Audio Amplifier Problem

[obscure]

Hello guys,

I would like to acquire sound via B&K microphone and get the SPL and frequency. There is a constant background noise in the lab as in the attachment. When I run the vi I got nearly 60Hz frequency result for the background noise. I used a frequency generator application and tried 400-500-700-1000-2500 Hz but got 59.9893-59.9868-59.9934-59.996-60.0044 Hz. I have B&K 1704, CCLD is on, and the gain is x10. I could not understand why I get the wrong frequency results. If you can help I would appreciate it. Thanks

[altenbach]

Unfortunately I cannot tell how the DAQ assistant is configured (I don't have drivers installed, so the panel does not open for me). Also, the use of dynamic data hides important information.

What is the purpose of the FOR loop?

Maybe you need more advanced processing than to simply get the dominant component. How many points are in the data?

[obscure]

@altenbatch thanks for the reply. Honestly, for loop doesn't have an important purpose. I use the vi without the loop also.  The samples to reas is 441k and the rate is 44.1 k. 

This's my first project so I'm a freshman.

[altenbach]

OK, so you have 10 seconds worth of sound data. Are the frequency components constant for that duration or can they change? Have you looked at the magnitude spectrum to see all the frequency components. Maybe you can just ignore the 60Hz and look at the rest of the transform. If the sounds changes over time, maybe you need JTFA.

[AnalogKid2DigitalMan]

Any chance your electrical connections are wrong or due to inadequate shielding you are picking up 60Hz AC power line noise?

You would not hear this component since it is purely electrical 'noise', not actual sound.

-AK2DM

[altenbach]

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@AnalogKid2DigitalMan wrote:

Any chance your electrical connections are wrong or due to inadequate shielding you are picking up 60Hz AC power line noise?

You would not hear this component since it is purely electrical 'noise', not actual sound.

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Agreed, but since they said "There is a constant background noise in the lab", I assumed it is audio noise (that might still originate from the net, of course). We also need to assume this is in the US. Other parts of the world run at 50Hz.

To the OP: can you attach the sound as e.g. a wav file instead of MP4?

[Yamaeda]

The sound clip sounds like a fan or ventilation noise. Try a Lowpass or bandpass filter.

[obscure]

Thanks for the reply. Most probably this 60 Hz is power line noise. The signal conditioner has red lights. I have checked and tried different BNC cables. I think not the wiring but the sensor has a problem.