decay charts I think for a full examination you should be looking at it down to the noise floor of the room.


There are often structural or other secondary resonances which are audible and distracting yet you will miss them if you look with a 40dB window on your graph and you are in a low noise room.
 
#6,987 ·

Quote:
Originally Posted by jim19611961  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952472

 
Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/6950_50#post_23952419


Jim - thanks for this. I can see exactly what you mean. This is the sort of analysis that I find very helpful. I have to say I haven't been aware of any wandering of the image, but do remember that I only use the system for movies, and voices are rarely just dead centre as one might expect from a vocalist on a music track. In fact, I have always thought (post treatments) that my imaging was really very, very good. That is not to say, of course, that it could not be better. But for a movies-only system, do you think I would benefit from the no doubt considerable time expenditure required to improve things?  If I used the system for music I would definitely adopt a different approach as any 'wandering' then would drive me nuts. But with movies, the actor is for ever (usually) moving about the screen, and visual dominance of our senses being what it is, the voice appears to follow the actor, even though we know it is actually (usually) rooted to the centre channel. So there is an element of wandering built in. I do think is perhaps easier to work with a room used exclusively for movies than it is for one used with music, or hardest of all, a room used for both.


Do you see any other problems in the 15 graphs I uploaded?


 
Quote:
Originally Posted by jim19611961  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952472
 
The first thing id do is make sure your data is good, That is, make sure the mic is EXACTLY the same distance from the L and R channels. Using OM, run track #2 (both channels, short sine sweep) and find the place where the 5-20K part of the graph is flat and maxed out in terms of splDB level. This is also a good way to determine if your listening chair is in the right spot.
 

Ah - first problem. My MLP is not, and cannot be, centred. :) Due to the crappy little room and the way it is, I have two listening chairs and neither can be in the centre spot. I have cheated a little and moved mine closer to the centre than the other (rarely used) chair but that is all I can do. It may be, in general, that the diktats of my room prevent me from ever getting a 'perfect' response (where perfect is defined as something like your own for this purpose).

 

 

Quote:
 Rerun the measurements.


If after this, there are still problems, they may be easy to fix. Lets see what the new data looks like first.
 

I assume that we are stymied by my observation above...

 
Quote:
 I agree that for movies, pinpoint exacting image locations is not as important (for reasons you pointed out). But getting this more right can only make things better.


It didnt see anything else at a glance with your other graphs that stuck out as bad to me 
 

Well, that is some good news then at least :)  Thanks for your help, as always. 
 
#6,988 ·

Quote:
Originally Posted by Nyal Mellor  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952480

 
Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6930#post_23951098


Nyal - does this summarise as 1/6 smoothing >300Hz and unsmoothed
 
#6,989 ·

OK, guys, no one has done anything to make my headache any better.

 

This is where I think we are:

 

- Below 300Hz, measure all speakers that contribute to bass response, i.e. left+right+subs, or center+subs.  Always use unsmoothed data.  Use these measurements to produce waterfalls, spectrograms, and decay graphs.

 

- Above 300Hz, measure left, center, and right speakers individually (with or without subs) to avoid undesirable interactions between speakers which gets worse at higher frequencies.  Publish frequency response graphs using 1/24 smoothing to observe any remaining issues, or using 1/6 smoothing to get a general feel of the progress that has been made (whatever that means).

 

BTW, regardless of what some of you think, the subject of the interaction between left and right speakers was raised by me several weeks back.  I was noticing a strangeness above 10KHz in the left+right graph that was not present in the individual left and right graphs.  That precipitated a discussion involving the importance of making sure the mic was placed in exactly the center between left and right speakers.  I believe Jim contributed to that discussion, as well as several others (sorry, don't have the time to dig out the original posts).  Since then, I have experimented several times by taking a left+right measurement, observing the flatness above 10KHz, and adjusting the mic in small increments either left or right, observing the effect on the graph's flatness.  The mic's position can make a significant difference with only a slight movement.  So, in retrospect, someone might be chasing what looks like a high frequency issue, when it is simply the interaction between the two speakers.

