Setting up Visual Analyser and capturing a frequency plot

[Dominic]

Capturing a frequency plot

A few people have asked me how to set up Visual Analyser and then how to capture data. I am by no means an expert as I only worked out how to get good results a few days ago. So if you see anything wrong and there is a better way of doing it please us all know. But here is how I have done it to get decent consistent results.

First we need to set up VA. Click on ‘setting’ at top left.

Under the ‘main’ menu
1. set your FFT rate to 16384
2. set your frequency sampling to 11025
3. click confirm and the spectra line resolution should change to 0.67Hz
4. Next go to the 'capture' tab and set the capture spectrum - spectrum average buffer to 10. There is capture scope window on this page as well so make sure you set capture spectrum.
5. save your settings. Apparently you can save these setting as default but I have to redo them every time I open VA so check before you start a new session.

Next test your mic
6. turn VA on with the button at top left.
Now check you are getting decent sound levels. The lines on the charts should be jumping all over the place from you voice. If you make a noise into the mic you should see it spike on the charts. If so all is good but if not you need to go to your sound card settings in windows. Set your mic boost higher until you get a decent response on the main chart.

You are now ready to capture data but first do a dry run so you can practice your taps. Nice consistent force and nicely timed taps are best and avoid the centre line. There are spots that sound louder for a given tap force so I try to tap on those spots.

7. Get your guitar ready with your tapping stick and the mic pointing at the soundhole. Trevor mentioned sitting on a chair with the guitar or just the body on your knee and I found this the easiest. Don’t damp the back of the guitar with your beer guts. I held the body by the neck mortise.

8. When you are ready, with VA still on, click the capture spectrum button at the right centre of the screen and start tapping your 10 taps with about 1.6 seconds between. Don't do it faster or you will get weird results. Going slower seems to be OK.

9. Keep tapping and when VA has recorded 10 buffers of data it will pop up the spectrum window with your completed frequency spectrum. You can then select the range up to 500Hz and it will zoom in.

10. You can save this as a text file then copy and paste it from there into excel for further analysis if you want.

You are done.

As I said, please correct me if I am wrong anywhere but I am getting consistent results using this method.

Hope this helps all you budding scientists.
Cheers
Dom

[Bruce McC]

Hope this helps all you budding scientists.
Cheers
Dom

Yeah but what about the budding luthiers????????

[Dominic]

Hey Bruce, do I sense a slight uneasiness with these methods in the tone of your post. Don't you think there is merit in doing this analysis? You Luddite

Despite what many people would have us believe, guitars are actually physical structures and must obey the laws of physics. So a good understanding of this can only be good for budding luthiers. The alternative is more frustration. Many will have felt this from the existing literature because it either does not tell you how to make you guitar sound better, or it just says something vague and unhelpful like, "keep shaving braces and flexing and tapping until you get the response you want". Without using science and numbers it is very difficult to give a 'budding luthier' any idea of the range of stiffnesses a top could be for a given guitar. And finding that sweet spot or range when we only make 6 to 12 guitars a year could take years and years and years. So I see great merit in doing this analysis.

Anyway Bruce, I wouldn’t mind testing your guitars at some stage. If you don’t mind dropping around on a weekend some time. Only take 30 minutes or so. I really liked the sound of your nylon strung OM in particular.

Cheers
Dom

[Bruce McC]

Yes Dom I am an old Luddite and not ashamed to admit it and
I am uneasy with all of this technical stuff because I don't understand it!
Thank you for your kind offer, which I most graciously will accept.

[woodrat]

We can make it as simple or a involved as we like but we all have the access to the bits and pieces we need if we have access to a computer as the Visual Analyzer is free and easy to set up and a microphone rounds out a very simple package. Just knowing where the 3 main resonances are and where they should be is great, as I didnt know before. For instance I have just found out that I have been building my backs too light....I thought "active back...thats good" ...what I didn't know was what was the best amount of activity to have in a live back. As Dom mentioned the literature up until now has been vague and sometimes unhelpful. Some of the publications I have bought have definitely not measured up to either my needs or expectations (hopes). I am just so glad that there is now a well of knowledge to draw from to be able to make our instruments proper tone machines and (at least on a rudimentary level) to understand why.
Thats what this forum is all about...helping one another to build better guitars and to better understand the instrument we all love.

Cheers

John

[woodrat]

Bruce, Dom is very helpful and you will definitely benefit from just knowing where the resonances are.

John

[Clancy]

Thanks for doing all the hard work for us Dom.
With this info I was capturing plots minutes after installing the software.
One day I'll explore the rest of the program. One day....

[Bruce McC]

Thanks for your help Dom, I have got as far as downloading VA, now all I have to do is follow the instructions above.

