Taking and Interpreting Measurements with REW (FREE eBook)

[Keith_W]

You're welcome guys. For any of you who have decided to check the longer document, you'll notice that it is already exceedingly long. I might change my mind and decide to write about Phase ... but that would at least double the length of the book and truly put it beyond the understanding of most people.

I dunno man, I try to be approachable and speak in a way that people understand, but I can see that even that is too much for some. I can write with technical language - that would keep it shorter, but fewer people would understand. Or I could write for the layman, and then the book gets so long and the people i'm aiming it at won't bother reading it. Writing is hard, and you can't please everybody.

 

[gorman]

I dunno man, I try to be approachable and speak in a way that people understand, but I can see that even that is too much for some. I can write with technical language - that would keep it shorter, but fewer people would understand. Or I could write for the layman, and then the book gets so long and the people i'm aiming it at won't bother reading it. Writing is hard, and you can't please everybody.

I commend you for this work and for the effort of making it understandable for non tech. Looking forward to the PDF of the second part.
THANK YOU

 

[Calypso1]

You're welcome guys. For any of you who have decided to check the longer document, you'll notice that it is already exceedingly long. I might change my mind and decide to write about Phase ... but that would at least double the length of the book and truly put it beyond the understanding of most people.

I dunno man, I try to be approachable and speak in a way that people understand, but I can see that even that is too much for some. I can write with technical language - that would keep it shorter, but fewer people would understand. Or I could write for the layman, and then the book gets so long and the people i'm aiming it at won't bother reading it. Writing is hard, and you can't please everybody.

If you try to please everyone, you may be disappointed in the outcome. Write at the level you believe best communicates the content and we will will have to use our grey matter and learn! Good work. Will you be addressing how to time align a sub in a 2.1 system using REW? Or, how does one select the correct crossover frequency between the sub and the mains? Lastly, after time aligning, crossover, and PEQ to a target, would you be addressing phase alignment. I only work with the frequencies up to the Schroeder frequency for my room. Great to have your expertise available in this form, thanks.

 

[Keith_W]

If you try to please everyone, you may be disappointed in the outcome. Write at the level you believe best communicates the content and we will will have to use our grey matter and learn! Good work. Will you be addressing how to time align a sub in a 2.1 system using REW? Or, how does one select the correct crossover frequency between the sub and the mains? Lastly, after time aligning, crossover, and PEQ to a target, would you be addressing phase alignment.

Sorry, but I am not going to do that. If I start going into DSP that's an endless rabbit hole, and this would completely spiral out of control. For a start, there are different procedures for minimum-phase and linear-phase DSP, and people already have trouble understanding the difference. And I were to focus only on minphase, there are a dozen or more minphase DSP units I have to write about, with specific instructions for each. MiniDSP already have an excellent REW tutorial.

This little eBook by necessity has to be limited in focus. I can't even write about all the different measurements, otherwise it will get so long that it becomes unapproachable. And ideally there will be a much longer discussion about acoustics and loudspeakers. What the CEA 2034 means, and what the heck Amir and Erin are talking about when they post all those loudspeaker reviews.

And please don't think of me as some kind of measurement authority. I am a self-taught amateur, and the only reason i'm writing about it is because there is a need for it, and other people who are more qualified than me haven't done it.

 

[Fidji]

Firstly - thanks a lot for this initiative. REW is such powerful tool for hobbyists so anything that helps to get more people using it is much appreciated.

When I got into REW and measurements, I got pointed to this paper, written by Nyal Mellor.

https://ampslab.com/RECOMMMENDED%20READ/LOUDSPEAKER%20MEASUREMENTS/acoustic_measurement_standards.pdf

Explains how to interpret data and is a good starting point, once you learn how to get meaningful measurements [which is nicely covered in your e-book]
Re measurements - it might be useful to add some tips&trick e.g. in my case [leather sofa] it helps to cover it with thick blanket in the area closest to mic [normal heavy blanket folded 4 times] or explain the concept of gating in measurements.

In my case ,especiall,y ETC per octave analysis and midrange decay explained lot of what I was hearing and helped me to get much better end result and pointed me to correct acoustic treatments strategy.

 

[JaMmy]

Thank you so much for this. I’ve searched everywhere for a guide to REW that is comprehensive enough to describe the entire measuring process and proper interpretation of the results but which doesn’t require degrees in electronics, computing and acronymology. You have hit my sweet spot Keith.

 

[gorman]

Re measurements - it might be useful to add some tips&trick e.g. in my case [leather sofa] it helps to cover it with thick blanket in the area closest to mic [normal heavy blanket folded 4 times] or explain the concept of gating in measurements.

But wouldn't that result in measurements that do not reflect the listening experience at the MLP? Unless you always have that blanket on the sofa?