 

Make any sense?  Whaddya think?
 
#6,990 ·

Quote:
Originally Posted by Nyal Mellor  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952519

 
Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6930#post_23951100


I thought I had a handle on this but the more I read the more uncertain I become .... so playing a mono source on a two channel system is a problem then due to this comb filtering?  I ask because I do this frequently on my separate stereo system and I don't hear anything odd even if I don't sit exactly equidistant from the speakers. 

Tis true, if you read a bit about what some of the detractors of stereo say about mono signals played back in both channels.
 

Interesting. I have a fair number of mono albums and I always play them back through the stereo pair of speakers. I shall have to listen more closely and perhaps play back through just one speaker and compare it with playback through both and see if I can hear a difference. Aaaaagghhh.... so far I have resisted going down the rabbit hole in the room where my two-channel music system lives! :)
 
#6,992 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/6950_50#post_23952565



Ah - first problem. My MLP is not, and cannot be, centred. :) Due to the crappy little room and the way it is, I have two listening chairs and neither can be in the centre spot. I have cheated a little and moved mine closer to the centre than the other (rarely used) chair but that is all I can do. It may be, in general, that the diktats of my room prevent me from ever getting a 'perfect' response (where perfect is defined as something like your own for this purpose).

Well, that will do it alright.


Have you considered a long couch instead of separate chairs in order to be able to be in the center and also compliment the addl seating?
 
#6,993 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/6950_50#post_23952582


Aaaaagghhh.... so far I have resisted going down the rabbit hole in the room where my two-channel music system lives!

You know, most of the rabbits down there are pretty cordial and not many of them bite
 
#6,994 ·

Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952582


Interesting. I have a fair number of mono albums and I always play them back through the stereo pair of speakers. I shall have to listen more closely and perhaps play back through just one speaker and compare it with playback through both and see if I can hear a difference. Aaaaagghhh.... so far I have resisted going down the rabbit hole in the room where my two-channel music system lives!

Taken to an extreme, you should do the safe thing and listen in mono...:with the chair angled perfectly toward that speaker, in a dedicated mono room....



I'm only partially kidding.


Talk about back to the future...a new rabbit hole underneath the original rabbit hole of REW and treatments...maybe you'd just be better off doing all your mono listening with a good pair of headphones and call it a day.
 
#6,995 ·

Quote:
Originally Posted by AustinJerry  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952573


OK, guys, no one has done anything to make my headache any better.


This is where I think we are:


- Below 300Hz, measure all speakers that contribute to bass response, i.e. left+right+subs, or center+subs.  Always use unsmoothed data.  Use these measurements to produce waterfalls, spectrograms, and decay graphs.


- Above 300Hz, measure left, center, and right speakers individually (with or without subs) to avoid undesirable interactions between speakers which gets worse at higher frequencies.  Publish frequency response graphs using 1/24 smoothing to observe any remaining issues, or using 1/6 smoothing to get a general feel of the progress that has been made (whatever that means).


BTW, regardless of what some of you think, the subject of the interaction between left and right speakers was raised by me several weeks back.  I was noticing a strangeness above 10KHz in the left+right graph that was not present in the individual left and right graphs.  That precipitated a discussion involving the importance of making sure the mic was placed in exactly the center between left and right speakers.  I believe Jim contributed to that discussion, as well as several others (sorry, don't have the time to dig out the original posts).  Since then, I have experimented several times by taking a left+right measurement, observing the flatness above 10KHz, and adjusting the mic in small increments either left or right, observing the effect on the graph's flatness.  The mic's position can make a significant difference with only a slight movement.  So, in retrospect, someone might be chasing what looks like a high frequency issue, when it is simply the interaction between the two speakers.


