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Interpreting audio measurement data - suggestion for an article

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Interpreting audio measurement data - suggestion for an article

PostPosted: Thu Jul 25, 2019 8:15 pm
by blinddrew
The problem with writing an effective subject line is that you then have nothing to put in the body text... ;)

Triggered by a thread in the DIY forum; we talk a lot on here (and in the magazine) about the importance of room treatment but I don't recall anything since I've been reading about to take effective measurements and then interpret them to work out effective treatments?
Or has this all be covered before my time?

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 7:00 am
by ef37a
blinddrew wrote:The problem with writing an effective subject line is that you then have nothing to put in the body text... ;)

Triggered by a thread in the DIY forum; we talk a lot on here (and in the magazine) about the importance of room treatment but I don't recall anything since I've been reading about to take effective measurements and then interpret them to work out effective treatments?
Or has this all be covered before my time?
,
It might have been covered Drew but I don't recall anything along the lines you suggest i.e. Measure then treat, then show results.

This could well be because the means to measure a room has for a long time been beyond the pocket of the average Joe and even the pros' probably baulked at the cost? Rather buy another mic pre/mic/top end D/A?

Not nearly so costly now and if such an article was considered maybe it could double up as a review of a couple of mic/software systems?

Dave.

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 7:19 am
by Matt Houghton
Your timing is impeccable... we have such an article in the pipeline.

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 8:21 am
by blinddrew
Happy to help! :)

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 11:15 am
by Rich Hanson
I see SOS have perfected their time machine. Or has Drew perfected his? I'm confused :geek:

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 12:51 pm
by blinddrew
That often happened with time travel.

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 1:39 pm
by Rich Hanson
* Often will have happened

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 1:45 pm
by Folderol
I know you are going to say that :tongue:

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 3:08 pm
by blinddrew
[actually managed to confuse myself about what the joke was - ignore!]

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 3:17 pm
by Rich Hanson
Oh dear, what am I going to have started here

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 4:21 pm
by Mixedup
Rich Hanson wrote:* Often will have happened

*Often will have been going to have had to happen. :?:

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 9:54 pm
by Dennis J Wilkins
If you think this forum has gone confusing, just try writing an article on room measurements and treatment, while beta testing the measurement software and remodeling your studio!

Hopefully we'll end up with a very useful tutorial that incorporates the latest software release from Room EQ Wizard and offers appropriate guidelines for frequency and time domain improvement. I plan to cover some acoustic theory, microphones, measurement techniques, software use and interpretation of results.

Stay tuned . . .

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 10:16 pm
by blinddrew
Excellent, thanks Dennis. I enjoyed your recent article and look forward to the next one. :)
And the fact that it comes just as I'm embarking on my own project is the icing on the cake. :thumbup:

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 11:01 pm
by Eddy Deegan
A week or so back I watched Studio Support Gnome make strange noises in the vicinity of a laptop in my home studio, after which he showed me some rather tasty 3D graphics of the areas of high and low pressure in the room while he swept through the frequency spectrum.

Watching the pressure distribution change in realtime as he did so, combined with his explanation of what was going on and why was a real eye-opener and I found the whole exercise fascinating. The day taught me much but in doing so it confirmed how much there is yet to learn.

I'm now looking forward to another SOS article I'll be scrutinising with a fine-toothed comb!

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 11:18 pm
by Dennis J Wilkins
by blinddrew » Fri Jul 26, 2019 10:16 pm -- And the fact that it comes just as I'm embarking on my own project is the icing on the cake.

by Eddy Deegan » Fri Jul 26, 2019 11:01 pm -- The day taught me much but in doing so it confirmed how much there is yet to learn.

Acoustics is extremely complex! While the usual simple treatment (mirror points) can make a huge difference in almost any room, it's very useful to observe both frequency and time domain effects, the latter requiring math-intensive analysis. Luckily there are affordable programs these days that can do the work. I've been using REW, which is excellent donation-ware and is near the end of 5.2 beta testing. Hopefully John (Mulcahy) will settle on a final REW 5.2 version soon since the last few minor beta updates have addressed some really small issues.

I started the article using the previous REW release 5.19 and found John had made some really useful improvements with 5.2, and since i want to keep the article up-to-date, I decided to revise it to 5.2. When I first used 5.2, I was analyzing audio files I'd made weeks earlier with 5.19, and was getting puzzling results. John advised me he had changed the swept-sine measurement file slightly, and as you might know, any minute change to the measurement file will greatly affect results! If you've ever used REW you know it can almost perform magic, but it must be used with the correct test signals.

So I've re-run a number of measurements and re-written some of the article since the program itself has changed in some areas. Now we're trying to figure out how to fit it all into a reasonable space without losing usefulness (my editor doesn't want it spread over six issues of Sound on Sound!).

Hopefully we'll get it sorted soon.

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Fri Jul 26, 2019 11:53 pm
by Eddy Deegan
It may be beyond the scope of the article but one of the things in my case is that was seeking to find an acceptable balance between the extremes of things that are as perfect as possible and things that compromise that, such as the space available in a domestic room, the materials it is constructed from, budgets and the equipment one needs to accomodate in the environment.

A useful outcome (one of of many) for me was an understanding of the compromises I would be making to accomodate equipment in certain parts of the room, how much attention I should pay to them (or not) and consideration of the money I was willing to spend treating the room to achieve the balance.

