Tap Testing

[seeaxe]

Here are some results from my first attempts at tap testing. First up is a comparison between taps on the centre of the bridge and the bass bridge wing of my current classical. Averages of ten taps each

008 Tap Tests.pdf

(192.2 KiB) Downloaded 574 times

Here is a 5 tap average of my Yamaha C70

Yamaha C70 Tap Tests.pdf

(176.83 KiB) Downloaded 512 times

and for comparison my 50 year old plywood dreadnought

Kiso Suzuki tap tests.pdf

(251.58 KiB) Downloaded 567 times

So this was basically just to see if the gear was working but results seemed to be sort of right so I carried out see what I could get done. I had a cloth under the strings and the soundhole was not plugged so these are all coupled results. I was holding each guitar in its normal(ish) position. I thought this was perhaps a useful indicator of what you can get done in a day. I would welcome any comments from those that have tapped before me! I dont pretend to know what any of this means yet

A couple of things I spotted.

There is a obvious spike on all the plots at 50Hz and another at 150Hz there might be one at 100Hz but it would be hidden under what I assume is the main air resonance. It doesn't appear at other multiples of 50. I'm assuming that's some power source affecting the results and am intending to ignore it.

The main (biggest) resonance is similar for all the guitar, nine a tad higher at 110. Its the same size as the C70 but it has a sound hole - I'll be blocking that see if it makes a difference. The C70 has a well defined second peak at 180 and 260. My self-built 008 has a second peak at 220. The dreadnought has similar peaks to the C70, second peak at 180 and another at 260 ish

As this is the first day I havent got round to uncoupled tests, but that's coming.

As I said above comments welcome!

[seeaxe]

I forgot the questions!

Can you set up VA to just export the data up to 500Hz?
How do you guys handle the text files - just open in Excel??

Cheers
Richard

[kiwigeo]

I forgot the questions!

Can you set up VA to just export the data up to 500Hz?
How do you guys handle the text files - just open in Excel??

Cheers
Richard

I'm pretty sure you can specify the frequency range.....without firing up my workshop laptop I cant tell you the settings to play with.
I import the text files into Excel and then plot up on a graph.
I usually get a 50Hz peak from laptop power pack and the pre-amp power pack as well. You can set up filters on VA but I've never been able to get a 50Hz high pass filter to work properly. One of the advantages of iStrobosoft is that it has a 50Hz hum filter built in.

[seeaxe]

Thanks Martin, Ill have another look. Do you use the text wizard to parse the incoming file?

[Trevor Gore]

Can you set up VA to just export the data up to 500Hz?

I'm still using v9, but when set up for guitar tapping you get a spectrum response to 5kHz. When you save the file, you get 0-5kHz (as you'd expect). When you import the .txt into Excel, you get the full 5kHz. The import wizard might let you import a part file, but it's but 2 seconds to import the lot and delete what you don't want.

How do you guys handle the text files - just open in Excel??

Use the import wizard to parse.

Unless you're normalizing a bunch of plots, there's not much need to import into Excel. The average of 10 taps can be set up in VA and you can zoom the spectrum window to get 0-500Hz (or any other range you want). When you hit save, the early versions (e.g v9) save a "dead" screen shot of what you have on your screen (so frame it right) plus a .txt file of the whole file as you had it set up (i.e. 0-5kHz) if that's how you set it up. The later versions save a file that VA can re-open, so you can zoom in, re-frame etc. like you can on the initial live file.

Check your signal levels by some other means than VA. What you have in your plots looks a little saturated (gain too high).

[seeaxe]

Thanks Trevor that's great. I did have the gain up really high as without it I wasn't getting much response. I twiddle some settings.

I'm practising by comparing a bunch of different guitars at present so I was importing to excel so I can easily plot the different curves on one graph .

I've been deleting the values abovel 500Hz in word.

Cheers
Richard