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analyze wav file

I have a wav file that is a recording of a tick in an engine as it idles. Is it possible to analyze and count the tick frequency inside labview?? I have the signal processing toolkit, but not the sound and vibration toolkit.
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Message 1 of 11
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Is it the acoustic data that you are hoping to process or is it vibration on the engine?

Listening to your engine it sounds like a big diesel, whats the engine build state (new, prototpe.....) ,what's the engine application, whats the perceived problem?

600RPM is low for an automotive application, so I guess we can count that out.

Any way its all possible without any of the toolkits but the toolkits save you shed loads of time and you are not so concerned about errors in coding.

 

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This was an auto engine in a vehicle as it idles. It was recorded with a Sony digital camcorder with electronic condensor microphone and a foam sock. It was about three inches from the cylinder head. The ticking noise should not be present. If it is ticking 5 times per second that would be the camshaft.  It was around 600 crank rpm and 300 camshaft rpm. We are just trying to estimate the frequency to narrow the focus of the component search.
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Well a bit light on the build and engine size etc. but here is a suggestion on what to do.

Stop as much of the background noise as possible (such as the speech etc), can be as simple foam.

I would get a sound source to set a calibration level if possble, be carefull in standard rooms / test cells, you can get nodes which make it difficult to repeat noise measurements, make sure you can choose a precise fixed position.

Then pass the incoming noise data into a Window and then FFT, and keep a record the amplitudes for that slice of data at the current speed / load.

Perform a speed sweep / load cycle and you can then see if the noise is related to the rotational speed or not. This will tell you if its a resonant component or gear mesh / torsional issue.

You can use a 3D picture plot, to plot speed versus frequency with ampitude/ intensity as the 3rd dimension, this makes it easy to make a good look at all the data. A waterfall graph tends to be hard to keep a track of.

Be aware that the camcorder isn't instrument quality recording and may mash the noise quite a bit, I would recommend that you sample the data directly using an DAQ board or use a DAT recorder.

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If you take the absolute value of the signal and then do a FFT, you will see a nice peak at 5.6 Hz or so.  The tick noise would appear to be made by several harmonics of this frequency summed together.  An FFT of the original signal shows the harmonics around 250 Hz being the dominant ones.

Message Edited by rpursley8 on 10-18-2005 02:58 PM

Message Edited by rpursley8 on 10-18-2005 03:01 PM

Randall Pursley
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Message 5 of 11
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You have to be real carefull with such low frequencies on microphones.
 
Some of the best mics only just get to the frequencies (< 10Hz) being talked about here and I don't think camcoders come anywhere near.
 
You could be looking at air pressure variations unless you are really very carefull, in engine test cells this is a real possibility, and particular care would have to be exercised!
 
As far as the noise is concerned, the data treatment is lightweight but it does depend on how much you know about the engine. The precise engine state is an important part of the diagnosis and an understanding of the sources of engine noise and causes.
 
Could simply be you need to change the oil 🙂
 

Message Edité par Conseils le 10-18-2005 09:59 PM

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Message 6 of 11
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Thanks for the effort. Can you show me some code?? My FFT results aren't showing anything over 1Hz frequency.

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I think I figured out my problem. I was unbundling the sample rate and inverting this to make the dt value when creating a waveform. This value was an enum and not the actual sample rate.
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Hi unclebump,
 
LabVIEW has multiple examples that take a .wav file and perform signal analysis. In LabVIEW, browse to Help >> Find Examples >> (Switch to Search tab and type wav). There you will see several examples. The two that I was checking out were SVXMPL_WAV Power Spectrum and SVXMPL_Getting Started with SVT (Simulated). They both perform signal analysis on .wav files.  Also, for other general examples regarding analyzing signals, switch back over to the Browse tab and expand the folder called Analyzing and Processing Signals. Here you will find more signal analysis examples.  
 
Hope this helps!
 
Best Regards,
 
Jonathan N.
National Instruments
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Message 9 of 11
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Those two vi's don't show up in my 7.0 examples. Can you give me the path to them?? Maybe they are in a higher version than mine.
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