shifting peak frequency

[Jaty22]

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

[santo_13]

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

[Jaty22]

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.

[Henrik_Volkers]

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

Have a nice weekend 🙂

[Jaty22]

Thank you, Henrik,

I don't expect any frequency shift.

Happy weekend to you too.

Jaefer

[dsb@NI]

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?

[Jaty22]

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

[santo_13]

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.

[dsb@NI]

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. 

[Jaty22]

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