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Contact Us
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Morset Sound Development
+47 73915000
Persauneveien 25
7045 Trondheim, Norway
contact@winmls.com
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Musical Acoustics
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Please post any message (including attachments) related to the usage of WinMLS for musical acoustics. Click here to see other articles.
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Subject violin acoustics
Date
Tue Oct 8 2002 14:07
Author Lars Morset
(morset@winmls.com)
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Dear Werner,
thank you for your questions. I will try to answer them.
>I'm trying out the WinMLS for the violin maker purposes. I >checked the frequency resolution of resonance peaks to be at >2,9 Hz. For tunig I realised as yet the resonance indication >by brocken tea leavs bouncing at resonance peaks with an >accuracy around +/-0.5Hz or less. How to arrive there with >WinMLS?
To get a frequency resolution of 1 Hz, you need 1 second of the signal in time domain. If the sampling frequency is 48000 kHz, this is 48000 samples. This can be set many ways in WinMLS, the easiest way is by going to the Measurement Settings Toolbar (found from the View menu) and make sure the sequence order is set to 16. The number to the right of the sequence order should then say 1.365 seconds. If the time window is set to include the whole time signal, you should get a frequency resolution >1 Hz.
The frequency resolution can be set as post-processing in WinMLS using the time data window (true frequency resolution), this is done from the time window toolbar. Another way is by setting the length of the FFT larger than the time window, this is done from Plot->General Frequency Domain Settings... Select the 'Use fixed size' radio button.
>I read the hints of pink noise generators and the higher >sampling frequency about 200 kS/s.
I am curious on why you would need a higher sampling rate? The sampling rate will not influence the frequency resolution if using WinMLS.
>How WinLMS can split the actuator frequency range like pink >noise or narrower?
You can make your own pre-filters. I will strongly recommend NOT to use random noise (like pink noise). The modern methods (MLS and sine sweeps) are much better. If you need a limited frequency range I would use a sine sweep, in the beta version of WinMLS you can define the start and end frequency.
>How WinLMS can generate a higher sampling rate and support >the higher bit resolution?
This is sound card dependent. WinMLS can measure up to a sampling rate of 215 kHz and 24 bits using the proper hardware.
>How WinLMS can run a swept sine wave?
To do this you need to download the beta version.
If you have not already download the release version, you may do it from:
http://64.41.85.4/downloadWinMLS/WinMLS2000/WinMLS2000_Release3Build010c.exe
Install it by double-clicking on the file.
Download the beta version from:
http://64.41.85.4/downloadWinMLS/WinMLS2000Update/WinMLSbeta4.exe
Strongly recommended: If you do not want to overwrite the current version of WinMLS, you should rename it from ‘WinMLS.exe’ to e.g. ‘WinMLSold.exe’
Double-click on the beta version file to unzip it and send us an e-mail with the new serial number.
If you are going to try the sine sweep method, make sure that you select "Sine Sweep" (change it from "MLS") in the Measurement Selection Toolbar.
Then go to Measurement->Swept Sine Settings... and increase the sweep duration to e.g. 11 seconds. At the very bottom you set the length of the impulse response, this should normaly be set to less than 2 seconds (change it from 4 which is the default).
>How WinMLS can generate an impulse to measure the resonance >decay in time?
The impulse response is "always" the result using WinMLS (This is true if you use WinMLS to measure systems, but not true if you use WinMLS to analyze signals. In your case you want to analyze the violin, which is a system not a signal).
You do not need to measure the impulse response using an impulse, it can be done more accurate using MLS or sine sweeps.
This is fundamental, but seems to be the hardest thing for us to explain to non-experts.
From the impulse response you can always find the frequency response (using FFT). You can plot waterfall, step response, energy-time-curve, Schroeder curve (which gives the decay range), etc... These are all plot types in WinMLS, and can be selected from the Plot Toolbar.
The advantage by using MLS or a sine sweep is that the signal-to-noise ratio is much better than with using an impulse.
For your violin measurement I recommend that you use the magnet-coil system we have developed. That will give
What do you recommend to complete WinLMS?
For your violin measurements I recommend our magnet-coil system to excite the violin. Do you want to excite at the violin bridge?
Where do you want to measure the response, on the violin body/bridge or the resulting sound pressure using a microphone?
I hope this helped.
Best,
Lars
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