The needs and desires, some negiotable some not, of the person who is seeking to improve the acoustics of an environment are I think very significant factors in any consultation process and speaking for myself I was very happy with the plan that emerged!

I may be diverging from the point of the article of course. I'm looking forward to reading it a lot :thumbup:

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Sat Jul 27, 2019 10:37 am
by blinddrew
I'll make sure to download the latest version of REW then. I'm reasonably comfortable with the maths side of things (it's 25 years since i finished my engineering degree but I like to think that the ability to think in the right way is still there :) ), and I've done a lot of reading on studio building and the fundamentals of sound/audio following some book recommendations on here. But, like Eddy, I know that I will be starting from a position of compromise and then making more from then on.
But it will be better than what I have now! :)

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Sat Jul 27, 2019 3:57 pm
by Hugh Robjohns
I have a great deal of respect and admiration for acousticians because their business -- more than any other in the audio world, I think -- involves a very great deal of interpretation and experience. There really is as much art as there is science involved!

We all readily accept that a hugely experienced recording engineer will be able to make a far better recording, apparently with much less effort, than we mere mortals can achieve. (Especially so in the world of classical recording.)

But the same is true -- but with tinsel and gold knobs on -- for acoustic design.

There are indeed some fantastic tools about -- like REW and others -- and they can draw very pretty pictures. But actually knowing what those pictures mean and how to interpret the results correctly, and then to understand what to do with that information is a whole different ball game. And one made a whole lot harder by the fact that moving the measurement mic 6-inches one way or the other can change the pictures dramatically!

This requirement for interpretation is not a unique condition to acoustics measurements, of course. It applies everywhere that scientific measurements are taken.

I know very well indeed that if I inadvertently have an inappropriate setting on the Audio Precision test set when I'm running bench tests on review gear I can get totally misleading results very easily. So it's absolutely vital that the tester has a good understanding and lots of experience before embarking on the testing. I think you almost need to know what the result should be, before it appears! :D

To highlight this very point, I recently had to explain (to a microphone design engineer) how to properly use a dual-channel oscilloscope for analysing a floating balanced source because he took the (very misleading) results he was seeing at face value without realising that it was a complete nonsense -- caused entirely by the inappropriate way he was making the measurement!

To be fair, it was an understandable mistake, but he now knows better because I questioned a statement he had made.. and thankfully he had the humility to listen to what I was saying. And I only recognised the problem and knew the right way because I had the luxurious benefit of being taught how to use the equipment correctly in that kind of situation by the BBC 35 years ago! Sadly, many others I've tried to help along the way have just blustered and BS'd... and still know no better! But that's another story!

Anyway, as has been said above, there are no absolutes in the real world of acoustics -- it's always all about compromises due to the physical building structure or fabric, the practical requirements of the space (especially in multi-purpose domestic rooms), and the available budget. So knowing what measurements to make, how to make them properly, how to interpret them, and how to use them to arrive at the best compromise really is a real art.

I don't want to put people off measuring their rooms -- it's a very interesting thing to do and it might lead to a whole new career! But I would urge some caution just because optimising the acoustics of a space it's not quite as simple and straightforward as it might appear.

Max is extremely good at it, but he's been doing it for a very long time and I'm sure has many tales to tell of the challenges and surprises he's had along the way!

H

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Sat Jul 27, 2019 5:10 pm
by Dennis J Wilkins
Good Morning (well, here in Colorado),

I wanted to note a couple things , and just like that a post from Doctor Hugh (congratulations, Hugh!) popped up which states a number of facts I was about to state (time machine? The Doctor?)!

Although I've been an engineer for longer that most (electronics and systems engineering) and worked with audio on the side for 50 (!) years, digging into room acoustics has been an eye (ear?) opener. As Hugh says, acoustics is as much art as science, and is extremely complex. There is no magic solution to turn a bedroom into Ocean Way or Abbey Road studios, but there are ways to greatly improve a room and tools to quantitatively assess acoustics at the beginning, middle and end of a studio upgrade project (assuming there ever is an end!).

As Hugh said, there are today some excellent, powerful tools to assess room/speaker acoustics, but "knowing what those pictures mean and how to interpret the results correctly, and then to understand what to do with that information is a whole different ball game". I'm hoping my experiences with improving a very bad (square) room and the results of measuring both frequency and time domain metrics can help others to make significant improvements. However, if one needs a really excellent studio and has the money, there are a number of professional acousticians who will provide the best possible solution, from making measurements and providing suggestions to complete construction projects.

For most 'home' recordists working within the bounds of a given room, speaker placement, listening position and acoustic treatment are probably the only physical improvements that can be made, but electronic correction (ARC or Sonarworks) can really clean up the low end which is quite impossible to solve in a small room by treatment alone.

And as Hugh said, moving a measurement mic a few inches can change the response significantly, especially in an untreated room. And even more surprising to me, is even with a mic at a fixed location, on a stand, moving one's head a few inches can significantly change the response at high frequencies!

Anyway, I am trying to cover all the above, and issues like the results of inadvertently using an inappropriate setting or test file, in my article. REW is a superb program, but as Hugh noted, even a small 'misuse' of such a tool can result in misleading conclusions. But as I've found in my slow, several-year project, even a small square room can yield extremely flat response with excellent imaging and acceptable decay characteristics.

Everyone have a fine weekend!

Re: Interpreting audio measurement data - suggestion for an article

PostPosted: Sat Jul 27, 2019 5:13 pm
by Hugh Robjohns
:thumbup: 8-)