 

[Keith_W]

Explains how to interpret data and is a good starting point, once you learn how to get meaningful measurements [which is nicely covered in your e-book]
Re measurements - it might be useful to add some tips&trick e.g. in my case [leather sofa] it helps to cover it with thick blanket in the area closest to mic [normal heavy blanket folded 4 times] or explain the concept of gating in measurements.

Hmm, when I wrote this eBook my intention was to strictly write about taking and interpreting measurements. And not preparing measurements for DSP. You don't need to gate your measurement unless you are planning to use it for some kind of correction.

I did think about writing about the difference between psychoacoustic smoothing and plain old Gaussian smoothing, but I thought that even that was too much. Just tell people to use 1/6 or 1/12 and that's it. I might remove stuff i've already written from the longer document just to make it shorter and more to the point.

And BTW, if you have a reflective surface like a leather sofa, you don't want to deaden reflections from it. Earl Geddes said that you want it to "stand out like a sore thumb" so that you know where to gate your measurement.

 

[Fidji]

But wouldn't that result in measurements that do not reflect the listening experience at the MLP? Unless you always have that blanket on the sofa?

You will have your body on the sofa instead of the blanket, depending on your size it can act like a bass trap in some cases ;-)

BTW it was something that professional calibrator has done when measuring my HT, this is when I have seen it, And as Keith said, it is much more relevant for EQ/DSP in order not to correct something that does nor need correcting.

 

[gorman]

You will have your body on the sofa instead of the blanket, depending on your size it can act like a bass trap in some cases ;-)

BTW it was something that professional calibrator has done when measuring my HT, this is when I have seen it, And as Keith said, it is much more relevant for EQ/DSP in order not to correct something that does nor need correcting.

Ok. My sofa is soft tissue, think it would absorb more than reflect anyway...

 

[gorman]

I did think about writing about the difference between psychoacoustic smoothing and plain old Gaussian smoothing, but I thought that even that was too much.

You could put it here as an extra. Always been curious about the subject.

 

[Sokel]

I read at your book that you couldn't find the REW's RT calc, here it is, you may want to include it:

 

[Keith_W]

D'OH! It was right in front of me the entire time and I didn't see it!!! Thank you @Sokel

 

[deepboy]

Thank you very much @Keith_W, i'm studying all your precious docs.

I might change my mind and decide to write about Phase ... but that would at least double the length of the book and truly put it beyond the understanding of most people.

Phase oh yesss. And I hope you or someone will write about crossovers + dsp.
Beyond understanding of ASR people?

.....the only reason i'm writing about it is because there is a need for it, and other people who are more qualified than me haven't done it.

Absolutely.

 

[Keith_W]

Hello all, the more advanced version of the eBook has been completed and uploaded. You can find the PDF here: link

I have decided I will write about phase, but that will be available later.

 

[Descartes]

Thank you so much!
Hopefully one day there will be a software using AI that can do all this automatically for people like me who are technologically challenged and don’t have the time or interest in doing all this work but rather spend time being outdoors!

 

[xanalog]

don’t have the time or interest in doing all this work but rather spend time being outdoors!

From what I understand; a user spends the time doing 'this' to enjoy the music to its fullest!
Some feel that 'this' time spend on optimization allows them to appreciate the music even more so.

It is not like you are going to keep doing 'this' forever and ever.
Enjoy the educational and sound quality benefits 'this' journey provides you.
Your namesake may remind you of "Cogito, ergo sum".

 

[Keith_W]

I think that learning to take and understand measurements is a hobby by itself. In fact, it is a far more worthwhile hobby than learning to read DAC and amplifier measurements because it impacts you directly. I don't care if one DAC is slightly more perfect than another DAC, to me that's navel gazing at inaudible differences but I get that some extremely nerdy people might find that enjoyable (no disrespect to Amir, ha ha!). But those massive flaws in listening rooms, and in particular YOUR listening room? Nobody is going to help you with that, you have to help yourself. The first step is to learn how to recognize the problem, and that's why I wrote these eBooks.

BTW, I have been asked to make Youtube videos on how to take and interpret measurements. I am not going to do that, I believe that reading is better than Youtube because you can absorb information at your own pace. You won't like my heavily Asian accented voice anyway. But if people have recommendations for Youtube channels that teach you how to take and interpret measurements, please post them here.

 

[Robocop]

I just watched Floyd Toole's Toronto AES you tube video. Excellent watch. I was intrigued with a point he made at position 1.57.51 regarding subwoofers/woofers.

He states "Always do low frequency measurements with all subwoofers operating". Then goes on to say many only measure one then calibrate it then move onto the next.

This is what I have done in stereo measured left sub then using REW implement filters, then repeat this for the right.

Based on Floyds advice should I be measuring both subs together then implementing filters to suit? Both subs would have the same filter settings I assume.

Robert

 

[gorman]

Both subs would have the same filter settings I assume.

Considering they're in different positions in your room, I very much doubt that.