Dynamic Signal Acquisition

cancel
Showing results for 
Search instead for 
Did you mean: 

shifting peak frequency

Hello,

 

I am measuring sound signals using a PCB microphone and NI9234 module. For identical conditions, the fft peak shifts by 2 to 10 Hz on both sides when I take multiple identical samples. Could anyone know the source of change please? The background noise is also similar throughout the measurement.

 

Many thanks for your reply and time

Jaefer

 

 

0 Kudos
Message 1 of 13
(2,627 Views)

Please provide more information about the signal source, connections, VI used to capture the signal, sampling rate and some sample data for review.

Santhosh
Soliton Technologies

New to the forum? Please read community guidelines and how to ask smart questions

Only two ways to appreciate someone who spent their free time to reply/answer your question - give them Kudos or mark their reply as the answer/solution.

Finding it hard to source NI hardware? Try NI Trading Post
0 Kudos
Message 2 of 13
(2,613 Views)

Thank you Santhosh;

 

Signal source: bubbling water in a tank

Matlab 2018a to acquire data

Sampling frequency 51200 Hz

sampling time 10 seconds

ICP® Electret Array Microphone model 130A23

NI 9234 

 

Data is so big to upload even for one sample.

0 Kudos
Message 3 of 13
(2,604 Views)

What phase noise ( jitter/ frequency shifts) do you expect from a bubbling water tank? 😄

Have a nice weekend 🙂

 

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


0 Kudos
Message 4 of 13
(2,585 Views)

Thank you, Henrik,

 

I don't expect any frequency shift.

 

Happy weekend to you too.

 

Jaefer

 

 

0 Kudos
Message 5 of 13
(2,576 Views)

Do you only care about low frequencies? If so, lower the sample rate by a factor of 10 or more and share multiple datasets. Give us some hints, what should I expect to see/hear from the spectrum of acoustic data from a bubbling tank?

Doug
NI Sound and Vibration
0 Kudos
Message 6 of 13
(2,570 Views)

Thank you, Doug.

 

I am interested in the peaks. If the parameters that bubble the tank do change during measurement, why does my peak frequency shift slightly? I just want to know the source of change.

 

My data file is more than 10MB, so I am not able to upload it here.

 

Jaefer

 

 

0 Kudos
Message 7 of 13
(2,562 Views)

One way to isolate if the shift in the frequency is in fact from the signal or an artefact of your code, connect the AI to a function generator that generates a clean sinewave, now your FFT should be consistent.

 

If the data file is larger, you can even do a smaller capture like 1 sec instead of the whole 10 sec. Do you think your issue will not be reproduced when using just a 1 sec capture?

 

BTW, you've not shared your MATLAB code so that any MATLAB experts could review whether you are doing things the right way.

Santhosh
Soliton Technologies

New to the forum? Please read community guidelines and how to ask smart questions

Only two ways to appreciate someone who spent their free time to reply/answer your question - give them Kudos or mark their reply as the answer/solution.

Finding it hard to source NI hardware? Try NI Trading Post
Message 8 of 13
(2,557 Views)

Try Santhosh's suggestion (input a known signal to your system). You could also try somebody else's code ( https://www.ni.com/en-us/support/downloads/drivers/download.dsa-soft-front-panels.html#).

 

That's the best I can offer with no data and no code. 

Doug
NI Sound and Vibration
Message 9 of 13
(2,552 Views)

Many thanks, Santhosh:

 

I will apply your suggestion

 

I am using very generic code (attached in the file). I am afraid less than 10 seconds of data may not reproduce the scenario.

 

Here I have attached a file that contains the code, setup, and frequency domain graph.

 

Kind regards

Jaefer

 

0 Kudos
Message 10 of 13
(2,535 Views)