REW Room Analysis


#1

I was perusing the internet, originally looking for methods to spectrum analyse music files (audacity looks the way to go) and I stumbled across topics mentioning using REW and a calibrated mic for room and equipment analysis. Has anyone partaken? I mean done an analysis of the way various frequencies are handled by their room and their kit?

Just curious.


#2

Yes.

Much on the old forum, though as it’s search capability is limited to the thread titles at the moment I’m not sure it’s easy to find (hopefully not too long before that changes). Also any links between threads won’t work as they related to the forum as it was live.

REW is a great tool, is free of charge (donations invited), just needs a measuring microphone. I use a Behringer ECM8000, but easier I think would be the one that REW recommend as I think it includes a USB interface.

It can show the room response at different positions, also distortion levels, and decay information etc. The data can be interpreted to diagnose a variety of room or speaker issues, including things like the contribution of early reflections.

I used REW to assist finding best speaker and listening positions in a problematic room, and also to set up my active crossover including phase correction, I also used it to set up DSP taming of some peaks in response when I use my speakers in a non-ideal position part of the time (a capability of my active crossover).

Also, some room treatment suppliers, the one I know is GK acoustics, can interpret REW data to advise on best room treatment should you go down that line.

Another person who I know has familiarity with it, and may be more knowlegeable that I, is @Xanthe.


#3

Thanks,

For the price of a hundred quid for the aforementioned USB mic I’m tempted to have a play. So I guess you simply play a white noise music file and record/measure and then analyse? Yes?


#4

With REW installed on a computer or laptop - and IIRC it is available for OC and Mac - you connect the mic to the computer, and audio output to your system (with a bit of fiddling the first time you set it up to get levels right). REW has a number of audio signal choices, but the one used for all the measurements I did involves a sine wave sweep from low to high frequency. You can adjust the range and speed of sweep. It records the sound picked up wherever the mic is positioned, and plots a variety of charts.

Depending on which data you are looking at you can overlay or subtract, to compare, and display multiple plots, enabling you to see changes easily, whether from moving the mic or speaker or anything else. You can select the ranges of the graph axes, and the amount of smoothing you want. And of course you can save and export the data files.


#5

I use a pair of highly tuned instruments to assess this - one on each side of my head :wink:


#6

Cheers… I get it now.


#7

Maybe your ears are sufficiently highly tuned to do it all - if so you are very lucky! :blush:

My ears are a little less well tuned, and so I found REW made the job of fixing my room issues far quicker (having started by ear), likewise setting up my tramping, because I could literally see the differences, and indeed from that see what the issues were, and assess changes. As one example, at one point there was something odd, but not specific audibly, just making me think was something wasn’t quite right but struggling to put my finger on it. I connected REW and immediately could see an odd sharp rise in distortion levels on one channel at a particular frequency, which was then very quickly traceable to a faulty drive unit.

With REW, setting up my active crossover was a doddle, tweaking the crossover points, adjusting relative levels and setting phase. Likewise for my non-optimum speaker position use, which is where they are for a significant part of the time, it was a simple matter to set up some DSP correction to compensate for the worst effects of the positioning making it sound good enough to enjoy using in that position, if not as good as when I move them to the optimum positions.


#8

I use REW with its recommended UMIK-1 USB microphone. I find it to be a very powerful, useful and convenient tool for making acoustic measurements of loudspeakers, and for assessing in-room performance. Making and interpreting these measurements is perhaps non-trivial. But if understood these measurements complement the listening we do with our ears, and perhaps also predictions from CAD modeling of room or speakers. A newcomer to this field can expect a significant learning curve. Once understood, REW can be a very useful tool. It is reasonably well documented, and there are online resources that might help - including a user forum.

Charlie


#9

Sounds not for the faint hearted then :wink:


#10

Yes I have… and created filter kernels in response. It was interesting. However I decided to use the info gathered with rew in the end to create an approx matching filter very much smoothed out iand some parts ignored using the parametric EQ. I found this prefereable.
One thing of note, the room response filter uses an FIR … which means it’s all about kernel sample size or ‘taps’. Therefore you should ideally create a filter kernel for each sample playback frequency. Create the responses and put in a zip file and load that zip file into Roon… Roon Core will then automatically select the optimum FIR filter kernel to match the media being played.


#11

Amazing :slight_smile: I keep on wondering about going the roon route… one day maybe.


#12

Just for clarification lest the OP be put off: Whilst REW is powerful, is capable of quite complicated things, and full interpretation can require a lot of knowledge and experience, it is not a difficult program to set up and use. And some levels of interpretation are easy and straightforward - e.g. seeing the major peaks and troughs in response, and the effect of moving things. There is an inbuilt quite comprehensive tutorial in REW if you want to understand it, and some members of this forum may be able to help with interpretation - and there are are other forums dedicated to REW and related things, as well as help available from the lines if GK if you are interested in room treatment.

One tip when you first use: don’t worry about the unsmoothed response that appears by default- with almost any system/untreated room combination that is likely to make you give up hifi! Some smoothing is normally needed - I suggest 1/12th octave as a starting point.


#13

Regarding DSP for room correction, generally speaking room treatment is better if it is practicable, and I suggest that a golden rule should be NEVER use DSP to try to correct a major null - if it is caused by cancellation in the room that is a very quick route to speaker damage.


#14

A lot on this month but I reckon one of the recommended USB Mics is on the shopping list for next month. Sounds like it will help with speaker and settee location/orientation.


#15

it might - but you will be better off using your ears I suspect…and you will have a more reliable result.


#16

Not what I found - but it may depend on what is going on in the room …and of course how good the ears are.


#17

tbh I was thinking the same :slight_smile:


#18

i guess your ears have to be upto it :grinning:

I found the Rew analysis insightful - but ultimately didn’t produce the best results - compared to taking the approximate response from Rew and then hand rolling a filter response in Roon Core that approximated it but optimised for best subjective sound… the tricky areas were in the bass area <100Hz


#19

Struggling manually, I first got REW to help with placement, actually finding positions with even(-ish!) response, which sounded perfectly good so I kept it. The great thing was the spread of assessing each change.

Then with my non-optimum positioning I used REW to see the outcome as I evened out the worst lumps as best I could with the Active XO’s limited spare DSP, capacity, not applying too much gain anywhere, and checking the outcome across the length of a sofa for a relatively wide sweet area. It was never going to produce a perfect response, but did better than I originally expected - I suspect I’d still be at it if I tried to do by ear!


#20

I did the REW thing and had a lot of fun doing it. But in the end I felt the system sounded much better with no DSP in roon. Maybe I’m lucky with my room acoustics, but I’m back to happily listening with no processing.