Make any sense?  Whaddya think?

One last thing: are we now, moving forward, no longer going to use FR graphs for the
 
#6,996 ·

Quote:
Originally Posted by sdrucker  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952533

 
Quote:
Originally Posted by kbarnes701  /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/6960#post_23952432


LOL. Well, yeah... it's why I wouldn’t choose speakers like that for a movies-system. One of the influential factors in choosing my M&K S150s is that they are an identical set across the front. As were my last speakers and the speakers before them and the speakers before them.... centre channel is so important for movies of course. Perhaps THE most important channel of them all.

Agreed. Of course, when I bought them I was thinking of music first, and tested the powered Mythos supertower speakers on music rather than movies.


In fact, timbre matching of the DefTech line aside, that's why I picked up a powered center channel ultimately, with the idea of having better blending across the three in-front speakers due to the extra amplification for mid-bass. I'd tried the non-powered Mythos Nine and Ten (the latter uses the same midrange/tweeters as the Mythos ST) and didn't like it as much because I felt that the mid-bass and upper midrange was lacking, and the center stood out. It certainly sounds better for music with the CS-8080 as the center. At one point, my bass feel was so good that listening to concert BluRays had an almost "live" feel to how the bass strings were plucked. I lost some of that while getting the center image down better, and with REW, as you know we're never happy with what we have...



OTOH, if I knew what we knew now, I might have played more with positioning and/or treatments before switching it out. However, a fair number of DT users like the powered centers, even if they have real subs.
 

Horses for courses. I think speakers with powered subs would be way too complicated for me!  I am firmly in the 'requires subwoofer(s)' camp these days and doubt if I would ever buy any 'full range' speakers again. In fact, my ancient stereo system has developed a problem in one of the speakers (cone surround has failed) and I am thinking of using this as an excuse to buy new speakers for the music system. The current speakers are 'slim towers' which I like because they obviate the need for stands - but my thinking ATM is two small 'bookshelf' speakers and a smallish sub hidden away somewhere. Mrs Keith has bought me a very nice CD thingy for Xmas which can hold thousands of CDs in uncompressed format (WAV) so I will ripping all my CDs to it in the new year. it is this gadget here:

 

http://www.cocktailaudio.co.uk/overview.shtml

 

Sorry to stray OT - I thought we perhaps needed a short break :)
 
#6,997 ·

Well, here are two new FR graphs:

 



 



 

The 1/6 graph makes me feel reasonably good.  the 1/24 graph makes me wonder where to start, given all the issues, which depresses me.

 

Here is the bass response:

 



 

In this case, I think the L+R measurement highlights the same problem areas that the individual speaker measurements show, so the combined measurement is probably useful (at least below 80Hz).
 
#6,998 ·

Quote:
Originally Posted by AustinJerry  /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/6950_50#post_23952573


OK, guys, no one has done anything to make my headache any better.


BTW, regardless of what some of you think, the subject of the interaction between left and right speakers was raised by me several weeks back.  I was noticing a strangeness above 10KHz in the left+right graph that was not present in the individual left and right graphs.  That precipitated a discussion involving the importance of making sure the mic was placed in exactly the center between left and right speakers.  I believe Jim contributed to that discussion, as well as several others (sorry, don't have the time to dig out the original posts).  Since then, I have experimented several times by taking a left+right measurement, observing the flatness above 10KHz, and adjusting the mic in small increments either left or right, observing the effect on the graph's flatness.  The mic's position can make a significant difference with only a slight movement.  So, in retrospect, someone might be chasing what looks like a high frequency issue, when it is simply the interaction between the two speakers.


Make any sense?  Whaddya think?

The bolded cant be the case when measuring the channels separately.


I agree that moving the mic location slightly can make very visible changed on the FR (even when measuring each ch separately).


While long all encompassing threads like this are neat in many ways, having relevant discussions buried and forgotten is one drawback.
 
Top