Power Spectrum or 1/n Octave

[Midlothian]

I now have a successful V.I. for doing realtime Noise & Vibration analysis with "tabs" to give Narrowband, 1/3 Octave, Full Octave etc. and it has been calibrated and verified. I edited the DAQ input and replaced it with a file input to read a pre-recorded ".wav" file and this works very well for the 1/n Octave pages but not the Power Spectrum pages. I have tried making the sample file different lengths but the effect is the same. It is like the Power Spectrum option requires more resources to process.

I tried to use the SV toolkit Power Spectrum but it seems to slice the sample into smaller chunks instead of feeding the extracted waveform into the existing real-time arrangement.

This option shown below works well for the 1/n Octave:

Not Working shown below with the Power Spectrum:

Message Edited by Midlothian on 11-20-2006 05:32 AM

[JamesC]

Hi Midlothian,

Please can you answer these question.

1) What version of LabVIEW are you using?
2) What version of the SVT are you using?
3) What are the properties of you wav file? (bits rate / Number of channels / Sample Rate / Sample Size)
4) Can you post your code and wav file? Or is the wav file to large.

Regards
JamesC
NIUK and Ireland

[Midlothian]

Hi JamesC

LabVIEW 8.20 and the SVT 4.0, both are latest release.

Wav files that are from DAQmx 9233 are 50 kS/s, 24 bit mono  1sec. , 10 sec. and 30 sec. sample sizes have been tried.

Message Edited by Midlothian on 11-21-2006 08:48 AM

[JamesC]

Hi Midlothian,

I have this working with some of the test files from the SVT (chirp.wav, Engine rev up.wav, DIN, Dual tone and so on). Without your wav file it will be hard narrowing down the problem. What I have found is that the data being sent fails the continuity check. If you open the "SVT Zoom Power Spectrum.vi" in the Narrowband spectrum then on the block diagram open "Data Valid check" on the block diagram of that change the boolean cluster of the "waveform check"

These will allow you to ignore some checks, this allowed me to actually get data back from the power spectrum.

Regards
JamesC
NIUK and Ireland

[Midlothian]

Thanks JamesC

That sounds promising. I attach a small 1sec sample from a calibrator set at 114db (ref 20mPa with 47.6 mV/Pa) an 1kHz.

Please remove or ignore the .jpg (it is added to permit forum upload).

[Midlothian]

JamesC,

Thanks for the pointer. I set the boolean for "ignore t0 continuity" to "true" leaving all the other checks and it now works correctly. The results are consistent with the calibrated signal; so all is well for the amplitude and frequency. I will leave this sub-vi in the edited state since it is unlikely to cause upset elsewhere. The ignore options could be "fed" from the higher level but this could change the behaviour of other toolkit VI's.

Cheers

[JamesC]

Glad to hear it worked for you.

Regards
JamesC
NIUK and Ireland