[Dominic]

No worries guys. Happy to help out as much as possible. Look forward to seeing more analysis of guitars as you get set up.
Cheers
Dom

[Tom West]

Dom: Thanks for the info on V.A.,I have it and Audacity downloaded and managed to get Audacity going but was stuck on V.A. Computer work to me is a struggle for my 70 year old ear separater. With your info I was able to finally get V.A. working..............now to see if I can decipher and make some good use of the data. Trevor and Gerard books are by far the best I've ever seen on the subject. Thanks again and take care.
Tom

[auscab]

I'm certainly the opposite of a luddite when it comes to machines and basic mechanics, I love the stuff

When it comes to what you are talking of hear though I need it described in layma's or a Laypersons description.

Thanks Dom and John

[foxfair]

Alternative tools for Mac user are
WavePad FFT Sound Analyzer, or AudioXplorer which is not actively developed anymore but still good to use.

[Craig Bumgarner]

Hello from Maryland, USA. I'm a new member and joined at the recommendation of the good folks at MIMF to further my understanding of Trevor Gore & Gerard Gilet's terrific book set. I read most of the Build volume last year and at the encouragement of MIMF have started in on Design. I've set up VA and am getting Frequency Response Curves similar to what I see in the book and on this sight. I'm sure I'll be asking more questions once I finish the book.

In the mean time, how does one save and call up spectrum captures? I right click on the spectrum capture window and Save Spectrum. This saves as .tee file. But how does one open this file again? Can it be converted to a .jpg somehow, so it can be posted? For now, I'm taking a screen capture and saving as a .jpg, which works but is a bit cumbersome.

Enjoying the forum and the books very much, lots of new ideas for me.

Thanks,

[Trevor Gore]

Hi Craig and welcome!

I think you are using a later version of VA than I normally use (I use v.9), but iirc, the .tee files open in VA as a "live" file, much like the live spectrum capture window.

If you click on "File" in the spectrum capture window you should have options to save as a .txt file, (just a list of numbers that can be imported to Excel etc.) and in v.9 at least, that also saves a .wmf file which is just a "dead" screen shot of whatever you have in the capture window.

The .wmf file will open in the default Windows picture viewer, or you can convert it to another format (e.g. .jpg) using an app such as IrfanView.

If this doesn't make sense, someone using one of the later versions will likely be along soon.

[charangohabsburg]

Hi Craig, welcome!

Trevor has already explained it. But if you don't yet have opened (from the capturing process) the "spectrum capture window" (which you need to have the file menu available) you can open the saved .tee files by selecting the "More" tab in the lower right area of the VA screen and hit the "Spectrum" button as per the attached screenshot, on the right:

ViewSavedSpectrum.gif (30.85 KiB) Viewed 34850 times

I am using VA version 2011.

Cheers,

[Craig Bumgarner]

Thanks Trevor and Marcus,

I'm using VA-11 and I don't see the option to save as a .wmf file, only .tee or .txt. , but maybe it is there somewhere. No big deal, I can use Alt+PrtScn to copy to clipboard, pasting into a graphic program and save as .jpg if and when I need that. For now .tee files and the ability to call them back up is what I need most of the time.

The opening of .tee files works just as you suggested Marcus, thanks for the instructions and screen shot.

Craig

[Trevor Gore]

Craig, in v.9, when you save as a .txt file, you automatically get the .wmf file (actually listed as .txt.wmf) so it's not an option, as such. v.11 might do the same. Just go looking for the .wmf file in the same place as the .txt file and see if it's there.

[Craig Bumgarner]

Yes, it works that way in VA 11, thanks.

[mqbernardo]

hey Craig, nice to see you here - i know you from the djangobooks forum, i can see you´re already in the gore/gillet book bandwagon. a lot to learn there...

good luck!
miguel.

[blackalex1952]

A good way to capture screen shots is with a free program called "Snipping Tool".
I would like to see a function in VA that allows the user to mark the frequency on each peak rather than just one at a time when you click the cursor over the peak.As an example, here is a snipping tool screenshot of a cheap Martin 0015 mahogany top with the peaks marked one at a time using "Paint". All comments welcome re the placement of the resonances in said Martin! Also, my old 1956 Maton Premier 45A archtop.

[blackalex1952]

Re posting-a better version of a terrible tap!
Also, I held this guitar at the neck where it joins the headstock. I believe we have, on the lowest frequency, the neck mode? Obviously I am new to all of this!These frequencies on each VA sample, seem to move around a bit...I have done some tea leaf reading, and confirmed the main ones. But this guitar is a little difficult to get good results from, being factory built, but it still had a characteristic Martin sound. I have concluded that the guitar is just stiff and the braces roughly shaved in a factory, the tea leaf patterns are not very even...The reason I am doing this, is as a preliminary to bracing my first soundboard,shaving braces and closing the box!All comments, help,opinions,guidance etc welcomed!

[kiwigeo]

Alex,

For tap testing I get best results are with the guitar held in playing position and the mic around 200mm from soundhole. I hang my mic from the ceiling and sit on a chair......distance from mic to guitar can be adjusted simply by moving sitting location.

For Chladni work I get best results with poppy seed.....

[Dave M]

to add to the info on VA I just noticed today that you can get it to print a spectrum with a white background rather than black which is bad for the ink usage and makes a poor print.

On the file menu check print white back colour then select print spectrum.